Leakage circuit breaker working principle _ leakage circuit breaker wiring diagram and the difference between leakage circuit breaker and air switch

A switch that automatically operates when the leakage current in the circuit exceeds a predetermined value. Commonly used leakage circuit breakers are divided into two types: voltage type and current type, and current type is divided into electromagnetic type and electronic type.

Leakage circuit breakers mainly consist of zero-sequence current transformers, electronic component boards, leakage trips and circuit breakers with overload and short-circuit protection. The leakage protection part of the leakage circuit breaker is composed of a zero-sequence current transformer (sensing part), an arithmetic controller (control part) and an electromagnetic release (action, execution part). All phases of the protected main circuit, the neutral line passes through the core of the zero-sequence current transformer, forming the primary side of the zero-sequence current transformer. The working principle of the leakage circuit breaker can basically be understood as: the earth leakage circuit breaker cannot protect the two-phase electric shock that contacts the two phases at the same time. For the sake of understanding, the following is a detailed description

In the figure, L is an electromagnet coil, and the knife switch K1 can be driven to open when the battery is leaking. Each bridge arm is connected in series with two 1N4007 to increase the withstand voltage. R3 and R4 have large resistance values. Therefore, when K1 is closed, the current flowing through L is small, which is insufficient to cause the switch K1 to be disconnected. R3 and R4 are voltage equalizing resistors of the thyristors T1 and T2, which can reduce the withstand voltage requirement of the thyristor. K2 is a test button that functions as a simulated leakage. Pressing the test button K2, K2 is turned on, which is equivalent to the leakage of the external line to the earth, so that the vector sum of the currents of the three-phase power line and the neutral line passing through the magnetic ring is not zero, and the detection coil on the magnetic ring a, There is an induced voltage output at both ends of b, which immediately triggers T2 conduction. Since C2 is pre-charged with a certain voltage, after T2 is turned on, C2 is discharged through R6, R5, and T2, so that a voltage is generated on R5 to trigger T1 to conduct. After T1 and T2 are turned on, the current flowing through L is greatly increased, the electromagnet is operated, and the drive switch K1 is turned off. The function of the test button is to check whether the function of the device is intact at any time. The principle of the electromagnet leakage caused by the leakage of the electric equipment is the same. R1 is a varistor that acts as an overvoltage protection. This basically constitutes the most important function of leakage protection in the working principle of the leakage circuit breaker.

When working normally, regardless of whether the three-phase load is balanced, the sum of the three-phase current phasors passing through the main circuit of the zero-sequence current transformer is equal to zero, so no induced electromotive force is generated in the secondary winding, and the leakage protector operates in a closed state. In the event of a leakage or electric shock, the sum of the three-phase currents is no longer equal to zero and is equal to a certain current value Is. Is will form a loop through the neutral point of the human body, the earth and the transformer, so that the secondary side of the zero-sequence current transformer generates an induced electromotive force corresponding to Is, which is added to the trip unit. When Is reaches a certain value, the trip unit acts. Push the lock of the main switch to break the main circuit.

Many people associate the leakage circuit breaker with the air switch. The two are very similar, and they are essentially different. Let's take a look at where they differ.

What is an air switch and what is a leakage switch:

1. The air switch is an air circuit breaker. The air circuit breaker is generally low voltage, that is, the rated working voltage is 1Kv. The air circuit breaker is a switching device that has various protection functions and can cut and close the circuit under rated voltage and rated operating current conditions. The type of protection function and the way it is protected are selected by the user as needed. Such as short circuit protection, over current protection, shunt control, under voltage protection. The first two protections are the basic configuration of the air circuit breaker, and the latter two are optional functions. Therefore, the air circuit breaker can also cut off the electrical circuit in the fault state (load short circuit, load over current, low voltage, etc.).

2. The correct name of the leakage switch is the residual current protection device (hereinafter referred to as RCD), which is an air circuit breaker with special protection function (leakage protection). It detects the residual current, which is the algebraic sum of the instantaneous values of the phase and neutral currents in the protected loop (including the three-phase unbalanced current and harmonic current in the neutral). To this end, the setting value of the RCD, that is, its current operating current IΔn, simply avoids the normal leakage current value, which is measured in mA, so the RCD can very sensitively cut off the ground fault of the protection circuit and can also be used as Protection against direct contact with electric shock.

The leakage protector is a protection device that detects the leakage current or electric shock current of the phase line occurring in the protected power grid, and acts as a trip signal to complete the action and complete the action trip task. In the low-voltage power grid with the leakage protector, under normal circumstances, the leakage current of the grid phase-to-ground (unbalanced leakage current for the three-phase grid) is small, and the operating current value of the leakage protector is not reached. The leakage protector does not work. When a fault such as electric leakage or personal electric shock occurs in the protected power grid, when the current of the component is reached by the leakage protector to reach the leakage or electric shock current value, the leakage protector will give an action trip command, so that the main control The circuit switch action trips and cuts off the power supply, thus completing the task of leakage or electric shock protection. In addition to the basic functions of the air circuit breaker, it can quickly break the switch when there is leakage in the load circuit (its leakage current reaches the set value) to avoid injury to personnel and disadvantages to electrical equipment in the event of leakage of the load circuit. influences.

3. The leakage switch cannot replace the air switch. Although the leakage switch has a more protection function than the air switch, the possibility of leakage due to the possibility of leakage during operation often occurs, resulting in frequent power failures and affecting the continuous and normal operation of the electrical equipment. Therefore, it is generally only used in the temporary circuit of the construction site or the socket circuit of industrial and civil buildings. The leakage switch can also be said to be a kind of air switch, and the mechanical action and arc extinguishing method are similar. However, since the leakage switch protects mainly the person, the general action value is milliampere.

In addition, China Electrical Trading Network learned that the leakage circuit breaker and the air switch action detection method are different: the leakage current switch uses the residual current protection device, which detects the residual current, that is, the phase line and the neutral current of the protected circuit are instantaneous. Algebraic values of values (including three-phase unbalanced currents and harmonic currents in the neutral line). For this reason, the current flow current can only avoid the normal leakage current value (milliampere level), so it can cut off the ground fault very sensitively and prevent direct contact with the electric shock. The air switch is a pure overcurrent trip.