Charge Injection Into Dielectric Oil From The Anode Or Cathode Under Ramped Voltage Application

Abstract

From an e a r l i e r study in s i l i c o n e o i l , the average cur ren t response t o r i s i n g and f a l l i n g vol tage appears on a log-log s c a l e with two l i n e a r port ions which a r e sharply divided a t high f i e l d [l]. Both of these two port ions obey the equation I a VS, i n which Su and Si a r e re fer red t o as the upper s lope and lower slope. Figure 1 gives a typical p l o t o f the average cur ren t a s a function of the t r i a n g u l a r applied voltage i n log-log sca le . According t o a theory o f charge t ranspor t in d i e l e c t r i c l iqu id [Z] , i t i s proposed t h a t under slow t r i a n g u l a r voltage waveform appl ica t ion t h e process may occur by in jec t ion of e lec t rons from the cathode in t h e highest f i e l d region. The lower s lope represents the cur ren t c h a r a c t e r i s t i c in the lower (intermediate) f i e l d region. The lower s lope i n the intermediate f i e l d s t rength regime has not so f a r been invest igated c lose ly . I t has been hypothesized t h a t the lower s lope o r i g i n a t e s in some pos i t ive ion i n j e c t i o n process very much as e lec t rons are in jec ted from t h e cathode a t the highest f i e l d s t rengths . Indeed, s i l i c o n e o i l i s a homocharge 1 iquid according t o the c l a s s i f i c a t i o n of Guizonnier [3] and as such wil l have e lec t ron i n j e c t i o n under the control of the cathode material sur face while pos i t ive ion production i s determined by the anode. In addi t ion t o any such process, pos i t ive ions can appear and remain in the l iqu id from other mechanisms.