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In lightning arrester, flash over occurs at
3 to 2.5 times arrester rating
3 to 4.5 times arrester rating
At arrester rating
Below arrester rating
3 to 4.5 times arrester rating
In a lightning arrester, the flashover voltage is the threshold at which the internal or external gap breaks down to discharge surge currents to the ground. For reliable operation, this flashover value is typically designed to be higher than the normal system voltage but restricted to approximately 3 to 4.5 times the rated voltage of the arrester to protect the insulation of the connected equipment.
In a lightning arrester, the flashover voltage is the threshold at which the internal or external gap breaks down to discharge surge currents to the ground. For reliable operation, this flashover value is typically designed to be higher than the normal system voltage but restricted to approximately 3 to 4.5 times the rated voltage of the arrester to protect the insulation of the connected equipment.
VfтАЛ=K├ЧVrтАЛ тАФ where VfтАЛ is flashover voltage, K is the coordination factor (3 to 4.5), and VrтАЛ is the rated voltage.
When a lightning surge hits the line, the voltage rises rapidly. The lightning arrester acts as a voltage-dependent resistor; once the voltage exceeds the spark-over threshold (3-4.5 times the rated voltage), the air gap ionizes or the nonlinear resistor drops in impedance. This creates a low-resistance path to the ground, diverting the surge current and clamping the voltage to a safe level, thereby preventing insulation failure in transformers and switchgear.
The lightning arrester must be able to withstand the system's normal operating voltage without flashing over.
The ratio of flashover voltage to rated voltage is critical for protecting equipment with lower Basic Insulation Level (BIL).
Surge diverters are specifically designed to limit the impulse voltage appearing across the protected equipment.
Effective protection of high-voltage transformers and cables.
Fast response time to high-frequency transients.
Capability to handle multiple surge discharges.
Subject to degradation due to moisture and pollution.
Requires periodic maintenance and testing of the spark gap.
Transmission line terminal protection.
Substation transformer busbars.
Distribution systems against atmospheric surges.
If the flashover voltage is too low, the arrester may operate during minor voltage fluctuations, leading to premature failure.
If the flashover voltage is too high, the surge may damage the insulation before the arrester can trigger.
B is correct тАФ the flashover voltage of a lightning arrester is designed to occur at 3 to 4.5 times its rated voltage to ensure optimal coordination between the surge protection and equipment insulation.
Always remember that the 'Impulse Ratio' for a lightning arrester should be greater than 1, ensuring the arrester responds faster to high-frequency transients than to standard power frequency waves.