Leakage protector has been widely used in recent years, especially the two network transformation to the leakage protector to open up a broad space, received a lot of social benefits. But how to make the leakage protector work properly, play its due role, in addition to improving the quality of products to ensure reliable operation, with the quality of the protected line and the leakage protector installation method has a great relationship.

　　What is three-phase four-wire earth leakage protector

　　Three-phase automatic earth leakage protector refers to the leakage current detection and judgement function, but does not have to cut off and turn on the main circuit function of three-phase automatic reclosing leakage protection switch can leakage protection device. The earth leakage protection relay consists of zero sequence transformer, disconnector and auxiliary contact for output signal. It can be used with high-current automatic switch as the total protection of low-voltage power grid or the leakage, grounding or insulation monitoring protection of the main circuit.

　　When there is leakage current in the main circuit, because the auxiliary contact and the main circuit switch's detachment detacher are connected in series to form a circuit. Therefore, the auxiliary contact is connected to the detachable detacher and disconnect the air switch, AC contactor, etc., so that it will be turned off and cut off the main circuit. Auxiliary contact can also be connected to the sound, light signalling device, issued by the leakage alarm signal, reflecting the insulation condition of the line.

　　Most of the three-phase four-wire total leakage protection switches are used for the total power control of the whole floor or the whole building. Its role is to protect the safety of the power supply line, leakage protection part is used to prevent the protected part of the wire (mostly refers to the fire wire) accidentally contact with the metal bracket, shell frame, scaffolding, walls, the earth and the possibility of fire accidents, such switches can automatically trip, cut off the power supply, to prevent accidents from occurring.

　　Leakage protector working principle is relatively simple, but in practice there will be this or that error, resulting in unnecessary false or refused to act.

　　The earth leakage protector consists of three parts: the stripping circuit, the overload protector device and the earth leakage trigger circuit.

　　The overload protector device consists of thermal elements EHl and EH2 made of bimetal. When the current exceeds 1.2 times the rated current, the thermal element is deformed and biased towards the top bar of the release due to the different metal expansion coefficients on both sides of the thermal element, causing the switch OF, SA to trip and disconnect the power.

　　TA is a zero sequence transformer. Normally, the absolute value of the currents in the main circuit fire line and zero line are equal, and the current vector sum is zero. No inductive voltage signal into the special integrated circuit IC, at this time its ④ foot output is zero, SCR due to the absence of a trigger signal and shut down. When a leakage occurs, the main circuit current is out of balance, the voltage signal induced by the TA is amplified by the IC. Start the internal blocking circuit to make the ④ pin output jump to a high level. The SCR will be triggered by the Q follower, and the AC switch composed of SCR and rectifier bridge VC will be switched on. Release coil L action. Suck the round iron column and drive the disconnecting mechanism to disconnect the switch. At this time, the reset button (yellow) automatically pops up. To distinguish the occurrence of leakage or overload fault. And quickly exclude (Note: When the power supply voltage is lower than 50V, the leakage protector refuses to act, but then the voltage has not reached the voltage that endangers personal safety).

　　Test button SB is used to simulate leakage current to check whether the leakage protector works reliably, the provisions of the monthly test. R2 is used to regulate the leakage action current, the set value of 22.5mA, the error is ± l%. Voltage-sensitive resistor RU used to absorb the power supply system of lightning and a variety of operational overvoltage, RU has a large energising capacity, a wide range of voltages, leakage current is small and fast response speed and other advantages, is the most ideal overvoltage protection components. Bi-directional diode D1 is used to limit the over-induced voltage in both directions to protect the IC from damage.

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