(1) The time constant of the 500KV power system increases. The 22KV system time constant is generally less than 60MS, and the 500KV system time constant is between 80MS-200MS, the system time constant increases, resulting in a longer decay time of the non-periodic component of the short-circuit current, and a longer transient duration of the short-circuit current.
(2) As the system capacity increases, the amplitude of the short-circuit current also increases.
(3) Due to the requirements of system stability, the action time of the main protection of the 500KV system is generally around 20MS, and the total removal time of the fault is less than 100MS. The main protection of the system operates during the transient process of the fault.
Due to a short circuit in the power system, when the transient current flows through the current transformer, a transient process is generated in the transformer. If no measures are taken, the core of the current transformer will soon become saturated. Especially on a circuit equipped with reclosing, when the transient process caused by the first fault has not been attenuated, the transient process of another short circuit is superimposed. Due to the existence of the residual magnetism of the current transformer, it may cause The iron core saturates faster. As a result, the accuracy of the current information of the current transformer is destroyed, causing incorrect operation of the relay protection.