Partial discharge (PD) defects can gradually deteriorate during operation and even lead to high energy discharge faults

which seriously threatens safe operation of transformer. In this paper

the PD test platform is set up based on a full-size 110 kV transformer

and three kinds of suspending discharge defects as suspending metal particles of high voltage lead

metal tip suspending near the high voltage lead and electrostatic ring suspension are designed. The step-boosting voltage method is adopted to test

and the variation of pulse current

ultrahigh frequency (UHF) and acoustic signals during PD development is recorded and compared as well as analyzed. It is found that the intense discharge stage of the three suspension defects is not obvious

the discharge energy before breakdown is relatively low

and the phenomenon of main frequency left-shift does not appear in the frequency-band of acoustic signal. Although the three defects are suspension potential discharge

yet their PD characteristics are obviously different. It is necessary to consider the defect situation in the true transformer in case of extracting defect characteristics

and the joint diagnosis of UHF and audible-ultrasonic signal can effectively identify suspension discharge. In this paper

the rules and characteristics of typical suspension discharge are obtained by defect simulation on a full-size transformer for the first time

which can provide a certain reference for online monitoring and fault alarm of transformer.