TRANSFORMER COMMISSIONING
Insulation Resistance All know that the resistance of a pure insulation is infinity. But to no extend we can make a pure insulation. So we have a small leakage current to flow through insulation depending upon the voltage applied. Thus as the result we get a resistance value in the range of Mega Ohms(MΩ) or Giga Ohms(GΩ). Here the applied voltage is DC. We have separate kit for injecting the DC voltage. Usually that equipment is known as megger. The two windings are connected as in the diagram above and Megger is used to measure the insulation resistance. It applies a high voltage normally 500V or 1kV for time period of minimum 30 seconds to One minute and the respective resistance are noted down. Usually for a new transformer, result value will be in Giga Ohms(GΩ). During the ageing, deposition of dust, moisture and other unwanted particles can cause the megger value to reduce. So to gain the resistance back to normal, the dust deposited should be removed, moisture shoul...