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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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System Earthing is used for which voltage level?
Medium
High voltage
Extra high voltage
All of above
All of above
Quick Summary: System earthing, which involves connecting the neutral point of a transformer or generator to the earth, is essential across all voltage levels to ensure safety, stabilize potential, and facilitate fault detection. It provides a low-impedance path for fault currents, allowing protective devices to isolate the faulty section effectively regardless of whether the system is medium, high, or extra-high voltage.
System earthing, which involves connecting the neutral point of a transformer or generator to the earth, is essential across all voltage levels to ensure safety, stabilize potential, and facilitate fault detection. It provides a low-impedance path for fault currents, allowing protective devices to isolate the faulty section effectively regardless of whether the system is medium, high, or extra-high voltage.
If=ZnVph — where If is the fault current and Zn is the neutral earthing impedance.
Vearth≈0 — the reference potential maintained for equipment safety.
The principle relies on the reference potential established by the Earth. By connecting the system neutral to ground, the voltage of the healthy phases remains constant relative to the earth during a single-line-to-ground fault. This prevents overvoltage stress on insulation and ensures that the fault current (If) is sufficient to trigger protective relays.
System earthing refers to the connection of the current-carrying part (neutral) of the system to earth.
It is mandatory for system stability and limiting overvoltages due to arcing grounds.
Choice of earthing method (solid, resistance, or reactance) depends on the system voltage class.
Prevents floating neutral which causes insulation stress in balanced three-phase systems.
Stable neutral potential
Easy identification and clearing of ground faults
Reduced transient overvoltage levels
Increases fault current magnitude for solid grounding
Requires complex relay coordination
Distribution transformers
Power transmission networks
Industrial substation busbars
Standard practice dictates that medium voltage systems (e.g., 11kV) often use resistance earthing to limit damage, while EHV systems (e.g., 400kV) use solid earthing.
Wrong options explanation: While options A, B, and C are technically correct, D is the encompassing answer because system earthing is a universal safety requirement across the power hierarchy.
D is correct — System earthing is a fundamental requirement for the safe and stable operation of all electrical systems, irrespective of their voltage level.
Always remember that 'System Earthing' relates to the neutral point, whereas 'Equipment Earthing' relates to non-current carrying metal parts; both are essential across all voltage levels.