This paper focused on the partial discharge properties of silicone gel used as an encapsulant in high voltage and high power IGBT power modules. A needle-to-plate electrode was applied to imitate the concentration of the electric field. Under 50 Hz AC voltage

the growth patterns of the electric tree were observed

and the phase-resolved partial discharges（PRPD） were measured. The growth and dissipation patterns of the electric tree were observed. The electric tree consists of tree-like cavities and spherical-like bubbles. It is found that the propagation direction of the electric tree is affected by electric field distribution and trap inside silicone gel. Furthermore

the electric tree is non-conductive due to the Si-O structure of the main chain. Thus

the propagation speed is independent of the length of the tree. Simultaneously

the unique self-healing properties of electric tree were observed in silicone gel after partial discharge. The self-healing mechanism was analyzed from the physical and chemical principles. The experimental results show that the PRPD in silicone gel is mainly distributed in the first and third quadrants

which conforms to the characteristic pattern of the typical internal creeping discharge in materials. With the propagation of the electric tree

the pulse frequency of partial discharge is almost constant

while the pulse phase gradually widens due to the effect of the space charge field. The research results in this paper will be helpful to guiding the application of silicone gel in the power modules.