Relay's Overcurrent And Overvoltage Protection
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Relay's Overcurrent And Overvoltage Protection

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Relay Protection Function

Overcurrent protection

Relay overcurrent protection is actually to prevent short circuits, where excessive current begins to flow in the circuit, which can cause significant damage to connected equipment.


Overload protection

Relay overload protection is actually to prevent overheating, which is caused by the overcurrent relay in the circuit during a specific time period. To ensure relay overload protection, slow acting circuit breakers and relay overload relays are usually used.


Overvoltage protection

If the overvoltage is caused by lightning strikes, switching surges, insulation failures, you can use varistors (VDRS), avalanche diodes, lightning rods, arc suppression horns, gas discharge valves, etc., to protect the power system.

Necessity Of Relay


The necessity of relay protection Relay is widely used in the consumer electronics industry and industrial equipment. It has a control system (also called an input loop) and a controlled system (also called an output loop). It actually uses a smaller current to control the A kind of "automatic switch" of high current. So it plays the role of automatic adjustment, safety protection, and conversion circuit in the circuit. 


In severe cases, the voltage spikes will exceed the rated voltage of the relay contacts and damage the contacts. It may be damaged suddenly and severely, or very slowly, and it will take many years to manifest. In addition, when the contact is disconnected and the current is interrupted, if the current flowing in the relay contact is too large, it will also cause damage.  If the relay winding is designed to have current flow only for a short period of time under normal working conditions, if the current flows unexpectedly for a long time, although the current is within the normal working range, the winding will eventually be burned.

Circuit Protection Scheme

Features of self - restoring fuses PPTC:
  • The resistance of PPTC is very smalland has little

    effect on the circuit

  • Only when the circuit is cut off, the fault is eliminated,

    and the PPTC is cooled, it will return to a low

    resistance state.

  • PPTC has a reset function, which helps to reduce

    maintenance costs and improve customer satisfaction.


Features of Varistor MOV
  • Within a certain current and voltage range, the

    resistance value changes with the voltage.

  • When the circuit voltage is normal, the resistance

    of the MOV is very high, which is equivalent to an

    open circuit.

  • When there is a peak voltage, it provides a non-linear

    current conduction channel to limit the voltage withina

    certain range to achieve the purpose of protecting the circuit.


The following figure shows a typical relay protection circuit. PPTC is connected in series with relay coils and relay contacts, which can limit the current in the event of faults and accidental overloads. When choosing PPTC, first consider the withstand voltage of PPTC and the maximum stability of relay operation. State current, operating time, temperature and other issues, please consult Intetech for details. MOV is connected in parallel with the contact, which can effectively prevent the relay of the contact from always failing. We protect it mainly to extend the use time of the relay, because the contact will always deposit carbon and age, and its surface is not as clean as it was originally. When the relay life is approaching the later stage, its contact resistance will increase rapidly.


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