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Lightning arresters are used for protection against
Direct lighting
Over voltage
Over current
None of this
Direct lighting
A lightning arrester (or surge arrester) is a protective device used in power systems to protect equipment insulation from damage caused by high-voltage surges, specifically those resulting from direct lightning strikes or switching transients. It functions by providing a low-impedance path to the ground for the excess surge energy while maintaining normal system voltage during operation.
A lightning arrester (or surge arrester) is a protective device used in power systems to protect equipment insulation from damage caused by high-voltage surges, specifically those resulting from direct lightning strikes or switching transients. It functions by providing a low-impedance path to the ground for the excess surge energy while maintaining normal system voltage during operation.
VsтАЛ=IsтАЛ├ЧZsтАЛ тАФ Relation between surge voltage, surge current, and surge impedance
IfтАЛ=RaтАЛVpтАЛтАЛ тАФ Follow current during discharge where RaтАЛ is arrester resistance
The arrester acts as a non-linear resistor. Under normal operating conditions, the resistance of the arrester is very high, effectively behaving as an open circuit. When a surge voltage (lightning strike) occurs, the arrester's resistance drops drastically to a very low value, allowing the surge current to discharge safely to the earth. Once the surge has dissipated, it returns to its high-resistance state to prevent power-frequency follow current.
Lightning arresters are connected in shunt with the equipment to be protected.
The breakdown voltage of the arrester must be lower than the Basic Insulation Level (BIL) of the equipment.
Modern arresters use Zinc Oxide (ZnO) blocks for excellent non-linear V-I characteristics.
The discharge path must have the minimum possible inductance to avoid high inductive voltage drops (V=LdtdiтАЛ).
Protects expensive power transformers and switchgear.
High speed of operation during surge events.
Self-restoring after surge dissipation.
Requires high-quality maintenance of ground connections.
Limited capacity to handle prolonged overvoltages.
High Voltage substations.
Distribution transformer protection.
Transmission line terminal equipment.
Option B (Over voltage) is a general term; while arresters protect against overvoltage, 'Direct Lightning' is the specific primary design intent for high-energy strike dissipation.
Standard lightning arresters are classified based on their discharge capability and current ratings.
A is correct тАФ Lightning arresters are specifically engineered to provide a safe discharge path for transient overvoltages resulting from direct lightning strikes or atmospheric discharges.
Always remember that the arrester must be placed as close as possible to the equipment it protects to minimize lead inductance, which would otherwise reduce protection effectiveness during high-frequency surges.