Updated: 4 days ago
Lightning Arrester is a device used for the protection of the electrical equipment against the lightning stroke.The lightning stroke is the high voltage transients caused by the travelling waves during lightning. We install the lightning protection devices to protect the transformer, transmission line and the major electrical equipment.
The electrical equipment are prone to damage against the transients,impulse, surge voltage and lightning voltage induced in the transmission line at the time of lightning or fault in the electrical network.
If there is no protection system against these induced high voltage, it can cause damage to the electrical equipment and the longer disruption of power supply.
Definition of Lightning Arrester:
The protective device used for protection of the electrical equipment against any power surges caused by lightning impulse voltage and surges is lightning arrester or surge arrester. We install the lightning arrester between line and earth. Thus, its location is in parallel circuit with the equipment.
The lightening arrester provides the low impedance path for those frequency which differ from the power frequency. The surge voltage find its path to earth through the arrester. Thus, electrical equipment remain protected. The surge impedance of the line provides impedance to limit the current.
The travelling wave can cause superimposition of high voltage over the power frequency and it may cause severe damage to equipment along with power outage.
Damages Caused by Lightning Wave
The electrical equipment like transformer,motor have capacity to sustain the voltage up to its maximum breakdown insulation level(BIL). If the voltage more than BIL appears across the equipment terminal, it can cause failure of the equipment caused by insulation failures.
The peak voltage increase at the time of the lightning and it may cause flash-over in the equipment like transformer, motor and transmission line. The direct stroke of lightning induce very high voltage in the transmission line and cause damage to insulator and connected equipment to transmission line.
Lightning Arrester Working
The lightning arrester has high impedance for power frequency. Thus, under normal operation the it behaves as a open circuit. In case of lightning strike, there is a sudden rapid rise in voltage.
Its resistance becomes very low for the lightning induced voltage, the current finds its discharge path to ground. After discharging the lightening surges, the arrester regains its resistance and behaves as a open circuit for power frequency.
The lightning arrester provides a path of low impedance for surges. The lightning arrester diverts the current to ground and clamp the high voltage.
As shown in below figure, the lightning voltage is ;
1. Clamped at point A, - Low Voltage
2 If not clamped - it may attain higher peak voltage
Characteristics of an Ideal Lightning Arrester
The current through the lightning arrester should be minimum during normal operating condition. It should have high impedance for power frequency.
The current must pass through it when there is surges, transients or lightning voltage.
It must have capacity to handle the discharge current during abnormal condition without being damage.
It must rebuild its insulation level for power frequency quickly after quenching of surge or travelling voltage.
Location of Lightning Arrester
We must install the lightning arrester as near as possible to the equipment for effective protection of the equipment against lightning and travelling waves. The arrester is installed between the line and earth.
For three phase system we install three numbers arrester i- one arrester per phase. The arrester has wide application for protection of transformer, motor, generator, transmission line etc.
The lightning arrester is located on both high and low side of transmission line to protect the transformer against lightning strike.