Join 60,000+ competitive exam aspirants
or with email
Your Cart
Subtotal₹0
Total₹0
Examoogle • User • info@examoogle.com • EE-2024-8821
Chapter 1 of 12 • Page 1 of 248🔒 Protected PDF • Watermarked
Join 60,000+ competitive exam aspirants
Isolated neutral system has the disadvantage of
Voltage oscillation
Difficult earth fault relaying
Persistent arcing ground
All of above
All of above
An isolated neutral system (ungrounded system) is prone to several stability and safety issues during a single line-to-ground fault. Because there is no low-impedance return path for the fault current, the system exhibits voltage instability, arcing phenomena, and makes the detection of specific fault locations extremely difficult for protective relays.
An isolated neutral system (ungrounded system) is prone to several stability and safety issues during a single line-to-ground fault. Because there is no low-impedance return path for the fault current, the system exhibits voltage instability, arcing phenomena, and makes the detection of specific fault locations extremely difficult for protective relays.
Vph=3VL — Normal phase voltage
Ic=3⋅ω⋅C⋅Vph — Charging current during ground fault
In an ungrounded system, a ground fault causes the healthy phases to rise to full line-to-line voltage relative to the ground. The charging current flowing through the system's distributed capacitance can be insufficient to operate standard overcurrent relays but sufficient to sustain an intermittent arc if the insulation is faulty, leading to 'arcing grounds'. This leads to high-frequency voltage oscillations and stresses on the system insulation.
In isolated systems, phase-to-ground voltage can reach full line voltage during a ground fault.
Arcing grounds occur when the intermittent arc through capacitance charges and discharges the line, leading to overvoltage transients.
Protective relaying is difficult because the fault current is limited by the system capacitance rather than a physical ground connection.
Continuity of service during the first line-to-ground fault
Lower initial installation cost (no grounding equipment)
High transient overvoltages
Risk of arcing grounds
Difficulty in fault localization
Risk of double-ground fault leading to phase-to-phase short circuit
Small industrial low-voltage networks
Mining and specialized underground installations
Voltage oscillation refers to the transient recovery voltage surges caused by the charging and discharging of line capacitance.
Difficult earth fault relaying exists because the ground fault current is very small and lacks a dedicated return path for sensors.
Persistent arcing ground causes severe insulation breakdown due to repetitive restriking of the arc.
D is correct — All listed phenomena (voltage oscillation, difficult relaying, and arcing ground) are inherent disadvantages of operating a power system with an isolated neutral.
Remember that while isolated systems provide continuity of supply, they are rarely used in high-voltage transmission due to the insulation cost required to withstand the 1.732× overvoltage occurring during ground faults.