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NTN TECHNICAL REVIEW No.86（2018）

[ New Product ]

Grid Connectable NTN Micro Hydro Turbine

1. Introduction

The energy issue is a global challenge that we haveto deal with to achieve a sustainable society. Some ofthe key initiatives include reduction of greenhouse gasemissions related to recent climate change, energysaving for phasing out fossil fuel dependency, anddiversifying energy sources by promoting use ofrenewable energy. Fig. 1 shows the actual power mixbefore the Great East Japan Earthquake and theprediction for FY2030. Renewable energy, inparticular, is assumed to more than double from theactual ratio before the Great East Japan Earthquake,indicating high expectations 1).

*Engineering Dept. Green Energy Products Division

Demand of renewable energy such as hydroelectric power generation isincreasing rapidly from rise of global warming and the interest to the energy mix.NTN already commercialized the NTN Micro hydro Turbine which is used inexisting agricultural canal and industrial canal and makes electric poweravailable in the place where the no power system exists. NTN develops GridConnectable NTN Micro hydro Turbine. This paper introduces the features andthe structure of the developed products .

Takashi ITOU*　 kanta KIMURA* Yasunari KANAMURA*

Securing the emergency power supply in case ofnatural disasters is also a great challenge. Althoughstandby generators are being installed for emergencypower sources, storage of fuel is another challenge.Renewable energy does not require storage of fueland can be used as an emergency power source.NTN has productized a Green Power Station, whichstores power from photovoltaic power generation andwind power generation into batteries and is used forlighting at night or as an emergency power source.Hydraulic power generation is a stable power

source with little variance compared to photovoltaic orwind power generation. NTN has developed andproductized the "NTN Micro Hydro Turbine" whichuses the energy of running water in waterways 2). NTNMicro Hydro Turbine is an independent power sourcewhich assumes private consumption by storinggenerated power in batteries for supply in the areaswithout good power infrastructure or as an emergencypower source in case of disasters.On the other hand, feed-in tariffs (FIT) started in

July 2012 to promote renewable energy in Japan. FITis a program to require power companies to purchasepower generated by renewable energy at a fixed price.Introduction of this program facilitates recovery ofcapital investment; therefore, installed bases ofphotovoltaic power generation is significantly growing.

Fig. 1 The power supply construction in FY2030

Energy saving Renewable　 Around 22-24%Nuclear

27% NuclearAround 20-22%

Total thermal62%

Total thermalAround 56%

100％90％80％70％60％50％40％30％20％

10％0％ Ave. of 10yrs

before earthquake FY2030

Geothermal around 1.0%

Biomass3.7～ 9.1％

PhotovoltaicAround 7%

HydropowerAround 8.8-9.1%

Wind around 1.7%

11%

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Grid Connectable NTN Micro Hydro Turbine

NTN's own market research revealed that there wasstrong demand for hydraulic power generation of thegrid connectable type, so that the generated powercan be sold, taking advantage of FIT. In addition,since the purchase price for hydraulic powergeneration of less than 200 kW is more profitable than200 kW or more, as shown in Table 1, adoption ofhydraulic power generation of less than 200 kW will belikely to grow 3).In this article, we describe the structure and

features of "Grid Connectable NTN Micro HydroTurbine" that NTN has developed which allows sale ofgenerated power.

2. Grid connection

Grid connection means that power generationfacilities such as photovoltaic power generation andhydraulic power generation are connected to powertransmission lines or power distribution lines of utilitycompanies, as shown in Fig. 2. By connecting powergeneration facilities to the grid, the generated powercan be sold to the utility companies.

Fig. 2 Image of grid connection

NTNmicro hydro

turbine

Gridconnectable

systemGrid Utility

company

Fig. 4 System configuration of Grid ConnectableNTN Micro Hydro Turbine

Controller Power conditioner

GridNTN

micro hydroturbine Grid connectable system

Fig. 3 NTN Micro Hydro Turbine

Table. 1 FIT price of hydro turbine

FY2017FY2018FY2019FY2020

Purchase period

1,000 kW or moreand

less than 5,000kW200kW or more

andless than 1,000kW

Less than200kW

24 yen + tax 29 yen + tax 34 yen + tax

20 years

Table. 2 Specification of NTN Micro Hydro Turbine

600

900

1,300

0.4

1.0

2.0

2

2

2

Hydro turbineblade diameter

mmOutput

kWRated

flow ratem/s

Recommendedwaterway exceeding

(mm)Width : 700Depth : 700Width : 1,000Depth : 1,000

Width : 1,400Depth : 1,400

3. Structure of Grid ConnectableNTN Micro Hydro Turbine

Fig. 3. shows the outer view of NTN micro hydroturbine, Table 2 shows the specification and Fig. 4shows the configuration of Grid Connectable NTNMicro Hydro Turbine.The AC power generated by NTN micro hydro

turbine is converted to DC power by the controller andinput to the power conditioner.The power conditioner is a device to convert the DC

power to AC power and transmit it to the grid. Thecontroller and the power conditioner are collectivelycalled the grid connectable system, which enablespower generated by the NTN micro hydro turbine to beefficiently transmitted to the grid and sold to the utilitycompany.

