CEB exp

Chapter 2 CEB Industrial Training Report

2.1 Protection Development Branch

2.1.1 Introduction

According to the schedule which was given by the Training Centre of Ceylon Electricity Board I

was appointed to the Protection Development Branch at Dematagoda for one week. This branch

stands for develop and monitor the protection system of the transmission network of CEB. This

branch is controlled by the Chief Engineer Mr.N.S.Wettasinghe and several Electrical Engineers

work under him. In the first day at the Protection Development Branch I gained a basic

knowledge about protection methods of transmission lines.

2.1.2 Transmission Line Protection Methods

Differential Protection

In this method fault is identified by comparing the current entering and leaving a protected

section. By comparing the magnitude and phase of the currents at the two ends, it is possible

to determine whether the fault is internal or external.

Over Current protection

Fault current varies with position of the fault. Variation is due to the impedance of the plant

between the source and the fault. Appropriate time intervals are given for each relay.

Operation of the relay is hence independent of the fault current. Relay nearest to the fault will

operate and trip the breaker.

Tripping Time

Department of Electrical Engineering Page 7University of Moratuwa

Fault Current

Figure 2.1 TRIP TIME CHARACTERISTIC


Distance Protection

Distance of a transmission line is fixed and determined at the time commissioning. It remains

constant under all system conditions. Hence measurement of distance of a transmission line

is a good concept. If the distance measured is less than the “known”, that indicates a faulty

condition. If it is more than the “known” it indicates a healthy condition. In this method an

impedance relay is set to operate when the impedance measured is less than the preset value.

Earth Fault Protection

Earth fault conditions are always associated with residual currents. Hence by detecting

residual currents earth fault can be detected. Earth fault currents can be of low magnitudes

and over current relays may not detect those. Therefore sensitive earth fault relays are used if

very low earth fault currents are to be detected.

2.1.3 Biyagama Receiving Station

When I was at the Protection Development Branch I got the chance to visit Biyagama Receiving

Station with an Electrical Engineer. At there I observed transmission line protection relay

installation which was being done by SIEMENS Company’s technical officers. As well as I was

able to observe and study the components and the switching network of the switchyard of the

Sub station. The single line diagram of the Biyagama Switching Station is provided in the Annex

A6,2,1,3.

2.1.4 Protection Monitoring System

This system has been implemented as a communication system which does network the

substations using fiber optic cables. All the Engineering PCs of all the connected substations can

be remotely accessed from master computer at the Protection Development Branch by using this

system. I was also able to observe how to access and control transmission line and relay data

using the master computer. A figure of the existing Protection Monitoring System is provided in

the Annex A7,2,1,4.



2.2 Asset Management Hydro Electrical

2.2.1 Introduction

Asset Management branch of CEB is situated in Kandy and it stands to handle and monitor the

protection of the generators of all CEB owned hydro power stations in Sri Lanka. Most of the

repairs and tests of protection equipments of the generators and relays are done in this branch.

This branch is supervised by a Deputy General Manager and I trained under the Chief Engineer

Mr. Tennakoon for one week.

2.2.2 Calibrating a Power and Energy Meter

When I was at the Asset Management Branch I was able to involve calibrating a YOKOGAWA

power and energy meter that had to be fixed to the control unit of the Inginiyagala power station.

Calibration was done by injecting current of 1A to the energy meter by using OMICRON testing

device. The results we obtained are as follows.

VT Ratio = 60:1 , CT Ratio = 80:1

Input Voltage Phase Angle Meter Reading Theoretical Value

63.5 V 0º 0.91 MW 0.9144 MW

63.5 V 20 º 0.86 MW 0.8592 MW

63.5 V -100 º -0.16 MW -0.1588 MW

63.5 V -20 º -0.32 MVAr -0.3127 MVAr

63.5 V -50 º 0.58 MW 0.5878 MW

2.2.3 Training Experiences

When I was at the Asset Management Branch I studied some operation and maintenance manuals

and project reports of Kotmale and Victoria projects. And also I involved in a testing which was

being done of a field failure relay which had been removed from New Laxapana power station.

The relay was tested for the correct functioning. In the final day of that branch I was able to

observe a testing of a VIBROSYSTM Air gap sensor which is used to measure the air gap length

of generators. The unit was tested to check whether it is working properly and found out that

there was a fault in the unit.


