Integrated solution for simulation, setting and testing of protective relays, with improved parameter determination, taking into account the affects of CT saturation

The trip characteristic of a differential protection relay is a function: I_differential=f(I_restraint). Beside the normal differential currents caused by the magnetizing current of the transformer and the effect of the tap changer, the restraint current is used to compensate any adverse influence of CT saturation in the event of high through fault currents. The correct setting of the trip characteristic in this area has always been a challenging task, since the exact values of restraint current and differential current are difficult to determine for each specific application. In 1994 during the 2^nd Omicron User Meeting, a computer program was presented, which has been developed to simulate the transient behavior of CTs. Based on this study further investigations have been done in order to improve the quality of the data input for the CTs, to include the simulation of the power transformer behavior, the generation of transient test files for relay secondary testing, the reporting of results and the analysis of the behavior of various protective relays. This article is also subjected to further approaches concerning the influence of the remanence, taking into account the analysis of a real world differential trip due to CT-saturation