103

RESEARCH & DEVELOPMENT

REPORT NO. RD 2047

APPLICATION OF HYDROELECTRIC TECHNOLOGY

IN STONECUTTERS ISLAND SEWAGE TREATMENT

WORKS

(Final Report)

Research and Development Section

Electrical & Mechanical Projects Division

Drainage Services Department

Jan 2008

i

EXECUTIVE SUMMARY

The objectives of this R&D Item No. RD2047 - Application of

Hydroelectric Technology in Stonecutters Island Sewage Treatment Works (SCISTW) are to investigate the technical feasibility of constructing a pilot hydropower plant in one of the Vertical Outlet Wells in SCISTW and to estimate its cost effectiveness if installed. PolyU Technology & Consultancy Company Ltd. was commissioned in February 2007 to undertake an assignment under the Consultancy Agreement No. DEMP/06/19 for this R&D Item.

Literature studies and market searches were conducted and relevant

information of similar project was collected. It is recommended that a hydropower plant with a three-phase asynchronous generator and a basic propeller type turbine can be installed in the Vertical Outlet Well of SCISTW. By utilizing the net available pressure of the outflow effluent, the hydropower plant can generate electricity to supply some of the E&M equipment in SCISTW.

Site measurements, including effluent outflow velocities, were made for

estimation of the static and dynamic heads of the outflow effluent inside the Vertical Outlet Well. A hydropower plant of 45kW capacity is proposed to be installed in the Vertical Outlet Well of Sedimentation Tanks Nos. 40 & 42. The designed effluent flow rates of the hydropower plant are in the range of 1.1 to 1.25 m3/s while the designed available net head is from 4.5 to 5.5m. Possible options in installing the hydropower plant at the Vertical Outlet Well were investigated. Taking into account of technical aspects and site constraints, the configuration with the generator and turbine integrated into one unit and mounted inside the Vertical Outlet Well is recommended. A motorized control valve will be installed on top of the Vertical Outlet Well to control the effluent flow to the hydropower plant. The generated electricity will supply to an existing electrical switchboard in SCISTW, in parallel with the electricity supply of CLP, i.e. the hydropower plant to be grid-connected.

The rated generation power of the proposed hydropower plant will only be

about 45kW and is within the 200kW limit under the “Technical Guidelines on Grid Connection of Small-scale Renewable Energy Power Systems” issued by the Electrical & Mechanical Services Department (EMSD). CLP had been provided with relevant technical information of the hydropower plant and was

ii

basically satisfied. Nevertheless, CLP advised that the detailed design of the hydropower plant is still required to be submitted to him for formal approval and whether standby charge will be required for the proposed grid-connected hydropower plant can be evaluated after this hydropower plant project has been formally approved for implementation.

It is expected that the proposed hydropower plant can provide a yield of

about 263,000 kWh per year. The saving in electricity cost is estimated to be HK$201,185 per year based on that no standby charge will be required by CLP. The environmental benefit is 62.4 Metric Ton Carbon Equivalent per year or 229 Metric Ton CO2 Equivalent per year. The estimated capital cost of installing the hydropower plant is about HK$5M. It gives a payback period of 26 years if only the financial aspect is to be considered.

Although the financial benefit of this project may not be very attractive, it is

considered worthwhile further exploring the application of hydroelectric technology at SCISTW in view of its environmental benefit in the reduction of greenhouse gas emission. If the pilot hydropower plant is decided to be installed, it will be able to be put into operation in end 2009. By then, more knowledge and experience in operating the hydropower plant could be obtained. It is also noted that the HATS Stage 2A project is undergoing, in which additional Sedimentation Tanks and their Vertical Outlet Wells will be built. If civil requirements of hydropower plant(s) are incorporated at the early stage of this project, the hydropower plant(s) can be designed with a lesser capital cost and better maintainability. Further study on the hydropower plants for the HATS Stage 2A project is recommended.

Consultancy Agreement No. DEMP/06/19

Application of Hydroelectric Technology

in SCISTW

( Final Report )

January 2008 Submitted by

PolyU Technology & Consultancy Co. Ltd.

The Government of the Hong Kong Special Administrative Region Drainage Services Department

Consultancy Agreement No. DEMP/06/19 - Application of Hydroelectric Technology in SCISTW (Final Report)

January 2008 2

TABLE OF CONTENTS

Page No.

1 INTRODUCTION ......................................................................................................................... 4 1.1 Background............................................................................................................................4 1.2 Scope of the Assignment .....................................................................................................4 1.3 Structure of the Report.........................................................................................................5

2 LITERATURE STUDIES ON HYDROELECTRIC TECHNOLOGY ................................ 7

3 SUITABLE TYPES OF TURBINES AND GENERATORS................................................ 10 3.1 Suitable Types of Turbines............................................................................................... 10 3.2 Suitable types of generators............................................................................................. 13

4 INFORMATION OF SIMILAR PROJECTS ......................................................................... 15 4.1 A 200 kW hydro plant in Puan Hydro, Korea.............................................................. 15 4.2 A micro hydro scheme at a waste water treatment plant in Emmerich of

Germany.............................................................................................................................. 16 4.3 A small hydroelectric station for the new waste water treatment plant in

Amann of Jodan ................................................................................................................. 17 4.4 A 1.35 MW hydro plant at The Point Loma Wastewater Treatment Plant ............. 18

5 TECHNICAL DETAILS AND BUDGETS OF SUITABLE TURBINES AND GENERATORS ............................................................................................................................ 19 5.1 Tyco-Tamar Design in Australia..................................................................................... 19 5.2 Gugler Hydro Energy GmbH from Austria ................................................................. 23 5.3 Kubota Corporation of Japan .......................................................................................... 27

6 MEASUREMENT OF FLOW VELOCITY OF THE FINAL EFFLUENT IN THE VERTICAL WATER OUTFLOW WELL ................................................................................ 29 6.1 Equipment specification................................................................................................... 29 6.2 Results of measurements and estimations .................................................................... 30

7 ESTIMATION OF STATIC AND DYNAMIC HEADS OF THE FINAL EFFLUENT IN THE VERTICAL WATER OUTLET WELL............................................... 32

8 DESIGN REFERENCES............................................................................................................. 33 8.1 Design Inputs ..................................................................................................................... 33 8.2 Relevant Standards, Code of Practice and other Manuals/References ................... 33

9 PROPOSED HYDROELECTRIC TECHNOLOGY APPLICATION IN SCISTW.......................................................................................................................................... 36

10 POSSIBLE OPTIONS FOR THE PROPOSED HYDROELECTRIC SYSTEM.............. 38 10.1 General................................................................................................................................. 38 10.2 Turbine / Generator SET.................................................................................................. 38 10.3 Control Valve/Gate........................................................................................................... 45 10.4 LV Switchboard ................................................................................................................. 47 10.5 Cable & Conduit Routing................................................................................................. 47


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11 HYDRAULIC DESIGN .............................................................................................................. 54 11.1 Surge PRESURE and Back PRESSURE.......................................................................... 54 11.2 Conclusions......................................................................................................................... 56

12 CIVIL & MATERIAL REQUIREMENTS .............................................................................. 57 12.1 General................................................................................................................................. 57 12.2 Support for the Turbine and Genentor.......................................................................... 57 12.3 BoTtom metallic screen and its Support........................................................................ 58 12.4 The guide tubes and its Support ..................................................................................... 59 12.5 Support for the Electricity Cables/conduits................................................................. 60

13 ELECTRICAL & MECHANICAL WORKS........................................................................... 61 13.1 Major Electrical Equipment ............................................................................................. 61 13.2 Hydro-Turbine ................................................................................................................... 61 13.3 Generator............................................................................................................................. 63 13.4 LV Switchboard and control panel................................................................................. 64

14 CLP’S REQUIREMENTS FOR ON-GRID CONNECTION.............................................. 75

15 OPERATION AND CONTROL OF THE HYDROPOWER PLANT .............................. 83 15.1 Normal Start-up................................................................................................................. 83 15.2 Normal Shut-down ........................................................................................................... 83 15.3 Emergency Shut-down ..................................................................................................... 84 15.4 Failure of Power Supply................................................................................................... 84 15.5 Control and INstrumentation.......................................................................................... 85 15.6 Maintenance issues............................................................................................................ 85

16 SPECIFICATIONS OF THE PROPOSED HYDROELECTRIC SYSTEM...................... 86

17 PROJECT INTERFACE AND IMPLEMENTATION SCHEDULE.................................. 88 17.1 Project Interface.................................................................................................................. 88 17.2 Implementation Schedule ................................................................................................ 88

18 BUDGETING................................................................................................................................ 89 18.1 Capital Cost and Recurrent Cost .................................................................................... 89

19 ANNUAL ENERGY YIELD, FINANCIAL AND ENVIRONMENTAL BENEFITS...................................................................................................................................... 91 19.1 Power & Energy Generation............................................................................................ 91 19.2 Power Utilization............................................................................................................... 92 19.3 Environmental Benefits .................................................................................................... 92

20 CONCLUSIONS & RECOMMENDATIONS ...................................................................... 95 20.1 General................................................................................................................................. 95 20.2 E & M EquipmeNt & Civil Work.................................................................................... 95 20.3 Construction Method Statement..................................................................................... 95 20.4 Project Interface and Implementation............................................................................ 95


January 2008 4

1 Introduction

1.1 BACKGROUND

The Stonecutter Island Sewage Treatment Work (SCISTW) is capable of handling a daily sewage flow of 1.7 million m3/d. After treatment, the effluent is discharged via a 1.7 km long submarine outfall to the western approach of the Victoria Harbour. There are 36 sedimentation tanks (excluding two prototype tanks) and 18 associated vertical outflow wells in SCISTW.

The vertical drop distance of water inside the vertical outflow well can be as high as 5.5 - 8m. The velocity near the bottom of the well can be greater than 7 m/s. Due to the difference in the static water levels, there is a potential to recover pressure energy of the effluent water at the vertical outflow well of the treatment works to generate electricity by a water turbine generator.

In February 2007, the Drainage Services Department (DSD) commissioned PolyU Technology & Consultancy Company Limited (PTeC) to undertake an assignment under the “Consultancy Agreement No. DEMP/06/19 – Application of Hydroelectric Technology in SCISTW” (hereinafter called “The Assignment”), with the objective to investigate the technical feasibility and cost effectiveness for constructing a pilot hydropower plant for the generation of electrical energy to be used as part of the electricity supply to the SCISTW by utilizing the net available pressure of the outflow.

1.2 SCOPE OF THE ASSIGNMENT

The scope of this Assignment comprises: -

To carry out literature studies and market searches to collect the up-to-date information including the technical data and job references, of the hydroelectric technology, in particular the application of low head micro-hydroelectric technology in sewage treatment plants;

To investigate the possibility of applying the hydroelectric technology in SCISTW from the engineering point of view, including the required civil modification works, liaison with CLP Power for connecting the hydroelectricity generation plant to his electricity supply grid, etc.; and

To carry out a preliminary assessment on the cost-effectiveness of applying the hydroelectric technology in SCISTW


January 2008 5

1.3 STRUCTURE OF THE REPORT

Following the introductory section, the remainder of this Report is structured as follows:-

Part A – Literature Studies and Market Searches

Section 2 – Literature Studies on Hydroelectric Technology

This will review the advantages and disadvantages of hydroelectricity, and their relevancy to this project.

Section 3 – Suitable Types of Turbines and Generators

This section will discuss the type of turbine and generator suitable for the application of this project.

Section 4 – Information of Similar Projects

A few examples of applications in water/sewage treatment plants will be given in this section

Section 5 – Technical Details of Suitable Turbines and Generators

This section will present technical details of some suitable turbines and generator collected from suppliers. Part B –Technical Feasibility of the Proposed Hydroelectric Technology

Section 6 – Measurement of Flow Rate of the Final Effluent in the Vertical Water Outlet Well

This section will present the measurement results of the flow rate. Section 7 – Measurement of Static and Dynamic Heads of the Final Effluent in the

Vertical Water Outlet Well

This section will present the measurement of static and dynamic head of the flow in the Vertical Water Outlet Well.

Section 8 – Design References

This section will contain the design references for the pilot hydropower plant.

Section 9 – Proposed Hydroelectric Technology Application in SCISTW

This section will highlight the description of the proposed hydro turbine system.

Section 10 – Possible Options for the Proposed Hydroelectric System

This section will summarise the options recommended for the pilot hydropower plant.

Section 11 – Hydraulic Design

This section will provide the hydraulic design for the pilot hydropower plant.

Section 12 – Civil Requirements

This section will give the details of the general arrangement of the hydroelectric system as well as the associated civil and structural requirements.


January 2008 6

Section 13 – Electrical & Mechanical Works

This section will present the electrical and mechanical works for the hydropower system.

Section 14 – CLP’s Requirements for On-grid Connection

This section will stipulate the CLP’s requirements for the on-grid connection of the proposed hydroelectric system.

Section 15 – Operational and Control of the Proposed Hydroelectric System

The operational requirements of the hydroelectric system will be discussed in this section.

Section 16 – Specifications of the Proposed Hydroelectric System

The construction method statement of the hydroelectric system will be provided in this section.

Section 17 – Project Interface and Implementation Schedule

This section will discuss the project interface and present a tentative implementation programme for the hydroelectric system.

Part C – Cost-Effectiveness of the Proposed Hydroelectric Technology

Section 18 – Budgeting

This section will discuss the estimated costs of the whole project

Section 19 – Annual Energy Yield, Financial and Environmental Benefits

This section will discuss the annual energy yield, financial and environmental benefits of the whole project

Part D – Conclusions and Recommendations

Section 20 –Conclusions and Recommendations

This section will summarise the whole project.


