Use of a digital simulator to test relays under critical operating conditions

An ENEL (the Italian National Electricity Board), the performance of a protective device was in the past verified, apart from operating experience, by means of so-called functional type tests, performed at the utility´s own laboratories. These tests not only take a very long time, but are also insufficient, in their conventional formulation, for defining the behaviour of a modern relay under all possible network or fault conditions. These considerations led to the development, by ENEL, of a computerized test system able to simulate the desired network and fault conditions. The authors briefly describe the test system, known as the `network simulator´, and two real cases in which it was applied. The first concerns the Presenzano hydroelectric pumped-storage power plant; the second deals with the new conversion substations of the SACOI 2 (Sardinia-Corsica-Italy) DC link. In both cases, a description is given of some significant tests performed and in the latter case, of the remedial action taken to overcome relay malfunctioning