Relay protection is a very important test in power system testing. It can detect faults or abnormal situations in the power system, thereby issuing an alarm signal, or directly isolating and removing the fault part. The instrument generally used in relay protection work is a microcomputer relay protection tester.

Because relays with contacts were mainly used to protect the power system and its components (generators, transformers, transmission lines, etc.) from damage during its development, it is also called relay protection.

Overcurrent protection is a protection method that causes the protection device to operate when the current exceeds a predetermined value. It mainly includes two types of short-circuit protection and overload protection. Short-circuit protection has the characteristics of large set current and instantaneous action. The characteristics of overload protection are mainly reflected in its small setting current and inverse time action.

Electromagnetic current trips (relays) and fuses in short-circuit protection are often used as short-circuit protection components. The time delay electromagnetic current relay in overload protection is often used as an overload protection element.

Overcurrent protection can handle different types of faults in sections and conditions. An over-current protection switch is set at each stage, and a part of the circuit is selectively cut off according to the current size, location, duration, etc. It is actually operated by three characteristics: inverse time characteristic, definite time characteristic, and quick-break characteristic.

Combining these three types, install them in different positions and set them reasonably, then the line can be protected by current, time, and section.

In addition to the different methods of relay protection, the microcomputer relay protection tester used is also different. There are also three types of testers: multifunctional, comprehensive, and common. The functional characteristics between them are different, and the tests implemented are also different.