Discussion of three-phase short-circuit criterion of phase selection relay based on delta variable element of phase current differential;

Based on this model,three-phase short-circuit of synchronous machines are emulated and computed .

Analyzes the cause of 6kV common box bus-bar three-phase short-circuit fault at No.

The three-phase short circuit currents of bulk electric power system are very high,and the high currents do harm to the working of the system.

Firstly,an example of three-phase short circuit is given.

De-excitation of steam-turbine generator after abrupt three-phase short circuit(ATPSC)is serious situation.

With analysis of electrodynamics force about three-phase short-circuit current,after stress analysis,the appearance of short huge electrodynamics force influence outdoor post-mounted vacuum circuit breaker greatly.

In short-circuit current calculations for Jiangsu Power Grid,it was found that the single-phase short-circuit current was bigger than the three-phase short-circuit current of 220 kV buses in some 500 kV substations and even exceeded the rated breaking ability of circuit breakers.

It is approached and analyzed some problems related to testing methods for no-load,three phase steady-state short-circuit and zeropowerfactor characteristic,as well as the confirmation of parameters of motors.