Application of Vacuum Circuit Breaker in Low Voltage Distribution System Software

Vacuum Circuit Breaker is widely used in low-voltage distribution system software in engineering construction, which is a kind of electrical components maintenance, with functions of short circuit maintenance, over-voltage protection, operation and protection, suitable for low-voltage distribution system software in industrial production and industrial building terminal equipment. If the design plan of Vacuum Circuit Breaker is not good in the distribution system, it will endanger the normal operation of the supply system circuit. Therefore, when designing low-voltage distribution system software, attention should be paid to the selective operation of Vacuum Circuit Breakers.

In order to ensure the reliability of low-voltage distribution system, the selectivity of low-voltage circuit breakers has become an important content in the design of terminal low-voltage distribution system.

Importance of Vacuum Circuit Breakers in Low-voltage Distribution Systems

In the distribution system protected by Vacuum Circuit Breakers: when an electrical fault occurs, the nearest circuit breaker Qn to the fault point will trip, while other circuit breakers at different levels will not trip, so that the power outage caused by the fault can be limited to the smallest range, and the other power supply circuits without fault can still maintain normal power supply, which is the requirement of selectivity for low-voltage circuit breakers. Non-selective low-voltage circuit breakers refer to the situation that when an electrical fault occurs, the nearest low-voltage circuit breaker QF3 will trip and cut off the fault, while other circuit breakers Qn, QF2, QF4 and QF5 are in the open state and cannot ensure normal power supply for other circuits without fault. The selectivity of low-voltage circuit breakers occupies a very important position in the design of low-voltage distribution system software, which can bring convenience to users and ensure the continuity of power supply circuit operation. Therefore, if there is no selective protection for household appliances, once an electrical fault occurs, the continuity of the distribution circuit cannot be guaranteed, and household appliances such as refrigerators and range hoods will be in the state of shutdown and waiting to restart, affecting the daily life of users.

How to Apply Vacuum Circuit Breakers in Low-voltage Distribution Systems?

In the low-voltage distribution system, Vacuum Circuit Breakers, along with pole mounted recloser, used can be divided into selective and non-selective types according to their protective performance. Selective low-voltage circuit breakers have two-stage protection and three-stage protection. The instantaneous characteristic and short delay characteristic are suitable for short-circuit action, while the long delay characteristic is suitable for overload protection. Non-selective low-voltage circuit breakers are generally instantaneous action, only used for short-circuit protection. Some are long-delay action, only used for over-load protection.

In the low-voltage distribution system, if the upper-level circuit breaker uses a selective circuit breaker, and the lower-level circuit breaker uses a non-selective circuit breaker or a selective circuit breaker, the selectivity is mainly achieved by utilizing the different delay actions or delay action times of the short delay trip unit. When the upper-level Vacuum Circuit Breaker has a delay action, the following issues should be noted:

• Regardless of whether the lower level is a selective circuit breaker or a non-selective circuit breaker, the instantaneous overcurrent trip unit setting current of the upper-level circuit breaker should generally not be less than 1.1 times the maximum three-phase short-circuit current of the outgoing line of the lower-level circuit breaker;

• If the lower level is a non-selective circuit breaker, to prevent the short-delay overcurrent trip unit of the upper-level circuit breaker from tripping first due to insufficient instantaneous action sensitivity of the lower-level circuit breaker when the protected circuit of the lower-level circuit breaker experiences a short-circuit current, the set current of the short-delay overcurrent trip unit of the upper-level circuit breaker should generally not be less than 1.2 times the instantaneous overcurrent trip unit of the lower level;

• If the lower level is also a selective circuit breaker, to ensure selectivity, the short delay action time of the upper-level circuit breaker should be at least 0.1S longer than that of the lower-level circuit breaker.

In general, to ensure the selective action between the upper and lower-level of low-voltage Vacuum Circuit Breakers, the upper-level circuit breaker should be equipped with a short delay overcurrent trip unit, and its tripping current should be greater than one level higher than that of the lower-level overcurrent trip unit, and at least the tripping current of the upper-level circuit breaker IOP.1 is not less than 1.2 times the tripping current IoP.2 of the lower-level circuit breaker, namely IOP.1≥1.21OP.2. By collaborating with remote terminal unit manufacturers, the selective action of Vacuum Circuit Breakers can be properly achieved in low-voltage distribution systems.

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