IMPROVEMENT OF POWER QUALITY OF A 
STAND-ALONE MICRO HYDRO POWER PLANT 
 
 
 
A.U.Walpola 
 
 
 
Department of Electrical Engineering 
University of Moratuwa 
Sri Lanka 
 
 
2005 
 
84139 
 
 
 
 
 
 
 
 
 
 
  
Abstract  
  
Stand-alone micro hydro power schemes providing electricity to rural villages in 
hilly areas in Sri Lanka where the grid electricity is not available has become a viable 
and popular alternative to grid electricity. For generation of electricity, most of the 
micro hydro schemes employ induction generators converted from ordinary 
induction motors. Due to many advantages such as robustness, lower cost, less 
maintenance, readily availability, induction machines are popular over traditionally 
used synchronous machines in this application. Micro hydro power plants, which 
employ capacitor-excited (self-excited) induction machines have been considered in 
this research work. 
 
Stand-alone micro hydro schemes are often located on streams and small rivers 
where the flowing water can be diverted to the generation of power without 
constructing reservoirs or ponds. Since these plants are usually less than 50 kW in 
capacity, they require little amount of water flow for its rated power output. Even 
though the water source of the plant is capable of supplying required flow for the 
majority period of an average year, there are some extended periods of drought, 
which results in reducing the rated flow to the plant. In such situations, micro hydro 
systems have problem of maintaining its power quality in terms of voltage and 
frequency, since the control systems are designed only for rated flow conditions. 
This results in variations in supply voltage and frequency thus making difficulties to 
the consumers such as reduction of voltage at customer end, inability to use 
fluorescent and CFL lamps, difficulty in using electrical motors and other appliances 
such as TVs. 
 
In this research work, the problem was analyzed using the existing micro hydro 
controllers and discussed the suggested solution by analyzing the required level of 
control of voltage and frequency in plant output in part flow conditions. Even though 
there are expensive alternatives for voltage and frequency control in such situations, 
emphasis made to economical development of such system to suit and feasible for 
  
actual implementation in community based micro hydro schemes. The suggested 
control system was designed using power electronics and discrete electronic 
components and it was tested at partial load conditions. Further another control 
system was suggested for simultaneous voltage and frequency control in rated flow 
conditions where existing controllers have the facility of controlling either voltage or 
frequency. 
 
