What are the four basic requirements for relay protection?
Selectivity, quickness, flexibility, reliability
But the specific depends on what kind of relay you want to choose the.
Reliability, selectivity, fastness, sensitivity.
Relay protection devices should meet the requirements of reliability, selectivity, sensitivity and speed: the four "sex" closely linked, both contradictory and unified.
First, the reliability --- refers to the relay protection device in the protection range of the action should be reliable action, in normal operation, should not be action should be reliable and not action. Any power equipment (lines, buses, transformers, etc.) are not allowed to operate without relay protection, reliability is the relay protection device performance of the most fundamental requirements.
Second, the selectivity --- refers to the first by the fault equipment or the line itself to protect the protection of the fault, when the fault device or the circuit itself or the protection of circuit breaker refused to be allowed by the adjacent equipment protection, line protection or circuit breaker failure protection To remove the fault. On the lower and lower power grid (including the same level) between the relay protection, should follow the principle of step by step to ensure that the grid failure occurs when the selective removal of the fault. Cut off the faulty part of the system, while the other non-faulty parts continue to supply power.
Third, the sensitivity --- refers to the device or line within the protected range of metal short circuit occurs, the protection device should have the necessary sensitivity coefficient (specified in the rules). This is achieved by setting the relay protection. Calibration of the set value is done once a year.
4, quick-moving means that the protection device should be removed as soon as possible short-circuit fault, its purpose is to improve system stability, reduce the failure of equipment and line damage, reduce the scope of failure to improve the automatic reclosing and standby equipment automatically put into effect The
