Dielectric Interfaces in DC Constructions: Space Charge and Polarization Phenomena

Abstract

Interfaces between dielectrics are considered one of the weakest parts of an insulation system but their behavior under electrical stress is not yet completely understood. In particular, when a dc voltage is applied, the electric field distribution at the interface is quite difficult to predict. This is mainly due to the accumulation of internal charge, which distorts the initial Laplacian field. To shed some new light on this topic, space charge measurements were performed on two types of coaxial XLPE-EPR interfaces. A numerical procedure, based on the Maxwell-Wagner theory for interfacial polarization, was developed for the estimation of the dynamic charge build-up at the interface. Experimentally obtained space charge profiles were compared to the calculated profiles. The limits of the Maxwell-Wagner model were assessed and the main parameters, which affect the interfacial polarization but which are not included in the model, were identified.

Interfacial charge behaviour at dielectric - dielectric interfaces

“…It is seen that, at about 1000s after voltage on, polarity at interface changes from negative to positive. Similar observation is reported by Rogti et al [12] in prestressed XLPE-XLPE interface and Bodega et al, [13,14] in XLPE-EPR interface. It would appear that at lower fields, negative interfacial polarisation charges (as predicted through equation (6)) dominantly accumulate at the interface.…”

“…The location of the positive polarity peak moves slightly from the interface towards the PE side of the interface. It may be argued that the change in polarity is caused by positive charge accumulation at the interface, at increased field values, due to injection of charge from the electrodes [13,14].Polarity reversal takes place when sufficient positive charge accumulates to negate the original negative polarity signal at the interface. Figure 8b shows the spatial distribution of charge under different applied fields, at 20 s from voltage off.…”

Maxwell–Wagner Effect in Multi-Layered Dielectrics: Interfacial Charge Measurement and Modelling

“…In these conditions, the interfacial charge is either positive or negative, with the convention of orientation given in Figure 2. The equations describing the non-stationary regime are the same and they are obtained by incorporating the time dependence of the fields E1 and E2 and writing the interfacial charge density in the form [16]:…”

Interfaces: To be avoided or to be treasured? What do we think we know?

“…5. Resorting to PEA space charge measurements [15], [25], [26], [27] In Fig. 6, it is shown how charge builds up at the interface after application of a dc voltage on a mini cable consisting of two concentric layers of XLPE and EPR.…”

“…Let us have a look at the behavior of these interfaces in terms of charge dynamics and polarization. In extruded type HVDC cables we encounter dielectric interfaces [23], [24] (in between dielectrics) and semicon-dielectric interfaces [20], [21] as shown in Fig. 3 and Fig.…”