1. The auxiliary contact position is not appropriate.
After the switch drops for many times, the mechanical part has movement and wear phenomenon, resulting in the deviation of the auxiliary contact position to the correct position. In the protection action trip, when the auxiliary contact is not disconnected, the export electrical appliances, electrical appliances and relay have returned, that is, the intermediate electrical appliance and relay contact is disconnected before the auxiliary contact.
This causes the middle appliance, the relay contact to disconnect the DC power supply and burn down. Therefore, in the accident, although the protection has been moved, but the switch did not move, resulting in a leapfrog trip.
2, the switch trip mechanism card strength.
Switch mechanism because of the lack of maintenance, the operation is not effective, there is a strong place, can not normally trip, make the middle appliance, relay coil for a long time, make the middle appliance, relay coil burned out, can not correct action.
3, the switch coil core off or stuck.
Due to the normal operation of the switch and the failure, the top wire is loose, resulting in the switch core to fall off. When the failure occurs, the switch can not be dropped, making the outlet intermediate appliance and relay charged for a long time, and burning the electrical appliance, relay coil or contact.
Extended data
Relays generally have induction mechanism (input part) that can reflect certain input variables (such as current, voltage, temperature, pressure, speed, light, etc.); and have actuator (output part) that can realize "on" and "break" control of the controlled circuit.
There is also an intermediate mechanism (driving part) for coupling the input amount and isolating between the input parts and the output parts of the relay, functional processing and driving the output parts.
As a control element, in summary, the relay has the following functions:
1) Expand the control range: for example, when the control signal of the multi-contact relay reaches a certain value, it can change, open and connect the multiple circuit according to different forms of the contact group.
2) amplification: for example, sensitive relay, intermediate relay, etc., with a very small control amount, can control a high power circuit.
3) Comprehensive signal: For example, when a plurality of control signals are input into the multi-winding relay in the prescribed form, the predetermined control effect is achieved through more synthesis.
4) Automatic, remote control, monitoring: for example, the relay on the automatic device, together with other electrical appliances, can form a program control line, so as to realize automatic operation.