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The power factor improvement has a great concern in the distribution system due to large motor installed in industrial system. The capacitor bank was installed to improve the power factor in the distribution system. Due to frequently capacitor bank switching has create transient phenomena in the distribution system and their effects the power quality. The aims of this research to study and simulate the effects of capacitor bank switching in the distribution system. The simulation has been conduct with PSIM software by modelled the system which contain of supply, load and three capacitor bank. The simulation was conducted with two conditions which are single bank and bank to bank switching. For single bank switching peak voltage of phase R reached about 60.9 kV and peak inrush current is reached about 6.7 kA. While for bank to bank switching the peak voltage of phase R reached as high as 59 kV and the peak inrush current is almost 8.2 kA.

This paper focused to determine the performance of Current Transformer (CT) operates under harmonics condition and their effects on transformer differential protection. A laboratory test has been implemented to determine the error produced by both CT and power transformer when operating under harmonic condition. The test was performing with the actual condition, where the power transformer is connected to an adjusted nonlinear load, so that the test can be conducted with several levels of total harmonic distortion current (THDi). The results shows, for THDi ranging from 16.70% to 40.88% the maximum errors occurred on CT at secondary power transformers is 27.21% and CT at primary power transformers is 8.12%. This error resulted in differential current flow 0.17A and relay trip without any fault. In this study it was found that the relays started to operate incorrectly on THDi 31.5%.