Theory and Procedure of the Experiment - 4


The two unit portable testing set is designed for the periodical testing of samples of insulating oils drawn from plant on site and for checking the dielectric strength of new samples of oil. The equpiment is designed to operate from 200/250V, 50Hz, Single phase AC supply. Test gap voltage upto 50kV, it consists of two units, one is containing the testing transformer and other is control and metering equipments. These equipments are kept in a metal box to provide full protection to the apparatus during transport and storage. The gap is adjusted between electrodes in accordance with British Standard Specification (BSS) no. 148.


  1. Place the High Voltage transformer unit about 7 away from the control unit.
  2. The control unit is connected to supply voltage taking care that the earth connections are effective.
  3. The multiple point control switch is set at its lowest tapping.
  4. The push button on control unit is pressed firmly for at least 5 seconds. Note that no Breakdown to occurs, in which case button should be released at once without delay. Break down is indicated by a continuous discharge across the gap, bubbling of oil in the cell and meter indicating a sudden voltage drop.