From a Novel

To ensure the power system operates safely and reliably, it is essential to monitor and evaluate the health condition of power equipment on-line or off-line. This study reviews the research status in condition monitoring and diagnosis of power equipment, including transformer, gas insulated switchgear, cable, external insulation, generator, and power capacitor in recent years. Although much progress has been made in technologies of condition monitoring and fault diagnosis such as test accuracy, fast and accurate fault localisation and recognition of fault types, there are still many deficiencies which needs further research work, including the reliability of signal collection from sensors, the accuracy of data treatment and analysis, anti-interference performance of test equipment, appropriate models used for condition evaluation. The prospective of condition monitoring and diagnosis technologies of power equipment are also presented in this study. It is proposed that the application of big data, internet of things and cloud computing should be expected and given special attention in the near future.

Condition monitoring and diagnosis of power equipment: review and prospective

In this paper, a Ni-doped MoS₂ monolayer (Ni-MoS₂) has been proposed as a novel gas adsorbent to be used in SF₆-insulated equipment. Based on the first-principles calculation, the adsorption properties of Ni-MoS₂ to SO₂ and H₂S molecules, the main decomposition components of SF₆ under a partial discharge (PD) condition have been studied. The adsorption energy, charge transfer, and structural parameters have been analyzed to find the most stable gas-adsorbed Ni-MoS₂. Furthermore, the density of states (DOS), projected density of states (PDOS), and electron density difference were employed to explore the interaction mechanism between SO₂, H₂S, and the Ni-MoS₂ surface. It is found that the H₂S molecule and SO₂ molecule interact with the Ni-MoS₂ surface by strong adsorption energy. Therefore, we conclude that the interaction between these two kinds of gases and the Ni-MoS₂ monolayer belongs to chemisorption, and the Ni-MoS₂ monolayer might be a promising gas adsorbent for the fault recovery of SF₆-insulated equipment. Additionally, we have to point out that all of the conclusions only considered the final adsorption energy, the barrier in the transition state has not been analyzed in this paper.

https://www.mdpi.com/2079-4991/8/9/646/pdf

A DFT Study on the Adsorption of H₂S and SO₂ on Ni Doped MoS₂ Monolayer

Power utilities are struggling to reduce power failure incidents in substations and their components to operate more reliably and economically [1]. Many power failures are produced directly or indirectly because of the insulation system of utility components [2], [3]. The selection of the insulation should ensure power plant operational continuity along with completely resolving or significantly limiting the actual power system's failures [4]. Gas insulated substations (GIS) have the best insulation performance which ensures achieving minimum failure incidents, although at high installation cost. The most common insulating gas used in GIS is Sulfur hexafluoride (SF 6 ) gas, which is widely used as an effective electrical insulation as well as an arc-quenching medium [5]. Basic GIS and gas insulated transmission lines (GITL or GIL) consist of a conductor supported by solid insulators inside an enclosure filled with SF 6 gas or its mixture [6].

Partial discharge detection and diagnosis in gas insulated switchgear: State of the art

The condition of the internal cellulosic paper and oil insulation are of concern for the performance of power transformers. Over the years, a number of methods have been developed to diagnose and monitor the degradation/aging of the transformer internal insulation system. Some of this degradation/aging can be assessed from electrical responses. Currently there are a variety of electrical-based diagnostic techniques available for insulation condition monitoring of power transformers. In most cases, the electrical signals being monitored are due to mechanical or electric changes caused by physical changes in resistivity, inductance or capacitance, moisture, contamination or aging by-products in the insulation. This paper presents a description of commonly used and modern electrical-based diagnostic techniques along with their interpretation schemes.

Electrical-Based Diagnostic Techniques for Assessing Insulation Condition in Aged Transformers

In this paper, to effectively distinguish between the aging and moisture of oil-immersed paper (OIP), and to enhance the accuracy of the nondestructive diagnosis of the insulating state for oil-paper insulation, we perform an in-depth study of the frequencydomain dielectric response theory. First, we present a theoretical explanation for frequency-domain spectroscopy (FDS) based on investigations into the mechanism and characteristics of conductivity loss and polarization loss. Secondly, we explore the classical loss characteristics by performing a systematic analysis of the relationship between the complex dielectric permittivity and the frequency based on the measured FDS curves. Finally, we study the influences of the aging condition and moisture content on FDS. We extract some of the characteristic parameters that are related to the insulation condition. The results obtained indicate that at low frequencies, the FDS characteristic was mainly influenced by the conductivity loss, which may be explained by the Dyre model. At high frequencies, the characteristic was mainly influenced by the polarization loss, which may be explained by the H-N model. In addition, the characteristic at mid-range frequencies was due to both the conductivity and polarization loss. The moisture content significantly affects only the conductance process. Therefore, the characteristic parameter, namely the DC conductivity σ 0, which is closely related to the conductance process, can be used to quantitatively describe the moisture content of OIP. Meanwhile, the characteristic parameters α, β, and τ, which are associated with the polarization process, can be used to quantitatively describe the aging status of OIP.