January 2008 7

Part A – Literature Studies and Market Searches

2 Literature Studies on Hydroelectric Technology Within the various sewage treatment plants in DSD, there are various locations of vast water flow rate at low water head. DSD would like to explore the possibility of applying hydroelectric system at these locations to recover partly the energy in the water flow, without scarifying the performance of the sewage treatment plants. If the concept can be applied, then it will

1. help to boost the applications of renewable energy in Hong Kong;

2. help to reduce the emission of green house gases in Hong Kong;

3. reduce electricity bills of DSD;

4. also act as a response to government initiatives of green features in infrastructure projects.

The following paragraphs are summary of literature studies on hydroelectric technology; a list of reference is attached at the end of this chapter. Hydro-electricity basically has following positive aspects:

1. Hydroelectric energy is a renewable energy source.

2. No carbon dioxide is emitted as a result of hydropower.

3. Hydroelectric energy is non-polluting. It does not cause chemical pollution of ground or water or the release of heat or noxious gases.

4. Hydroelectric energy has no fuel cost and has relatively low operating and maintenance costs, so it is a good investment in times of inflation and can provide very low cost electricity.

5. Hydroelectric stations have a long life. Many existing stations have been in operation for more than half a century and are still operating efficiently.

6. Hydropower station efficiencies of over 90% can be achieved, making it the most efficient of energy conversion technologies.

7. Hydroelectric energy technology is a proven technology that offers reliable and flexible operation.

8. Hydropower offers a means of responding within seconds to changes in load demand.


January 2008 8

9. A dam can be a useful resource for leisure, fishing, irrigation or flood control.

Point #6 may not apply in the sewage treatment plants of DSD. 90% efficiency can only be achieved in hydroelectric station of very large scale and high head. Point #8 does not apply in the proposal of this case. The output power will not be controlled but be simply fed into the grid. Obviously Point #9 does not apply in the sewage treatment plants of DSD. There are however some social, ecological and hydrological effects have to be taken into consideration when planning a hydroelectric power station. These effects can be enormous if the system is very large:

1. Hydropower is only suitable for sites with large volumes of flowing water. Decreased rainfall, due to climate change, would reduce the electricity available.

2. Considerable capital investment is required, especially for large schemes.

3. Dams cause large areas upstream to be flooded. This may cause displacement of people and will destroy animal habitat and flora.

4. Flooded vegetation will rot anaerobically and emit methane, a potent greenhouse gas.

5. The dams and diversion of water may also change the groundwater flows in the local area and this can change the ecology of the area.

6. Damming the river reduces flooding which reduces the amount of silt carried downstream. It also increases the amount deposited in the dam. This may mean that the dam has to eventually be dredged while downstream there is reduced fertility in the soil.

The flow rates (as detailed later) in the sewage treatment plants of DSD are large and relatively fairly constant (as against rainfall throughout a year). Hence Point #1 is not applicable. No additional dam or reservoir is required to be constructed to hold the water. Hence the Point 3 to 6 are not applicable. Fortunately, most of the demerits mentioned here are not valid in the sewage treatment plants of DSD, maybe with only Point #2 as the exception. However, in the proposed pilot project, only one pilot hydro generator plant will be installed in one of the 18 vertical outflow wells at SCISTW. Hence the capital investment will not be too large. However, there is one specific point which need to be considered seriously in application of hydro plant in sewage treatment works as compared to other areas of applications. That is sewage water to be highly corrosive and hence all the involved equipment have to have enough protection against it. This point will add considerable amount to the capital cost of the equipment and support structure of the equipment. Therefore, overall speaking, application of hydroelectricity technology to recover energy from sewage water in general has more merits than demerits.


January 2008 9

Reference:

Adam Harvey, “Micro-hydro Design Manual”, Intermediate Technology Publications 1993.

Jiandong Tong, “Mini Hydropower”, John Wiley & Sons, 1996.

FM Griffin, “Feasibility of Energy Recovery from a Wastewater Treatment Scheme”, Proceedings of Hydropower Developments Conference, IMechE, 1997.

Edward, B.K., “The economics of hydroelectric power”, Cheltenham, UK ; Northampton, MA : Edward Elgar, 2003

Grigsby, L.L., “The electric power engineering handbook”, Boca Raton, Fla.: CRC Press, 2005.


January 2008 10

3 Suitable Types of Turbines and Generators

Turbine and generator are the two most important components in a hydroelectric project. This Section will discuss the suitable types of turbines and generators to be used in the pilot project.

3.1 SUITABLE TYPES OF TURBINES

Turbines can be classified as high head (more than 100 m), medium head (20 to 100 m) or low head (less than 20 m) machines. Turbines are also be classified by their principle of operation and can be either impulse turbines or reaction turbines.

Table 3.1: Selection of turbine types based on available water head

high head medium head low head

Impulse turbines

Pelton

Turgo

cross-flow

multi-jet Pelton

Turgo

cross-flow

Reaction turbines

Francis propeller

Kaplan

Turbine selection is based mostly on the available water head, and less so on the available flow rate. In general, impulse turbines are used for high head sites, and reaction turbines are used for low head sites. In most sewage treatment plants of DSD, low head should be the usual cases. Hence, only reaction turbines are discussed here.

The reaction turbines considered here are the Francis turbine and the propeller turbine. A special case of the propeller turbine is the Kaplan. In all these cases, specific speed is high, i.e. reaction turbines rotate faster than impulse turbines given the same head and flow conditions. Therefore a reaction turbine can often be coupled directly to a generator without requiring a speed-changing mechanism. Some manufacturers even make integrated turbine-generator sets of this type. Significant cost savings are made in eliminating the speed changing mechanism and the maintenance of the integrated hydro unit is very much simpler. Actually, the Francis turbine is more suitable for medium heads than low heads, while the propeller is more suitable for low heads.


January 2008 11

Figure 3.1 Selection of turbine based on available water head and power output (Source:

http://www.tamar.com.au/)

Francis turbines can either be volute-cased or open-flume machines. The spiral casing is tapered to distribute water uniformly around the entire perimeter of the runner and the guide vanes feed the water into the runner at the correct angle. The runner blades are profiled in a complex manner and direct the water so that it exits axially from the centre of the runner. In doing so, the water imparts most of its pressure energy to the runner before leaving the turbine via a draft tube.

Figure 3.2: Francis turbine (source: adapted from http://lingolex.com/bilc/engine.html & http://starfire.ne.uiuc.edu/~ne201/1996/schoenau/wheel~1.html)


January 2008 12

The Francis turbine is generally fitted with adjustable guide vanes. These regulate the water flow as it enters the runner and are usually linked to a governing system which matches flow to turbine loading in the same way as a spear valve or deflector plate in a Pelton turbine. When the flow is reduced the efficiency of the turbine falls away.

The basic propeller turbine consists of a propeller, similar to a ship's propeller, fitted inside a continuation of the penstock tube. The propeller usually has three to six blades, three in the case of very low head (just a few meters) units and the water flow is regulated by static blades or gates just upstream of the propeller. This kind of propeller turbine is known as a fixed blade axial flow turbine because the pitch angle of the rotor blades cannot be changed. The part-flow efficiency of fixed-blade propeller turbines tends to be very poor.

Figure 3.3: Axial flow propeller turbine

For the intended location on the application in SCISTW, the head is low (less than 10 m) and there are more physical constraints in installing Francis turbine, an axial flow propeller turbine is more suitable for installation, such that the propeller is installed with its axis is vertical.

Kaplan turbines, is a special type of propeller trubine, in which the pitch of the blades and the guide vanes can be adjusted. They are well-adapted to wide ranges of flow or head conditions, since their peak efficiency can be achieved over a wide range of flow conditions by controlling the gates openings and the pitch angles of the blades. Semi Kaplan turbines are the same as Kaplan turbines, but now the guide vanes are fixed, only the pitch of blades can be changed.

Figure 3.4: Kaplan turbine


January 2008 13

Figure 3.5 A drawing showing arrangement for a vertical axis “Saxo” axial flow Kaplan turbine (Source – Bofors-Nohab brochure “Small scale hydro turbine program” 5702)

Anyway, the flow rate at the intended location is relatively constant, hence basic propeller type turbine, not Kaplan type, is more preferable to increase the robustness of the trubine (need no blade angle changing mechanism) and to reduce the complication in control. However, Kaplan type turbine can also be considered.

3.2 SUITABLE TYPES OF GENERATORS For the power range of tens of kilowatt grid-connected renewable energy systems, the commonly used generators are:

o Three-phase synchronous generator and

o Three-phase asynchronous generator (also commonly referred as three-phase induction generator).

In theory, any DC generators can also be used and then DC can be converted to three-phase AC via a three-phase grid-connected inverter. However this configuration is not recommended for the proposed system, due to the overall efficiency is low for this configuration in the proposed power range and the complications in the maintenance of the generator and the system.


January 2008 14

Induction generators are generally more appropriate for relatively smaller systems (in tens/hundreds kilowatt, not megawatt scale). They have the advantage of being rugged, almost maintenance-free and cheaper than synchronous generators (around 10% to 25% lower in price for the range of tens of kilowatt). In fact, the choice on synchronous generators is quite limited for power range of tens of kilowatt. The induction generator is, in fact, a standard three-phase induction motor, wired to operate as a generator. Hence the choice of induction generators at tens of kilowatt power range is many. Induction generators can also allow for a wider variation of shaft speed (hence the water flow rate). Synchronous generators are generally appropriate for multi megawatt systems. They have the advantage of slightly higher efficiency and the excitation is directly controllable. Hence the excitation can be controlled for maintaining the stability, VAR compensation and voltage regulation of the power grid. In the proposed hydro plant, it is recommended to use induction generator. The reasons are:

o The water flow rate in the proposed hydro plant is likely to have some variations (although small) due to the variation of amount of the incoming sewage water. Induction generator is more capable in coping with these variations.

o In the proposed system, the expected range of power is tens kilowatt. It has little impact of the stability of the very large power grid of CLP Power. It is not required to control the excitation of the generator of this hydro plant to help to stabilize the power grid.

o The efficiency of induction generator at tens/hundreds kilowatt range is well over 90% and it is only slightly (1 to 2 %) less than that of synchronous generator.

o The capital cost of induction generator of this power range should be 10% to 25% lower than that of synchronous generator.

o The only regular maintenance required for induction generations of this power range is the regular lubrication of the shaft bearings and the replacement of shaft bearing after long years of services. While these maintenance items are also required by synchronous generators, synchronous generators need regular replacements of carbon brushes and polishing of slip rings. Hence the maintenance cost of an induction generator of this power range should be only 40% to 70% that of a synchronous generator.

o The advantage of using synchronous generator as VAR compensator is not an important point in this case.


January 2008 15

4 Information of Similar Projects This Section gives a few examples of applications of hydroelectricity in water/sewage treatment plant in the world. One of it is as small as only 13 kW, while there is also an example of 1.35 MW rated output from the generator. This illustrated that the applications are in general feasible.

4.1 A 200 KW HYDRO PLANT IN PUAN HYDRO, KOREA

The turbine generator unit is located in an underground powerhouse which delivers water to a water treatment plant, as well as providing electrical power to the facility.

Turbine: 500mm Propeller type

Generator: rated power 200 KW @ 1200 RPM

Rated head: 19.6 m

Rated flow: 1.18 m3/sec

The 500 mm Propeller turbine

Water treatment facility

Dam feeding the facility

500 mm runner

Figure 4.1: Photos of the hydro plant in Puan Hydro, Korea (Source :

http://www.dtlhydro.com/puan.htm)


January 2008 16

4.2 A MICRO HYDRO SCHEME AT A WASTE WATER TREATMENT PLANT IN EMMERICH OF GERMANY

This is a very small hydro plant at a waste water treatment installation.

Technical Data:

o Average output power: 13 kW

o Water head: H=3.6 to 3.8 m

o Water flow rate: Q = 400 l/s

o Generator type: Asynchrongenerator 15 kW, 400V/50Hz

o Expected annual yield: 65,000 kWh

Figure 4.2: Photos of the hydro plant at Emmerich of Germany (Source:

http://www.people.freenet.de/hydropress/index_Hp_neu_Flyer.htm)


January 2008 17

4.3 A SMALL HYDROELECTRIC STATION FOR THE NEW WASTE WATER TREATMENT PLANT IN AMANN OF JODAN

The town of Amann of Jodan has decided to equip itself with a new wastewater treatment plant. In this region, the purification of water is of vital interest and the volume of water to be treated is high: 277,000 m3/day. The engineers who designed the installation, which was commissioned in 2005, found a way to reduce the operating costs of this type of installation. Yearly production has been targeted at 21,900,000 kWh in the long run by turbining of waste water upstream and downstream from the station. The company that is going to build and operate the new sewage treatment plant in Jordan, entrusted the turbining design to a minihydraulics laboratory in Switzerland. This laboratory decided to use the height difference between the town of Amann (site of the pre-treatment plant) and the sewage treatment plant in As Samra (103.5 m), in order to produce electricity between the outlet of the treatment plant and the run-off into the Oued Duleil (47.8 m). The company also claimed that there is great potential for electricity production in a treatment plant, and most sites do not use this potential. Indeed, the digestion gas (biogas) that is produced can be transformed into electricity thanks to a TOTEM (Total Energy Module) and surplus hydraulic pressure can be turbined. When the conditions to use these two potentials are combined, a sewage treatment plant can produce more electricity than it consumes. The engineers of the company realized that the height difference and flow were financially interesting at the Amann site. They decided to recover the surplus pressure at the entrance to or at the outlet of the sewage treatment plant by replacing the dissipating valves with turbo generators thus allowing for the production of electricity. They distinguish between two types of energy recovery. In the first type, raw sewage is turbined at the outlet of the sewage pipes that transport the waste water from the town upstream from the treatment plant. In the second type, treated water from the treatment plant is turbined at the outlet of a pipe or at a stream or river, like in a conventional hydro-electric installation. The town of Amann will make significant energy savings using the principle which was decided upon. Indeed, sewage treatment plants use a great amount of energy. The driving force needed for the sifters, mixers, pumps, fans, etc. consume great quantities of electricity.


