and conclude that the effect
of moisture content on breakdown characteristics of oilpaper
insulation. He also studied on the breakdown characteristics of
XPLE under AC, DC and pulsating voltage [6], appointing
that pulsating voltage has obvious effect on detecting internal
defects of XPLE. Reference [7] gives a brief introduction
about the surface electric strength of processed pressboard
under pulsating voltage (p=0.4~2.2). Mosinski, F. researched
the electrical strength of oilpaper insulation under composite
ac and lighting impulse voltages [8]. His work indicates the
existing of AC voltage decreases the breakdown voltage of
lighting impulse and the breakdown voltage of composite
voltage is lower than that of AC voltage. In recent years, as
the development of DC transmission, a series of researches
about insulating properties of oilpaper insulation under
pulsating voltage has been launched in china. Reference [9]
studies the breakdown voltage of insulation oil and insulation
paper under pulsating voltage. The author appointed that the
breakdown voltage of oil changes slightly as AC component
increases, while the oilpaper changes obviously. Reference
[10] further researches the effect of preset AC component and
DC component on breakdown characteristics of needle plate
model.