(1) Selectivity: refers to that when the Electrical fault occurs, the relay protection device acts and only removes the fault element. Minimize the scope of power outages as much as possible to continue the operation of non faulty parts of the system. Divide into main protection and backup protection. Main protection refers to the protection that can reflect the fault of the component itself and quickly remove the fault as required; Backup protection refers to the protection that functions when the main protection or circuit breaker fails to operate.
(2) Quick action: refers to the shortest possible time for the action of relay protection devices.
(3) Sensitivity: refers to the ability of relay protection devices to respond to faults or abnormal operating conditions that occur within their protection range.
(4) Reliability: refers to the reliable operation of the relay protection device when a fault occurs within the specified protection range that it should operate, without refusing to operate; And in any other situation where the protection should not operate reliably, that is, without misoperation.