January 2008 18

4.4 A 1.35 MW HYDRO PLANT AT THE POINT LOMA WASTEWATER TREATMENT PLANT

The Point Loma Wastewater Treatment Plant of San Diego (California, USA) is located on a bluff above the Pacific Ocean. Treated wastewater (“effluent”) is discharged into the ocean through a 7.2 km ocean outfall after a 27-m drop from the plant to the outfall. A 1,350 kilowatt hydroelectric plant captures the energy of the effluent as it flows down the outfall connection. The power plant, partially funded by a grant from the California Energy Commission, produces up to 1.35 megawatts for sale to the electric grid, enough power to supply energy to 10,000 homes. Opened in 1963, the Point Loma Wastewater Treatment Plant treats approximately 662,000 m3/day of wastewater generated in a 1,165-km2 area by more than 2.2 million residents in 12 municipalities. Located on a 16-ha site on the Point Loma bluffs in San Diego, the advanced primary treatment plant has a capacity of 908,400 m3/day.

Figure 4.3: The 1.35 MW generator of the hydroelectric project being installed in the Point Loma Wastewater Treatment Plant (source: Wastewater Department, City of San Diego

Metropolitan).


January 2008 19

5 Technical Details and Budgets of Suitable Turbines and Generators

The following turbine and generator suppliers have been approached and those gave responses are:-

(i) Tyco-Tamar Design of Australia (ii) Gugler Hydro Energy GmbH of Austria (iii) Kubota Corporation of Japan

Data were collected from these of turbine and generator suppliers. This section will present those in the relevant rating range to the proposed project.

5.1 TYCO-TAMAR DESIGN IN AUSTRALIA Tyco-Tamar Design in Tasmania of Australia can supply series of micro to small trubine/generator set with power output from the generator varies from less than a kw to hundreds of watt. Those suitable ones (both in available water head and the rated power, hence the estimated flow rate) off the shelf are high-lighted in red in the table.

Table 5.1: Models of micro to mini turbine generator sets from Tyco-Tarmar Design Co. Ltd.

Turbine Type

Code Head range (m)

Electrical Range (kW).

Pelton LCP1 16 to 100 0.1 to 3 Turgo Impulse LCT1 6 to 42 0.1 to 3

Pelton AP2 28 to 120 0.85 to 9.1 " " AP3 34 to 150 1.9 to 15

Turgo Impulse AT1 20 to 70 0.8 to 7 " " AT2 10 to 90 0.49 to 15 " " AT3 6 to 80 0.45 to 15 " " AT3 twin 4 to 50 0.25 to 15

Pelton SP3 60 to 150 6 to 24 " " SP3 twin 60 to 150 8 to 38

Turgo Impulse ST3 55 to 100 12 to 34 " " ST3 twin 45 to 70 19 to 34 " " ST4 25 to 120 7 to 77 " " ST4 twin 25 to 80 16 to 90


Turgo Impulse ST5 30 to 130 14 to 140 " " ST5 twin 30 to 110 30 to 230

Pelton SP5 120 to 230 55 to 150


January 2008 20

Turgo Impulse ST6 30 to 200 22 to 440 " " ST6 twin 30 to 190 50 to 640



January 2008 21

Turbine

Type Code Head range

(m) Electrical

Range (kW). Francis F6 2 to 20 0.1 to 8.5

" " F9 2 to 30 0.5 to 45 " " F10 2 to 50 0.8 to 70 " " F12 2 to 50 0.9 to 104 " " F14 2 to 50 1.4 to 153 " " F16 2 to 50 2.0 to 220 " " F18 2 to 50 2.8 to 300

Turbine Type

Code Head Range (m)

Electrical Range (kW)

Semi Kaplan FS2 - 110 1 to 20 0.3 to 3.5 " " FS2 - 135 1 to 20 1.7 to 15.4 " " FS2 - 165 1 to 20 2.6 to 23 " " FS2 - 200 1 to 20 3.7 to 33 " " FS2 - 245 1 to 20 5.7 to 50 " " FS2 - 300 1 to 20 8.5 to 75 " " FS2 - 365 1 to 20 12.6 to 113 " " FS2 - 450 1 to 20 19.2 to 171

Figure5.1: An example of a 110 kW Semi-Kaplan turbine, Model FS2-365, (with hydraulically operated turbine blades) at assembly stage (Source: Tyco-Tarmar Design Co. Ltd.)


January 2008 22

Figure 5.2: Left: Hydralical power pack with PLC for the controlling the main inlet valve and the blades of the semi-Kaplan trubine to maintain optimum efficiency. Right: The main

electrical cabinet which contains the electrical switch gear, gnerator protection, local power distribution circuit breakers, a PLC, and other asscoiated control and electrical equipment.

(Source: Tyco-Tarmar Design Co. Ltd.) As mentioned in previous section, Francis type trubine is not recommended due to the head and the physical constainted in the site, only Kaplan or semi-Kaplan trubine from this company will be considered. Then, it seems that the most appropirate one is model FS2-245 semi-Kaplan turbine/generator set: the head can range from 1 to 20m, while the output power ranges from 5. 7 to 50 kW. The company claims that units can be designed and manufactured to suit the particular site to gain maximum efficiency.


January 2008 23

5.2 GUGLER HYDRO ENERGY GMBH FROM AUSTRIA Gugler Hydro Energy GmbH is a company of 80-year old and she specializes in small trubine. She claimes that she is worldwide successful as complete provider of small hydropower plants with its innovative products. Gugler Hydro Energy GmbH offers a three-blade Kaplan turbine (model: Gugler KT 50) of turbine diameter of 0.5m, it has mannual adjustable runner blades, fixed wicket gates, the other technical details are:

Net head range (Hn): 1-6 m Discharges rate range (QA): 300-1,500 litre/sec Rated trubine output (PT): 2.5 – 60 kW Rated generator output (PG): 1.8 to 50 kW Turbine speeds (n1): 350-1,000 rpm Runaway speeds (nd): 1,200-3,200 rpm Generator speed (n2 at 50 Hz/60 Hz): 1500-1800 rpm

Limits and parameters:


January 2008 24

Operation curves of the KT-50 turbine/generator set is shown in the following figure.

Figure 5.3: Operation curves of the KT-50 turbine/generator set of Gugler Hydro Energy

GmbH

Figure 5.4: the KT-50 turbine/generator set of Gugler Hydro Energy GmbH


January 2008 25

Another suitable candidate for the proposed project from Gugler Hydro Energy GmbH is its KT-35 model. Its technical details are:

A three blade Kaplan runner Runner diameter 355 mm Manual adjustable runner blades Fixed wicket gates;

Net head range (Hn): 1-6 m Discharges rate range (QA): 100-750 litre/sec Rated trubine output (PT): 2.5 – 40 kW Rated generator output (PG): 1.8 to 35 kW Turbine speeds (n1): 350-1,000 rpm Runaway speeds (nd): 1,200-3,200 rpm Generator speed (n2 at 50 Hz/60 Hz): 1500-1800 rpm

Limits and parameters:


January 2008 26

Figure 5.5: Operation curves of the KT-35 turbine/generator set of Gugler Hydro Energy

GmbH


January 2008 27

5.3 KUBOTA CORPORATION OF JAPAN

Kubota Corporation established in 1890 and now is a stock-listed company at Tokyo, Osaka, New York and Frankfurt. It has about 24,000 employees and a net sales amount of US$600 million/year. Kubota can supply a turbine/generator set of 45 kW rated power output suitable for this project.

The technical details the turbine generator set are:


January 2008 28

Figure 5.6: Operation curves of the 45 kW Turbine – gnerator set from Kubota Corporation

(Note: the term “reverse running pump turbine” is used here in the manufacturer’s data sheet, however it should be the same as the “basic propeller type”).


January 2008 29

Part B –Technical Feasibility of the Proposed Hydroelectric Technology

6 Measurement of Flow Velocity of the Final Effluent in the Vertical Water Outflow Well

The water flow rates at three different points inside one of those deep vertical outflow wells were measured through tailor-made supporting rigs and a test instrument procured specifically for this project. The measurement was conducted on 23rd July 2007, from 9:00 am to 5:30 pm.

6.1 EQUIPMENT SPECIFICATION Test device - Safety factor = 1.25 - Anticorrosive materials

Flow meter - Range of measurable flow velocity ~ 0 to 9.8 ms-1 - Real-time monitoring - Anticorrosive materials

Figure 6.1: The flow meter sensor used in the measurements


January 2008 30

6.2 RESULTS OF MEASUREMENTS AND ESTIMATIONS Measurement Position 1 Depth = 4480 (mm) Effective Depth = 1800 (mm) Time interval = 60 (s) Number of turns - Sample 1 = 879 (Turns), 4.76 ms-1 - Sample 2 = 877 (Turns), 4.75 ms-1 - Sample 3 = 862 (Turns), 4.66 ms-1

Average measured flow velocity =

4.72 ms-1

Theoretical maximum flow velocity at that point

5.94 ms-1

Measured/Theoretical= 79% ______________________________________________ Measurement Position 2 Depth = 5980 (mm) Effective Depth 3300 (mm) Time interval = 60 (s) Number of turns - Sample 1 = 1113 (Turns), 6.06 ms-1 - Sample 2 = 1108 (Turns), 6.03 ms-1 - Sample 3 = 1115 (Turns), 6.07 ms-1 Average measured flow velocity =

6.05 ms-1

Theoretical maximum flow velocity at that point =

8.05 ms-1

Measured/Theoretical= 75% ______________________________________________ Position 3 (the estimated position of the turbine)

Depth = 7480 (mm) Effective Depth (the depth is too deep to be measured by the instrument)

4800 (mm)

Theoretical maximum flow velocity at that point =

9.7 ms-1

Estimated flow velocity, based on Measured/Theoretical=~75%, as obtained in above 2 measurements

7.2 ms-1

______________________________________________


January 2008 31

Remarks: 1. The conversion from the number of turns to flow rate (in ms-1) is based on the conversion

information provided from the manufacturer of the flow rate sensor. 2. The theoretical maximum flow velocity is calculated from equation of basic free fall in vacuum.

Hence there is expected difference between theoretical maximum flow velocity and the actual velocity due to fluid viscosity and air pressure.

3. The reason for measurements cannot be taken for position 3 is the limitation of the length measurement rod, otherwise the mechanical strength of the whole set up will be too weak.

Figure 6.2: Measurement configuration


January 2008 32

7 Estimation of Static and Dynamic Heads of the Final Effluent in the Vertical Water Outlet Well

Based on the results of the above section, the velocity of the flow at the position of the turbine is about 7.2 ms-1. Hence the dynamic head at the location = v2/(2g) = 2.64 m

While the static head is estimated to be 4.8 m. Hence the total head in the worst case is 7.44m. Note this is the worse case, as (i) the installation of the guide tube and turbine in the well will reduce the flow velocity, (ii) the velocity of the flow used here is the velocity at the centre of the flow which is the highest, (iii) it may not be a full-bore condition at the top part of the well (the effective head is likely to be 4.5 m).


January 2008 33

8 Design references

8.1 DESIGN INPUTS

In this Report, design inputs for the hydropower plant shall include taking references to all statutory requirements, design standards, codes and guidelines, at both local and international dimensions.

