Harmonic Analysis of New Breaker Switched Capacitor Bank Installations: A case study

Abstract

The quality of electric power supply has a great concern and it has been a continuous topic of interest for decades. Transient originated from capacitor bank switching is one of the main reason which affects the power quality. If capacitor banks are not properly selected and placed in the power system they could amplify and propagate harmonics, deteriorate the power quality to an unacceptable levels. On the other hand those transients negatively affected on the various equipment such as switchgears. Therefore analysis of capacitor bank performance under harmonic conditions is an essential step when designing capacitor banks. In this paper, one of the key grid substation in Sri Lankan power system; Thulhiriya is considered as a case study. A 10 MVAR shunt capacitors is already in operation at Thulhiriya GSS (Grid Sub Station). A 15 MVAR new capacitor bank is planned to be added at the neighbouring Kegalle GSS. The selected substation was modelled using Power Factory DIgSILENT simulation software to analyse the transients and harmonics. Different operating scenarios were studied, and the results were compared with the normal operation of Thulhiriya GSS. As the simulation results depicts addition of Kegalle GSS has increased number of parallel and series resonant frequencies. In principle, this situation can be generalize for substations having similar load profiles. Therefore when planning capacitor banks for a substations nearby existing capacitor banks, it is very important to do a detail investigation in order to identify possible resonance conditions. Such resonance conditions needs to be rectify by upgrades to the existing capacitor bank and such upgrades can be part of the new capacitor bank project.