Design and evaluation of a circulating current differential relay test system

This paper describes how an EMTP based simulator can be used in conjunction with a relay test set to type-test a protection relay operating within a circulating current differential protection scheme. The combination of a simulator and a test-set is designed to replace a high power synthetic test plant that has been used for more than 30 years for type and approval testing of differential protection relays. The paper will include results that describe the operating performance of the new test system, on both internal and external faults, and these will be compared with experimental results obtained from an identical set of tests on the synthetic test plant.