Effect of Space Charge on Interface Discharge Characteristics in Multilayer Dielectric

In direct current field, space charge is the key factor affecting insulation performance. In multilayer composite insulation structure, the interface of two insulating media is more likely to accumulate space charge due to discontinuity, which becomes the weak link of the whole insulation system. In flexible HVDC engineering, the optical internal discharge of fiber insulator is probably related to the accumulation of space charge at the interface of optical fiber sheath and coating layer. In this paper, finite element method was used to simulate the accumulation of space charge in a double-layer dielectric composed of fiber jacket and coating based on Maxwell-Wagner polarization model and bipolar carrier transport model. Then the relationship between interfacial discharge characteristics and space charge was studied. The results showed that the charge accumulated at the interface at normal temperature was mainly caused by polarization. However, at higher electric field strength, the injection of space charge gradually increased, and the cumulative effect of interface charge was more obvious. When the interface accumulated space charge, the initial discharge voltage decreased greatly. The interface discharge characteristics are closely related to the space charge behavior at the interface.