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General rule of value of insulation resistance per KV operating voltage in transformer is__________.
3┬аM\Omega/kV operating voltage at 50┬░C
2┬аM\Omega/kV operating voltage at 60┬░C
5┬аM\Omega/kV operating voltage at 50┬░C
5┬аM\Omega/kV operating voltage at 60┬░C
2┬аM\Omega/kV operating voltage at 60┬░C
The insulation resistance of a transformer is a critical parameter used to assess the health of the internal dielectric system. For oil-filled transformers, the standard industry practice is to maintain a minimum insulation resistance of 2 M╬й per kV of the rated voltage, measured at an oil temperature of 60┬░C.
The insulation resistance of a transformer is a critical parameter used to assess the health of the internal dielectric system. For oil-filled transformers, the standard industry practice is to maintain a minimum insulation resistance of 2 M╬й per kV of the rated voltage, measured at an oil temperature of 60┬░C.
RinsтАЛтЙе2├ЧVkVтАЛ┬аM\Omega
Insulation resistance (IR) measurement, performed using a megger, indicates the state of moisture, contamination, and degradation of the transformer insulation. As the temperature of the insulating oil and cellulose increases, the insulation resistance decreases exponentially. Therefore, reference values are strictly tied to a standard operating temperature (60┬░C) to ensure consistency in diagnostic results.
The 2 M╬й/kV rule is a minimum safety benchmark for transformer site testing.
IR values are highly temperature-dependent; temperature correction factors must be applied if testing is done at temperatures other than 60┬░C.
A declining trend in IR values over successive annual tests indicates accelerated aging of solid insulation (paper) or degradation of oil dielectric strength.
Simple non-destructive diagnostic test
Provides immediate indication of moisture ingress
Essential for pre-commissioning checks
Cannot detect local partial discharge sites
High temperature sensitivity requires correction tables
Provides a bulk measurement of winding insulation only
Routine Preventive Maintenance (PM)
Transformer Commissioning
Post-fault diagnostics
The rule of 2 M╬й per KV is widely adopted in Indian standards (e.g., CBIP manuals) for oil-filled power and distribution transformers.
If the IR value is significantly below 2 M╬й/kV, the transformer oil usually requires filtration or the winding needs drying out.
B is correct тАФ The standard maintenance rule for transformer insulation resistance is 2 M╬й per kV of operating voltage at a reference temperature of 60┬░C.
Remember that IR values roughly halve for every 10┬░C increase in temperature; always verify the temperature correction factor before concluding the transformer is faulty.