The effect of interface of electrode and liquid on space charge injection in transformer oil under impulse voltage

Electrode have an important influence on the breakdown of liquid dielectrics. The interface of electrodes and liquid dielectrics may affect the injection and distribution of space charge in liquid dielectrics, and thereby affecting the breakdown of liquid dielectrics. To find experimental evidence, the Kerr electro-optic method was used to observe the space charge in transformer oil under different electrode materials (Brass, Aluminum). With the use of array photodetector, the space-time evolution of space charge in liquid dielectrics can be directly measured under a single impulse voltage. The results show that when impulse voltage was applied to the electrodes, the Br (+)-Br (-) electrodes injected unipolar positive space charges, the Al (+)-Al (-) electrodes injected unipolar negative space charges, the Br (+)-Al (-) electrodes injected bipolar homo-charges, and the Br (-)-Al (+) didn't inject significant space charges. The reason of this phenomenon may be the different properties of electric double layer formed by different electrodes and transformer oil. Considering that the homo-charge injection can weaken the electric field near the electrode, the breakdown voltage under Br (+)-Al (-) should be highest, which is consistent with other researchers' conclusions. This study provides an experimental basis for selecting a suitable electrode combination to strength the breakdown voltage of transformer oil.