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Chapter 1 of 12 тАв Page 1 of 248ЁЯФТ Protected PDF тАв Watermarked
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The protection against direct lightning strokes and high voltage steep waves is provided by
Ground wires
Lightning arresters
Lightning arresters and ground wires
Earthing of neutral
Lightning arresters and ground wires
Protection of power transmission lines requires a multi-layered approach: ground wires (shield wires) are used to prevent direct lightning strikes from hitting the phase conductors, while lightning arresters (surge diverters) are installed at terminals and substations to bypass high-voltage steep-fronted surges to the ground.
Protection of power transmission lines requires a multi-layered approach: ground wires (shield wires) are used to prevent direct lightning strikes from hitting the phase conductors, while lightning arresters (surge diverters) are installed at terminals and substations to bypass high-voltage steep-fronted surges to the ground.
VsurgeтАЛ=Z├ЧIsurgeтАЛ тАФ Represents the surge voltage magnitude developed by a traveling wave in a line of characteristic impedance Z.
i(t)=dtdvтАЛC тАФ Relates the steepness of the voltage wavefront to the discharge current through protective capacitance.
Ground wires are placed above the phase conductors to provide an electrostatic shield; if lightning strikes, the current is diverted through the tower structure to the earth. Lightning arresters, such as Valve-type or Metal Oxide Varistors (MOV), provide a low-impedance path to earth when system voltage exceeds a specific threshold, effectively clipping the transient wave amplitude.
Ground wires are typically connected to the tower tops and provide continuous shielding along the span.
Lightning arresters exhibit high impedance during normal operating conditions and very low impedance during surge conditions.
The combination ensures both physical interception and surge magnitude suppression.
Direct strokes are the primary cause of insulation flashovers in high-voltage overhead lines.
Comprehensive protection against both external atmospheric surges and internal switching transients.
Prevents catastrophic equipment failure at substation transformer terminals.
Increases the overall capital cost of the transmission line infrastructure.
Requires periodic maintenance of grounding electrodes for effective dissipation.
Extra High Voltage (EHV) Transmission lines.
Substation busbar protection.
Distribution transformers.
Ground wires are often referred to as 'Shield Wires' or 'Earth Wires'.
Option B (Lightning arresters only) is insufficient because they cannot prevent direct strokes to the line conductors, which could cause mid-span flashovers.
C is correct тАФ Protection against direct strokes is handled by ground wires, while lightning arresters manage the mitigation of high-voltage steep-fronted surges.
Always remember that lightning arresters are connected in parallel with the equipment to be protected, whereas the earthing of the neutral is primarily for system stability and fault current detection.