A surge absorber, also known as a lightning absorber, is a device that is designed to protect electrical equipment and systems from the damaging effects of high voltage surges caused by lightning strikes and other sources of electromagnetic interference (EMI). These surges can have amplitudes of up to 15,000 volts, which can easily damage or destroy sensitive electronic equipment if not properly protected.
The damage caused by high voltage surges is not only a function of the amplitude of the surge, but also the steepness of the wavefront. The steeper the wavefront, the more damage that can be caused to the equipment connected to the line. To mitigate this, surge absorbers are used to reduce the steepness of the surge wavefronts, thus minimizing the risk of damage to the equipment.
Surge absorbers work by absorbing the energy contained in the surge voltage, effectively "damping" the wavefront and reducing its steepness. This is in contrast to a surge diverter, which diverts the surge voltage to the earth, preventing it from entering the equipment in the first place. Both surge absorbers and surge divers can protect equipment from surges, but they do so in different ways.
Types of Lightning Absorbers or Surge Absorbers:
- Condenser or Capacitor Surge Absorber
- Inductor and Resistance Surge Absorber
- Ferranti Surge Absorber
1. Surge Absorption Using Capacitor or Condenser:
A surge absorber can be implemented using a capacitor connected between the line and the earth, as shown in figure (a). The capacitor acts as a high pass filter, allowing high frequency surges to pass through while blocking low frequency signals. This is because the reactance of a capacitor, represented by Xc, is inversely proportional to the frequency of the signal. At high frequencies, the reactance of the capacitor is low, meaning that it behaves like a short circuit. This allows high frequency surges to pass through and be neutralized by being grounded.
On the other hand, at low frequencies, the reactance of the capacitor is high, meaning that it behaves like an open circuit. This prevents low frequency signals from passing through, allowing normal line current to flow through the device as shown in figure (c). This is why the capacitor can act as a surge absorber, protecting equipment from high frequency surges while allowing normal operation at low frequencies.
When the capacitor is connected across transformer winding, it prevents the transformer from damage caused by high frequency surges. Because transformers are sensitive to high frequency transients, the capacitor helps to neutralize these surges before they can reach the transformer, thus protecting the transformer from damage.
In summary, A surge absorber implemented by connecting a capacitor between the line and the earth, the capacitor acts as a high pass filter that allows high frequency surges to pass through while blocking low frequency signals. The capacitor's reactance (Xc) is inversely proportional to the frequency, at high frequencies the reactance is low and the capacitor acts as a short circuit, neutralizing the surges to the ground, at low frequencies the reactance is high and the capacitor acts as an open circuit, allowing the normal line current to flow through the device, protecting the transformer from high frequency surges.
2. Surge Absorption Using Parallel Combination of Inductor and Resistance:
Surge absorption can also be achieved by using a parallel combination of an inductor (also known as a choke) and a resistor connected in series with the power line, as shown in figure (a). The inductor is a passive component that stores energy in a magnetic field when current flows through it. The reactance of an inductor is represented by XL, and it is directly proportional to the frequency of the signal and the value of the inductor, XL = 2Ï€fL.
When a high frequency surge occurs, the reactance of the inductor is high, meaning that it behaves like an open circuit. This prevents the surge from passing through the inductor, and the surge will have only one path to take, which is through the resistor. As the surge passes through the resistor, it is dissipated as heat, owing to the property of the resistor. This effectively absorbs the energy of the surge and protects the equipment connected to the power line.
On the other hand, under normal operating conditions, if the frequency is low, the reactance of the inductor is also low. It acts as a short circuit to the line currents, and the current flows to the power line. This ensures that the equipment connected to the power line is not affected by the surge absorption circuit, and it can continue to operate normally.
In summary, Surge Absorption Using Parallel Combination of Inductor and Resistance is a method to protect equipment from high frequency surges by using a parallel combination of a choke (inductor) and a resistor connected in series with the power line, At high frequency, the reactance of the inductor is high and it acts as an open circuit, the surge has got only one path i.e., through the resistor, when the surge passes through the resistor, they are dissipated as heat, under normal operating conditions, if the frequency is low, the reactance of the inductor is also low and acts as a short circuit to the line currents, and the current flows to the power line.
3. Ferranti Surge Absorber:
Ferranti Surge Absorber is a type of surge protection device that utilizes an inductor connected in series with the power line, as shown in figure (a). The inductor used in this type of absorber is an air-cored inductor that is insulated with a grounded metallic sheet. The insulated metal sheet acts as a dissipater, which helps dissipate the surge's energy.
The Ferranti Surge Absorber is equivalent to a transformer whose secondary is earthed or short-circuited. The primary winding of this transformer is formed by the inductor, and the secondary winding is formed by the dissipater. The transformer action utilizes the energy generated during the surge formation, preventing the winding from damage.
When a surge occurs, the energy generated is utilized efficiently by the transformer action. The energy is transferred from the primary winding (inductor) to the secondary winding (dissipater), where it is dissipated as heat. This effectively absorbs the energy of the surge and protects the equipment connected to the power line.
In summary, Ferranti Surge Absorber is a type of surge protection device that utilizes an inductor connected in series with the power line, the inductor is air-cored and insulated with a metallic sheet that is grounded. The insulated metal sheet acts as a dissipater, it is equivalent to a transformer whose secondary is earthed or short-circuited, the primary winding of this transformer is formed by the inductor, and the secondary winding is formed by the dissipater, during surge formation, a huge amount of energy is generated and the energy is utilized for the transformer action, thus preventing the winding from damage.
Comparison Between Surge Absorber and Surge Diverter:
What is Surge Diverter?
A surge diverter is a protective device that conducts high voltage surges on the power system to the ground. It is commonly called a lightning arrester and its main function is to protect electrical equipment and systems from the damaging effects of lightning strikes and other high voltage transients. The surge diverter is connected between the terminal of the equipment and the ground and provides protection against direct lightning strokes but not against the traveling waves which can reach the terminal. It is commonly used in outdoor settings and can have a longer lifespan than other types of surge protection devices.
What is Surge Absorber?
A surge absorber is a device that decreases the steepness of a waveform at a particular surge and thereby minimizes the danger due to overvoltages. It is also called a surge modifier. The surge absorber is connected between the line and the ground, it also protects the other apparatus from the danger of overvoltages. It can be used in a variety of settings and can have a limited lifespan. Surge absorbers can be less expensive than other types of surge protection devices, but may require maintenance.
Comparison Table Between Surge Absorber and Surge Diverter:
| Surge Diverter | Surge Absorber |
|---|---|
| Conducts high voltage surges to ground | Decreases steepness of waveform to minimize overvoltage danger |
| Commonly called a lightning arrester | Also called a surge modifier |
| Connected between equipment terminal and ground | Connected between line and ground |
| Provides protection against direct lightning strokes | Also protects other equipment from overvoltages |
| Classified into 5 different types | Available in 3 different forms |