In order to study the effect of inorganic nano filler on the insulating properties of polyimide（PI）films

PIthin film

10 wt. % PI/SiO

2

thin film and 10 wt.% PI/Al

2

O

3

thin film were made based on in situ polymerization meth-od. The conductivity

thermal gravimetric analysis（TGA）and breakdown field strength are tested. Besides

thecurve of corona resistant time along with the change of temperature is gained. The re

sults indicate that the conductivi-ty decreases in the sequence of PI/SiO

2

film

PI/Al

2

O

3

film

and PI film

but the breakdown field strength is on thecontrary. When the decomposition temperature at 5% weight loss

the temperature of PI/Al

2

O

3

film and PI/SiO

2

film ishigher than that of pure PI film by 17.5 ℃ and 11 ℃ respectively. With the increase of temperature

the corona resis-tance time of three kinds of films is decreased

and the time of two nano films is higher than that of the pure PI film.When the temperature is less than 210 ℃

the corona resistance time of PI/SiO

2

film is the longest because its con-ductivity is the highest. When the temperature is greater than 210 ℃

the corona resistance time of PI/Al

2

O

3

film isthe longest because of the highest thermal conductivity and thermal stability. The organic inorganic interface andhigh thermal stability of inorganic nano particles are the main reasons for the insulation properties of PI films. The studyprovides a theoretical basis for the improvement of the turn to turn insulation level of the frequency conversion motor.