Megger | Definition and Working Principle

Megger | Definition and Working Principle

Megger Definition

Megger or Megaohm meter is an instrument that measures the insulation resistance of electric circuits relative to the earth and one another.
Meggar | Definition and Working Principle

Megger Working Principal

A Megger consists of an e.m.f. source and voltmeter. The scale of the voltmeter is calibrated in ohms (kilo-ohms or megohms, as the case may be). In measurements, the e.m.f. of the self-contained source must be equal to that of the source used in calibration.


Meggar | Definition and Working Principle
Above Image shows diagrammatically a Megger whose readings are independent of the speed of the self-contained generator. The moving system incorporates two coils 1 (current coil) and 2 (pressure coil) mounted on the same shaft and placed in the field of a permanent magnet (not shown) 90° apart. The generator energizes the two coils over separate wires. Connected in series with one coil is a fixed resistance R1 (or several different resistances in order to extend the range of the instrument). The unknown resistance Rx is connected in series with the other coil. The currents in the coils interact with the magnetic field and produce opposing torques.

The deflection of the moving system depends on the ratio of the currents in the coils and is independent of the applied voltage. The unknown resistance is read directly from the scale of the instrument. (The accuracy of measurement is unaffected by variations in the speed of the generator between 60 and 180 r.p.m.).


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