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Thermal Relay

The different part of the thermal relay is shown in the figure. The names of the parts are given below:-

  1. Heating Coil
  2. Bimetallic strip
  3. Insulated Contact arm
  4. Relay Contact


In this thermal relay, the bimetallic strip is being heated by means of heating coil which is supplied through a current transformer. The relay contract point is fixed at the insulated arm and a spring S is connected at the end of the insulated arm. The tension of this spring can be varied by rotating the sector-shaped plate A.
Under normal condition, Bimetallic strip remains straight, but when the strip is heated by heating of heater, it bends and the tension of the spring is released, thus the relay operating temperature can be varied by varying the tension of the spring. Pl, note that the bimetal element consists of two nickel alloyed steel strip and welded together. These strips have a high heat resistivity and free from thermal secondary effects.

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