Capacitor switching transient analysis on a transmission grid substation (case study : Thulhiriya GSS)

Abstract

The quality of electric power system has a great concern and also it has been a constant topic of study. A transient originated from capacitor bank switching are main reason which affects the power quality. The analysis, simulation and optimal use of capacitor banks under harmonic conditions are required in a power network to optimally locate and sizing of a capacitor bank. If the capacitor banks are not properly selected and placed in the power system they could amplify and propagate harmonics, deteriorate the power quality to unacceptable levels and the transients produce under different conditions will be negatively affected to the switchgears in the substation. The breaker switched capacitor (BSC) banks are commonly used for power factor correction, reactive power requirement and voltage support by many utilities in the world. Ceylon electricity board (CEB) has also installed total of 370 Mvar capacitor banks island-wide in transmission grid substations (GSS) in 33 kV level. The motivation for the study is the failure of 100 Mvar BSC banks installed at the Pannipitiya GSS after putting in to operations. After this incident the Thulhiriya GSS and Athurugitriya GSS BSC banks were switched off since they also came under same project with same equipment. In this study the Thulhiriya GSS was selected as the case study to analyze the switching transients of the 33 kV BSC banks to the system. Data for the selected substation were recorded and analyzed and the selected substation was modeled using PSCAD simulation program to analyze the transients and harmonics. The objective of the study is to investigate the particular BSC bank is safe for operations without under utilizing by comparing the obtained simulated results with the standards and specifications, observe the switching transients and harmonics, introduce a safe region for closing of the BSC banks, introduce a proper sequence for closing of the BSC banks and introduce time delays for back to back switching of the BSC banks with minimum effect to the quality of the waveform. The results obtained for the particular substation are expected to be extrapolated to a general concept to suit the whole substations in the CEB network.