8.2 RELEVANT STANDARDS, CODE OF PRACTICE AND OTHER MANUALS/REFERENCES

The proposed works shall be designed based on the relevant codes and standards that meet the Drainage Services Department, other local government department, and utility companies’ requirements as well as to follow the good engineering practice on similar works. The following codes of practice, standards and other manuals/references with the associated amendments and additions shall be adopted for the design of the Project:

Table 8-1 Relevant Design Standards, Code of Practice and other Manuals/References

For Civil, Structural and Geotechnical Works: 1 General Specification for Civil Engineering Works, Volumes 1, 2 and 3, Civil Engineering

Department

2 Stormwater Drainage Manual, DSD

3 Building Department Practice Note for Authorized Persons & Registered Structural Engineers No. 141 — Foundation Design

4 BS 8007 — Code of Practice for Design of Concrete Structure for Retaining Aqueous Liquids

5 BS 8110 — Structural Use of Concrete

6 BS 4482 — Specification for cold reduced steel wire for the reinforcement of concrete

7 BS 4483 — Steel fabric for the reinforcement of concrete

8 BS EN 752-2 — Drains and Sewer Systems Outside Buildings – Performance Requirements

9 BS EN 752-3 — Drains and Sewer Systems Outside Buildings – Planning

10 BS EN 752-4 — Drains and Sewer Systems Outside Buildings – Hydraulic Design and Environmental Considerations

11 BS EN 295 — Vitrified Clay Pipes and Fittings and Pipe Joints for Drains and Sewers

12 BS 5400-1 — Steel, Concrete and Composite Bridges. General Statement

13 BS 5400-2 — Steel, Concrete and Composite Bridges. Specification for Loads

14 BS 5400-4 — Steel, Concrete and Composite Bridges. Code of Practice for Design of Concrete Bridges

15 BS 8010 — Code of Practice for Pipelines

16 BS 4449 — Specification for Carbon Steel Bars for the Reinforcement of Concrete

17 BS 4027 — Specification for Sulfate-Resisting Portland Cement

18 BS 4248 — Specification for Supersulphated Cement

19 BS 8004 — Code of Practice for Foundations


January 2008 34

20 BS 534 — Specification for Steel Pipes, Joints and Specials for Water and Sewage

21 BS 970-1 — Specification for Wrought Steels for Mechanical and Allied Engineering Purposes. General Inspection and Testing Procedures and Specific Requirements for Carbon, Carbon Manganese, Alloy and Stainless Steels

22 BS 4504-3.3 — Circular Flanges for Pipes, Valves and Fittings (PN designated). Specification for Copper Alloy and Composite flanges

23 CIRIA report No. 78 Mechanical and Electrical Works: 24 Standard Specifications of the Water Supplies Department

25 General Requirements for Electronic Contracts, Specification No. ESG01, Electronics Division, Electrical & Mechanical Services Department, EMSD

26 Supply rules and other requirements of the CLP Power Hong Kong Limited.

27 Renewable Energy Systems and CLP’s Electricity Grid, CLPP

28 Code of Practice for the Electricity (Wirings) Regulations, EMSD

29 General Specification for Electrical Installation in Government Buildings of the HKSAR, Architectural Services Department, ASD

30 Regulations for Electrical Installations, Institution of Electrical Engineers, UK

31 Technical Guidelines on Grid Connection of Small-scale Renewable Energy Power Systems, 2005, EMSD

32 IEEE Standard 1547 for Interconnecting Distributed Resources with Electric Power Systems

33 UL 1741, Inverters, Converters, Controllers and Interconnection System Equipment for Use with Distributed Energy Resources

34 EA G59/1, Recommendations for the Connection of Embedded Generating Plant to the Public Electricity Suppliers’ Distribution Systems

35 Code of Practice for Energy Efficiency of Electrical Installation, EMSD

36 Guidelines on Energy Efficiency of Electrical Installation, EMSD

37 Addenda to Guidelines on Energy Efficiency of Electrical Installations, EMSD For Design of Building Services: Electrical Installation 38 Electrical Ordinance

39 IEE/IET Regulation

40 Codes of Practice for Electricity (Wiring) Regulation, EMSD

41 General Specification for Electrical Installation in Government buildings

42 BS 6651 — Code of Practice for Protection of Structures Against lighting

43 CIBSE Code

44 Code of Practice for Energy Efficiency of Lighting Installation, EMSD

45 Guidelines on Energy Efficiency of Lighting Installations, EMSD

46 Addendum No. 1 to Guidelines on Energy Efficiency of Lighting Installations, EMSD Fire Services Installation 47 Codes of Practice for Minimum Fire Service Installations and Equipment, Fire Services

Department (FSD)

48 FSD Circular Letters


January 2008 35

49 L.P.C. Rules

50 Requirement of Water Authority

51 BS 5839 — Automatic Fire Detection and Alarm System

52 Fire Offices’ Committee Rules

53 General Specification for Fire Service Installation in Government Buildings, Hong Kong MVAC Installation 54 The requirement of the Hong Kong Fire Services Department including “Codes of Practice

for Minimum Fire Service Installations and Equipment, and Inspection and Testing of Installations and Equipment” issued by the FSD, together with FSD circulars/letters/amendments.

55 Building Ordinance and the affiliated regulations

56 General Specification for Air-conditioning and Refrigeration, Ventilation and Control Monitoring and Control System Installations in Government Buildings

57 CIBSE Guide


January 2008 36

9 Proposed Hydroelectric Technology Application in SCISTW

The proposed pilot hydropower plant incorporates a turbine to convert energy in the form of falling effluent water in the vertical outflow well of the sedimentation tanks of SCISTW into rotating shaft power. The static pressure head between the water level of the tank and the water level of the horizontal trench at the bottom ranges from about 4.5 to 6 metres depending on the operating conditions and the exact location of the turbine.

The shaft power is then converted to electricity by a generator coupled to the turbine. The output voltage is expected to be 380 V three-phase AC and then connected to a switchboard and control panel.

The hydro-turbine is designed to work under maximum 6 m static head under operating conditions. The effective static head is about 4.5m while the efficient operating flow rate is from about 1.1 to 1.25 m3/s. The maximum power output from the generator shall be approximately 45kW to 50kW. Besides, the hydro-turbine shall be designed to cater for the start up under hydro-static /surge conditions that may be as high as 17 metres total head equivalent. This head will be diminished as the turbine flow increases to the normal operating range as specified.

As mentioned above, the estimated maximum power output of the system is about 45kW to 50 kW, and this is basically the maximum allowable output from a turbine with the given possible water head, typical machine efficiency and physical internal dimension constraints of the well. The dimension constraints limited the external size of the whole setup to be within 1.2 m in diameter. Then with reasonable allowance for fixture mounting, the effective diameter of the turbine can only be about 1 m in diameter. After experience gained in this pilot project, this maximum power output for subsequence installation may be increased slightly by increasing the effective diameter of the turbine without affecting the overall external diameter.

Power generated by the hydro-turbine generator will be utilized at the SCISTW to provide co-generated power with the utility to the all electrical installation within SCISTW. All power generated by the hydro-turbine driven generator shall be utilized on site as a reduction in the amount of power received from the utility. There will be no export (to outside of SCISTW) of the power by the turbine generator. The hydro-turbine generator unit shall always operate in conjunction with the utility supply, and shall not operate independently without the utility.


January 2008 37

Figure 9.1 Schematic of power flow of the hydro plant

Local LV Distribution Board

Turbine Generator LV Switchboard

Effluent Outflow Water


January 2008 38

10 Possible Options for the Proposed Hydroelectric System

10.1 GENERAL

Major equipment/facilities to be incorporated in the hydropower plant include turbine, generator, control valve/gate, LV switchboards and control panel. The turbine and the generator will be installed in a vertical outflow well. The control valves/gates will be installed at the top of the well. The LV switchboard and control panel will be installed inside an existing switchboard room near the vertical outflow well. Additional small cable conduits will also be required to be installed between the generator and the LV switchboards/control panel.

10.2 TURBINE / GENERATOR SET

The turbine has to be mounted vertically inside the vertical outflow well in order for the turbine to capture the water flow with minimum civil modification works. Of course, another alternative is to re-route that part of effluent water to a separate structure (next to the vertical outflow well) which houses the turbine in whatever orientation. However, this alternative is not recommended in this report due to the complicated civil modification works involved.

The selected vertical outflow well for this pilot project is #40-#42 (i.e the well between tank #40 and tank #42). The reason of the selection is:

♦ This well is near the upstream end of the effluent water flow (in fact the 2nd first well along the flow path) under all these wells. In case, there are needs to stop the flow of effluent water under this well during turbine installation period, the operations of other wells are minimally affected.

♦ Although this well is not the first well in the flow (well #44-#46 is the first one), it very often operates together with the well #44-#46. Therefore there will be no effluent water flow from well #44-#46 to well #40-#42.

♦ The reason of not selecting the first well #44-#46 is that there is an existing odour eliminator at the top of the well.

If the odour eliminator can be removed, it is better to install the hydroelectric system to the first well #44-#46.


January 2008 39

Figure 10.1: Diagram and photo shows the location of Tank #40 and Tank #42 which will be used in the pilot hydro project.


January 2008 40

Figure 10.2: Relative locations of the some of tanks and some of the wells; the pilot project will use Tank #40 and Tank #42, and also Well #40-#42 (not to scale).

Tank #46

Tank #44

Tank #42

Tank #40

Tank #38

Tank #36

Tank #34

A platform, a local LV switchboard is under this here

Well #44-#46

Well #40-#42

Well #36-#38

Well #34


January 2008 41

Figure 10.3: Upper diagram is the cross section of a typical tank and vertical outflow well. Lower diagram is a photo showing the top of one of the vertical outflow wells (covered), note: one can see a very wide access road is at ground level just next to these wells, this road can be

used for transportation and installation of the set up


January 2008 42

There are three possible ways of mounting the generator

(a) The generator is mounted at the top of the vertical outflow well such that the axle of the generator can be coupled to the axle of the turbine.

Advantages of this method:

♦ The generator is not installed under the water. Hence the construction and requirements is less demanding.

♦ The gravitational loading of turbine and the generator now separately act on two different locations. The weight of the turbine acts on the wall sides of the well, while the weight of the generator acts on the footing mounted on the top of the well. Therefore the civil work to be done on the interior wall of the well is less.

♦ Easy access to the generator for maintenance can be possible.

Disadvantage of this method:

♦ The length of the coupling between the generator and the turbine is very long, about 8m. And this coupling shaft/device has to work under the strong effluent water current. There should be at least two intermediate support along the shaft. It is not easy to maintain the mechanical steadiness of the coupling shaft/device even with these supports.

Figure 10.4 shows the location of the proposed turbine / generator set in case (a).

Water Inflow

Turbine

Generator

The vertical outflow well

4.8m


January 2008 43

(b) The generator and turbine are integrated into one unit and mounted inside the well


♦ This will result a more compact design.

♦ There is no coupling problem between the turbine and the generator. Hence it gives a more stable operation in mechanical terms. The overall efficiency should be slightly higher than case (a).


♦ The generator has to work under water and hence the demand on its design is higher.

♦ The whole set has to be hoisted up for maintenance, even if only the generator needs maintenance (it is expected that the generator needs more frequent maintenance than the turbine).

Figure 10.5 shows the location of the proposed turbine / generator set in case (b).

(c) The generator mounted at the same level as the turbine, but outside the well.


♦ The generator is not installed under the water. Hence the construction and requirements is less demanding.

Turbine

Generator


Water Inflow

Support for the generator/turbine set

4.8m


January 2008 44

♦ The gravitational loading of turbine and the generator now separately act on two different locations. The weight of the turbine acts on the wall sides of the well, while the weight of the generator acts on the footing mounted at ground level outside the well. Therefore the civil work to be done on the interior wall of the well is less.

♦ Easy access to the generator for maintenance.


♦ The civil work involved will be much larger than case (a) and (b)

♦ There is difficulty in the water sealing for the coupling between the generator and the turbine.

♦ If the axis of the turbine is vertical, then a complicated coupling device is needed between the turbine and the generator. This will reduce the efficiency and reliability of the system. If the axis of the turbine is horizontal, the physical size of the turbine has to be increased, which may not be feasible in this very limited space situation.

♦ This will add certain restriction on the height of the installation of the turbine

Figure 10.6 shows the location of the proposed turbine / generator set in case (c).

After consideration of all the 3 ways of mounting the generator and the site situation, the method of case (b) is recommended in this report. It is a much proven way of mounting. Requirements on the civil aspect, the generator and the turbine will be detailed in later Sections of this report.

Turbine


Water Inflow

Generator

4.8m


January 2008 45

10.3 CONTROL VALVE/GATE

The cross-section of the vertical outflow well is rectangular in shape of about 2m x 1.25 m with effective length of about 5.8 m. After the installation of turbine and its guide tube, there is still room at the side for by-passing “surplus” water flow.

Bottom screen

Figure 10.7: Location of the control gate (side view, not to scale)

Figure 10.8: Location of the control gate (top view, not to scale)

Turbine

Generator


Water Inflow

Support for the generator/turbine set Control gate

Vertical guide tube for flow (in doted lines)

Water inflow to turbine

The vertical outflow well (area 2m x 1.25 m)

Control gate

Vertical guide tube for flow (in doted lines) (largest part should be with a diameter of 1 2 m)

Surplus water flow into the side of the vertical guide tube

Turbine & Generator

Horizontal guide tube for flow (in doted lines)

Horizontal guide tube for flow (in doted lines)

Effective height of the well = 5.8m

4.8m


January 2008 46

A motorised control valve/gate will be installed on the top of the vertical outflow well for controlling the water flow into the turbine. Hence the gate can be used (i) to start the turbine smoothly at the start of the operation and to remove any large surge pressure on the turbine, (ii) to control the generator to run at about synchronous speed during the grid-connection process, (iii) to control the power output after grid connection is made, and (iv) to ensure the turbine will not run over speed.


January 2008 47

10.4 LV SWITCHBOARD

An existing LV switchboard is used to house the LV switchgear that connect the generated electricity from the turbine generator to the existing LV distribution board.

The proposed LV switchboard (2-SWB-003) is inside a switchroom situated near the vertical outflow well (within 60 m of cable length). The location of the switchroom can be shown in Figure 10.2 or 10.9.

10.5 CABLE & CONDUIT ROUTING

There are power and control cables connecting the LV switchboard and the turbine/generator set. The proposed cable & conduit routing is shown in Figure 10-9.

Figure 10.9 shows the routing of cables/conduits (red lines), from the Well #40-#42, cross Bridge A, along Bridge B, into the room under the platform next to Tank#34 (the red line

turns into red dotted line, then to the local LV switchboard.

Tank #46

Tank #44

Tank #42

Tank #40

Tank #38

Tank #36

Tank #34

A platform, a local LV switchboard is under this here

Well #44-#46

Well #40-#42

Well #36-#38

Bridge B Bridge A


January 2008 48

Figure 10.10 shows part of the routing of cables/conduits (red lines), from the Well #40-#42, cross Bridge A (all under the grid)

Bridge A

Well #40-#42

Cable in red line under the grid


January 2008 49

Figure 10.11 shows part of the routing of cables/conduits (red lines), cross Bridge A, to Bridge B, along Bridge B (all under the grid)

Well #40-#42

Bridge A

Bridge B

Cable in red line under the grid


January 2008 50

Figure 10.12 shows part of the routing of cables/conduits (red lines), along Bridge B ( under the grid), coming out from Bridge B, round a corner and then enter into a room under the

elevated platform next to Tank #34.

