What are the main overcurrent protection devices

In the event of a phase-to-phase short-circuit fault or an increase in abnormal load or a decrease in the insulation level, the current will suddenly increase and the voltage will suddenly drop. When the fault current in the line reaches the action value of the current relay, the action of the current relay selectively cuts off the fault line according to the selective requirements of the protection device.

Overcurrent protection mainly includes two types of short circuit protection and overload protection.

The characteristics of short circuit protection are large setting current and instantaneous action. Electromagnetic current releases (or relays) and fuses are often used as short-circuit protection components; overload protection features low setting current and inverse time limit action. Thermal relays and time-delay electromagnetic current relays are often used as overload protection components. In the absence of too much inrush current, fuses are also often used as overload protection components.

In the protection zero-connection system, when a fuse is used for short-circuit protection, the rated current of the melt should be less than 1/4 of the single-phase short-circuit current; when it is protected by a circuit breaker, the circuit breaker will act instantaneously or short-delay overcurrent release The set current should be less than 2/3 of the single-phase short-circuit current.

During the operation of the power system, various failures and abnormal operating conditions may occur. The most common and dangerous failure is the occurrence of various forms of short circuits. When a short circuit occurs, the short circuit current flowing through the fault point is large and may be destroyed. The stability of the system running in parallel, so overcurrent protection needs to be configured in the system. However, in some cases, even if the operating value and time of the overcurrent protection device used are well-matched, it may malfunction due to failure to cooperate well with other protections in the system, causing the entire system to malfunction. Therefore, with the increasingly tight grid structure, whether the overcurrent protection can operate correctly is very important for the safe and stable operation of the power system.