Partial discharge (PD) detection is an important tool for evaluating the insulation condition of high-voltage power equipment. This paper investigates a diagnostic system consisting of a magnetic sensor with dedicated electronic circuitry. The investigated sensor is based on the giant magnetoresistance (GMR) effect, which enables the possibility of contactless detection of magnetic fields caused by PD currents. However, the bandwidth of the circuitry can be a limiting factor. In order to exploit the bandwidth of an extra high-sensitivity adapted giant magneto-resistive (xMR) sensor, this paper describes dedicated designs for compensation and signal conditioning of the xMR signals. Typical performance has been evaluated, including frequency response and time-domain response to fast calibrator pulses by the xMR sensor with the implemented circuit. The results show that the xMR sensor with the implemented circuit covers a relatively broad bandwidth and can detect PD pulses with a minimum amount of 10 pC, preliminarily verifying its possibility to detect PDs. Using this xMR system, magnetic signals from an experimental model producing surface discharges have been detected and compared with simultaneously measured signals from a high-frequency current transformer (HFCT). The results show that the xMR system can measure the magnetic fields produced by the PD currents.@en

Partial discharges (PD) detection is an effective diagnostic method to assess the insulation condition of electrical power equipment in the high-voltage laboratory or field tests. This paper presents a non-contacting PD detection method for power equipment. The method is based on an extra high-sensitivity adapted giant magneto-resistive (xMR) sensor that measures the magnetic field produced by the PD currents. Firstly, this paper describes the sensor’s relevant principle and signal conditioning circuit. Next, the sensor’s typical performance, including the frequency response and time-domain response to calibrator PD pulses, is measured and compared with our previous work. The results indicate that the xMR system’s bandwidth is improved to the MHz range. Finally, PD experiments are carried out and compared with measurements using a commercially available high-frequency current transformer (HFCT), which allows for verification of the coherence of the results concerning the PD pulses and phase-resolved PD (PRPD) patterns. The results show that PD in a cross-linked polyethylene (XLPE) cable or a gas-insulated system (GIS) with artificial discharging defects is successfully measured, demonstrating the sensitivity and performance of the xMR system for PD detection.@en

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.

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Partial discharge (PD) detection is essential for evaluating the insulation condition of power equipment. In this paper, the use of a high-sensitivity giant magnetoresistance (GMR) sensor with designed circuits for non-contacting PD detection is presented. Using this GMR system, magnetic signals have been successfully measured that are emitted in laboratory setups of a cross-linked polyethylene (XLPE) cable section and of a gas-insulated system (GIS) with artificial discharging defects. Comparison with simultaneously detected signals from a high-frequency current transformer (HFCT) demonstrates the high sensitivity and performance of the xMR system for PD detection.@en

In practice, High-voltage (HV) cables are occasionally exposed to impulse and superimposed transient conditions, which may initiate partial discharges (PD) temporarily. Whether such PDs persist under AC voltage after the transient conditions have vanished, is at focus in the research described in this paper. Since for cross-linked polyethylene (XLPE) cables the accessories are weak links in the HV cable insulation system, we investigated the PD behavior of an artificial joint defect in a HV cable model under impulse and superimposed voltages. By applying a dedicated PD measuring system it was found that, the impulse and superimposed voltages can initiate PD in the artificial defect, which under local electrical field conditions can persist for some time. The different parameters of the applied voltages have different effects on the PD behavior.@en

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.

