Surge Absorber|3 Types of Surge Absorbers

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Surge-Absorber

A surge absorber is a protective device which reduces the steepness of wave front of a surge by absorbing the surge energy. A surge absorber is a device to protect electrical equipment from over-voltage transients caused by external or internal events.

The travelling waves set up on the transmission lines by the surges may reach the terminals apparatus and cause damage to it.

The amount of damage caused not only depends upon the amplitude of the surge but also
upon the steepness of its wave front.

The steeper the wave front of the surge, the more the damage caused to the equipment.

Also Read: Lightning Arrester|ESE Lightning Arrester & Conventional Iightning Arrester

Surge Absorber

In order to reduce the steepness of the wave front of a surge, we generally use surge absorber.


A surge absorber is a protective device which reduces the steepness of wave front of a surge by absorbing surge energy.

The surge absorbers are used for protection against low – voltage high – frequency oscillations.


Although both surge diverter and surge absorber eliminate the surge, the manner in which it is done is different in the two devices.

The surge diverter diverts the surge to earth but the surge absorber absorbs the surge energy.

A few cases of surge absorption are discussed in this post.

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Condenser surge absorber


A condenser connected between the line and earth can act as a surge absorber.

condenser-surge-absorber

The above fig shows how a capacitor acts as surge absorber to protect the transformer winding.

Since the reactance of a condenser is inversely proportional to frequency, it will be low at high frequency and high at low frequency.

Since the surges are of high frequency, the capacitor acts as a short circuit and passes them directly to earth.

However, for power frequency, the reactance of the capacitor is very high and practically no current flows to the ground.

parallel combination of choke and resistance

Another type of surge absorber consists of a parallel combination of choke and resistance
connected in series with the line as shown in Fig. gien below.

parallel combination of choke and resistance surge absorber

The choke offers high reactance to surge frequencies (XL = 2 π f L). The surges are, therefore, forced to flow through the resistance R where they are dissipated.

Ferranti surge absorber

ferranti surge absorber


the Fig. given above shows the another type of surge absorber, Ferranti surge absorber.

It consists of an air cored inductor connected in series with the line.

The inductor is surrounded by but insulated from an earthed metallic sheet called dissipator.

This arrangement is equivalent to a transformer with short-circuited secondary.


The inductor forms the primary whereas the dissipator forms the short-circuited secondary.

The energy of the surge is used up in the form of heat generated in the dissipator due to transformer action.

This type of surge absorber is mainly used for the protection of transformers.

The fig below shows the schematic diagram and the equivalent circuitof 66 kV Ferranti surge absorber .

66kv-ferranti-surge-absorber

What is difference between lightning arrester and surge absorber?

A Surge absorber does not absorb a flash of lightning or is not used to protect a device from a direct lightning strike.

The surge absorber limits the voltage surge caused by lightning and protects the equipment installed in parallel.

Read More on Lightning Arrester

  1. Lightning Arrester|ESE Lightning Arrester & Conventional Iightning Arrester
  2. Lightning Arrester Types|5 Types of Lightning Arresters
  3. Surge Absorber|3 Types of Surge Absorber
  4. Lightning Arrester Objective Questions|Surge Absorber MCQ Questions

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