Electrical arc can not only induce the dielectric characteristic loss of silicone oil

but also increase the local temperature of silicone oil. So it is very important to investigate effects of electrical arc on properties of silicone oil. We studied effects of electrical arc on dielectric properties and initial discharge patterns of silicone oil using a needle-plate electrode. Experimental results show that sustained electrical arc discharges break the silicone’s long chain

and form black sludge

accompanying a gradually change of the liquid color from colorless to brown

and finally dark in the end; The amount of black sludge increases with the discharge capacity

but decreases the breakdown voltage and initial discharge voltage of oil. When the arc discharge ca

pacity increases to 1.98×10

10

pC

the value of dielectric loss factor（tanδ） increases from 0.002% to 1.3%

while the volume resistivity and breakdown voltage of silicone oil（ρ） decrease from 1.25×10

13

?·m and 45.8 kV to 7.8×10

10

?·m and 16 kV

respectively. In addition

the initial discharge voltage of oil declines from 24 kV to 10 kV.