What is Surge Absorber or Lightning Absorber?
A surge absorber is a protective device that absorbs the high voltage surges and reduces the steepness of the surge wavefronts. The traveling waves set up by the surges on the transmission lines caused due to lightning and electrostatic induction possess an amplitude of 10 to 15kV, which has the ability to damage the equipment connected to that line.
The damage caused depends not only on the amplitude of the traveling wave but also on the steepness of the wave. More the steepness in the traveling wave, damage caused to the equipment will be more.
Thus in order to reduce the steepness of the surge wavefronts a surge absorber is used, thereby minimizing the danger caused due to overvoltages. Though the surge diverter and surge absorber eliminate the surge, the operation behind it is different. The surge diverter diverts the surge voltage to the earth by restricting it from entering the equipment, while the surge absorber absorbs energy contained in the surge voltage.
Types of Lightning Absorbers or Surge Absorbers :
The most commonly used surge or lightning absorbers are,- Condenser or capacitor surge absorber.
- Inductor and resistance combination surge absorber.
- Ferranti surge absorber.
Surge Absorption Using Capacitor or Condenser :
In this type of surge absorption, a capacitor is connected between the line and the earth as shown in figure (a) below. This arrangement acts as a surge absorber. When connected across transformer winding, it prevents the transformer from damage.
We know that the capacitor reactance Xc is inversely proportional to the frequency i.e., Xc ∝ 1/f. At high frequency i.e., under fault conditions, the capacitor reactance will be low and act as a short circuit to the surges shown in figure (b) and neutralize them to the ground. At low frequency i.e., under normal operating conditions, the capacitive reactance is high and acts as an open circuit as shown in figure (c). Therefore, line current flows to the device.
Surge Absorption Using Parallel Combination of Inductor and Resistance :
Surge absorption using a parallel combination of choke and resistance in series with the line is as shown in figure (a) below. Here, the choke is nothing but the inductor.
We know that, in the case of an inductor, XL = 2Ï€fL. At high frequency, XL is more and hence it acts as an open circuit as shown in figure (b). When the inductor is open-circuited, the surge has got only one path i.e., through the resistor referring to figure (b).
When the surge passes through the resistor, they are dissipated as heat owing to the property of the resistor. Under normal operating conditions, if the frequency is less, then XL is also less and acts as a short circuit as shown in figure (c) to the line currents, and the current flows to the power line.
Ferranti Surge Absorber :
In this type of absorber, an inductor is connected in series with the line as shown in figure (a) below. The inductor is air-cored and insulated with a metallic sheet that is grounded. This insulated metal sheet acts as a dissipater. This type of setup is equivalent to the transformer whose secondary is earthed i.e., short-circuited. Its primary winding is formed by the inductor and secondary winding is formed by the dissipater.
We know that a huge amount of energy is generated during surge formation and the energy is utilized for the transformer action. Even during the surge formation, the energy obtained is utilized efficiently and prevents the winding from damage.
Comparison Between Surge Absorber and Surge Diverter :
| Surge Diverter | Surge Absorber |
|---|---|
| It is a protective device that conducts high voltage surges on the power system to the ground. | It is a device that decreases the steepness of a waveform at a particular surge and thereby minimizes the danger due to overvoltages. |
| It is commonly called a lightning arrester. | It is also called a surge modifier. |
| It is connected between the terminal of the equipment and the ground. | It is connected between the line and the ground. |
| It provides protection against direct lightning strokes but not against the traveling waves which can reach the terminal. | It also protects the other apparatus from the danger of overvoltages. |
| It is classified into five different types. | It is available in three different forms. |