Surge absorbers are protective devices used to absorb the complete surge i,e. due to lightening surge or any transient surge in the system unlike the lightening arrestor in which a non-linear resistor is provided which provides a low resistance path to the dangerously high voltages on the system to the earth.
Ferranti surge absorber Surge absorber is of following types:
Ferranti surge absorber: Ferranti surge absorber consists of an air core inductor which is connected in series with the line and surrounded by an earth metallic sheet. The earth metallic sheet is known as dissipater, The dissipater is insulated from the inductor by the air as shown in Figure. This surge absorber acts like an air-cored transformer whose primary is the low inductance inductor and the dissipater as the single-turn short circuit secondary. Whenever a travelling wave is incident on the surge absorber, energy is transformed by mutual inductance between the coil and dissipatcr. Because of the series inductance the steepness of the wave is also reduced.
ERA surge absorber:
An improved form of the surge absorber is the Electrical Research Association (ERA)-type surge Filter as shown in Figure incorporated a gap G and expulsion gap E. When a wave reaches the inductor L, a high voltage is induced across it causing the gap G to break down putting the resistor R and expulsion gap E into circuit. An incoming wave is thus flattened by the inductor and the resistor and its amplitude is reduced by the expulsion gap.
