1. The most important characteristi

1. The most important characteristic of traction power supply system protection is divided into multi-power supply and multi-dead zone. The so-called multi-power supply, is when the traction network short-circuit, not only bilateral power supply to the short-circuit point on both sides of the traction substation, but all the traction substation through the traction network to short-circuit point power supply. The so-called multi-dead zone is the "dead zone" in the protection due to the characteristics of the traction power supply system itself and the particularity of the protection object. The most basic requirement of any protection is to "cut off the power supply" and "eliminate the dead zone" when short circuit occurs. In view of these two points, traction power supply system in addition to the protection commonly used in the AC system, the special protection measures such as the internal joint trip of Traction substation, the bilateral joint trip of traction network and Di/dt are also set up, which can completely meet the requirements of cutting off power supply and eliminating dead zone when the traction power supply system fails. For the relay protection of any power supply system, the reliability always takes the first place, but for the DC traction power supply system, the quick-acting performance can be regarded as the same important protection characteristic as the reliability, therefore, the DC side protection uses millisecond electrical protection equipment, such as DC quick circuit breaker, di/dt protection, in order to cut off the DC short-circuit current when it rises, not allowing the short-circuit current to reach the steady-state value. As for selectivity, it is in the DC traction power supply system in a secondary position, its protection is set to "rather error action, not action" . MISOPERATION can be corrected by auto-reclosure, but non-operation is terrible because the DC arc produced when the traction power supply system is short-circuited can keep burning for a long time if the power supply is not cut off quickly But the AC ARC is different, its voltage can be zero-crossing surface automatically extinguished.