Low-voltage distribution cabinet neutral line disconnection protection device

Abstract

The invention relates to a low-voltage distribution cabinet neutral line fracture protection device and a detection method and belongs to the electric power equipment technical protection field. The invention aims to provide the low-voltage distribution cabinet neutral line fracture protection device and detection method which are simple in structure, easy to implement and can assist in quickly judging the fracture condition of a neutral line. According to the technical schemes of the invention, the power source input end of a voltage reduction and rectification circuit is connected with the output end of a load side alternating current voltage; the power source output end of the voltage reduction and rectification circuit is connected in series with a voltage stabilization circuit, and then is connected with the power source input ends of a signal monitoring circuit, a logic judgment circuit and a signal output circuit; the input end of the signal monitoring circuit is connected with the neutral line of the load side alternating current voltage; the output end of the signal monitoring circuit is connected with the first input end of the logic judgment circuit; the output end of the signal output circuit is connected with the second input end of the logic judgment circuit; an execution circuit is connected in series between the logic judgment circuit and the signal output circuit; and the execution circuit is connected with a three-phase linkage circuit breaker.

Description

technical field [0001] The invention relates to a neutral wire disconnection protection device of a low-voltage power distribution cabinet, which belongs to the technical field of electric equipment protection. Background technique [0002] In the three-phase four-wire system where the neutral point of the low-voltage distribution transformer is directly grounded, the power supply is usually symmetrical, but there is always current in the neutral line due to the asymmetry of the three-phase load; due to the unbalanced three-phase load , The disconnection of the neutral line will often lead to a substantial increase in the phase voltage of the user, affecting the safety of electrical equipment. [0003] In actual operation, the disconnection of the neutral line is very easy to occur due to external force, oxidation, etc., between the neutral line terminal of the distribution transformer and the general protection switch of the low-voltage integrated box, which has brought ser...

AI Technical Summary

Problems solved by technology

[0005] One method is to install repeated grounding on the neutral line to achieve overvoltage protection, so that after a disconnection occurs, the neutral point of the power supply and the user's neutral point can continue to be connected through repeated grounding. However, repeated grounding is only suitable for relatively heavy loads below 10kw. For light lines, when the load is slightly heavy, its effect is small, and the investment is large, the effect is poor, and the later maintenance workload is large;

[0006] The second method is neutral line broken zero-sequence current differential protection. Two current transformers with the same transformation ratio are installed in the neutral line and three-phase line of the power distribution cabinet respectively; when the neutral line is intact , the currents on the secondary sides of the two current transformers are equal in size and opposite in phase, and the relay does not act. After the neutral line is disconnected, the current flowing through the relay becomes the sum of the three-phase currents. At this time, the relay will be activated and a signal will be sent at the same time. To the shunt release, the circuit breaker trips, cuts off the load power supply, and serves the purpose of protecting the electrical facilities, but this type of protection device is expensive and the wiring is complicated;

[0007] The third method is overvoltage protection, which mainly uses the action relay to trip the main switch when the voltage of each phase rises greater than the rated phase voltage after the neutral line is broken. When the neutral line is intact, the three-phase overvoltage relay is equal to the load Phase voltage, and it is the rated phase voltage of the power grid, the relay does not act; when the neutral line is disconnected, any phase will have overvoltage, the relay acts and sends a signal to the shunt release, the circuit breaker trips, and the load power is cut off; this type of protection The device is greatly affected by the three-phase unbalance. When the unbalance of the three-phase load is less than 25%, the overvoltage protection device is sensitive and can accurately judge the disconnection of the neutral line and trip; once the three-phase load is unbalanced When it exceeds 25%, the actual voltage of each phase will be seriously distorted, which will lead to the difficulty in realizing the criterion and the phenomenon of malfunction of the protection device

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