the megger tester is an instument for measuring very high resistance values. the term Megger is derved from the fact the fact that the device measures resistance values in the megohm range. Its primary function is to test the insulation found in power transmission systems, electrical machinery, tranformers, and so on. To measure the high-resistance values, a high dc voltage is established by a hand-driven gennerator. If the shaft is rotated above some set value, the output of the generator will be ficed at one selectable voltage, typically 250,500,or1000V. A photograph of the commercially available Megger tester is shown in Fif. 7.48. the unknow resistance is connected between the terminals marked Line and Earth. For this instument, the range is zero to 2000M