Table 2.1 RESULTS OF THE CALIBRATION


2.3 Sapugaskanda Grid Substation

2.3.1 Introduction

According to my schedule I was appointed to the Transmission Operation and Maintenance

Branch at Dematagoda in my third week of training. Chief Engineer of that branch assigns me to

train at Sapugaskanda Grid Substation for one week. Sapugaskanda grid substation is situated

near Kiribathgoda and it is supervised by an Electrical Superintendent. Four 132kV transmission

lines come to the substation from Biyagama and Kelanitissa while eleven feeders go out. This

substation consists of four 132kV/33kV power transformers and a Gas Insulated Switching (GIS)

system. Although it has 4 transformers 3 of them had been burnt and the total load was delivered

through one transformer which was running under full load when I arrived there. And there was

a newly installed transformer which had to be commissioned.

2.3.2 Commissioning of newly installed power transformer

Features of the newly installed transformer

Type: DT 4W 35800/132

Rated frequency: 50Hz

Type of cooling: ONAN/ONAF

Rated power: 23,000/31,500kVA

Rated current: 100,6/137,8 A

Symmetrical short circuit current: 1.33kA

Connection symbol: YNd1

Max ambient temperature: 40oC

Temperature rise of top oil/winding: 50/55oC

Impedance voltage at 75oC (%)

@ 145,200V – 11.06 @ 132,000V – 10.35 @ 112,200V – 9.53

At 31,500kVA duration maximum: 2s

When I reached the substation the final oil filling process under vacuum of the transformer was

being performed. In the following days several tests of commissioning the transformer were

carried out. And I was also able to involve and observe Insulation resistance test, Polarity test



(Vector group), Ratio test, Short circuit test and Thermometer test which were done for the new

transformer.

Obtained results of the Ratio test

Tap

No.

Primary(V) Secondary(V) Name plate ratio

Measured ratioRY YB BR ry yb br

1 393 394 393 89 89.3 89 4.4 4.41

2 393 394 393 89 89 89 4.35 4.42

3 394 395 393 90 90 90 4.3 4.38

19 393 393 393 111 111 3.5 3.5 3.54

20 393 393 392 112 112 3.45 3.45 3.51

21 392 393 392 114 114 3.4 3.4 3.44

Obtained results of the Insulation Resistant test

HV to (LV + Ground) – 5kV

Time (Min) Resistance(GΩ)1 10.2 3 16.95 18.8

10 22.7

LV to (HV + Ground) – 5kVTime (Min) Resistance(GΩ)

1 10.7 3 17.45 21.1

10 27.2

The polarization index should be greater than 2 of a transformer which has a good insulation level.


At there I was able to observe the way of measuring the breakdown voltage of transformer oil.

Also I observed a test which was done to measure the moisture level of the transformer oil and

found the result as 11 PPM. In addition to that I obtained a fair knowledge about the 33kV GIS

system.


Polarization Index = MΩ (10 min)

MΩ (1 min)

= 22.7 = 2.23

10.2

Polarization Index = MΩ (10 min)

MΩ (1 min)

= 27.2 = 2.54

21.1

Table 2.2 RESULTS OF THE RATIO TEST


2.4 Generation Planning Branch

2.4.1 Introduction

Generation Planning Branch of CEB is situated in the CEB Head office building. This branch is

supervised by a DGM and I trained under the Electrical Engineer Mr.Anuradha for one week.

The major task done by this branch is planning the future electricity generation system of the

country in order to meet the future electricity demand. When planning this system primarily the

capability of the existing generating system is assessed. Then analyze whether it can meet the

energy demand in future. If the existing system fails to do that a candidate system should be

prepared to satisfy the demand. Details and costs of candidate thermal and hydro plants which

are to be considered for system addition are obtained from various pre-feasibility and feasibility

studies commissioned by the CEB in the recent past. Every year this branch publishes a Long

Term Generation Expansion Plan (LTGEP) for 10 years and I was able to study the LTGEP

2009-2022 plan when I was there.

2.4.2 National Demand Forecast

To plan the future generation system a forecast of the future electricity demand is strongly

required. Therefore every year a report for 20 years which contains the predictions of the future

energy demand in the country is also published by this branch and it is called as the National

Demand Forecast. This forecast is done by analyzing the past data such as GDP, past electricity

demand, total energy losses and etc. And I was able to study the National Demand Forecast

(2008-2028) when I was there.

