Updated: Mar 2
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 the protection system against these induced high voltage is not installed 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 called lightning arrester or surge arrester. The lightening arrester is installed between line and earth. Thus, the lightning arrester is installed in parallel with the equipment to be protected at switchyard and substation.
The lightening arrester provides the low impedance path for those frequency which differ from the power frequency, and thus the lightning or surge voltage is passed through the arrester to earth and equipment remains 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 is designed 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.
Working of Lightning Arrester
The lightning arrester or surge arrester has high impedance for power frequency. Thus, under normal operation the lightning arrester behaves as a open circuit. In case of lightning strike, there is a sudden rapid rise in voltage. The resistance of arrester becomes very low for the lightning induced voltage, and the current is discharged to ground through the arrester. After discharging, the arrester again gains 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 clamped at point A, if not clamped it may attain higher peak.
Characteristics of an Ideal Lightning Arrester
The current through the lightning arrester should be minimum during normal operating condition. The lightning arrester should have high impedance for power frequency.
The current must pass through the lightning arrester when there is surges, transients or lightning voltage.
The lightning arrester must have capacity to handle the discharge current during abnormal condition,without getting damaged.
The lightning arrester must rebuild its insulation level for power frequency quickly after quenching of surge or travelling voltage.
Location of Lightning Arrester
The lightning arrester is installed 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 three numbers arrester is installed - one arrester per phase. The arrester is used to protect 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.