The principal factor of insulation erosion is partial discharge. Bubble is the key weak factor of oil-paper insulation

and its content and dielectric strength are affected by the hydrostatic pressure to a large extent. To understand the tendency that discharge in oil-paper insulation varies with hydrostatic pressure

a whole sealing pressure adjustable partial discharge testing platform is developed. The discharge of needle-plate discharge under different hydrostatic pressures is researched

and the influencing mechanism is analyzed. It is revealed that the partial discharge inception voltage and the breakdown voltage increase with the rise in hydrostatic pressure

and the increase rate declines gradually. The peak value of partial discharge

the average discharge value

the discharge repetition rate

discharge current and discharge power under operation condition decrease with the rise in pressure. This is because hydrostatic pressure can change the solubility and compression degree of the gases in oil. The results can provide an experimental basis and theoretical support to the oil-paper equipment design and their reasonable operation.