Investigating dc polyethylene threshold by space charge. Current and electroluminescence measurements

Abstract

It has been proposed recently [l] that the lowest level of dc field, above which electrical degradation may occur, is associated with the formation of space charges in insulation. Therefore, inference of field levels above which space charge accumulates in a given material may provide fundamental information for material characterization and system design. Threshold field values were estimated through evidence of space charge accumulation derived from conduction current, space charge amplitude and electroluminescence (EL) counts vs. electrical field characteristics. Press-molded plates of polyethylene-based materials were used for this investigation. In order to be able to detect even by EL experiments the presence of the space charge accumulated at low fields, measurements were carried out during both polarization and short-circuit of specimens. It is shown that the threshold corresponding to the onset of EL upon grounding the specimen is close to the space charge accumulation threshold derived from space charge and conduction current measurements. This earlier value is considerably lower than the one previously detected from constant dc-voltage EL measurements, thus confirming that even at low fields and in the presence of voltage reversals or transients, space charges can trigger luminescence phenomena. The methodology developed in this paper enlarges the applicability of the EL technique to accommodate a wider electrical field range in view of insulation characterization.

Space charge and associated electroluminescence processes in XLPE cable peelings

“…Electrodes were made of semicon (high voltage, anode) and aluminium (cathode). Tests with gold electrodes prepared by cold sputtering were also performed [3,4]. Electroluminescence was detected through a photomultiplier (PM) working in photon counting mode, using specimens metallized on both surfaces with semitransparent layers of gold deposited by cold sputtering.…”

“…The procedure adopted to measure EL during depolarization was slightly different. We have already reported that under short-circuit conditions, the EL is a transient process occurring immediately after grounding the sample [4]. The analysis of the EL decay necessitates a shorter sampling time which has been chosen at 10 ms. Voltage was applied to the specimen by using a high voltage switch which can be used to ground the sample after the polarization time.…”

Determination of threshold electric field for charge injection in polymeric materials

“…However, this value is significantly lower than the value of 10 kV/mm mentioned in literature for polyethylene. 5,6 As the blocking layer was fluorinated polyethylene, its dielectric properties such as permittivity and conductivity are different from the normal one; therefore, it is possible the charges accumulated at the interface between the two layers may be related to the Maxwell-Wagner polarisation.…”

Review of high voltage direct current cables

“…The injection of charge carriers occurs at the conductor/solid insulator interface when the applied electric field is higher than the threshold field for the specific dielectric material. For example, the threshold for PE is about 10 kV/mm [88]- [90]. The injected charge carriers are expected to have the same polarity of the related electrode, i.e., positive charges are injected from the anode, and negative charges are injected from cathode, which is called homo-charges.…”