A novel error compensation algorithm for three-current transformer connection

Under fault condition, primary current of a current transformer (CT) has high magnitude and may include decaying dc offset. This can result in saturation of magnetizing core of the CT and the secondary current is thus distorted. The distorted current is likely to cause malfunction of protection relays or control devices. Therefore error compensation methods are studied. Most attentions are paid to a single CT. However, CTs are usually connected together for different protections and control devices. For example, three CTs are linked for three-phase current protection and zero-sequence current protection of transmission lines. This paper proposes a novel error compensation algorithm for 3-CT connection. Due to the existence of neutral circuit, the three CTs are affected each other and error compensation methods for a single CT cannot be applied. The error compensation algorithm is derived based on the physical configuration of the 3-CT connection. It is evaluated by EMTP simulation data and case studies are included. Protection relays and control devices can achieve better performance using the compensated current measurements.