2.4.3 WASP Simulation Software

After preparing the demand forecast, generation plan is prepared using the simulation software

WASP (Wlen Automatic System Planning Package). The key inputs for the software are study

period, demand and load duration data, plant data, committed development plan, emission factor

for each plant, reserve margin, spinning requirement in the system, development cost,

construction period, economic parameters and etc. When I was at this branch I experienced how

to implement a Generation Expansion Plan using this software and I studied the output report

given by the software as well.



2.5 Transmission Planning Branch

2.5.1 Introduction

Transmission Planning Branch of CEB is situated in the CEB Head office building. This branch

is supervised by a DGM and I trained under the Electrical Engineer Mr.Priyadarshana for one

week. The major task done by this branch is designing of grid substation and transmission lines

according to the upcoming generation plans. Every year this branch publishes a Long Term

Transmission Development Plan for a time period of 8 years. This plan is prepared by analyzing

the Long Term Generation Expansion Plan, National Demand Forecast and Regional medium

voltage distribution plan. Preparing tender documents and shifting of transmission lines when

required are also functions of this branch. A schematic representation of the transmission process

is provided in the Annex A8,2,5,1.


When I was at the Transmission Planning Branch I was able to study the Long Term

Transmission Development Plan (2008-2016) and I obtained a fair knowledge about the

procedure of preparing a Transmission Development Plan. And also I learn the way of preparing

a Grid wise Demand Forecast. As well as I was able to obtain a fair knowledge about the

Moragolla hydro project which is currently in its feasibility study stage. At there I experienced

how to implement a Transmission Development Plan using the simulation software “PSSE”

(Power System Simulation for Engineering). In addition to that I met an Electrical Engineer from

New Zealand who had come to the Transmission Planning Branch to monitor an existing project

and he gave me a presentation about the SWER (Single Wire Earth Return) technology which is

used to distribute electricity in rural areas in countries like Australia and New Zealand.



2.6 Sapugaskanda Diesel Power Station

2.6.1 Introduction

Sapugaskanda Deisel Power Station is supervised by its Chief Engineer and I trained under him

for one week.First stage of the Sapugaskanda Diesel Power Station was implemented in 1984

with four 20MW diesel generators. First expansion of the plant has been commissioned in 1998

with another four 10MW diesel generators. In the second expansion of the Sapugaskanda Diesel

Power Station four additional 10-MW diesel generator sets were installed, and commissioned in

1999 increasing the installed capacity from 120 MW to 160 MW. When I was there I was able to

obtain a fair knowledge about the process of generating power in the power plant.

2.6.2 Generation Process In this power plant the generated are operated using diesel engines. Therefore Fuel is the major

material which needs more to do the operations in the power station. There is a fuel supply line

to the power station from the Ceylon Petroleum Cooperation. Heavy fuel is pumped through that

line and there are 4 storage tanks inside the plant premises to store the heavy fuel. And there are

also 2 storage tanks to store diesel. Although it is called as a diesel power station heavy fuel is

used to operate the engines. But diesel is used as the fuel at the starting of the engines. After

running sometime from the starting fuel type is converted to the heavy fuel. Heavy fuel is not

directly supplied to the engines due to its high viscosity. Therefore there are two fuel treatment

houses in the power station to treat the heavy fuel and 3 storage tanks to store the treated heavy

fuel. Before the fuel is sent to the treatment plants there are sludge separator units to separate the

sludge from the heavy fuel. Lube oil is supplied to the generators through separate lines.

Engines are cooled using the water and there is water storage tank which has volume of 3000 m³

to store the cooling water. Engine cooling procedure is done in a closed cycle. The water that

comes out of the engines after absorbing the heat is sent to a cooling tower and sent back again

to circulate inside the engines. As well as there is a separate radiator bank to cool the water that

comes out from the engines in the Station B. The Process Flow Diagram of the power station is

provided in the Annex A9,2,6,2.

When I was there I was able to observe and study the above whole process. As well as I was able

to study the switch yard of the power station and learn about the duty which is done by the

control rooms.