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NTN TECHNICAL REVIEW No.86（2018）

4. Functions of the components ofthe grid connectable system

(1) ControllerThe controller consists of rectifying circuitry which

rectifies the power generated by the generator andcontrol circuitry which controls the Grid ConnectableNTN Micro Hydro Turbine. The controller has thefollowing functions:1) Converts (rectifies) the AC power generated by the

generator to DC power and inputs it to the powerconditioner.

2) Monitors the generated power and rotational speedof the generator.

3) Controls the rotational speed of the hydro turbineblades in order to push out foreign objectsentangled in the blades 2).

(2) Power conditionerThe power conditioner is a device to convert the DC

power converted by the controller to AC power, whichis transmittable to the grid, and transmit it to the grid.In the grid connectable system of "Grid ConnectableNTN Micro Hydro Turbine," the maximum power pointtracking (MPPT) is adopted for the control ofmaximizing power generation.

5. Power generation control of GridConnectable NTN Micro Hydro Turbine

MPPT is a control to automatically maximize powergeneration.By applying MPPT to power generation control for

hydraulic power generation, the load to the generatoris changed to control the rotational speed of theturbine blades, while measuring generated power, forthe speed to obtain the maximum power generation.The Grid Connectable NTN Micro Hydro Turbine hasmodels for 0.4 kW, 1 kW and 2 kW of powergeneration and the standard implementation of MPPTfor systems with less than 2 kW power generation isthe first in the industry. MPPT implementation in theGrid Connectable NTN Micro Hydro Turbine has thefollowing benefits:

· Eliminates the need for measuring the width, waterlevel, and flow rate of the waterway to which thesystem is to be installed and adjusting the controllerto the result, achieving a significant reduction ininstallation time and cost.

· Enables maximization of power generation, evenwhen the water level or flow rate changes in thewaterway.

The following is the control process of MPPT (Fig. 5):(1) Reduce the rotational speed of the turbine blades

from N1 to N2 to increase the power output fromP1 to P2.

(2) Reduce the rotational speed of the turbine bladesfrom N2 to N3 to increase the power output fromP2 to P3.

(3) When the rotational speed of the turbine bladesdecreases from N3 to N4, power output changesfrom P3 to P4.

(4) As the power output decreases to P4, therotational speed is increased back to N3.

(5) When the rotational speed of the turbine bladesincreases from N3 to N2, power output changesfrom P3 to P2.

(6) As the power output decreases to P2, therotational speed is decreased back to N3.By repeating this process, generated power is

maximized.

However, when MPPT was applied to hydraulicpower generation, there were cases where themaximum power generation could not be attained bythe following:When the flow rate and water level of the waterway

changed abruptly in a short time and deviated from themaximum power point of MPPT, the control could notfollow the change and the load to the generatorcontinued to increase causing a shortage of turbineblade torque driven by the water flow and reduction ofturbine blade rotational speed. This phenomenonoccurs when, in Fig. 6 "Rotation speed of blades vs.torque characteristic diagram," the operating condition,which is usually at point (1), moves to the stall regionsuch as point (2), causing reduction of rotationalspeed and torque of turbine blades, resulting in lowerpower generation.

Fig. 5 Control Method of MPPT

Maximum point of generated power

P3P2P4

P1

N4 N3 N2 N1Turbine blade rotational speed

Gene

rate

d po

wer

(1)

(2)(5)(6)

(3)(4)

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Fig. 8 Test lig layout of field test

NTNmicro hydro

turbine

NTNmicro hydro

turbine

Controller

Controller

Electronic load

Simulated powersupply load

Powerconditioner

(a) When electronic load is connected

(b) When power conditioner is connected

Fig. 9 Result of field test

1000

800

600

400

200

00 100 200 300 400

Generated power voltage V

749W

Gene

rate

d po

wer

W

Fig. 6 Rotation speed of propeller vs torque characteristic diagram

Flow rateHigh

Flow rate Low

(1)

(2)

Stall region

Turbine blade rotational speed

Turb

ine b

lade

torq

ue

Fig. 7 Field test

The Grid Connectable NTN Micro Hydro Turbinecompares and controls the turbine blade rotationalspeed and generated power at all times so thatmaximum power is attainable and the operatingconditions never move into the stall region.The problem has been resolved by incorporating

control to detect the deviation of the operating point anddrive the MPPT to return to the maximum power point,even when the conditions move into the stall region.

Table. 3 Test condition

Hydro turbine blade diameterWater depth

Flow rate in the demonstration test

φ900670 mm2.0 m/s

Item Condition

means it has tracked the maximum power generationwell.

