A relay protection tester is a core device used to verify the performance of relay protection devices. Its working principle can be summarized as “signal excitation – behavior detection. ” The tester has a built-in high-precision programmable power supply, capable of simulating various operating. The first relays were Electromechanical (EM): machines with moving parts actuated by coils connected to current and voltage sources. After the neutral line of the high and low voltage sides is. Protection relays play a key role in modern energy systems.