INTRODUCTION

The performance of a microprocessor-based relay is highly dependent on the performance of the analog channels measurement of the relay, as protection functions operate on these values. The failure of an analog measurement channel, either due to a failure in the external measurement circuit, or due to an internal failure inside a UR CT/VT module, can cause incorrect operation of protection functions. The UR CT/VT modules with Enhanced Diagnostics (module types 8L, 8M, 8N, 8R, 8S, 8V) can detect the failure of an analog channel measurement due to internal failures of the CT/VT module, alarm for failure of the module, and block tripping from any protection function associated with this module. This feature is available when using firmware 5.20 or later within the UR family and therefore field-proven since 2006.

Analog data integrity validation

The CT/VT input modules (8L, 8M, 8N, 8R, 8S, 8V) use an analog data integrity check to verify the performance of the analog measurement channels. This feature uses an additional analog hardware channel that has as its input, an analog sum of Sa = Xa – Xb + Xc + Xn, where X stands for either Voltage or Current phases A, B, C, and N analog inputs, to monitor the integrity of analog data.