Automatic reclosing leakage protection switch circuit

The circuit has three characteristics. First, it is different from the general single-shot switch. It can automatically reclose and test power after a period of time after the switch is opened, which can avoid people running around due to accidental leakage and tripping, or even accidents caused by operating in the dark. Second, it uses the normally closed contacts of the contactor to supply power. The contactor is in the released state under normal circumstances, so it does not consume electricity at ordinary times. Third, the electronic circuit is usually in the power-off state, which not only eliminates static consumption, but also will not be easily affected by abnormal power sources such as lightning due to long-term power-on.

The circuit is shown in the attached figure. It mainly consists of the main control circuit, leakage detection circuit, and delay circuit. Its working principle is as follows: Under normal conditions, the normally closed contact JC-1 of the AC contactor JC is closed to supply power, and the normally open contact JC-2 is disconnected. The normally open contact JH of the relay J1 of the leakage detection circuit is also disconnected, so the JC coil and the subsequent delay circuit are not energized.

When the load leaks, there is an induced current (voltage) in the transformer HG, the thyristor SCR is turned on, J1 is energized, JH is attracted, and JC is energized. JC-I disconnects the load power supply. JC-2 is closed for self-protection, the leakage detection circuit loses power, and JC is released again. At the same time, the delay action circuit is energized. The city power is stepped down by transformer T, rectified by VD5~VD8, filtered by C2, and stabilized by IC1 to obtain a 12V DC power supply. At the beginning, the timing circuit IC2 (2) and (6) pins are high level because the voltage across C3 cannot suddenly change, and the (3) pin is low level, and the relay J2 is released.

After C3 is charged through resistor R2 for a period of time, the potential of IC2 (2) and (6) pins drops to 2/3 of the power supply voltage, and the (3) pin outputs a high level. J2 is energized, and its normally closed contact J2-1 is disconnected. JC loses power and is released. JC-2 is disconnected, and the subsequent delay circuit also returns to the power-off state.

JC-I is closed to test power supply. If the load end is accidentally leaking electricity, normal power supply will be restored at this time; if the leakage point still exists, it will trip again and wait for inspection.

Among them, R2 and C3 are set for anti-interference to prevent the circuit from malfunctioning due to noise. JC-3 can discharge the charge on capacitor C3 at the moment of JC test power supply, ensuring that the circuit can quickly return to the initial delay state. When the light-emitting diode LED lights up, it indicates that the circuit is in the delayed closing state.

Component selection: The leakage detection circuit can be modified from the detection part of the existing leakage protection switch, as long as the original magnetic coil is replaced by a small 220V relay. J2 uses a small 12V DC relay. Jc can use a 220V AC contactor according to the load size. IC2 uses a time base circuit such as NE555.

After the assembly is completed, the resistance value of the resistor R1 can be adjusted as needed to make the delay time between one minute and several minutes.

This circuit is a unidirectional application. It is not difficult to find from the circuit principle that it can be used in three-phase AC protection circuits with just a slight change.