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Isolated neutral transmission system is not recommended as
System insulation is over stressed due to over voltages
Insulation over stress may lead to its failure resulting in Phase to phase fault
System is not adequately protected against earth fault
All of above
System is not adequately protected against earth fault
An isolated neutral (ungrounded) transmission system is generally avoided because it lacks a fixed reference potential. This makes the system susceptible to severe arcing grounds and high transient overvoltages, which stress the insulation beyond its design limits.
An isolated neutral (ungrounded) transmission system is generally avoided because it lacks a fixed reference potential. This makes the system susceptible to severe arcing grounds and high transient overvoltages, which stress the insulation beyond its design limits.
VfaultтАЛ=3тАЛ├ЧVphaseтАЛ тАФ Healthy phase voltage to ground during an earth fault
IcтАЛ=3├ЧVphaseтАЛ├Ч╧ЙC тАФ Capacitive charging current during earth fault
In an ungrounded system, the neutral potential 'floats' relative to ground based on phase-to-ground capacitances. During a single-line-to-ground fault, the healthy phases rise to line-to-line voltage instead of phase voltage relative to ground (VphтАЛ├Ч3тАЛ). Additionally, the capacitive charging current during intermittent faults can trigger high-frequency arcing, leading to dangerous voltage surges (arcing grounds) that threaten equipment integrity.
Grounding provides a path for fault currents, facilitating quick isolation.
Isolated systems make fault detection difficult due to low fault current magnitudes.
Transient overvoltages (arcing grounds) are common in ungrounded systems.
Equipment insulation must be rated for line-to-line voltage in ungrounded systems.
Continuous operation during a single line-to-ground fault
Low magnitude of ground fault current
High transient overvoltages
Difficulty in locating ground faults
Risk of phase-to-phase conversion of faults
Low voltage distribution networks where continuity is critical
Specific industrial processes requiring no supply interruption
In grounded systems, the neutral is held at 0V, ensuring that insulation is only subjected to phase voltage.
Option C is correct as fault detection requires a return path (grounding impedance), which is absent in an isolated system.
D is correct тАФ Isolated neutral systems suffer from poor fault detection, severe overvoltage stress due to capacitive effects, and increased risk of equipment insulation breakdown.
Always remember that while isolated systems allow for temporary operation under fault, the 'Arcing Ground' phenomenon caused by the charging current (IcтАЛ) makes them unreliable for long-term usage compared to solidly grounded or impedance grounded systems.