Finally, it was discussed to extend the improvement of power quality at customer end 
by reducing the harmonics that create by the electronic switching in the control 
systems. 
DE CLARA TlON 
I hereby declare that this submission is my own work and that to the best of my knowledge and 
behalf it contains no material previously published or written by another person or material. 
which to substantial extent has been accepted for the award of any other academic qualification 
of any university or institute of higher learning except where acknowledgement is made in the 
text. 
~ 
A.U.Walpola 
PG/EE/13/2000 
August. 2005 
@~ 
Dr. D.P.T. ~anayakkara 
Project Supervisor 
:lc/" Awrust. 2005 •••• • ::::> 
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Abstract 
Preface 
Contents 
List of Figures and Tables 
Acronyms 
Chapter 1: Introduction 
l.l Stand-alone micro hydro systems 
Contents 
1.2 Electricity generation from micro hydro system 
1.3 Objective ofthe thesis 
Chapter 2: Outline of Project Implementation 
2.1 Outline of approach 
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2.2 Significant power quality problems identitied with micro hydro power 
supply 
2.3 Instrumentation 
Chapter 3: Induction Generators in Micro Hydro SchemeS:• ... 
J I Introduction to induction generators in micro hydro schemes 
3.2 Operation of an induction generator 
Chapter 4: Control Systems in Present Micro Hydro Schemes 
4.1 Structure of ordinary induction generator control ler 
4.1.1 Phase angle control type IGC 
4.1.2 Pulse Width \ttodulation type IGC 
4.2 Active and reactive power control by IGC 
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Chapter 5 : Shortcomings Associated with Ordinary IGCs 
5.1 Introduction 
5.2 Outline of shortcomings associated with present IGCs 
5.3 How partial flow situation occur at micro hydro power plants ? 
Chapter 6: Performance of IGCs Under Different Flow Conditions (A 
Case Study) 
6.1 Details of micro hydro plant where measurements were taken 
6.2 Case I- Operation of micro hydro plant under design (rated) flow 
6.3 Case II - Operation of micro hydro plant under partial flow situation 
I 
Chapter 7 : Improvement of Power Quality at Partial Generation 
Situation 
7.1 Voltage and Frequency control during panial generation situation 
7.2 Design aspects of modified IGC 
7.2.1 Voltage sensing circuit 
7.2.2 Frequency sensing circuit 
7.2.3 Power supply to IGC 
7.2.4 Constant reference voltage generation 
7.3 IGC operation under partial flow situation 
7.4 Results of performance of new design 
Chapter 8 : Discussion 
8.1 Advantages of Proposed System 
8.2 Disadvantages of Proposed System 
8.3 Further Improvements 
Chapter 9 : Conclusion 
References 
Appendices 
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Appendix I : Alteration to windings of induction motors for use as induction 
generator 
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Appendix 2 :Active and reactive power control by IGC 
Appendix 3 : Connection of excitation capacitance to an induction generator 
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List of Figures and Tables 
VI 
1. List of Figures 
Figure 1.1 General arrangement of stand-alone micro hydro system 
Figure 1.2 (a) Excitation capacitance connection for single phase systems 
Figure 1.2 (b) Excitation capacitance connection for three phase s~ems 
Figure 1.3 
Figure 2. I 
Figure 3.1 
Figure -t 1 
Figure .+.2 
Figure -L3 
Figure 5.1 
Figure 5.2 
Figure 6.1 
Figure 6.2 
Figure 6.3 
Figure 6...1-
Figure 7.1 
Figure 7.2 
Figure 7.3 
Figure 7...1-
Figure 7.5 
Figure 7.6 
Figure -. 7 
Figure -.s 
Voltage and magnetizing current variation over excitation capacitance and 
corresponding frequency variation 
Instrumentation for measurement of electromechanical parameters 
Transmission of power in an induction generator 
Block diagram of phase angle control type IGC 
Waveform pattern of phase angle control type IGC 
Block diagram of pulse width modulation type IGC 
Y.lonthly average rainfall in different micro hydro sites 
Monthly average generation of micro hydro plants (Deraniyagala and 
Rathnapura micro hydro plants) 
Variation of voltage and currents at rated tlow condition 
Variation of voltage and frequency at rated.,;tlow condition 
Variation of voltage and currents at partial tlow condition 
Variation of voltage and frequency at partial tlow condition 
Modified IGC for voltage and frequency control during partial t1ow conditions 
Voltage sensor circuit 
Frequency sensor circuit ......... ~~ 
...... 
DC power supply circuit for IGC 
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Constant reference voltage generation 
Operation of IGC and corresponding voltage and frequency variation in suppl~ 
Output power with variation of turbine tlow 
Output voltage with variation of generator output power 
VII 
Figure 7.9 Ballast load switching with output power at reduced flo""' 
Figure 7 .I 0 Excitation capacitance variation with output power at reduced flow 
Figure 7.11 Frequency response to output power 
Figure A I ( 1) Alteration to the winding of an induction motor to be operated as a single phase 
generator 
Figure A 1(2) Alteration to the winding of an induction motor to be operated as a three phase 
generator j 
Figure A2( l) Phase angle control by IGC 
Figure A2(2) Control of active and reactive power 
Figure A3( I a) Connection of excitation capacitance to a single phase system 
Figure A3( l b) Phasor diagram for single phase system 
Figure A3(2a) Incorrect connection of capacitors in a single phase system 
Figure A3(2b) Phasor diagram for incorrect system 
2. List of Tables 
Variation of supply voltage and currents at rated flow condition 
Variation of supply voltage and frequency at rated flow condition 
Variation of supply voltage and currents at partial flow condition 
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Table 6.1 
Table 6.2 
Table 6.3 
Table 6A 
Table 7.1 
Table 7.2 
Table 7.3 
Variation of supply voltage and frequency at partn11 flow condition 
Switching pattern ofballast load 
Switching pattern of excitation capacitance 
Measured data with the modified controller 
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ACRO:W7v1S 
IGC - Induction generator controller 
ELC - Electronic load controller 
kWh - Kilo Wan hour 
kW - Kilo Wan 
kVA - Kilo volt-amperes 
kHz Kilo Hertz 
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uF - Micro Farad 
Vret - Reference voltage 
Vav - Average voltage 
v 
'll - Maximum voltage 
Vr:ued - Rated Voltage 
F"31ed - Rated frequency 
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'lominal national voltage 
AVR - Automatic voltage regulator 
RP~1 - Revolutions per minute 
PWM- Pulse width modulation 
IGBT - Insulated gate bipolar transistor 
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