Leakage relay is a device that detects line touch (leakage) current and sends a mechanical open/close signal to the control circuit. It can be combined with low-voltage circuit breakers or AC contactors of various specifications to form a residual current action protector. In the current well-developed rural low-voltage power grid protection mode (second or third level) against leakage, it has become an important component of the overall protection of the circuit and plays an important role in preventing line and equipment leakage and electric shock to individuals.
As the leakage relay is used for equipment protection, its safety performance should be verified. For this reason, the leakage relay is equipped with a test button to test the protective performance of the leakage relay. When the button is pressed, the test current flows through the magnetic ring, and the leakage relay should quickly act. If the leakage relay does not act, it means that there is a fault and must be stopped immediately. The commonly used leakage protector is equivalent to a combination of automatic switch and leakage relay, mainly used for personal safety protection. For 50 Hz AC current, the current of 2 mA is noticeable to the human body, and 30 mA or more can be fatal. Therefore, attention should be paid to the size of the leakage protector operating current when selecting. In order to reliably operate under small signals, the leakage protector is equipped with electronic circuits to prevent false triggering with small signals.
The leakage relay is composed of a detection device, a test device, a tripping mechanism, a contact part and a fixed part. The detection device is used to detect whether there is leakage, and the tripping device is used to trip the contact.
The earth leakage relay working principle is: a magnetic ring made of a magnetic material is fitted on the incoming line of the electrical equipment, and all power lines pass through the ring. In normal use, the load side does not form a loop with the ground, so the total current passing through the magnetic ring is zero. For the entire magnetic ring, this means that no current flows through it, so no magnetic flux is generated inside the magnetic ring. If there is current flowing through the load side to the ground, a magnetic flux proportional to the leakage current will be induced in the magnetic ring. At this time, if a coil is wound on the magnetic ring, an induced electromotive force will be generated in the coil. The size of this electromotive force reflects the magnitude of the leakage current. In the leakage relay, the coil on the magnetic ring is connected to the leakage tripping device coil, and when the magnetic ring coil generates an induced current, the iron in the tripping device is reset.
Determine the model of the leakage relay according to the protection object, such as rated current and leakage current.
The protected power grid should be a central grounded system. In the protected line, the neutral wire is not allowed to be grounded again, and the protective ground wire should not pass through the magnetic ring and should not be mixed with the neutral wire.
In order to prevent the tripping current of the leakage tripping device coil from decreasing due to the long leads, the cross-sectional area of the leads should be larger.
Regular testing should be carried out during use to promptly detect faults in the leakage relay. The installation of a leakage relay should not lead to complacency in the use of electricity.