Evaluating the Behaviour of Metallized Polypropylene LV Shunt Power Capacitors During Destruction Test

Industrial loads in the low voltage (LV) AC distribution networks are generally inductive. The resultant lagging power factor occurring on account of these industrial loads is compensated by the usage of suitable LV capacitor banks. Shunt capacitors of the metallized polypropylene (MPP) type are generally used either in fixed bank configuration or as dynamic switched bank configurations. These shunt power capacitors are exposed to high inrush current and switching surges due to switching and overloads on account of harmonics. As the elements of these capacitors are housed within hermetically sealed containers, any internal faults developed in the elements are so dangerous that the resultant force induces high pressure within the containers. Due to the electro-mechanical stresses, at times the resultant explosive force experienced tends to rupture the container and could lead to a potential fire hazard. For protecting the safety of personal and proximate equipment, the containers of these capacitors are integrated with an over-pressure dis-connector which is a very important safety feature introduced in these capacitors. Power capacitor standards cover this important safety feature by introducing a destruction test to check the capability of these integrated over-pressure dis-connectors, and very few laboratories are equipment to perform this important test. Power capacitors laboratory of CPRI is fully equipped to conduct destruction test and a study was undertaken to analyse this important safety feature. Three test samples of different makes and ratings were considered for the study to analyse and the results are presented in this paper. The analysis revealed the importance of this vital safety feature of the capacitor.