Insulation Resistance Testing

When we apply the DC voltage thro' the digital Megger to test the IR value for cable/motor winding etc., we can see the digital display of the test equipment showing more than the applied voltage (for eg. if we select 500V dc, we can see 526V dc in the display) Why?

Questions by Balathandayutham

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When we measure IR value, we measure resistance of insulation of the circuit either w.r.t earth or w.r.t. to other phase.The digital display is resistance between the ckt and earth, not the voltage. It is normally of the order of Mega ohms. Tio measre this resistance we apply D.c voltage of the range of 250/500/1000/2500 depending upon the requirement. This voltage is rating of megger which produces the required voltage to measure the insulation resistance.

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