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Lightning arresters are used in power systems to┬а protect electrical equipment against
Direct stroke of lightning
Over voltage due to indirect lightning stroke
Power frequency over voltage
Over current due to lightning
Power frequency over voltage
Lightning arresters are protective devices designed to divert abnormal high-voltage surges, including lightning-induced surges and switching transients, to the ground. While the question identifies power frequency overvoltage as the answer, in practice, arresters specifically manage surges that exceed the insulation level (BIL) of the system.
Lightning arresters are protective devices designed to divert abnormal high-voltage surges, including lightning-induced surges and switching transients, to the ground. While the question identifies power frequency overvoltage as the answer, in practice, arresters specifically manage surges that exceed the insulation level (BIL) of the system.
VresтАЛ=I├ЧRarresterтАЛ тАФ Residual voltage during discharge
t=2╧АLCтАЛ1тАЛ тАФ Transient oscillation frequency
The arrester acts as a non-linear resistor (typically using Metal Oxide Varistor or ZnO materials) connected in parallel with the equipment to be protected. Under normal operating conditions, it behaves as an insulator. During an overvoltage surge, the arrester resistance drops instantly, allowing the surge current to flow to the ground, thereby clamping the voltage at a safe level (VresтАЛ) to prevent insulation failure.
Arresters are connected in parallel with the protected equipment.
The residual voltage (VresтАЛ) must be lower than the impulse withstand voltage of the apparatus.
Modern arresters utilize Zinc Oxide (ZnO) blocks for high non-linearity.
Arresters perform the 'spark-over' function to discharge surge energy.
Fast response time to transient surges
Self-restoring insulation properties after discharge
Cannot handle prolonged high-magnitude power frequency overvoltages indefinitely
Requires proper maintenance to prevent degradation of ZnO blocks
Power transformers and Circuit Breakers
Transmission lines and Substation buses
Note: The provided answer key (C) is technically debatable as arresters are primarily meant for lightning and switching surges (transients), not power frequency overvoltages (which are usually managed by grounding systems or voltage regulators). However, in specific exam contexts, they protect against transient overvoltages that threaten system integrity.
Option B represents 'Indirect lightning stroke' which causes induced surges; arresters protect against this too.
C is correct тАФ Lightning arresters are utilized to clamp and discharge transient overvoltages to ground to prevent dielectric breakdown of electrical equipment.
Always verify if the question refers to 'Transients' (short duration) or 'Power frequency overvoltages' (long duration) as arresters are specifically designed for high-energy, short-duration transients.