INSTRUMENTATION CHANNEL ERROR CORRECTION AND ITS EFFECTS ON PROTECTIVE RELAYS

Abstract

The objective of this research is to propose an on-line instrumentation channel error correction method within merging unit (MU) and to investigate its effects on protective relays. The physically-based high fidelity models of entire instrumentation channel are developed, which consist of the instrument transformer, the instrumentation cable and the burden resistor. A dynamic state estimation algorithm is constructed to estimate the primary values on a sample by sample basis. The introduction of MU enables that each instrumentation channel of a MU can be designed to provide corrected primary values. Therefore, the proposed error correction method can be an integral part of MU so hat MU reports directly primary values that have been corrected, which is applicable in real-time protective relays. An alternative method to validate the estimated samples is presented via substation level dynamic state estimation using legacy or estimated measurement samples, respectively. To evaluate the effects of errors on protection relay actions, the performance of three typical protection schemes are presented using estimated measurement samples and legacy measurement samples, respectively. The results show that when large instrumentation channel errors introduced by current transformer (CT) saturation, using the legacy measurement samples may lead to dependability problem for distance relay and security problem for current differential relay and setting-less relay. However, the relay performance (dependability and security) can be greatly improved and the mis-operations can be avoided using the estimated measurement samples.