Insulation faults of transformers are usually caused by deterioration and aging of oil-paper insulation due to partial discharge（PD）

therefore

it is necessary to study live detection technology of PD for ensuring safe operation of a transformer. In this study

the ultra-high frequency（UHF） signals of partial discharge induced by the insulation defects of needle-plate and suspended potential

which were prepared in laboratory

were investigated

and the discharge spectrums of both defects were obtained in the process of applied voltage increasing. The result shows that for the needle-plate defect

discharge signals were firstly observed at the near peak of negative halfcycle of the applied voltage

and then symmetrically distributed around the peak of voltage waveform. For the suspended potential defect

discharge signals were firstly observed near the peaks of positive and negative halfcycles of the voltage

then the signals distributed in the whole first and third quadrants with the voltage increasing.Besides

two kinds of insulation defects were designed and set in a 110 kV transformer

and the real-time live detection technology was employed for measurement and analysis of the PD signals. This study may lay a foundation for application of the PD live detection technology to insulation fault diagnosis of transformers.