2.7 Kotmale Hydro Power Station

2.7.1 Introduction

Kotmale Power Station is Supervised by its Chief Engineer and I trained under 4 Electrical

Engineers for one week. The Kotmale project was one of the first projects taken up under the

development of Mahaweli Complex. The Kotmale project was started with the construction of an

87 m high Rockfill dam across the Kotmale Oya. The water stored in the reservoir is conveyed

through an underground tunnel system to an underground power station situated in the belly of

the Atabage Mountains at about 7.2 km away from the dam for generation of electric power.

After power generation, this water is discharged through the outfall into the mahaweli ganga at

the Atabaghe Oya confluence.

Kotmale Power Station was commissioned in 1986 with three 67MW generators and still it

contributes about 445 GWh of power to the national grid annually. The underground power

station the power station consists of 3 vertical francis turbines which have the ratings of 67MW

at 201.5m head and at the speed of 375 rpm. Unlike the other power plants the power house,

administration office and the control room of Kotmale Power Station are located in 3 places far

apart from each other. Power house which contains turbines and generators are located

underground and there is a separate tunnel to enter that. The Administration building is situated

near that tunnel entrance while the Control room and the switch yard is situated top of the

Atabage Mountain.


When I was there I was able to study the control room of the power station and observe how to

start a machine and connect to the system being in the control room. As well as I studied the

switch yard, single phase power transformers and auxiliary transformers and obtained a fair

knowledge about the switching network. And also I got the opportunity to go the underground

power house and observe some steps of an annual maintenance of a generator which was being

performed. At there I got the chance to enter in to the penstock and walk trough the spiral casing

of a turbine while inside of that was being cleaned. And also I observed the downstream surge

chamber. During that week I got the chance to involve in a first aid training program which was

held for the workers of the power station.



2.8 System Control Centre

2.8.1 Introduction

System Control Centre of CEB is situated in Dematagoda and it is supervised by a DGM. During

the one week period at there I trained under the Chief Engineer of that branch. Main task done by

this division is balancing the power generation and demand in the country to maintaining a high

quality power supply. It is done by controlling the output of all the generators in power plants by

communicating with the power plants. System Control Centre maintains a direct connection with

all the major electrical power generating stations via power line carrier system.

2.8.2 Duties and Functions

System Control Centre decides which power generators should run at a particular time of the

day. The decisions are made by the System Control Engineer by analyzing the load curve which

is updated every time using SCADA system. When the demand increases above the supply

system frequency tends to drop down. But it is the responsibility of the systems control branch to

control the system frequency within standard limits between 49.5Hz – 50.5Hz. Since the total

demand varies every time system frequency controlling normally handed over to one hydro

power station. But this plant can control the system frequency up to some extend only according

to the total demand. When controlling the hydro power plants’ output, water management

directives also should be considered since the irrigation system is not only used by the power

plants and water levels of the reservoirs also should be considered. In addition to that this branch

prepares a Monthly Rolling Planned Outage Report including all the generators’ planned

outages. This report is very helpful in planning daily generation procedures. The Monthly

Rolling Planned Outage Report for the month of May in 2010 is provided in the Annex

A10,2,8,2.

As well as this branch is responsible for the coordination and operation of the 220kV and 132kV

transmission network. The operation of the transmission system is planned by the System

Control Branch when an interruption is required in transmission lines.



2.8.3 Policy on Power System Operation in CEB

System Operation Priority

Safety of persons

Protection of equipment

Availability of Supply

Quality of supply

Economics of system operation

System Voltage

As Normal

220 kV ( ± 5% )

132 kV ( ± 10% )

33 kV ( ± 2% )

System Frequency

The statutory frequency limit is 50 Hz ±1%.

Spinning Reserve

Spinning Reserve Margin to be not less than 5% of gross generation.

Maximum Generator Unit

The maximum load of any generation unit shall be less than 20% of gross generation.


When I was there I learned how to balance the supply and the demand by dispatching the power

generation. And I analyzed every time the load curve, the system voltage and the power

generation data which were being updated by SCADA system. As well as I studied the water

management directives which had been assigned for the week I was there and learned the

importance of that. Also I experienced how to take most suitable and economical decision when

deloading the thermal power generation. In addition to that I was able to learn how to plan

transmission line interruptions by analyzing the Load Flows using “Power World Simulator”

software.


Water Usage priority

Water service and drainage

Environment

Irrigation

Power

Under emergency

220 kV ( + 5% or – 10% )

132 kV ( ± 10% )

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