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Neutral earthing is provided for
Safety of equipment and personal against the lightning and voltage surges
Reducing the voltage stress on line and equipment with respect to earth under various operating and fault conditions
Controlling the earth fault current for protective relaying
Both (a) and (d)
Both (a) and (d)
Neutral earthing (grounding) refers to connecting the neutral point of a star-connected transformer or generator to the earth. It provides a low-impedance path for fault currents, ensures equipment and personnel safety against overvoltages, and enables the operation of protective relays by providing a reference potential.
Neutral earthing (grounding) refers to connecting the neutral point of a star-connected transformer or generator to the earth. It provides a low-impedance path for fault currents, ensures equipment and personnel safety against overvoltages, and enables the operation of protective relays by providing a reference potential.
VphтАЛ=3тАЛVLтИТLтАЛтАЛ тАФ Relationship between phase and line voltage
IfтАЛ=Z0тАЛ+Z1тАЛ+Z2тАЛVphтАЛтАЛ тАФ Zero sequence fault current calculation
During a line-to-ground fault, the neutral earthing ensures that the faulted phase voltage is clamped to the neutral potential, preventing the healthy phase voltages from rising to line-to-line voltage levels. This minimizes electrical stress on insulation and allows the zero-sequence current to return to the source, which can be detected by protective relays to isolate the faulty section.
Neutral earthing stabilizes the potential of the circuit with respect to ground.
It allows the use of earth-fault protective relaying.
Prevents arcing grounds in ungrounded systems.
Limits transient overvoltages resulting from switching surges or lightning.
Improved protection against overvoltages
Simplified relay coordination
Increased personnel safety
Reduction of arcing ground faults
Requires complex protective relaying for earth faults
Possible interference with communication lines during fault current flow
Transmission lines
Distribution transformers
Industrial power systems
Option D is the most comprehensive as it covers both safety (lightning/surges) and protective relaying requirements.
In India, the IS standard (IS 3043) provides detailed guidelines for code of practice for earthing.
D is correct тАФ Neutral earthing is essential for both protecting equipment from transient overvoltages and ensuring the sensitive operation of earth fault protective relaying systems.
Always remember that neutral earthing (system grounding) is different from equipment grounding (body earthing); the former is for system stability/protection, while the latter is strictly for human safety.