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The control system in substations generally operates at
110 V
220 V
400 V
Both (a) and (b)
Both (a) and (b)
Substation control and protection circuits are powered by DC batteries to ensure reliability during AC supply failures. The standard voltage levels used for these auxiliary control circuits are 110 V DC and 220 V DC.
Substation control and protection circuits are powered by DC batteries to ensure reliability during AC supply failures. The standard voltage levels used for these auxiliary control circuits are 110 V DC and 220 V DC.
P=VтЛЕI
VDCтАЛ=VbattтАЛтИТIтЛЕRintтАЛ
In a substation, the control bus supplies power to protective relays, circuit breaker trip coils, indication lamps, and alarm circuits. By using a dedicated DC supply system (Battery Bank + Battery Charger), the control system remains functional even during a complete grid blackout, which is essential for safely operating switchgear.
DC supply is chosen for high reliability during AC faults.
110V DC is common in medium voltage substations.
220V DC is often preferred in EHV (Extra High Voltage) substations to minimize voltage drop over long control cables.
The supply is floating relative to the earth to detect ground faults easily.
Operational during AC supply failure
High reliability for circuit breaker tripping
Easier fault detection in control circuits
Requires maintenance of battery banks
Higher initial cost for battery chargers and storage
Risk of voltage drop over long cable distances
Protective relay powering
Circuit breaker trip/close coils
Substation lighting and signaling
Standard DC control voltages are defined by IEC and IS standards for substations.
Option C (400 V) is typically not used for control purposes as it poses a higher risk of insulation failure and personnel safety concerns for low-voltage control cabinets.
D is correct тАФ Substation control systems commonly utilize both 110 V DC and 220 V DC supply voltages to maintain reliable operation of protective equipment.
Always remember that protective systems must remain energized even when the main bus is tripped; therefore, battery-backed DC is always preferred over AC for control.