By using pulse-electro-acoustic space charge measurement method

space charge accumulation and field distribution of polyethylene(PE)films were measured respectively at room temperature(ΔT=0 ℃)and under temperature gradient(ΔT=40 ℃)

when positive or negative DC of 50 MV/m was applied for 2 h. And the space charge profiles and field distributions under temperature gradient were investigated during the different reverse polarity. The tests show that the maximal field enhancement factor remains almost unchanged whatever the reverse polarity is. The maximal transient field appears near the high temperature side during voltage polarity reversal from positive to negative but near the low temperature side during voltage polarity reversal from negative to positive

and the spent period gets shorter to reach the maximum during polarity reversal from positive to negative than during the opposite reversal.