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The earth wire is earthed in the overhead line at every____
5.6 KM
6.5 KM
65 KM
56 KM
6.5 KM
Quick Summary: In overhead transmission line installations, the earth wire (or shield wire) is provided for lightning protection and must be periodically connected to the earth at specific intervals to dissipate the surge current effectively. It is a standard practice in power system engineering to ground the earth wire at every 6.5 KM to ensure the path impedance to ground remains low.
In overhead transmission line installations, the earth wire (or shield wire) is provided for lightning protection and must be periodically connected to the earth at specific intervals to dissipate the surge current effectively. It is a standard practice in power system engineering to ground the earth wire at every 6.5 KM to ensure the path impedance to ground remains low.
Zs=CL — characteristic surge impedance of the line requiring shield wire protection
The primary mechanism is the reduction of surge impedance and potential rise during a lightning strike. By grounding the shield wire at intervals of 6.5 KM, the reflection coefficient for traveling waves is managed, and the overall tower footing resistance impact is minimized, protecting the main power conductors from direct lightning strokes.
The earth wire is placed above the phase conductors to intercept lightning strokes.
Effective grounding prevents the 'back-flashover' phenomenon in transmission towers.
Grounding interval depends on soil resistivity and the lightning flash density of the geographical region.
6.5 KM is the standardized limit used in Indian distribution and transmission practices.
Reduces potential rise on towers during lightning strikes.
Provides a low impedance path for surge currents.
Enhances overall power system reliability.
Increases structural load on transmission towers.
Requires regular maintenance of grounding pits and connections.
HV transmission lines
Distribution overhead networks
Substation incoming line protection
This value is specific to standardized rural and sub-urban overhead distribution guidelines.
The wrong options (5.6 KM, 56 KM, 65 KM) are commonly used as distractors in competitive examinations to test memory of empirical standards.
B is correct — In overhead lines, the shield or earth wire is grounded at every 6.5 KM interval to ensure effective lightning protection.
Always verify if the question pertains to transmission or distribution, as grounding intervals can vary based on the voltage level and line configuration.