Cable in red line

Bridge B


January 2008 51

Figure 10.13 shows part of the routing of cables/conduits (red lines): once inside the room under the elevated platform, there are cable trays for running the cables/conduits

Cable in red line above the tray

A hole on the wall for cables to go outside, the other side of this hole is also shown in last figure


January 2008 52

Figure 10.14 shows part of the routing of cables/conduits (red lines): the cable trays run across the ceiling of the room and then move down to enter the bottom of the local LV switchboard


January 2008 53

Figure 10.15: A photo shows how cables on the vertical trays entering the raised floor of the

local LV switchboard room


January 2008 54

11 Hydraulic Design

This section will provide the hydraulic design for the pilot hydropower plant

11.1 SURGE PRESURE AND BACK PRESSURE

11.1.1 Surge Analysis

The purpose of the surge modeling is to assess the surge potential resulting from a shutdown or starting of the operation of hydro-turbine driven hydropower generator during adverse operating conditions. Hydraulic transients or surges (also sometimes called water hammer) are pressure changes that occur any time the velocity of flow changes. Velocity changes in the well by starting or stopping of the flow, sudden closure or opening of a valve or check valve, or the loss of power to pump motors. The most severe surge condition for the purposed turbine location would occur as the start of the flow in the well and results in a sudden change on the mechanical load of the hydro-turbine.

The mathematical relationship between the pressure change, dp, and the change in velocity, dv, is as follows:

dp = a(dv)/g

where: a = water pressure wave speed = about 914 m/s, and

g = gravitational constant = 9.8m/sec2

The velocity of flow through the well varies along with the depth of well, but at estimated location of the turbine, the velocity is about 7.2 m/s (from a previous section). Therefore it can be seen that for an abrupt (instantaneous) start of flow condition, the resulting pressure increase would be 914 x 7.2/9.8 = 292.5 m = 672 psi. This is a very large value. In practice, velocity changes must occur over some extended period of time so the resulting pressure spike will be considerably less.

However, now control gate will be installed at the top of the well and will be controlled to open very slowly, the duration of the opening process is in the order of a minute or minutes (say at least 30 second) instead of sub-second range. Hence the surge pressure should not be a problem here, should be at least less than one-thirtieth of the above calculated value, i.e. less than 10m surge pressure. Together with the worse case static head and dynamic head about 7 m (as discussed in a previous section), the total maximum possible transient head should be less than 17m.

17 m transient head is not a high value, and the turbine should be able to handle this transient surge without damage.

11.1.2 “Back Pressure” Issue

The effective cross section area for the flow through the turbine is much less than the cross section of the original vertical outflow well. There may be worries for building up of “back


January 2008 55

pressure” and finally sewage water accumulates in the tanks and raise the water level beyond the limit. However, it should be note that there is a by-pass path next to the turbine (please refer to Figure 10.8). Even under the case of a completely closed gate, the sewage water can flow freely down the by-pass path. The cross section of this by-pass path should be at least 0.8m x 1.0m. Even assume the effective length of the vertical well to 5.5m, while assume effective head of 4.5m, the maximum possible flow rate under very restricted flow assumptions (refer to next paragraph) should be well above 2 m3/s, which is much higher than the maximum expected flow rate of the well. Hence there is so “back pressure” issue in this case; i.e. installation of the turbine should not affect the handling capacity of the tanks.

Pressure loss in a pipe: ∆p = λLρω2/(2D) Where: ∆p is the pressure loss

λ is the coefficient of friction of the pipe L is the effective length of the pipe ρ is the density of the fluid of the flow ω is the vecocity of the flow D is the effective diameter of the pipe

Available pressure in a vertical pipe: ∆p = ρg∆H Where: ∆p is the available pressure

ρ is the density of the fluid of the flow g is the gravity constant (9.81 ms-2) ∆H is the effective length of the pipe

Equating the above two equations to make that the available pressure from the gravity all losses in the flow, this gives

∆H g =λLω2/(2D)

Rearranging it gives:

ω =√(2gD∆H/(λL))

In the proposed case, make a very worst case assumption for the by-pass path: D=0.8 m, ∆H =4.5m, L = 5.5 m, and assume a very rough inner tube surface of λ=0.15, this gives ω = 9.3 ms-1.

Assume the average velocity is only half of the 9.3 ms-1, with a D=0.8 m, the flow rate will be 2.32 m3s-1.

This means that the by-pass path can allow up to 2.32 m3s1 of water to pass through. While the estimated actual total flow rate in the well is about 1.1 to 1.6 m3s1, therefore the by-pass path is large enough even the control valve is totally shut off. In fact the current design flow rate via the turbine can be up to 1.25 m3s1. Hence even with the top total flow rate of 1.6 m3s1,


January 2008 56

the flow rate through the by-pass path should be less than 3.5 m3s1 when the control valve is fully opened.

However one should note that with the installation of the control valve and the horizontal guide tube, the water level at the horizontal channel would be raised by 0.3 m. to 0.5 m. Anyway, this still should not affect the top water level of the sedimentation tank, as the horizontal channel is at a level lower than the top water level of the sedimentation tank.

11.2 CONCLUSIONS

(1) The hydraulic analysis shows that the total maximum possible transient head should be less than 17m of water head acting on the turbine.

(2) The “back pressure” should not be an issue in the design due to the existence of a large by-pass path next to the turbine.


January 2008 57

12 CIVIL & MATERIAL REQUIREMENTS

12.1 GENERAL

The proposed site for the pilot hydropower plant is discussed in a section above, and the details of the general arrangement of the proposed hydropower plant as well as the associated civil and structural requirements will be discussed in this section.

12.2 SUPPORT FOR THE TURBINE AND GENENTOR

The integrated turbine and generator set will be located in the well at very lower end side. The cross section of the well is rectangular in shape, while the turbine generator is basically circular in shape. The set will be hanged from a support which is mounted at the top of the well, as shown in Figure 10.7.

The dead weight of the turbine and generator set is about 5,000 kg. The maximum transient pressure head is estimated to be 17m with the maximum possible cross section area of the turbine (0.5m)2 × π = 0.79 m2. Therefore the total maximum transient loading on the support is 5000 + 17x0.79x1000=18,430 kg, while the maximum steady loading on the support should be less than 5000 + 7x0.79x1000=10,430 kg. These are the required loading withstand capability for the support of the turbine generator set. The support is expected to be made of galvanised steel of heavy gauge with good corrosive resistant coating (meeting ASTM A 653 standard or equivalent), to allow its long life operation over the sewage water.

[ASTM A 653: Standard Specification for Steel Sheet, Zinc-Coated (Galvanized) or Zinc-Iron Alloy-Coated (Galvannealed) by the Hot-Dip Process]

Additional loadings that may need to be considered for the structure of the metallic support of the turbine generator set are:

additional imposed loads during installation /maintenance/operation process of the plant, including imposed loads due to construction plant,

wind load during installation/maintenance/operation (if appropriate). (That is, this metallic support will also be used to hoist up or low down the turbine generator set in the well

The expected weight of the support should be less than 400 kg. Therefore one has to check whether the existing civil structure around the well can withstand maximum static loading of 10,430 kg + 400 kg = 10,430 kg, and total transient loading of 18,430 kg + 400 kg = 18840 kg. One also has to check the per unit area floor loading capability of the existing civil structure around the well, so that a proper design on the foot padding of the metallic support for the turbine and generator set can be carried out.

Again additional loadings that may need to be considered for the civil structure of the area around the well are:

additional imposed loads during installation process of the plant, including imposed loads due to construction plant,


January 2008 58

wind load during installation/operation (if appropriate).

Site investigation reveals that there are wide internal access roads right next to the well, and the area around the well is free (please refer to Figure 10.3). Hence there should not be any problem in using a heavy truck with a large hoisting machine for the civil work, as well as the installation of the guide tubes, the turbine generator set and other equipment.

A preliminary assessment indicates that the existing civil structure should be able to support loading that mentioned above, as the weight of water that each tank can hold is more than 2,800,000 kg. Hence the static load of 10430 kg and transient load of 18840 kg are only a tiny part of the water loading.

12.3 BOTTOM METALLIC SCREEN AND ITS SUPPORT As a means of providing a safety net for workers during installation and maintenance, as well as a security net to catch any large broken pieces of equipment - say, turbine blade (just imagining very worse cases), a strong rigid metallic screen should be installed at the very bottom of the vertical outflow well before installation of any other things inside the well. The screen should be in metallic grid form of 100mm x 100 mm grid size, made of grade 316 steel bars by welding. The screen should completely cover the whole lower opening (2m x 1.25m) of the vertical outflow well. As the size of the grid is large, its impact on the flow is very minimal. The screen should be mounted securely by strong anchors onto the four inner walls of the vertical outflow well. The screen itself and the mounting should be strong enough to support at least 2,400 kg, which is the impact force for a 80 kg person falling from a height of 8 m (i.e. about the top of the support state in Section 12.2 (assuming a safety factor of 2, and impact timing of 1 second). To ensure the overall water proof capability of inner lining of the vertical outflow well is not affected, all the supports of the guide tubes should be mounted on the wall only by chemical capsule anchors to ETA-05/0231 standard or equivalent. [ETA-05/0231: European Technical Approval – MKT Chemical Anchor V] The MKT Chemical Anchor V is a bonded anchor (capsule type) consisting of a glass capsule MKT V-P and a threaded anchor rod with hexagon nut and washer of sizes M8, M10, M12, M16, M20 and M24. The anchor rod (including nut and washer) is made of galvanised steel, hot-dip galvanised steel, stainless steel 1.4401, 1.4404, 1.4571 or 1.4578 or made of high corrosion resistant steel 1.4529 or 1.4565. For this pilot project, it is preferred to use rod, nut and washer made of high corrosion resistant steel 1.4529 or 1.4565. The glass capsule is placed into the hole and the anchor rod is driven by the machine with simultaneous hammering and turning. The anchor is anchored via the bond between anchor rod, chemical mortar and concrete. Even the supports are mounted on the inner walls of the well by chemical anchors; the water proof linings on the walls should still be repaired by the original designated lining contractor


January 2008 59

after the completion on the mounting of the anchors. This is to ensure that the water proofing characteristic will not be damaged, and the warranty on the lining will also not be damaged.

12.4 THE GUIDE TUBES AND ITS SUPPORT As indicated in Figure 10-7 and 10-8, there are two guide tubes/pipes to guide the water to flow through the turbine - the upper guide tube (horizontal) and the lower guide tube (vertical). The lower guide tube is not for the support of the turbine or generator. Therefore the mechanical strength of the tubes itself and its associated support need not account for the weight or loading from the turbine and generator, but has to account for the weight of itself, side water pressure, and possible reaction torque from the turbine and generator. It is not expected to use steel for these tubes. However, the materials still need sufficient strength and strong resistance against the corrosion from the sewage water. Therefore it is recommended to use Fibreglass Reinforced Plastic (FRP) or equivalents to construct the tubes. The required specifications for the FRP materials should make reference to ASM RTP-1 or ASTM C-582 or the equivalents. [ASME RTP-1, "Reinforced Thermoset Plastic Corrosion Resistant Equipment"] [ASTM C-582, "Standard Specification for Contact-Molded Reinforced Thermosetting Plastic (RTP) laminates for Corrosion-Resistant Equipment"] It is expected that the thickness of the tube should be of at least 16mm of FRP materials. The lower guide tube (total length about 5.8 m; the largest diameter about 1.2m) should be supported at two positions, i.e. the lower end and the upper end. The lower support should be in form of a bracket which is preinstalled strongly in the well before the installation of the lower guide tube. It should also provide a good shaped seat for the lower portion of the lower guide tube to sit into the support properly without much additional fixtures, as there may not be much space left in the well for the worker to install the additional fixtures. The upper support of the lower tube should also be preinstalled before the installation of the lower guide tube. Once the lower guide tube is in position, additional fixtures can be used to fix the upper part of the lower tube to the upper support. Once the lower guide tube is properly installed, the turbine generator set can be installed with the help of the support mentioned in Section 12.2. During this stage the hand railings along edge of the workman platform at the top of the well has to be removed temporarily to allow additional space for manoeuvring the turbine-generator set. After the installation of the turbine-generator set, then the upper guide tube will be installed. The materials of the upper guide tube is expected to be the same as the lower guide tube. Again, to ensure the overall water proof capability of inner lining of the vertical outflow well is not affected, all the supports of the guide tubes should be mounted on the wall only by chemical capsule anchors to ETA-05/0231 standard or equivalent.


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Even the supports are mounted on the inner walls of the well by chemical anchors, the water proof linings on the walls should still be repaired by the original designated lining contractor after the completion on the mounting of the anchors. This is to ensure that the water proofing characteristic will not be damaged, and the warranty on the lining will also not be damaged.

12.5 SUPPORT FOR THE ELECTRICITY CABLES/CONDUITS

In the outdoor paths of the electricity cables/conduits, there are already supports available on the bridges. Hence there are no special requirements to build additional supports for the cables/conduits.

For the indoor paths of the electricity cables/conduits, there are already existing cable trays. Provide that the final design indicates that the size and weight of cables are not significant, these existing cable trays can be used.


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13 ELECTRICAL & MECHANICAL WORKS

13.1 MAJOR ELECTRICAL EQUIPMENT

The electrical and mechanical works for the pilot hydropower plant includes but not limited to the supply, installation, testing and commissioning the following:

Hydro-turbine

Induction generator

Control panel and accessorises.

LV Switchboard

13.2 HYDRO-TURBINE

Hydro-turbine is used to convert energy in the form of falling water from the sedimentation tank into rotating shaft power.

It is designed to provide most efficient operational range of flows 1.0 to 1.25 m3/s and the available net effective heads ranges from 4.5 to 5.5 meters during normal operating conditions.

