ALSTOM GRID UK LTD, United Kingdom
2013. - 10 с.Correct and predictable performance of current transformers (CTs) is crucial for reliability of protective relays connected to these CTs. The straightforward testing of HV and EHV current transformers together with protective relays is constrained by the size and capabilities of test devices, which does not allow using the primary current injection methods in most practical situations. Therefore, manufacturers of numerical protection IEDs have been using various CT models for a long time.
The accuracy of these models has an immediate impact on security and dependability of protection devices. For example, if a specific CT model does not reproduce some important physical phenomena, then a saturation detector or a waveform recovery algorithm developed and tested using this model might fail in a real application.
CT models based on Jiles-Atherton theory of hysteresis have become an industry standard since they were implemented in RTDS® and PSCAD® systems. These models are essentially fixed CTs + leads + burden constructs, because the secondary current waveform is obtained as a solution to a set of combined equations describing both the internal CT physics and the electrical network of the burden [1]. Such an approach naturally limits the range of available CT schemes and burden options.
