Internal failure detection and protection on capacitor banks

Abstract

This paper describes a solution of a protection algorithm intended to detect internal element failures for large capacitor and filter banks. For such banks typically H configuration is used. Different fuse arrangements are also discussed. The basic concept is to detect and record the number of failed elements; to identify the failure locations; to alarm failures to the supervisory system and finally to trip the bank when remaining capacitor elements are endangered. Capability to identify the failed part of the bank will save time for the maintenance team and consequently will minimize overall outage time of the whole bank. A simulation model of a typical utility capacitor bank configuration is used with different combinations of internal capacitor element connections. The tests of capacitor bank internal failure have been verified and recorded in the simulation model. The protection algorithm is then developed based on the ratio and the angular difference between the phase currents and the unbalance currents to detect different element failure cases even with many combinations that comprise simultaneous element failures in different capacitor units in different quadrants, which may cancel the unbalanced current produced in the neutral connection current transformers for capacitor internal faults detection. Finally, the protection algorithm developed for the internal failure detection and protection is verified using a relevant simulation environment. The paper covers the protection of shunt and series capacitor banks used for several industrial and utility applications, e.g. FACTS (Flexible Alternating Current Transmission Systems) products. The paper concludes with information for possible future work in the related topics.