Partial discharge (PD) detection is a standardized technique to qualify the insulation condition in power equipment. The main purpose of the article is to evaluate the performance of an extra high-sensitivity adapted giant magneto-resistive (xMR) sensor for non-contacting PD detection. First, compensation and signal conditioning circuits of the sensor are designed. Frequency response and time-domain response to fast calibrator pulses of the sensor with the implemented circuit are measured. Besides, PD experiments based on corona and surface models are carried out and compared with measurements using a high-frequency current transformer (HFCT). The results show that the xMR system can measure the magnetic fields produced by the PDs at distances up to 50 cm. The correlation between the HFCT and xMR signals is proportional under different voltages, showing that PDs can be effectively detected and evaluated by this method. PDs in a cross-linked polyethylene (XLPE) cable with an artificial discharging defect are successfully measured, demonstrating the sensitivity and performance of the xMR system.

The advent of new combinations of equipment and integrations of different power grids can potentially be accompanied by transient voltage phenomena which affect the reliability of electrical insulation systems. In particular, this affects insulation susceptible to partial discharge behaviour due to additional transient waveforms. Nowadays in transmission grid planning, overhead lines are increasingly combined with underground power cables. In switching such connections impulses could occasionally occur and superimpose on the normal AC voltage which will lead to superimposed transient waveforms. Those transient voltages will impose an additional stress on the cable insulation that could trigger partial discharges, that sustain. This paper reviews our recent research of some cable insulation defects of industrial relevance by partial discharge measurement on high voltage power cables stressed by different waveforms, including impulses, superimposed transients on AC voltage. This paper identifies achievements and at the same time challenges still to be solved in partial discharge measurement under different waveforms.

A partial discharge (PD) measuring system has been deployed in order to identify and measure PD in a high voltage (HV) cable joint under impulse and superimposed voltages under laboratory conditions. The challenge is to enable the detection of PD during the impulse conditions. The method of measurement has been investigated by introducing an artificial defect in the cable joint in a controlled way to create conditions for partial discharges to occur. Next the HV cable system is subjected to AC, impulse and superimposed voltage. Two high frequency current transformers (HFCT) installed at both ends of the cable joint were used to identify PD from the cable joint and to separate PD from disturbance. Transient voltage suppressors and spark gaps are applied to protect the measuring equipment. Band pass filters with selected characteristics are applied to suppress transient disturbances and increase the chance to detect PD during the impulse. PD signals are separated from transient disturbances during data post processing and by means of pulse polarity analysis. The developed system enables the detection of so-called main and reverse discharges respectively occurring during the rise and tail time of the superimposed impulse. The measurement results obtained show the effectiveness of the presented PD measuring system for investigating the effects of voltage transients on a HV cable system in laboratory conditions.

This paper investigates the triggering and development of partial discharges at artificial defects in the cross linked polyethylene (XLPE) insulated cable with accessories under superimposed voltage. The experiments are conducted on a 4-meter long 6/10 kV commercial XLPE cable sample, which is assembled with a cable joint and terminations. Defects are fabricated on purpose in the cable accessories. The cable sample was subjected to the superimposed voltage of 50 Hz AC with impulse voltage. Partial discharge activities are measured by a HFCT sensor and analyzed by PDflex. The measurement results show that, the impulse voltage could trigger partial discharges, which might be kept sustained by the AC voltage. The partial discharge activities are influenced by the AC voltage level, which is determined by the PDIV and PDEV.

Copoly(2-nonyl-2-oxazoline)-stat-poly(2-dec-9′enyl-2-oxazoline)s can be crosslinked by the thiol-ene reaction with glycol dimercaptoacetate. The copoly(2-oxazoline)-stat-copolyester is tested as dielectric for high-voltage applications, either as unfilled resin or as composite with nanoscaled fillers of silica, alumina, and hexagonal boron nitride. During AC voltage tests, all materials have an average breakdown strength of 45–50 kV mm⁻¹. For DC voltage tests, samples with SiO₂ (hBN) have an average breakdown strength of ≈100 (80) kV mm⁻¹, while the unfilled copoly(2-oxazoline) has an average breakdown strength of ≈60 kV mm⁻¹. Permittivity measurements at 20 °C and 50 Hz reveal that all nanocomposites are dielectrics (D = 0.06–0.08), while the unfilled copoly(2-oxazoline)s has a high loss factor of D = 8.43. This phenomenon can be retraced to the phase separation in the crosslinked copolymer, the M-OH functionality of silica and alumina particles, and models of polymer–particle interactions such as the Tanaka model, revealing that the nanofillers reduce the interfacial and dipolar polarizability.

Gas Insulated Switchgear (GIS) has been in use in transmission system for more than 30 years with good reliability. However, in our case study of 631 CB-bays of GIS operating under tropical conditions, we observed failure rates over twice the value reported in the 3^rd CIGRE's survey of 2007. Following this observation, it becomes practically important to develop a condition assessment model for GIS operating under tropical conditions. As a part of this process, knowledge rules for humidity content in SF₆ insulation were investigated through the experiment inside the HV Laboratory in TU Delft with a solidand- gas insulation setup with AC voltage stress. The controlled parameter used in the experiments were resembling the actual condition in tropics. In this paper, the condition assessment model for GIS is proposed. To support the model, different diagnostics to assess the critical components of GIS operating under tropical conditions are discussed. Following that, an example of knowledge rules to interpret the outcome from the diagnostics is also given.

Many researchers have reported an improvement of the properties of polymer dielectrics by introducing nanofillers. However, the influence of ambient conditions and sample storage under different conditions are often not taken into account. The epoxy matrix itself is a polar polymer susceptible to water absorption, and the presence of hydrophilic nanofillers such as silica will enhance the uptake of moisture from the environment. The dielectric response both of neat epoxy resin and an epoxy-based nanocomposite under an electrical stress greatly depends on the amount of absorbed water. This study investigates the effect of water absorbance on the dielectric spectrum of epoxy-silica nanocomposites containing different concentrations of nanoparticles.