The leakage protector has high sensitivity and fast action for electric shock and leakage protection. The structure and principle of electromagnetic leakage protection are the same as other protective electrical appliances, such as fuses, automatic switches, etc. Automatic switches and fuses pass load current when they are normal, and their action protection value should be set to avoid normal load current, so their main function is to cut off the phase-to-phase short circuit fault of the system (some automatic switches also have overload protection function). The leakage protector uses the residual current of the system to react and act. During normal operation, the residual current of the system is almost zero, so its action setting value can be set very small (usually mA level). When the system is electrocuted or the equipment casing is energized, there is a large residual current. The leakage protector detects and processes this residual current and reliably cuts off the power supply.
When electrical equipment leaks, it will present abnormal current or voltage signals. The leakage protector drives the actuator to act by testing and processing the abnormal current or voltage signals. We call the leakage protector that acts according to the fault current a current leakage protector, and the leakage protector that acts according to the fault voltage a voltage leakage protector. Voltage leakage protectors have been basically eliminated due to their complex structure, poor stability of action characteristics, external interference and high manufacturing cost. The research and application of leakage protectors at home and abroad are mainly based on current type leakage protectors.
The leakage protector uses a part of the zero-sequence current in the circuit (usually called residual current) as the action signal and uses electronic components as the intermediate mechanism. It has high sensitivity and complete functions, so this protection device has been used more and more widely. The leakage protector consists of four parts: Famous Encyclopedia String
Detection element: The detection element can be said to be a zero-sequence current transformer. The protected phase line and neutral line pass through the ring core to form the primary coil N1 of the transformer, and the winding wound on the ring core forms the secondary coil N2 of the transformer. If there is no leakage, the sum of the current vectors flowing through the phase line and the neutral line is equal to zero, so the corresponding induced electromotive force cannot be generated on N2. If leakage occurs, if the sum of the current vectors of the phase line and the neutral line is not equal to zero, an induced electromotive force will be generated on N2, and this signal will be sent to the intermediate link for further processing. Famous Encyclopedia String
Intermediate link: The intermediate link usually includes an amplifier, a comparator, and a release. When the intermediate link is electronic, the intermediate link also requires an auxiliary power supply to provide the power required for the electronic circuit to work. The function of the intermediate link is to amplify the leakage signal of the zero-sequence transformer and output it to the actuator.
Actuator: This structure is used to receive the command signal of the intermediate link, perform actions, and automatically cut off the power supply in case of failure.
Test device: Since the leakage protector is a protective device, it should be checked regularly to see if it is in good condition and reliable. The test device simulates the leakage path by connecting the test button and the current limiting resistor in series to check whether the device can work normally.