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This paper investigates the partial discharges (PD) at artificial defects in a cross-linked polyethylene (XLPE) insulated cable joint under superimposed voltage. The experiments are conducted on a 16-meter long 150 kV commercial XLPE cable, together with a cable joint and two terminations. Defects are fabricated on purpose in the cable joint. The cable system was subjected to a 50 Hz AC voltage, being in between PD extinction and inception values, superimposed with a lightning impulse voltage. Partial discharges are measured by two HFCT sensors at the two ends of the cable joint. The measurement results show that, the impulse voltage could trigger partial discharges. The partial discharge occurrence is mainly influenced by the time period during which the applied voltage is higher than PDIV.@en

This article contains the development of the Health Index (HI) and the Risk Assessment (RA) models for Gas Insulated Switchgear (GIS) operating under tropical conditions. A case study of 631 bays of GIS in tropics with service time from 1 up to 30 years is used during the development of the models. The basis for the HI model is the condition assessment of subsystems in GIS. This assessment translates the measured parameters from GIS subsystems into condition status based on a set of norms and rules. The condition status is presented in a score, where the non-linear scaling is chosen as it allows the poor parameters to really stand out. On the other hand, the RA model calculates the risk of a GIS major failure. The Total Failure Probability (TPF) unifies six risk indicators of GIS failures under tropical conditions. The risk may fall into one of the four categories, namely: Low, Medium, High, and Very High.@en

This paper proposes a risk assessment model for Gas Insulated Switchgear (GIS) operating under the tropical conditions. The model is a part of decision support tools at the tactical level of Asset Management in electricity network business. The model used the Asset Health Index (AHI) to estimate the likelihood of failure, while the consequences were defined by the business of a transmission utility in a case study. Risk discussed in the model is risk if a failure occurs in GIS. The output classifies the risk into five levels, namely, Very Low, Low, Moderate, High, and Very High.@en

Humid insulating gas (SF6) has been observed in a case study of 631 CB-bays of Gas Insulated Switchgear (GIS) operating under tropical conditions. The routine gas quality check in the case study reported that 20% of the non-Circuit Breaker enclosures have humidity above the value recommended by the IEEE and IEC standards. Therefore, an investigation into the flashover characteristics of a spacer in humid SF6 has been initiated in the High Voltage Laboratory of TU Delft, The Netherlands. The setup is a small model resembling the insulation system of a GIS with controlled parameters of humidity content and gas pressure. The electrical stresses in the test are AC, LI+, LI−, and SI with homogeneous, quasi-homogeneous-, and inhomogeneous field configurations. In general, the humidity does not influence the withstand strength of the spacer as long there is no condensation. When condensation occurred, the flashover voltage dropped by 28% during the test under AC at 2.6 bars, and by 38% during the test under LI+ at 2.5 bars; both with quasi-homogeneous field configuration. In the test with homogeneous field setup, the flashover voltage was dropped by 67% under LI+ at 3.4 bars. In our setup, it has also been observed that the flashover-drop due to condensation is higher than due to a 2-mm aluminum particle attached to the sample close to the high electric field region simulating the inhomogeneous field configuration.@en

In practice, cross-linked polyethylene (XLPE) power cables can be subjected to alternating voltage with superimposed impulse transients. Such impulse transients may initiate partial discharges (PD) in insulation defects even below AC inception voltage. An initiated PD may persist under AC, which will cause insulation degradation. This paper investigates the PD behavior in MV XLPE cable accessories under impulse transients. Different scenarios of PD behavior are measured, described and analyzed. Based on the results, the effects of impulse transients on PD are summarized.@en

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.

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A Health Index model (HI model) for Gas-Insulated Switchgear (GIS) operating in tropical environment has been proposed in this paper. The model has the foundation on the condition assessment of subsystems of components in GIS. The condition indicators (CI) were captured from the Routine Visual Inspection (RVI) and the Diagnostic Test and Measurements (DM) on GIS. After then, a set of "norms" translates the condition indicators into one of logarithmic-base 3 condition codes (CC), before finally converted into an index from 1 to 5. Failure Susceptibility Indicators (FSI) have also been introduced in the model. FSI might initiate an onset of a failure mode, but it is not part of the asset health index. Triggers for FSI can be due to three factors, namely, environmental, GIS’ operational experience, GIS’ design/ make. The final output of the model consists of an index and a worksheet of FSIs coded with colors.@en