Axial-flow propeller type hydro-turbine is recommended for the project. The hydro-turbine shall be equipped with valve/gate for control of turbine flow. The shape and quality of the valve/gate shall conform to the hydraulic model to assure proper flow characteristics of water entering the guide pipes of the turbine.

Suggested specifications of the turbine are:

Type: Axial-flow propeller type

Rated effective head: ~ 4.5 m

Useful range of flow rate, at least: 1 m3/s – 1.25 m3/s (preferably 1 m3/s to 1.6 m3/s)

Rated flow rate: about 1.16 to 1.2 m3/s

Rated rotation speed: should match with the generator, expect to be around 430 to 450 rpm

Efficiency (turbine & generator combined) at rated flow rate: at least 70%

Efficiency within the useful range of flow rate: at least 55%, with most of them above 65%. Fluid type: Sewage water Range of fluid temperature: 4 degree C to 40 degree


January 2008 62

Dead weight (together with generator): should be not more than 5,000 kg Installation orientation: flow direction is vertical, rotational axis is vertical Coupling between turbine and generator: direct, it is preferable to integrate the turbine and the generator together. Thrust bearing: in water turbine Bearing type & lubricant: - Radial : anti-friction, grease - Thrust: anti-friction, grease Gland seal: mechanical seal Material (includes casing, impeller, shaft): Stainless steel, grade 316 or higher Paint (both inside and outside): thermal set plastic coating system


January 2008 63

13.3 GENERATOR

The generator is used to convert shaft power to electricity. The generator type is recommended to be induction type, rated at about 45kW, 3 phases, 380V, 50 Hz. The generator should be physically integrated with the turbine as a single unit.

The stator of the generator, if possible, should be equipped with temperature sensor.

The speed and power output of the hydro-turbine is to be determined by the flow rate. During start-up, prior to connecting the electric output of the turbine driven generator, the flow rate should be controlled to bring the turbine up to a speed matching the 50 Hz utility power supply. Once the turbine driven generator is connected to the distribution system, the flow through the turbine determines the power output of the turbine. The flow through the turbine is controlled by the valve/gate near the tope of the vertical outflow well. The valve/gate is motorized control which is controlled by a control feedback control system with the speed of the generator as the input.

Suggested specifications of the generator are:

Type: built-in 3-phase squirrel cage induction generator, dry type Rated output power: 45 kW Rated voltage: 380 V Rated frequency: 50 Hz Dead weight (together with turbine): should be not more than 5,000 kg Installation orientation: flow direction is vertical, rotational axis is vertical Coupling between turbine and generator: direct, it is preferable to integrate the turbine and the generator together. Thrust bearing: in water turbine Bearing type & lubricant: - Radial : anti-friction, grease - Thrust: anti-friction, grease Gland seal: mechanical seal Material (includes casing, shaft): Stainless steel, grade 316 or higher Paint (both inside and outside): thermal set plastic coating system


January 2008 64

13.4 LV SWITCHBOARD AND CONTROL PANEL

13.4.1 Basic Schematic Diagram

As identified in a previous Section, the power generated by hydropower system is to be connected to and to be consumed by the existing LV system of the Treatment Works. The single line diagrams of the existing LV switchboards are shown in Figure 13-1 to 13-4.

Figure 13-1 Single Line Diagram of the Existing LV Panel for the SCISTW Sedimentation Tanks E & M Equipment , 2-SWB-001 & 2-SWB-003


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Figure 13.2: A close-up of the right-top part of Figure 13.1


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Figure 13.3: A close-up of the left-bottom part of Figure 13.1


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Figure 13.4 : Typical arrangement of switchboards 2-MCC-001, 2-MCC-003, 2-MCC-005, … 2-MCC-0013 and 2-SWB-005, all these boards are fed from 2-SWB-001 & 2-SWB-003 via an interlock. This indicates

that 2-SWB-001 & 2-SWB-003 will not be connected together.


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The new hydro generator circuit will feed electricity via the existing spare panel on 2-SWB-003 with a 100A fused switch as shown in Figure 13.5 and 13.6

Protection against reverse power flow into the 11k/380V transformer will be provided by a reverse-power-flow relay, with its CTs and voltage tapping points are installed at the main incoming point of 2-SWB-003 switch board. These CTs & voltage tapping points can also be used by CLP Power for their power-and-energy meter. There will be space available on incoming point of 2-SWB-003 to let CLP Power the energy-and-power meter (if needed), for monitoring the excess power and energy generated by the hydro-generator as shown in Figure 13.5.

Figure 13-5 Addition on the existing 2-SWB-003 switchboard

,


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13.4.2 Protection Provisions

The protection provisions in the existing LV panel will be basically unchanged, except the addition of reverse power flow detection and the CLP’s energy-and-power meter.

The protection of the additional LV part (the hydrognerator circuit) is shown in Figure 13.6.


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Figure 13-6: Details of the connections the hydro-generator, the switchgears and protection relays

Legends: Power Control Sense Signal Legends of other symbols will appear in next page.

EF

TRIP

Y point neutral earthing

OC

TRIP

UB

VT

OV UV

OF UF

Manual OFF/ Auto SYN (Syn. Check

Relay)

CLOSE

VT

TRIP

LM RP Ha

VT

Power & Energy

V

I

Speed/

Slip Remote ON/OFF operation by DSD

Operator

Hydro generator circuit (New)

CB-1

CB-1

Control & Monitoring Panel (new) in Main Control Room

CB-1 Ctrl Integration

Syn. Signal

OS OT

Ta

Te

Hydro-Generator

VT

Ta

Feeding to 380V, 100 A fuse switch at 2-SWB-003

SCADA

Power and energy information, CB-1 status to CLP, if needed.

A 3-phase whole current check meter may be installed here by CLP. DSD will provide 100A pre- & post-meter 4-pole switches (with one of them lockable) and other meter provision (e.g. meter board) accordingly.


January 2008 71

Symbols in Figure 13-6: CB: Circuit Breaker (CB-1 is a 4-pole 100A circuit breaker) VT: Voltage transformer (if needed, or just a direct tapping) Ta: Tachometer for sensing shaft speed of the generator Te: Temperature sensor for the internal windings of the generator : Current transformer RP: Reverse Power Flow Relay LM: Loss of Main Relay UV: Under-voltage Relay OV: Over-voltage Relay UF: Under-frequency Relay OF: Over-frequency Relay OC: Over-current Relay EF: Earth Fault Current Relay UB: Unbalanced Current & Voltage Relay OS: Over-speed Relay OT: Over-temperature Relay Syn. check relay: Synchronization check relay


January 2008 72

Protection Related to CB-1 RP: If there is reverse power flow (active power into CLPP network), it will trip CB-1. The

point of detection of reverse power flow, in this case, can be on the LV side of 11kV/380V transformer of 2-SWB-003, as agreed by CLP Power. Note.: as indicated in Fig.13.4, 2-SWB-001 & 2-SWB-003 will not be connected at any circumstances. Hence the point of detection of reverse power flow needs to be installed on the 2-SWB-003 side only, but not on 2-SWB-001.

LM: If loss of mains is detected at mains side of CB-1, it will trip CB-1 within 0.1 second. This provides the “anti-islanding” function of the grid-connection requirements.

UV: If under-voltage is detected, it will trip CB-1

OV: If over-voltage is detected, it will trip CB-1

UF: If under-frequency, it will trip CB-1

OF: If over-frequency is detected, it will trip CB-1

OC: If over-current is detected in the hydro generator circuit, it will trip CB-B1.

EF: If earth-fault current is detected at earthed neutral point of the generator, it will trip CB-1.

Har: If the harmonic contents of the current are large at output of the generator, it will trip CB-1.

UB: If unbalanced current or voltage is detected among the three phases of the generator, it will trip CB-1.

OS: If over-speed of the generator is detected, it will trip CB-1.

OT: If over-temperature of the winding of the generator is detected, it will trip CB-1.

Syn. check relay: This relay will not allow CB-1 to be closed, unless synchronization conditions are all met.

Initial proposed settings of the above relays are as follows. Other relay settings shall be determined during the detailed design stage.


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Table 13-1: Relay Settings for CB-1

Item No. Relay type Value (if any)

1 UB Negative sequence voltage is more than 2% of the positive sequence voltage. Negative sequence current is more than 5% of the positive sequence current.

2 UV -10% from nominal voltage

3 OV +10% from nominal voltage

4 UF 47.0 Hz

5 OF 51.0 Hz

6 Har. THD of all harmonics > 5%, or THD of even harmonics is more than 25% of the odd THD limits

Note.: The time delay of the tripping function should be 0.1 second.

13.4.3 System Earthing

As indicated in the diagram of Figure 13-6, the neutral point of the generator will be earthed individually.

13.4.4 Metering Point of the Generator and Metering Point of the Whole System

As indicated in above discussions, the “metering point” of the generator can be regarded as at the main side of CB-1. The output power and output energy will be at this point available to CLPP, in real time, via their SCADA system. While the metering point of the whole system (old and new together) remains the same as in the old system, i.e. at the CLPP side.

In addition, as mentioned above, CLPP can consider installing a 3-phase 100 A whole current meter at the main side of CB-1. Pre- & post-meter switches of 4-pole type should be provided by DSD.

13.4.5 Fault Level Considerations

In this initial stage of design, expected p.u. impedance of the generator is about 0.08. The rated power of the generator is only 45 kW. Hence the impact on the fault level is very minimal, less than an increase 500 A at the bus of 2-SWB-003. This should not affect the system or the design of the remaining part of the system.

13.4.6 Power Quality Consideration

No adverse impact on power quality is expected in this system as compared with other renewable energy systems, since no power electronic devices are involved in the system. The voltage and current harmonics from the generator is expected to be very low. However, harmonic current protection, unbalanced voltage protection and unbalance current protection are included in the system design for additional protection.


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13.4.7 Monitoring and data logging, as well as control

There should be a small scale of SCADA system (as indicated in Figure 13.6), to monitor and log the voltage, current, power, energy, speed of generator, synchronization signal and status of CB-1. These signal can be transmitted to SCADA system of CLPP if needed.

Attached to this SCADA system, there should be a feedback control system to control the operation of the whole system. The control system will execute the control strategy as detailed in Section 15.

13.4.8 Other System Protection Measures or Features to Fulfil Grid Connection Requirements

Other system protection measures or features to fulfill grid connection requirements include:

(1) The CB-1 should be lockable and readily accessible, so as to authorized electrical workers to manually isolate the hydro generator from the original electrical installation.

(2) Warning labels will be displayed at all electrical equipment fed from the two (old and new) LV panels, the label will alert the maintenance personnel that there are dual power supply sources (from CLPP and RE) in the system.

(3) Updated circuit diagram will be displayed in the room of the LV panel 2-SWB-003 and near the generator. This is to facilitate maintenance personnel in properly shutting down the grid connection arrangement under normal and emergency operations.

(4) A suitable qualified on-site person in DSD will be designated to communicate directly with CLPP; hence there is a direct communication between DSD and CLPP to ensure safe operation of the grid connection.

(5) Equipment of high reliability will be selected in the installation to ensure that the reliability level of the new system is comparable with the existing system.


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14 CLP’s Requirements for On-grid Connection

Since the rated generation power of the installation is only about 45 kW, it is within the 200kW limit stipulated in the “Technical Guidelines on Grid Connection of Small-scale Renewable Energy Power Systems (2005 Edition)” issued by EMSD. Hence the CLPP’s requirements are just based on those requirements listed in the Technical Guidelines. The following is the table of the requirements of the Technical Guidelines and the corresponding actions of the pilot project to fulfill these requirements.

Table 14.1: The requirements of the Technical Guidelines and the corresponding actions of the pilot project to fulfill these requirements

The requirements of the Technical

Guidelines

The corresponding actions of the pilot

project to fulfill the requirements

Incorporate an "anti-islanding" function in the

design of the SREPSs (Small Renewable

Energy Power Systems). This function can

automatically disconnect any grid-connected

SREPS from the Distribution System in the

event that the Grid is deenergized for

whatever reasons. The purpose of an "anti-

islanding" function is to ensure that SREPS

would not continue to supply power to the

Distribution System so as to allow electrical

workers to work safely on the Grid or the

Distribution System during the power

interruption.

The protection function - LM (loss of mains)

protection as listed in Section 13.4.2.

Install a lockable switch at a readily

accessible position to allow authorized

electrical workers to manually isolate the

SREPS from the Grid whenever necessary.

The lockable switch, in this case, is CB-1,

and it is required as lockable as listed in

Point# 1 in Section 13.4.7

Display warning labels at all electrical equipment

with dual power supply sources so as to alert the

maintenance personnel.

One of the measures as listed in Point #2 in

Section 13.4.7.

Update circuit diagrams regularly and

display them at appropriate locations to



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facilitate maintenance personnel to properly

shut down the grid connection arrangement

under normal and emergency operations.

Section 13.4.7.

Establishing a direct communication

channel between the Owner and the Utility

is essential to ensure the safe operation of

the SREPS and the Grid. Designate a

suitably qualified person to communicate

directly with the Utility under normal and

emergency operations.


Section 13.4.7.

Carry out assessment on the new fault level

due to the connection of the SREPS to the

Grid such that all equipment in the

Distribution System and the Grid can

operate safely under the new fault level.

The assessment was done in Section

13.4.5. The increase is estimated to be an

increase of 500 A only on the fault current.

Hence all equipment should be operated

safely under the new fault level.

Install facilities with synchronization check

function, whenever necessary, to circuit

breakers or contactors designated for

making electrical connection to the

Distribution System. The connection of the

SREPS to the Distribution System would

only take place when they are operating in

synchronization, i.e. the differences in

voltage magnitude, phase angle, and

frequency of these two power sources are

controlled within acceptable limits.

