Voltage withstand properties of the insulation of different types of medium voltage covered overhead line conductors

Using covered conductors in overhead lines has become a widespread practice for increasing the reliability of distribution grids. To determine the ability to withstand prolonged voltage stress of different insulating materials, 10 different types of covered conductors with a rated voltage of 20 kV were tested by placing grounded copper wire electrodes on the outer surface of the conductor. In the tests, 3 grounding points were applied to each tested conductor. The conductors were energized to a standard testing voltage of 14 kV and the accumulative time until puncture of the insulation was measured. Some conductors showed a high variability of withstand times, possibly due to presence of weak spots in the insulation. On average, conductors insulated with PE performed best in the tests, PE/XLPE combined insulation was second best and XLPE insulated conductors exhibited the shortest withstand times.