Evaluation and Mitigation of Power Quality Problems in the Ethiopian Electric Power Supply System

Abstract

Power quality and reliability are the two important newlinephenomena used in evaluating the performance of an electric newlinesupply system. In this thesis work the evaluation of power newlinequality and reliability of the Ethiopian Electric supply system newlinewas performed and the results compared to international newlinestandards. Then after appropriate power quality problem newlinemitigation techniques were proposed for the identified power newlinequality problem issues. Power quality problem issues may arise newlineeither from the generation side, transmission section, newlinedistribution network or from customer side installations and/or newlineloads. Until recent times power distribution companies and newlineconsumers of an electrical power gave more emphasis for the newlinereliability of the supply system while giving less attention to the newlinequality of power. But, the fast growth of renewable power newlineintegration like wind and solar to a power system network along newlinewith meteoric rise of non-linear loads, are bringing serious newlinechallenges for quality of conventional unidirectional power flow newlinefrom generation to consumption points. Ninety percent of newlineEthiopia s electrical power demand primarily generated from newlineHydro stations. Wind energy penetration into the power system newlineof Ethiopia is also increasing in recent years in order to alleviate newlinethe huge energy shortage crisis that faced during time of extended dry season. Despite Ethiopia s effort to upgrade its newlinev newline newlinepower generating capacities in the past couple of years, the newlinechronic interruption of electric power at big cities and villages newlinemake customers worry about the quality of power they have newlinebeen getting from the electric Utility provider. Repeated power newlineinterruption and power quality problems are common in many newlineparts of Ethiopia. Sometimes extended blackouts covering large newlineareas of the country is creating huge economic burden for newlinebusinesses, bakery houses, individual households, industries, newlineshops and so on. newlineIn this particular power quality evaluation work the newlinestandard power quality evaluation and analysis proceduresanalysis carried newlineout at the secondary of the steel factory premise transformers, it newlineobserved that the 5th and 7th spectral harmonic current newlinecomponents have a major effect in the supply system of the newlinefactory with 25% and 20% harmonic distortion level newlinerespectively. Besides, it observed that the steel manufacturing newlineindustry is working with poor power factor of 0.75 which is newlinebelow the minimum threshold standard of 0.85 set by the newlineEthiopian electric utility (EEU). From the power quality newlineevaluation and analysis carried out at the main Debre Zeit newlinesubstation, it observed that the 5th and 7th harmonic current newlinecomponents have significant magnitude in half the section of the newlinesubstation 15kV bus bar. The sources of these harmonic currents newlinewere the rectifiers used in the large DC milling motors located newlinein the old production line of the zuqualla steel rolling mill newline(ZuSRoM) factory. Through the techniques implemented to newlinemitigate these harmonic currents at the main substation, the newlineharmonic currents at the bus bar had reduced significantly. The newlinetotal harmonic distortion (THD) of current and voltage at the newlinepoint of common coupling (PCC) of the Adama-I wind farm newlinemodel were within permissible limit. In its present operation newlinevii newline newlinecondition, the power quality of the wind farm is within tolerable newlinerange and therefore do not have negative impact on the performance of the grid supply system. newline As an alternative source of power and to ensure reliable newlineand high quality power supply to certain group of consumers newlinelocally and to strengthen the grid power quality problem newlinemitigation efforts, an isolated hybrid power supply system was newlinemodelled and analysed. Using this hybrid supply model the newlineoptimal hybrid architecture had been identified. Other newlineperformance characteristics of the hybrid architecture were also newlinethoroughly investigated for its practical implementation. newline The mathematical modelling of power factor correction newlinecapacitors and harmonic filters had been done by giving due newlineemphasis for resonant condition. Also, the mathematical newlinemodelling and algorithm for load shifting had been proposed newlineand analysed to shift some of the loads of the steel newlinemanufacturing industry from grid peak to off-peak hours. newlineFinally, the cost benefits analysis of the proposed power quality newlinemitigation techniques had been carried out in order to newlineunderstand their feasibility.