This is a function provided by the Syn.

Check Relay as listed in the Section 13.4.2.

Incorporate protection function in the design

of the SREPS to avoid unsynchronized

connection. To enable fast restoration of

supply after power failure, the Utility has

equipped with auto-switching and auto-

reclosing facilities that would operate soon

The design, listed Section 13.4, will avoid

unsynchronized connection. And the hydro

generator system will not reconnect

automatically itself after it is tripped off by

whatever reason. It has to be reconnected

manually.


January 2008 77

after power failures. If the Distribution

System is still energized by the SREPS,

unsynchronized connection which would

damage equipment of both parties, may

occur.

Incorporate facilities to isolate the SREPS

from the Distribution System automatically

when fault occurs in the SREPS.

The isolating switch, in this case, is CB-1,

which will automatically isolate the

hydrogenerator system under various faults

as listed in Section 13.4

Use 4-pole type circuit breakers or isolators

on all isolation points of the SREPS to allow

complete isolation from the Distribution

System when the SREPS is not in service.

This arrangement is to ensure that the

Distribution System would remain intact and

not be affected by the SREPS.

The isolating switch, in this case, is CB-1,

which is a 4-pole circuit breaker as listed in

Section 13.4.2, as well as the pre- or post

meter switch.

Incorporate appropriate protection facilities

in the design of the SREPS to avoid

damages to the SREPS caused by transient

abnormalities that would occur in the

Distribution System and the Grid, such as

supply interruption, voltage and frequency

fluctuation, voltage dip, etc.

The protection function listed in Section

13.4.2 included the tripping of CB-1 under

the cases of over-voltage, under-voltage,

over frequency, under frequency, and loss

of mains, earth fault protection etc.

Incorporate facilities in the SREPS which

can automatically disconnect the SREPS

from the Distribution System when

sustained voltage and frequency

fluctuations are detected in the Distribution

System. The time delay setting before

automatic disconnection can take place may

make reference to the recommendations of

international standards as given in Appendix (III)

and agreed by both the Owner and the Utility.





of mains, etc. The time delay setting is

suggested to be 0.1 second, which is the

standard as suggested in the related IEEE

standard.


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Incorporate facilities in the SREPS which

can automatically re-connect the SREPS

back to the Distribution System after

fluctuations in voltage and frequency in the

Distribution System have been cleared. The

time delay setting before re-connection can

take place may make reference to the

recommendations of international standards

as given in Appendix (III) and agreed by

both the Owner and the Utility. The time

delay is to avoid repeatedly operation of the

circuit breakers due to premature electrical

connection.

The hydro generator system will not

reconnect automatically itself after it is

tripped off by whatever reason. It has to be

reconnected manually. And this

reconnection process is just like starting the

system again manually.

Select an inverter, with high reliability, such

as having a high "mean-time-to- failure"

index. This is essential since the inverter is

the principle component in the SREPS that

directly connects the SREPS to the Distribution System.

There is no inverter in the system.

Set the operating levels of all the protective

devices in the Distribution System to suit the

new fault level. This arrangement is to avoid

improper operation of protective devices

during fault conditions.

As mentioned above, the change in fault

level is very small. Hence no change in

operating level of the protective devices is

required in this case.

Incorporate a fast responding voltage and

frequency regulator that can adjust the

output of the SREPS to match the voltage

and frequency of the Distribution System.

This would reduce electrical stress on the

SREPS and help to minimize failure.

The generator used is an induction generator,

which will automaticlly adjust the output to

match the voltage and frequency of the

Distribution System, in a fast way.

Provide an automatic disconnection function

in the SREPS that can operate when the

voltage and frequency of the Distribution





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System deviate outside the allowable limits

persistently for a pre-determined period

recommended by international standards as

given in Appendix (III) and agreed by both the Owner and the Utility.


of mains, etc. The setting can be adjustable

such that it suits the requirements as

required by CLPP.

Install an inverter with power conditioning

function to control the harmonic currents

and the output power factor of the SREPS

within an acceptable range such that the

SREPS can operate efficiently and other

parties would not be affected.

There is no inverter in the system. Anyway,

the harmonic relay listed in Section 13.4.2

will ensure that the output current from the

generator has to meet a certain requirement

which is adjustable to a level as required by

CLPP.

Install an isolation transformer on the output

side of the power inverter to eliminate the

possibility of injection of direct current from

the SREPS into the Distribution System.

Excess direct current injected into the

Distribution System would distort its voltage

and cause problems to other connected

equipment.

There is no inverter in the system and the

generator is an AC generator. Hence no DC

will be produced and no additional isolation

transformer is needed.

Install a fast responding voltage and

frequency regulator to minimize voltage

flickering in the Distribution System which is

undesirable to other connected electrical

equipment.

The generator is a 3-phase cage-type

induction machine. Voltage flickering at the

output is not expected. Anyway, there will

be protection by tripping of CB-1 under the

cases of over-voltage, under-voltage, over

frequency, under frequency, etc.

Evaluate the electromagnetic compatibility

requirements specified in international

standards as given in Appendix (III) at the

design inception stage. Conducted or

radiated electromagnetic emissions from the

SREPS would then be properly controlled

so as not to interfere with the normal

operation of other electrical equipment in


induction machine and there is no inverter

or other power electronic equipment in the

system. Hence there should be no

conducted or radiated electromagnetic

emissions.


January 2008 80

the Distribution System.

Design a SREPS with three-phase inverter

or three identical single-phase inverters to

supply current which is balanced over the

three phases to the Grid. This would

minimize voltage and current unbalance in

the three-phase supply system and would

ensure that the capacity of the Distribution

System can be fully utilized. However, this

provision is not applicable if the site is being

supplied or will be supplied with single-

phase power from the Utility.


induction machine and there is no inverter.

Hence there should not be problem of

voltage or current balancing. Anyway, there

is a voltage and current unbalancing relay

installed as listed in Section 13.4.2.

Additional control and monitoring facilities to

measure and monitor the performance of

the SREPS.

As shown in Figure 13.6, it is expected to

have a SCADA system to measure and

monitor the output voltage, current, power

energy, status of CB-1, speed and the

generator, etc in the system.

A data collection and reporting system to

provide real time data, data summaries and

failure reports.

As shown in Figure 13.6, it is expected to

have a SCADA system to measure and

monitor the output voltage, current, power

energy, status of CB-1, speed and the

generator, etc in the system. This data can

be provided to CLPP as required.

In the Testing and Commissioning phase of

the project:

(a) To test all the protection level and time

delay settings.

(b) To check the operation of the

antiislanding function.

All these will be done in the Testing and

Commissioning stage.


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(c) To check the operation at all isolation

points.

(d) To check that all the warning labels,

equipment labels and circuit diagrams are

displayed in appropriate locations.

(e) To check and record the voltage and

current output of the SREPS including

power factor, direct current level and total

harmonic distortion.

Post-installation Obligations of the Owner:

(a) After the SREPS is put into normal

operation, the Owner should provide the

Utility with information on the electrical

energy output of the SREPS on a regular

basis, e.g. bi-monthly, if requested by the

Utility. The Utility may also install check

meters to monitor the electrical energy

(kWh) output of the SREPS.

(b) Periodic inspection of the SREPS by

registered electrical worker is

recommended. The Owner can consider

adopting an inspection arrangement similar

to the requirements as stipulated in the

Electricity (Wiring) Regulations of the

Electricity Ordinance for fixed electrical

installations. It is not necessary for the

Owner to submit the relevant inspection

certificate and checklist to the Utility.

(c) The Utility may conduct on-site

All these will be left to the detailed

discussion between DSD and CLPP.

However, space for installation of check

meters to monitor the electrical energy

(kWh) output of the hydrogenerator will be

factored into the design of the switchboard

of the hydrogenerator.


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inspections and request the Owner to

perform verification tests on the operation of

the SREPS. In this regard, the Utility may

request the Owner to provide access and

the test results.

(d) It is important for the Owner to compile

an operation and maintenance manual to

record all procedures needed to operate

and maintain the SREPS including all

protection settings and test results.

Regarding grid connection operational

procedures which form part of this manual,

the details should be agreed by the

Owner and the Utility. This manual should

be reviewed regularly and modified where

necessary.

(e) The Owner should inform the Utility on

any change in power rating or modification of

the SREPS. In addition, the Utility will also

need to be informed when the SREPS is

decommissioned.

A meeting was held with CLPP on the grid connection issue of the pilot project and technical data related to the grid connection have been passed to CLPP. CLPP is basically satisfied with the technical aspects of the proposed design, after some minor revisions on the design (This report already included the minor revisions). However, once the detailed design is available, a formal application together with the detailed electrical design drawing should be submitted to CLPP for formal approval. In addition, in the detailed design, a detailed operation procedure for the grid connection of the hydro unit is required to be developed by owner (DSD) and agreed by the utility. The DSD is also required to report the energy of the hydro unit monthly to the utility.


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15 Operation and Control of the hydropower plant

The operations of the hydropower plant under different scenarios are described as follows:

15.1 NORMAL START-UP

(1) Check all machinery and prepare for operation.

(2) Activate the hydro-turbine control panel, and the power pack for the gate servo motor.

(3) Verify that the gates operated by the hydraulic servo-motor are fully closed and CB-1 is in OFF position.

(4) If Tank #40 & #42 is not filled with water, fill it with water until there are water fall through the by-pass path next to the generator.

(5) The servo motor should be controlled to gradually open the gate slightly to get the turbine spinning, and brought up to approximately operating speed at no load., i.e. a speed slight higher than the synchronous speed of the generator.

(6) Starting of the turbine should occur over a time span of not less than 3 minutes to minimize the potential for damage from surge.

(7) Once the turbine is up to speed, a CLOSE command can be sent to the control system of CB-1. The synchronization relay will check for conditioning of synchronization (mainly, the speed is about that of the synchronous speed and the voltage magnitude and sequence are about the right magnitude and direction). If the condition of synchronization is met, a CLOSE signal will be sent from the control system of CB-1 to CB1. And now the generator’s electrical output is connected to the 2-SWB-003.

(8) Once connected to the utility, the turbine speed is governed by the utility power frequency, as well as the flow rate. Adjusting the gate and thus the flow rate will adjust the electrical output of the hydro-turbine driven generator.

(9) Once connected to the electrical system, the flow through the turbine can be increased by further opening the gate to the desired flow rate and electrical output. It can also be put into automatic operation such that the gate is automatically control to maintain a given power output, as far as the actual flow is allowed. There should be a feedback type of control system to execute this automatic control.

15.2 NORMAL SHUT-DOWN

(1) The shut-down procedures are the reverse of start-up. The flow through the turbine is gradually decreased by closing the wicket gates, and more water will flow through the by-pass path next to the generator.


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(2) Once flow is reduced to the point of zero electrical output, the circuit breaker to the plant switchgear is opened, and the wicket gates are closed tight. The turbine will stop.

(3) Shut-down of the turbine should occur over a time span of not less than 3 minutes to minimize the potential for damage from surge.

15.3 EMERGENCY SHUT-DOWN

The turbine generator system will have a number of following malfunction protections to shut-down the plant.

Temperature sensors will be used to monitor generator winding temperature. Any value higher than normal range will result in a warning, followed by a fault that will cause a shut-down.

Tachometer will be used to monitor the speed of generator. Either over-speed or under-speed will trigger a fault to shut-down the plant.

Electrical output will be monitored for consistency with the system. Abnormal conditions will cause a warning and/or shutdown.

Loss of load will cause a shut-down.

Upon shut-down fault, the wicket gates will close at a controlled rate such that full closure will occur in not fewer than 3 minutes. This shut-down will happen automatically, regardless of other operations at the plant.

15.4 FAILURE OF POWER SUPPLY

The hydro-turbine driven generator cannot operate by itself to maintain power output. It must be connected to the utility for proper speed control. Thus, if there is loss of utility connection, or any kind of loss of load, the turbine will immediately trip the circuit breaker to disconnect from the line, and execute a fault shut-down as described above.

The hydro-turbine wicket gates are operated by the electric system. They will close to shut down the turbine. The control system and the motor of the wicket gate should be powered by emergency supply such that the whole shunt down procedure can be executed in case of failure of mains.


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15.5 CONTROL AND INSTRUMENTATION

The following instrument shall be provided for the operation control and monitoring of the operating conditions of the hydro-turbine generator system.

(a) Temperature sensors of generator winding

(b) Tachometer for speed of generator

(c) Ammeter, voltmeter, energy meter and power meter

A temperature monitoring system for the generator windings is used to monitor the winding temperature to give alarm signals upon detection of any malfunction.

A tachometer for the generator is used for achieving synchronization and controlling the power output of the generator after synchronization.

As indicated in Fig.13.6, it is expected to install a SCADA system to monitor and log the data of current, voltage, power, energy, speed of generator, status of CB-1, etc. The readings of these parameters will be used to show the status and performance of the power generation system. And these data will be given to CLPP as required.

15.6 MAINTENANCE ISSUES

The system is almost maintenance free. The only two maintenance items are regular bearing lubrication and regular checking (WR2) of wiring (both the generator and the switchbroad) according to the CoP (Wiring regulation). The former is likely to be done annually while the latter is once every 5 years. The former has to be done with the turbine be hoisted up from the well, while the latter can be done remotely from the cable ends, without physical access to the generator/turbine (This is usually done together with the WR2 wiring checking of other electrical installation). The hoisting arrangement of the turbine can be made easily with the installed support of the turbine (discussed in Section 12.2). Hence it is supposed to need no additional equipment for hoisting.

