Enhanced Adaptive Protection Method for Capacitor Banks

This paper presents balance equations for ultra-sensitive protection of shunt capacitor banks taking into account both an inherent (pre-existing) unbalance in the protected bank, and an unbalance in the power system. Four methods are derived: voltage differential, neutral voltage unbalance, phase current unbalance, and neutral current unbalance. These methods are generalizations of the known protection techniques and allow for ultra-sensitive protection with no delay required to ride through system unbalance conditions, or degraded sensitivity to overcome inherent bank unbalance. Additionally, the methods are immune to homogeneous thermal or ageing changes in the capacitor bank, and to switching transients. These novel algorithms facilitate auto-setting of the capacitor bank relay - an automatic process of nulling out preexisting bank unbalance as well as constant errors in instrument transformers and the relay itself. The paper derives equations for the operation of auto-setting and explains the application of this concept. The principle of auto-setting is extended in this paper to provide for continuous adjustment of the relay for maximum sensitivity and security.