Abstract: The present invention is a method and apparatus for testing the condition of insulating systems. The insulating system is charged up by a dc voltage and then discharged. The return voltage appearing after discharge is assessed and the quotient of the peak value of the return voltage and the charging voltage is measured. According to the invention the charging is done in time-interval of 10.sup.-3 -10.sup.4 seconds, with a ratio of charging to discharging time in the range of 0.1-100. The measurement cycle is repeated several times with other charging/discharging times, but with the same charge/discharge ratio. The resulting spectrum of values may be compared with a reference whereby the state of the insulating system can be assessed. An apparatus for implementing the method the apparatus for implementing the said method consists of a high voltage source, a switching circuit and voltage measuring units.

Abstract: High voltage insulator is produced by inserting a fiber reinforced core into the mold and filling the mold from the bottom through a casting pipe line attached to a tank for a ready to use liquid silicon rubber mixture, and transferred to the heated mold where crosslinking of the mixture occurs.