The outage time for maintenance is estimated to be less than 24 hours. However it is expected that the maintenance of the system is carried out at the same time during the maintenance of the sedimentation tank which usually lasts for days.


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16 Specifications of the Proposed Hydroelectric System.

Detailed specifications of various parts of the system are given in previous sections. This Section summaries some of the key specifications.

Turbine:

Type: Axial-flow propeller type

Rated effective head: ~ 4.5 m

Useful range of flow rate, at least: 1 m3/s – 1.25 m3/s (preferably 1 m3/s to 1.6 m3/s)

Rated flow rate: about 1.16 to 1.2 m3/s

Rated rotation speed: should match with the generator, expect to be around 430 to 450 rpm

Efficiency (turbine & generator combined) at rated flow rate: at least 70%

Efficiency within the useful range of flow rate: at least 55%, with most of them above 65%. Fluid type: Sewage water Outer diameter: about 1m Generator: Type: built-in 3-phase squirrel cage induction generator, dry type Rated output power: 45 kW Rated voltage: 380 V Rated frequency: 50 Hz Dead weight (together with turbine): should be not more than 5,000 kg Installation orientation: flow direction is vertical, rotational axis is vertical Coupling between turbine and generator: direct, it is preferable to integrate the turbine and the generator together. Thrust bearing: in water turbine Materials: Materials (includes casing, impeller, shaft): Stainless steel, grade 316 or higher Paint (both inside and outside): thermal set plastic coating system


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Guide tubes: Outer diameter: less than 1.2 m Materials: Fibreglass Reinforced Plastic (ASM RTP-1 or ASTM C-582 or equivalent or higher).

Control valve: Type: motorised Maximum flow rate: 1.6 m3s-1 Materials : Stainless steel, grade 316 or higher


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17 PROJECT INTERFACE AND IMPLEMENTATION

SCHEDULE

17.1 PROJECT INTERFACE

The hydroelectric system requires interconnection with the existing LV power supply system and control panel, as well as the outflow well. Therefore, both the construction and operation of the pilot hydropower plant should ensure minimal interruption and interface with the routine operation of the existing plant.

17.2 IMPLEMENTATION SCHEDULE

A tentative implementation schedule of the project is proposed in the following table.

Table 11.1 Key Days of Implementation Schedule

Tasks/ Activities Key Dates 1. Approval of Project Funding April 2008

2. Contract Commencement October 2008

3. Testing & Commissioning October 2009

4. Completion of the project December 2009


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18 Budgeting

18.1 CAPITAL COST AND RECURRENT COST

The estimated budget of the pilot projects are:

Item Cost (HK$) The integrated hydroturbine and generator unit

2,875,000

Guide tubes around the turbine Control gate Bottom screen Support for the integrated hydroturbine and generator unit Support for the guide tubes and control gate/valve Installation cost of the above items Additional LV switchboard and associated electrical equipment/sensors.cabling and its installation cost Administration and other cost of the contractor Service charge of the consultant on detailed design

1,890,000 (The following is not included:

Fees related to CLPP’s grid connection, interfacing with existing SCADA system, if

required)

Consultancy fee for detailed design

240,000

Total

5,005,000

Note: The above cost estimation does not include any costs from CLPP. Confirmation with CLPP is required.

Note: The feedback of hydrogenerator suppliers was not satisfactory. Amongst the hydrogenerator suppliers approached, only Kubuta Corp. and Gugler Hydro Energy replied with a budget. The above budget estimation is based on using the integrated turbine-generator set supplied from Kubuta Corporation. The cost of the turbine-generator set (of much lower specifications in materials used) alone (simply freight to Hong Kong without insurance, installation or others) is HK$0.7M if a turbine-generator set from Gugler Hydro


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Energy, However, this option needs the generator to be installed at the top of the well, which will lead to a great difficulty on installation of the long shaft between the turbine and the generator as explained earlier in Section 10, this will in turn will largely raise the cost of other part of the system and cannot ensure reliable operation. Hence this option is dropped in this proposal.

Recurrent cost: The only regular maintenance required for the system is regular greasing on the bearings. During this process the two associated sedimentation tanks have to be suspended from operation. The upper horizontal flow guide tube has to be opened and the whole turbine generator set has to be hoisted up by the support on the top of the well. The estimated cost of the maintenance work is HK$10,000 per year.


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19 Annual Energy Yield, Financial and Environmental Benefits

19.1 POWER & ENERGY GENERATION Daily flow rate data of 2005 and 2006 were provided by DSD. It is found that the annual average daily flow rate of the whole sedimentation tank is about 1,400,000 m3/day. The minimum daily rate is ~1,200,000 m3/day, while the maximum daily rate is ~1,650,000 m3/day (there were only 5 exception days in 2005, in which the diary flow rate is higher than 1,650,000 m3/day). That means the daily variation is mostly within +18% / -15% of the average flow rate. Hence the flow rate is relatively fairly constant as compared with many hydroelectric projects, in which the flow rates fluctuated significantly between dry season and wet season. It is understood that the final target flow rate of the current SCISTW setup (without new additional sedimentation tanks) is an annual average daily flow rate of about 1,700,000 m3/day. There are currently 18 vertical water outflow wells along the two sides of the sedimentation tank (excluding two wells for the two proto-type tanks). In general, roughly, about two-third of the sedimentation tank (that means also only 12 vertical water outflow wells) are used at any instance, while the others are under maintenance/ inspection/ checking/ modifications/ idle or other activities. Based on the above data, the average volume flow rate over a day in each of the vertical water outflow wells varies most from 1.16 m3/s to 1.6 m3/s, with an average of ~1.35 m3/s, at the current flow rate data. This average will go up to 1.64 m3/s when the target capacity of the current SCISTW setup is reached. Based on the civil work drawing of the sedimentation tank, the total water heads inside the vertical water outflow wells are about 5.8 m. A reasonable estimation of the effective head is 4.5 m (after taking into the length of the turbine itself, length for installation of the mounting supports and safety screen). Hydroelectric power systems of this order of water head and the above mentioned average flow rate of a few m3/s are classified as low-head micro-hydroelectric power system. Annual energy yield and cost saving based on current average flow rate From the above information - the current minimum flow rate data of 1.16 m3/s and average flow rate of 1.35 m3/s, the maximum allowable flow rate of the selected turbine is 1.25 m3/s with an effective head of 4.5 m. At 1.25 m3/s and effective head of 4.5 m, the selected generator output is about 70%; hence the average output power of the generator is 45 kW. Assuming the system running in only two-third of the year (in the rest of time, the associated well/tanks are under maintenance/inspection/checking/modifications or other activities), the total energy yield will be about 263,000kWh in a year.


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From the current electricity bill (the one dated 24-09-2007) of SCISTW the following data are extracted:

Demand charge per month for each kVA above 5000 kVA: HK$112/kVA Net energy charge for each kWh above 1,946,000 kWh: HK$0.535/kWh (which includes fuel clause of HK$0.02/kWh).

Saving in electricity bill:

Assuming a reduction of 45 KVA (the average output power) in month peak demand, saving in demand charge is about HK$60,480 per year. Saving in energy charge is about HK$140,705 per year Total saving is HK$201,185 per year.

The only regular maintenance required for the system is regular greasing on the bearings. During this process, the two associated sedimentation tanks have to be suspended from operation. The upper horizontal flow guide tube has to be opened and the whole turbine generator set has to be hoisted up by the support on the top of the well. The estimated cost of the maintenance work is HK$10,000 per year. Taking into account the yearly maintenance cost, the net saving is about HK$191,185 per year. With the estimated cost of the project of HK$5,005,000, a simple analysis gives a pay back period of 26 years, which is relatively long. However, as a pilot project, one should not emphasis on the monetary benefit only, but should also consider the environmental benefits (please refer to sections below) and the demonstration function of the project. This type of project is the first kind in Hong Kong.

19.2 POWER UTILIZATION

The generated power is recommended to be connected to low voltage grid for fully utilization as there are many electrical equipment at the sedimentation tanks to consume the electrical power generated. There should not be any surplus of generated power to flow out from the electrical distribution system. As mentioned in the above sub-section, the expected power from the generator is 45 kW and the annual yield is expected to be about 263,000kWh. All these power and energy will be consumed within the switchboard of 2SWB003.

19.3 ENVIRONMENTAL BENEFITS

The generation of electricity locally by the hydrogenerator can reduce the amount of electricity generated by the fossil fuel generators of the CLPP at the remote location. Taking into account of at least 10% loss in the transmission and distribution, the amount of reduction of electricity need of be generated by the fossil generators for this project is about 110% * 263,000kWh/year = 289,000 kWh/year.

The range of emission factors for different types of fuel have been analyzed through various studies. The results can be expressed in grams of carbon-equivalent (including CO2, SO2, CH4, N2O, etc.) per kilowatt-hour of electricity (gCeq/kWh). The graph in Figure 19.1 below shows data from existing power plants.


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Figure 19.1 Range of total greenhouse gas emission from electricity production chains with different type of fuels/sources (unit in gCeq/kWh) (Source: IAEA, International Atomic Energy Agency)

In Hong Kong, the one of the three main types of fuel used by CLPP is coal. Therefore to make thing simple, the data of “coal – 1990 technology (low)” from Figure 19.1 is referred. Taking only the stack emission (not include emissions from other chain steps, say power plant construction, decommissioning, etc.), then one can take the value of 216 gCeq/kWh, while the corresponding value for hydroelectric is basically zero (again from Figure 19.1).


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Therefore the environment impact of the proposed hydroelectric project is a save of 289,000 kWh/year * 216 gCeq/kWh = 62,424,000 gCeg or about 62.4 MTCE (Metric Ton Carbon Equivalent).

1 metric ton carbon equivalent (MTCE) = 3.667 metric tons of CO2 equivalents (TCO2E) (source: Document EPA-F-05-002, February 2005, from Environment Protection Agency of United States.)

If one likes to convert the environment impact to CO2 equivalent, the value is 62.4 MTCE * 3.667 = 229 TCO2E/year

There is no mature emission trading scheme in the region around Hong Kong. But just for information, the price of CO2 in the emission trading market of European Union Emission Trading Scheme in about the last 2 months (1/Aug & 29/Sept of 2007) was about 21 Euro/TCO2E or HK$210/TCO2E. Then 229 TCO2E/year translates into HK$48,000/year. However CO2 price can vary a lot in a year and among different regions.

Figure 19.2: Market price of CO2 in emission trading market of European Union Emission Trading Scheme (Source: www.co2prices.eu)


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20 CONCLUSIONS & RECOMMENDATIONS

20.1 GENERAL

The proposed pilot hydroelectric project in SCISTW will generate 45 kW of rated power. The expected yield per year is about 263,000 kWh/year. The reduction of the electricity bill is estimated to be HK$201,185 per year, based on that no standby charges is required by CLPP. The environmental benefit is 62.4 Metric Ton Carbon Equivalent/year or 229 Metric Ton CO2 Equivalent/year, while the estimated cost is HK$5,005,000. It gives a payback period of 26 years.

20.2 E & M EQUIPMENT & CIVIL WORK The major electrical and mechanical equipment for the pilot hydropower plant includes a hydraulic turbine and a generator complete with flow control gates and flow guide tubes. Hydro-turbine is used to convert energy in the form of falling water from the sedimentation tank. The selected turbine is designed to provide most efficient operational range of flows from 1.1 to 1.25 m3/s. The available net heads range from 4.5 to 5.5 meters during normal operating conditions and the cross section of the well is 2m × 1.25m. The generator is rated at 45kW, 3 phases, 380V, 50 Hz. Control gate is for the flow control of the turbine generator. LV switchboard shall also be installed for connecting the generated electricity to the grid.

The turbine generator set is to be located at one of the 18 existing vertical outflow well of the sedimentation tanks. The additional LV switches and associated equipment will be located in the existing LV switchboard. The electricity cables from the turbine generator set to the LV switchboard room will be laid in cable conduits to be mounted on the top surface of the sedimentation tanks.

20.3 CONSTRUCTION METHOD STATEMENT

First of all, a support system will be mounted on the top of the vertical outflow well. This support system will be used during construction and installation stage, and will also be used as the major support of the turbine/generator unit after the installation. A strong metallic screen will be installed at the bottom of the vertical outflow well. This strong metallic screen will act as both a kind of safety measure during construction stage and a security measure to catch any large piece of broken part from the system. The supports for the flow guides of the turbine will be mounted on the inner side walls of the well. The vertical guide tube will be lowered from the above to seat properly on the guide support without much additional fixtures. The turbine/generator set will then be lowered from above and hanged from the support system. Finally, the horizontal flow guide tube and the control gate will be installed near the top of the well. By-pass path exists next to the vertical guide tube of the turbine to allow excess water to flow.

20.4 PROJECT INTERFACE AND IMPLEMENTATION

The proposed pilot hydroelectric project is technically feasible. Although the financial benefit of this project may not be very attractive, it is considered worthwhile implementing this project in view of its environmental benefit in the reduction of greenhouse gas emission.


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It is expected that during the construction of the proposed works, there will have a certain extent of interface with the operation of the existing plant. The pilot hydroelectric generator will be able to be put into operation in end 2009. Further implementation of the hydroelectric generators in the existing sedimentation tanks will depend on the performance of the pilot hydroelectric generator after it is put into operation.

It is also noted that the HATS Stage 2A project is undergoing, in which additional sedimentation tanks will be built. If civil requirements of the hydrogenerator can be incorporated at the early design stage of the project, one can consider some other configurations to incorporate the hydrogenerators. Hence it will reduce the capital cost of the whole hydroelectric project and as well facilitate the maintenance requirements of the system. Further study on the hydrogenerators for the HATS Stage 2A project is recommended.

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