The residual current operated circuit breaker, also known as the leakage protection switch, is an electrical safety device.
When leakage and electric shock occur and the action current value specified by the protection switch is reached, the residual current operated circuit breaker can automatically disconnect the power supply within a limited time to protect personal and property safety.
Working principle of residual current circuit breaker
When electrical equipment leaks electricity, two abnormal phenomena will occur: first, the balance of the three-phase current is destroyed and zero-sequence current appears; second, the metal shell that is not charged normally has a voltage to the ground (normally, the metal shell and the earth are both at zero potential).
The role of the zero-sequence current transformer: The leakage protection switch obtains abnormal signals through the current transformer detection, and converts and transmits them through the intermediate mechanism to activate the actuator and disconnect the power supply through the switch device.
The structure of the current transformer is similar to that of the transformer. It consists of two mutually insulated coils wound on the same core. When there is residual current in the primary coil, the secondary coil will induce current. Working principle of leakage protection switch: Install the leakage protection switch in the line, connect the primary coil to the line of the power grid, and connect the secondary coil to the tripper in the leakage protection switch.
When the electrical equipment is operating normally, the current in the line is balanced, and the sum of the current vectors in the transformer is zero (the current is a directional vector, such as the outflow direction is "+" and the return direction is "-", the currents flowing back and forth in the transformer are equal in magnitude and opposite in direction, and the positive and negative currents cancel each other out).
Since there is no residual current in the primary coil, the secondary coil will not be induced, and the switch device of the leakage protection switch is in a closed state.
When the equipment casing leaks and someone touches it, a shunt is generated at the fault point. This leakage current returns to the neutral point of the transformer through the human body-earth-working ground (not through the current transformer), causing the current flowing in and out of the transformer to be unbalanced (the sum of the current vectors is not zero), and residual current is generated in the primary coil.
Therefore, the secondary coil will be induced. When the current value reaches the action current value specified by the leakage protection switch, the automatic switch will trip and cut off the power supply.