Most protection and control equipment is usually tested in the open-lo
op mode. However, dosed-loop testing is often the only cost-effective
approach. This paper highlights the areas where closed-loop testing of
protective relays and control equipment is preferable. Test setups wi
th a real-time digital simulator for closed-loop testing of protective
relays, power system stabilizers, and controllers for controlled clos
ing of individual poles of a shunt capacitor breaker are described.