Advantages of HTS cables are higher current carrying capability, very low thermal interaction with underground infrastructures, and very low external magnetic field designs. These advantages make them interesting for implementation in dense urban areas. There are several experiences worldwide with HTS cables at various voltage levels, but the long-term experience is still limited. As a result, various aspects of HTS performance, such as long-term reliability, are unclear and further study is required. This paper provides an overview of insulation materials, background, and uncertainties of recommended electrical insulation testing. The application of power law and the length effect will be discussed. This discussion may help to give direction and assure the quality of HTS cable for ongoing studies.@en

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.@en

Five types of nanofillers, namely, silica, surface-silylated silica, alumina, surface-silylated alumina, and boron nitride, were tested in this study. Nanocomposites composed of an epoxy/amine resin and one of the five types of nanoparticles were tested as dielectrics with a focus on (i) the surface functionalization of the nanoparticles and (ii) the water absorption by the materials. The dispersability of the nanoparticles in the resin correlated with the composition (OH content) of their surfaces. The interfacial polarization of the thoroughly dried samples was found to increase at lowered frequencies and increased temperatures. The β relaxation, unlike the interfacial polarization, was not significantly increased at elevated temperatures (below the glass-transition temperature). Upon the absorption of water under ambient conditions, the interfacial polarization increased significantly, and the insulating properties decreased or even deteriorated. This effect was most pronounced in the nanocomposite containing silica, and occurred as well in the nanocomposites containing silylated silica or non-functionalized alumina. The alternating current (AC) breakdown strength of all specimens was in the range of 30 to 35 kV·mm−1. In direct current (DC) breakdown tests, the epoxy resin exhibited the lowest strength of 110 kV·mm−1; the nanocomposite containing surface-silylated alumina had a strength of 170 kV·mm−1. In summary, water absorption had the most relevant impact on the dielectric properties of nanocomposites containing nanoparticles, the surfaces of which interacted with the water molecules. Nanocomposites containing silylated alumina particles or boron nitride showed the best dielectric properties in this study.@en

High current capability, good integration in urban area and zero external magnetic field are advantages of HTS cables that make them interesting for implementation in the Netherlands. So far experience with HTS cable projects is good, but still limited. Yet there is a need for a proper testing practice. Due to limited operational experience, various aspects remain to be studied. This paper focuses on electrical testing of electrical insulation, the application of power laws and the length effect. These issues are yet to be resolved, but the paper discusses their background and uncertainties. This may give direction to the ongoing studies in order to assure quality of HTS.@en

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.

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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.

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Poly(2-nonyl-2-oxazoline)80-stat-poly(2-dec-9′-enyl-2-oxazoline)20 and poly(2-dec-9′-enyl-2-oxazoline)100 can be synthesized from the cationic ring-opening polymerization of monomers that can be derived from fatty acids from renewable resources. These (co)poly(2-oxazoline)s can be crosslinked with di- and trifunctional mercapto compounds using the UV-induced thiol-ene reaction. The complex permittivity of the corresponding networks increases with the temperature and decreases with the network density. In a frequency range from 10−2 to 106 Hz and at temperatures ranging from −20 to 40 °C, the changes of the real part of the complex permittivity as well as the loss factor can be explained by interfacial polarization within the material. At a temperature of 20 °C and a frequency of 50 Hz, the permittivity of the crosslinked (co)poly(2-oxazoline)s covers a range from 4.29 to 4.97, and the loss factors are in the range from 0.030 to 0.093. The electrical conductivities of these polymer networks span a range from 5 × 10−12 to 8 × 10−9 S/m, classifying these materials as medium insulators. Notably, the values for the permittivity, loss factor and conductivity of these copoly(2-oxazoline)s are in the same range as for polyamides, and, hence, these copoly(2-oxazoline)-based networks may be referred to as “green” alternatives for polyamides as insulators in electronic applications.@en