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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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Which is the first equipment seen in the substation while coming from transmission system?
Circuit breaker
Lightning arrester
Current transformer
Transformer
Lightning arrester
The lightning arrester (LA) is the first equipment installed at the entrance of a substation. Its primary purpose is to protect the substation equipment from high-voltage surges caused by lightning strikes or switching transients on the incoming transmission lines.
The lightning arrester (LA) is the first equipment installed at the entrance of a substation. Its primary purpose is to protect the substation equipment from high-voltage surges caused by lightning strikes or switching transients on the incoming transmission lines.
Vsurge=I×Zsurge — basic relation for voltage surge
R(V)≈k⋅V−α — non-linear resistance characteristic of the arrester
The lightning arrester acts as a non-linear resistor connected in parallel with the equipment it protects. Under normal operating conditions, it offers very high resistance and acts as an insulator; however, during a voltage surge, its resistance drops significantly, providing a low-impedance path to the ground to safely discharge the overvoltage.
Lightning arresters are connected between the phase conductor and the earth.
They must be located as close as possible to the equipment they are intended to protect.
Modern substations use Gapless Zinc-Oxide (ZnO) type lightning arresters.
Voltage rating is chosen based on the system maximum phase-to-ground voltage.
Protects insulation of transformers and switchgear
Reduces the cost of insulation requirements for station equipment
Self-restoring (automatically returns to high-resistance state)
Requires proper maintenance to prevent degradation
May fail if the discharge current exceeds the energy absorption capacity
Power transmission substations
Distribution transformers
Switchyards and high-voltage rotating machinery
The sequence of equipment from the transmission line is typically: Lightning Arrester → Line Trap → Wave Trap (if used) → CT/PT → Circuit Breaker → Isolator → Transformer.
Option A (Circuit Breaker) is for switching; Option C (CT) is for measurement/protection; Option D (Transformer) is for voltage conversion.
B is correct — Lightning arrester is the first piece of equipment encountered to provide primary surge protection.
Remember the sequence 'LA-CT-CB'—many competitive exams specifically test the order of equipment in a substation switchyard.