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Examoogle • User • info@examoogle.com • EE-2024-8821
Chapter 1 of 12 • Page 1 of 248🔒 Protected PDF • Watermarked
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Protection against travelling waves provided by
Earthing screen
Ground wire
Surge diverter
None of above
Surge diverter
Quick Summary: A surge diverter (or lightning arrester) is the primary protective device used to safeguard power system equipment from high-voltage transients caused by lightning strikes or switching operations. It acts by providing a low-impedance path to the ground for the surge current, effectively limiting the overvoltage across the equipment insulation.
A surge diverter (or lightning arrester) is the primary protective device used to safeguard power system equipment from high-voltage transients caused by lightning strikes or switching operations. It acts by providing a low-impedance path to the ground for the surge current, effectively limiting the overvoltage across the equipment insulation.
V=I×Zsurge — relates surge voltage, current, and line surge impedance
Vresidual=Vdischarge — voltage appearing across the arrester during current flow
Under normal operating conditions, the surge diverter acts as an insulator, blocking the flow of power frequency current. When a travelling wave (high voltage) arrives, the voltage across the diverter exceeds its breakdown value, causing it to become a low-impedance conductor. The surge current is shunted to the earth, protecting the equipment, and after the surge passes, the device reverts to its high-impedance state to prevent follow-through current.
Earthing screens and ground wires protect against direct lightning strokes on transmission lines (shielding).
Surge diverters are specifically designed to dissipate the energy of traveling waves arriving at the terminal equipment.
A good surge diverter must have low residual voltage and high energy-handling capability.
Protects sensitive insulation of transformers and switchgear.
Operates extremely rapidly (microsecond range).
Requires high-quality grounding for effective operation.
Can be damaged by excessive continuous power follow-through currents.
Power Transformers.
High Voltage Circuit Breakers.
Rotating machinery in power plants.
Option A and B (Earthing Screen and Ground Wire) provide shielding protection against direct lightning strikes to the line conductors but do not actively divert traveling waves that have already entered the line.
The most common type of modern surge diverter is the Metal Oxide Varistor (MOV) arrester, which lacks a spark gap.
C is correct — Surge diverters provide the essential discharge path to ground to dissipate the energy of travelling waves.
Always distinguish between 'Shielding Protection' (Earthing screens/ground wires) which prevents strokes, and 'Surge Protection' (Diverters) which handles existing surges.