The phenomenon of lightning is a discharge of electric charge from a charged cloud towards the ground. The cloud potential is significantly higher during a thunderstorm than the ground potential, and the surrounding air loses its insulating properties. It is a capacitor composed of a cloud and ground with air as its dielectric.
It is necessary to break the potential gradient of the air, around 30kV/cm, to cause lightning. Lightning occurs when there is a significant potential difference between the cloud and ground, which breaks the air’s gradient of the potential.
This guide is all about Lightning arresters and types of lightning arresters in detail.
Lightning Arresters are protective devices that protect electrical equipment from high voltage surges caused by lightning strikes.
Connecting the arrester to the equipment (or overhead transmission line) will connect one end to the spark gap and the other to the ground.
As for the resistors, they are not regular resistors but non-linear resistors since their resistance decrease with increasing voltage and vice versa. Due to the high surge voltage generated by a lightning strike, this resistor will have low resistance and produce a low voltage when lightning strikes.
The spark gap of an overhead transmission line must not initiate an arc at its stable operating voltage, but only at extremely high voltages that break the air insulation of the line.
An arc will be initiated when a lightning strike breaks the air insulation, resulting in an arc and a fall in the non-linear resistor’s resistance. It results in the surge flowing to the ground along a low resistance path.
Working Principle of lightning arrester
As a lightning arrestor works, the voltage surge travels through the conductor until it reaches its installed location. This will allow voltage surges to discharge away from the lightning arrestor for a moment, breaking down its insulation. As soon as the system voltage falls under the fixed value, the environment and conductor will be insulated again. In addition, the flow of current toward the ground will be stopped.
Types of lightning arrester
1. An electrolyte arrester
In such arresters, there is a large capacity for discharging. A thin film of aluminum hydroxide is deposited on aluminum plates immersed in the electrolyte, enabling the process to work. In the presence of a low voltage, the plate acts as high resistance, but in the presence of a voltage above a critical value, it acts as low resistance.
When a voltage exceeds 400 volts, a puncture is caused, and current flows to earth. It stops leakage when the voltage remains normal at 440 volts when the arrester offers high resistance in the path.
2. An arrester for Horn Gap
The air gap of this type of arrester is formed by two metal rods bent into horn shapes. It is essential to keep this shape as we descend, gradually decreasing the distance between the rods. An arc current limiter is present in series with the resistor.
3. Arrester for oxide films
It is composed of lead peroxide pellets covered with a thin layer of litharge and enclosed in a diameter tube. There is a series spark gap in the tube.
Overvoltage’s result in an arc passing through the spark gap and applying an additional voltage to the pellet column, causing a discharge. As soon as the pellet gun has discharged, its resistance increases until only a minimal amount of current flows through it. As a result of the series of spark gaps, this small current is finally interrupted.
4. Space Gap Arrester
These devices are equipped with an air gap between two different spheres. An electric line connects one of the spheres, and a ground connection connects the other. Despite the small space between the spheres, they are very close together.
5. The multi gap arrester
An arrester with multiple air gaps is known as a multigap arrester because it uses several cylinders made of zinc alloy to create the gaps. With a series resistor, the top cylinder is connected to the line, and the bottom cylinder is connected to the ground.
Through a shunt resistor, the cylinder at the center usually has earth potential since it is connected to the cylinder at the bottom. Surges will pass through the air gaps and the cylinders rather than the shunt resistor in the event of an air insulation breakdown.
6. Arresters of the expulsion type
Protector Tube type arresters are also known as Expulsion type arresters, and they can protect voltages of up to 33kV. Spark gaps in this arrester type are contained inside fiber tubes, unlike other types. As well as the external series gap, an external series gap handles the standard operating voltage. Ensure that the main fiber tube is not leaking currents or experiencing corona discharge by doing this.
7. A Pellet-Type Arrester
With glass tubes filled with lead pellets, these arresters can be designed. Lead peroxide is applied inside and coated with lead oxide on the outside.
There is no powerful conductive reaction between lead oxide and lead peroxide. When lead oxide is heated, it becomes lead peroxide, used to conduct current. The lead peroxide will be reversed into lead oxide whenever the current flow is transmitted. The use of this type of arrester is not widespread.
8. Arrester for sphere gaps
Usually, air gaps are provided between spheres in such devices. There is a minimal distance between the two spheres. The spheres are connected to the line through a choking coil inserted between the phase winding and transformer winding.
It is necessary to set the air gap between the arresters so that the discharge must not occur under normal operating conditions. As the heated air around the arc rises, the arc travels up the sphere until it is interrupted automatically.