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Which method is used for the measurement of insulation resistance?
Kelvin's bridge
Wheatstone bridge
Megger
Both B and C
Megger
A Megger (Mega-ohmmeter) is a portable instrument specifically designed to measure very high electrical insulation resistance, typically in the range of Mega-ohms (M╬й).It operates by applying a high DC voltage to the insulation and measuring the leakage current, providing a direct reading of resistance.
A Megger (Mega-ohmmeter) is a portable instrument specifically designed to measure very high electrical insulation resistance, typically in the range of Mega-ohms (M╬й).It operates by applying a high DC voltage to the insulation and measuring the leakage current, providing a direct reading of resistance.
R=IVтАЛ тАФ Ohm's law applied to insulation leakage where R is in M╬й
P=VI тАФ Power dissipation associated with the applied high-voltage test
The Megger consists of a permanent magnet DC generator (hand-cranked or battery-operated) and an ohmmeter mechanism. When the generator is turned, it produces a high DC voltage across the insulation. The internal moving coil meter measures the ratio of voltage to current, which is proportional to the resistance, resulting in a deflection of the needle on a calibrated scale.
Meggers typically use a voltage of 500V, 1000V, or 5000V DC.
The reading is independent of the speed of the hand crank due to the use of a cross-coil ohm meter movement.
It is primarily used for testing transformers, cables, and rotating machinery insulation.
Before testing, equipment must be discharged to prevent erroneous readings and damage to the device.
Portable and requires no external power source if hand-cranked.
Provides a direct and quick indication of insulation status.
Cannot measure very low resistances accurately.
Destructive if the insulation is already compromised and exposed to excessive voltage.
Transformer winding insulation testing.
Electrical cable dielectric integrity check.
Preventive maintenance of circuit breakers and switchgear.
Kelvin's bridge is used for measuring very low resistances (typically < 1╬й).
Wheatstone bridge is used for measuring medium resistances (typically 1╬йto 100k╬й).
Megger is the standard choice for high-resistance insulation measurements.
C is correct тАФ The Megger is an instrument specifically designed to measure high insulation resistance values by applying a high DC voltage.
Always remember: Kelvin's Bridge is for Low R, Wheatstone Bridge is for Medium R, and Megger is for High R (Insulation).