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Insulation resistance of HV circuit breaker is more than ___________.
1000 M╬й
500 M╬й
2000 M╬й
400 M╬й
2000 M╬й
The insulation resistance of high voltage (HV) circuit breakers is a critical diagnostic parameter used to ensure the integrity of dielectric materials. According to IS (Indian Standards) and IEC guidelines, for a healthy HV circuit breaker, the insulation resistance (IR) measured between live parts and earth, and across the open contacts, must typically be greater than 2000 M╬й.
The insulation resistance of high voltage (HV) circuit breakers is a critical diagnostic parameter used to ensure the integrity of dielectric materials. According to IS (Indian Standards) and IEC guidelines, for a healthy HV circuit breaker, the insulation resistance (IR) measured between live parts and earth, and across the open contacts, must typically be greater than 2000 M╬й.
R=IVтАЛ тАФ Ohm's Law governing the insulation resistance calculation during Megger testing.
ITotalтАЛ=IVтАЛ+ISтАЛ тАФ The total leakage current is the sum of volume leakage current and surface leakage current.
The measurement is performed using a high-voltage megohmmeter (Megger), which applies a DC voltage (usually 2.5 kV or 5 kV) across the insulation. The device measures the leakage current ILтАЛ and calculates resistance using Ohm's Law R=ILтАЛVтАЛ. High resistance indicates that the dielectric medium (SF6, Vacuum, or Oil) and the solid insulating supports are free from moisture, carbonization, or surface tracking.
Tests should be performed at a voltage rating appropriate to the equipment's rated voltage (e.g., 2.5 kV for 11kV/33kV breakers).
Humidity and temperature significantly affect the insulation resistance values.
A sharp decrease in IR value is a major indicator of moisture ingress or degradation of the interrupting medium.
Measurements are typically recorded 'Phase to Earth', 'Phase to Phase', and 'Across open contacts'.
Non-destructive testing method when performed within rated voltage limits.
Helps in identifying early-stage insulation breakdown before catastrophic failure occurs.
Value depends significantly on ambient temperature and humidity conditions.
Does not reveal the exact location of the insulation failure, only its presence.
Routine preventive maintenance of substation circuit breakers.
Post-installation commissioning of switchgear equipment.
Diagnostic testing after a fault clearing operation.
The 2000 M╬й threshold is a standard benchmark for HV equipment to ensure adequate dielectric strength under normal service conditions.
Lower values (e.g., 500 M╬й) may be acceptable for medium voltage or aged equipment, but 2000 M╬й is the target for high-reliability HV assets.
C is correct тАФ The minimum insulation resistance required for a healthy HV circuit breaker is 2000 M╬й.
Always correlate IR values with the Temperature Correction Factor; if the temperature is high, the IR value will be lower than the rated value.