Leakage protector has high sensitivity and quick action in response to electric shock and leakage protection, which is incomparable with other protective appliances, such as fuse, automatic switch and so on.Automatic switch and fuse normally through the load current, their action protection value to avoid the normal load current to set, so their main role is to cut off the system phase short circuit fault (some automatic switch also has overload protection function).And leakage protector is the use of residual current response and action in the system, the normal operation of the system of the residual current is almost zero, so it's the set values for the action to be setting is small (typically for mA level), personal electric shock occurs when the system or equipment shell charged, appear larger residual current, leakage protector, by detecting and processing after the residual current movements in a reliable way, cut off power supply.

When the electrical equipment leaks electricity, it will present abnormal current or voltage signal. The leakage protector will prompt the action of the actuator by detecting and processing this abnormal current or voltage signal.We according to the fault current action leakage protector is called current type leakage protector, according to the fault voltage action leakage protector is called voltage type leakage protector.Due to the complex structure of voltage type leakage protector, poor stability of operation characteristics due to external interference and high manufacturing cost, it has been basically eliminated.At present, the research and application of leakage protector at home and abroad are dominated by current type leakage protector.

Current type leakage protector is a part of the zero sequence current in the circuit (usually called residual current) as the action signal, and most of the electronic components as the intermediate mechanism, high sensitivity, complete functions, so this protection device is more and more widely used.Current type leakage protector consists of four parts:

1. Detection element: the detection element can be said to be a zero-sequence current transformer.Protected phase line and neutral line through the annular core, a coil N1, constitutes the transformer coil winding on the circular iron core constitutes the transformer secondary coil of N2, if there is no leakage occurs, then through the phase line and neutral line current vector and is equal to zero, so also does not produce corresponding induction electromotive force in N2.If a leakage occurs, the sum of the current vectors of the phase line and neutral line does not equal to zero, generating an induced electromotive force on #$, and the signal is sent to the intermediate link for further processing.

2. Intermediate link: the intermediate link usually includes amplifier, comparator and tripper. When the intermediate link is electronic, the intermediate link also needs auxiliary power supply to provide the power needed for the work of the electronic circuit.The function of the intermediate link is to amplify and process the leakage signal from the zero sequence transformer and output it to the actuator.

3. Actuator: this structure is used to receive the command signal of the intermediate link, implement the action and automatically cut off the power at the fault.

4. Test device: as the leakage protector is a protective device, it should be regularly checked whether it is intact and reliable.The test device simulates the leakage path through the series connection of test button and current limiting resistance to check whether the device can work normally.