Basic requirements for relay protection
When short-circuit happened to electrical equipment or lines, high short-circuit current will be generated, voltage of power grid will decrease, electrical equipment will be burned and if it is serious, stable operation of power system will be damaged, even the grid will be influenced.
In order to clear faults correctly and quickly and recover power system to normal as soon as possible, reliability, selectivity, quickness and flexibility of relay protection are required.
It means that when the fault occurs, the protection related with it will act reliably. No refusing no misacting.
When there is fault, the protection device will isolate the fault element to reduce the power off area.
Cut off the fault as soon as possible. The cut off time include relay protection acting time and CB tripping time.
It refers to the response ability for relay protection to faults in protected area, requiring the protection device responses flexibly when there is fault and abnormality happened to protected equipment no matter where is the short circuit, what kind of short circuit and operation modes.