Partial Discharges in Cavities and their Connection with Dipoles, Space Charges, and Some Phenomena Below Inception Voltage

G E Vardakis,A Nterekas,M Danikas

doi:10.48084/etasr.3593

Abstract

This paper tries to relate Pedersen’s model on partial discharges and work carried out by Bruning and co-workers on the possibility of the existence of charging phenomena below inception voltage, which may eventually cause deterioration of polymeric insulation. Moreover, with the aid of the Electromagnetic theory, some aspects of the Pedersen’s model are tried to be clarified, especially those which are correlated with space charges, electric dipoles, charge distribution, charge dynamics, and partial discharge activity.

Highlights

INTRODUCTIONPedersen’s model [1] was proposed as an alternative to the traditional capacitive model [2, 3] for the interpretation and/or prediction of partial discharges in enclosed cavities in solid dielectrics
Pedersen’s model [1] was proposed as an alternative to the traditional capacitive model [2, 3] for the interpretation and/or prediction of partial discharges in enclosed cavities in solid dielectrics. This model is based on electromagnetic theory and gives the magnitude q induced on the measuring electrode by the partial discharge in a cavity, in terms of a variety of parameters, as is shown in (1): q = kΩεrε0 (Ei – El) ∇ሬԦߣ଴ (1) where k is the geometrical cavity factor, Ω the cavity volume, Ei the inception electric field for streamer inception, El the limiting electric field for ionization, εr and ε0 are the relative permittivity of the surrounding dielectric material and the permittivity of the free space respectively, and λ0 is the function giving the ratio of the electric field at the position of the cavity to the voltage between the electrodes
According to [1], the charge deposited on the cavity surface S can be considered as an electric dipole, the moment of which μ, is given as: μ = ∫ rσdS (2)

Summary

INTRODUCTION

Pedersen’s model [1] was proposed as an alternative to the traditional capacitive model [2, 3] for the interpretation and/or prediction of partial discharges in enclosed cavities in solid dielectrics. Even though there is a disagreement as to whether the net charge within the cavity remains zero [1, 6], it is evident from [1] that Pedersen’s model tries to relate dipole moment with charge dynamics inside the cavity and with even minute discharge currents. Dipole moments within the cavity are supposed to induce charges and eventually cause the recorded partial discharge currents. In [10, 20], it was remarked that, having an enclosed cavity in polyethylene, a conducting path caused the magnitude of quite low current pulses (1-10mA) which is substantially different and quite lower than current pulses of about 1A measured with other more conventional arrangements [21] It was mentioned in [6] that there are doubts whether the net charge in a cavity is zero or can supposed to be equal to zero. P=Pa+∆P (10) The resulting induced charge on the i-th electrode is given by (11):

DISCUSSION AND COMMENTS

CONCLUSION