Grid Connectable NTN Micro Hydro Turbine

6. Demonstration test in the actual waterway

The demonstration test of the developed gridconnectable system was conducted to evaluateperformance. The configuration of the demonstrationtest is shown in Fig. 7 and the test condition is shownin Table 3. The demonstration test verified the trackingperformance of the maximum power generation byMPPT of power conditioner. The waterway used for thedemonstration test did not have enough water and aportion of the turbine blades was out of water.First, the maximum power generation of the

waterway under the demonstration test was verified byconnecting the electronic load to the controller output,as shown in Fig. 8 (a), changing the generatedvoltage (proportional to the rotational speed of theturbine blades) and measuring the generated power.The results are shown in Fig. 9. The maximumgenerated power was 749 W.Next, the power conditioner was connected, as

shown in Fig. 8 (b) for the measurement. In thisdemonstration test, simulated power supply load wasused to simulate the condition of grid connection.Fig. 10 shows the results of the generated power.

The generated power was 738 W on average, which

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NTN TECHNICAL REVIEW No.86（2018）

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7. Mechanism for easy operation "Easy Lifter"

When waterways are swollen by heavy rain fromtyphoons, etc, driftwood and debris may damage thehydro turbines. This should be avoided. If turbineblades can be lifted above water level, they can bemore safely operated. NTN micro hydro turbine can beequipped with a mechanism, “Easy Lifter,” totemporarily lift the turbine blades from the water inemergency.In addition, this mechanism can also be used to

safely and easily lift the blades without requiring heavymachinery such as cranes for periodic maintenance,allowing time and cost reduction for maintenance andinspection tasks. Fig. 11 shows the condition ofnormal operation and Fig. 12 shows how the bladesare lifted up. There are two ways for operating "Easy Lifter." Fig.

13 shows the lever type, where the turbine connectedto the rotational shaft is manually operated by a leverpivoting at the NTN bearing unit, and Fig. 14 showsthe worm gear type where electric motors can bemounted.

Fig. 12 After lifting up blade unit

8. Conclusion

In this article, we have described the functions andfeatures of "Grid Connectable NTN Micro HydroTurbine" which allows the sale of electric powergenerated by NTN micro turbine, configuration andperformance of the controller and power conditioner ofNTN's highly efficient and proprietary grid connectablesystem, and "Easy Lifter", which allows temporarylifting of the turbine blades from the water.The market for hydraulic power generation using

agricultural waterways, etc. is expected to grow withhigh demand for hydraulic power generation systemwith shorter recovery of capital investment and ease ofoperation. We will continue to work toward higherefficiency and respond to the needs for broaderadoption of micro hydro turbines.

NTN is also working on fulfilling related productsusing natural energy, including photovoltaic and windpower generation for diversification of energy sourcesand achievement of a sustainable society.For example, the demand and application area are

expanding for NTN Hybrid Street Light 4), which was

Fig. 13 Lever type

Rotating axis

Support beam

NTN bearing units(both sides)

Operating lever

Fig. 14 Worm gear type

Coupling

Worm gear

Rotating axis

Support beam

NTN bearing units(both sides)

Fig. 11 Normal operation

Fig. 10 Result of field test

1000

800

600

400

200

00 200 400 600 800

Time sec

738 W (ave)

Gene

rate

d po

wer

W

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launched in 2016. NTN Hybrid Street Light has beenadopted, as an independent power source andstructure for the application “Disaster Relief Map,” thelargest disaster rescue/prevention map in Japandeveloped by Osaka University and “MimamoriRobokun III,” Wi-Fi communication infrastructureequipped with a monitoring camera developed by the“National Activity Support Network for LocalMunicipalities,” a non-profit organization 5). "MimamoriRobokun III" is equipped with a monitoring cameraand Wi-Fi equipment as a standard, as well as a LEDlight, and requires stable power supply even in anenvironment not favorable for wind or daylightconditions. Therefore, a higher power capacity versionof the hybrid street light was newly introduced at theGreen Power Station. We will continue proposing locally produced and

consumed energy through development andmarketing of products that use natural energy in orderto achieve a low-carbon society. In addition, we willcontribute to the safety and security of localcommunities by demand stimulation at the localgovernments and local community associations.

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Takashi ITOU

Green Energy Products DivisionEngineering Dept.

Kanta KIMURA

Green Energy Products DivisionEngineering Dept.

Yasunari KANAMURA

Green Energy Products DivisionEngineering Dept.

Photo of authors

Grid Connectable NTN Micro Hydro Turbine

References1) Ministry of Economy, Trade and Industry: Long-

term Energy Supply and Demand Outlook andrelated materials

2) Tomoya Kawai, Hiroki Mukai, Tomomi Gotou,Micro Hydro Turbine, NTN TECHNICAL REVIEW,No. 84, (2016) 29.

3) Ministry of Economy, Trade and Industry homepage: "Nattoku! Renewable Energy"

4) NTN news on new products, "NTN LaunchesExtremely Silent Hybrid Street Lights,"https://www.ntnglobal.com/en/news/new_products/news201600059.html

5) NTN news on new products, NTN Participates in“Joint Research for Creating MechanismsRegarding Disaster Prevention Monitoring andTourism through Use of IT,”https://.ntnglobal.com/en/news/press/news201700089.html

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