![]() ![]() ![]() The relay switches from one to the other as a function of the present system conditions. The SEL-487B uses a filtered percentage-restrained differential element characteristic with two separate slopes. ![]() For an alternative guide on state simulation testing, refer to the SEL application guide Testing Slope 2 in the SEL-487B Bus Differential and Breaker Failure Relay (AG2009-11). This application guide demonstrates steady-state, single-phase testing of the SEL-487B Bus Differential and Breaker Failure Relay differential element and does not require state simulation. This testing method more accurately mimics realistic conditions on a power system however, steady-state, single-phase testing may be preferred because it is simpler and can be done manually. ![]() This is an automated test involving application of a pre-fault state followed by a fault state. An alternative testing method uses state simulation. In addition, single-phase testing simplifies the test and is suitable for all test sets, including test sets that do not have the six current channels necessary to drive a three-phase test. Although this does not simulate actual conditions on a system, it does provide adequate proof that the relay has been set as desired. INTRODUCTION One way to test a differential element is to use a steady-state, single-phase current injection method. Single-Phase Testing of the SEL-487B Differential Element Without State Simulation Chris Burger ![]()
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