A dielectric loss testing device based on current comparator bridge was developed for testing the aging of insulator and evaluating insulation status of in-service GIS insulator. The dielectric loss standard device was used to verify the developed device. The results show that the measurement error of the developed device is within 2%

which can ensure the effectiveness of the test results. The new insulators and the insulators after five-year service were sampled to test their capacitance and dielectric loss. At the voltage of 20 kV

the new insulators showed good electrical insulation property

and their capacitance and dielectric loss did not change during test;however

the insulators after five-year service showed obvious change in the testing data of capacitance and dielectric loss

especially in the data of dielectric loss. Therefore

the dielectric loss can be taken as a characteristic parameter to evaluate aging status of the basin-type insulators.