In a static relay, what component is used to open or close the relay contacts?

The correct answer is a thyristor. In a static relay, a thyristor serves as the key component that controls the opening and closing of the relay contacts. A thyristor is a semiconductor device that can be turned on and remains on until the current flowing through it is interrupted. This ability to control high power circuits allows static relays to function effectively for various applications, including motor control and protective relay systems.

Unlike other components, such as transistors or field-effect transistors (FETs), which may be used for signal amplification or switching in lower power applications, a thyristor is specifically designed for high voltage and high current control. Diodes allow current to flow in one direction and cannot be used to switch contacts in the same manner as a thyristor. Therefore, the use of a thyristor is essential in static relays to ensure reliable and efficient operation when actuating contacts without mechanical movement.