Explanation and analysis of oil-paper insulation based on frequency-domain dielectric spectroscopy

Partial discharge (PD) detection is essential to the operation of high-voltage systems. In this context, we investigate the basic characteristics of light emission during PDs in SF6 gas from the perspective of insulation diagnosis. A synchronous system is constructed using three optical photoelectric instruments with separate wavelength responses in the ultraviolet (UV, 189–352 nm), visible (VIS, 381–675 nm), and near-infrared (NIR, 737–920 nm) spectral ranges and a wide-band PD current pulse detector with a response of 1 pC. The results indicate that light emission depends upon the type of insulation defect and discharge energy. An increase in PD charge gives rise to more components in the spectral range from UV to VIS, and the presence of an insulator surface in discharges yields a more complex VIS-to-NIR spectrum. The phase-resolved partial discharge pattern (PRPD) of UV light pulses can reasonably reflect the electroluminescence process in the presence of the insulator surface and weak corona at negative voltage points. The PRPD of VIS light describes the features of the actual PD pattern in most cases. In comparison with the other two spectral ranges, light intensity in the VIS range is more sensitive to changes in gas-pressure-normalized voltage (Vrms/p). The linear fitting analysis of the relationships between the light intensity and PD charge shows that UV light detection has a greater sensitivity to the PD charge and that UV detection exhibits a greater degree of linearity. NIR detection is applicable only to severe PDs. We believe that our findings can significantly aid in application of optical PD diagnosis in SF6 gas insulated systems.

Statistical Analysis of Partial Discharges in SF6 Gas via Optical Detection in Various Spectral Ranges

The invention discloses a portable partial discharge detecting and diagnosing device. The device comprises a partial discharge detector, a cable, a pre-sensor and a charger device, wherein the partial discharge detector comprises a lower computer and an upper computer; the lower computer comprises a simulation unit module, an FPGA module, an ARM module, a clock and reset module and a power management module; the upper computer is a Linux industrial personal computer. The portable partial discharge detecting and diagnosing device is provided with a 14-bit 100MHz two-channel acquisition system having the maximum storage depth of 64Mbit; the display of the characteristic spectrum of defects and the model identification of faults can be completed accurately in such a manner of PRPD clustering analysis in combination with impulse waveform time-frequency analysis; meanwhile, a radio-frequency sensor and an ultrahigh-frequency sensor are simultaneously provided, and the pulse current detection and the ultrahigh-frequency detection on primary equipment can be completed by replacing the pre-filter; the device is small in volume, light in weight, and capable of supplying power to a battery and convenient for field live testing and polling of a transformer.

Portable partial discharge detecting and diagnosing device

This study focuses on partial discharges (PDs) in the gaseous void in an insulator under aperiodic switching impulse (SI) and oscillating SI (OSI). The PD measurements are carried out using a 110-kV GIS model with an artificial known void defect in a basintype insulator. Experiments show that the PD sequences under SI and OSI are composed of the main discharge, which occurs at the rising edges or the peaks of the applied impulse, and the polarity reverse discharge, which occurs at the falling edges or troughs. For a new sample, the 50% PD inception electric field (PDIE50) under different stress types obviously decreases with increasing void radius, and their values follow the pattern PDIE50, OSI > PDIE50, SI > PDIE50, AC. For an aged sample, the difference between the experimental PDIEs and the streamer inception value becomes close. The relationships between the time lag and the applied voltage can be calculated by the V–t curves, which roughly describe the distribution of the time lag under impulses. The experiment indicates that OSI can more easily excite PD compared with SI. Repeated tests show that the magnitudes and numbers of the main and reverse PDs gradually change as the test is repeated.

Partial discharges in void defect of gas insulated switchgear insulator under standard aperiodic and oscillating switching impulses

The invention discloses a partial discharge measurement device for a GIS device under site impulse voltage. The device is used for conducting partial discharge measurement on the GIS device when the GIS device conducts site impulse withstand voltage experiments, the device is used for detecting insulation defects which may exist in the GIS device, and the reliability of the safe operation of the GIS device is improved. The partial discharge measurement device comprises open-loop type rogowski coil sensors, a double-layer shielding cable, a signal differentiator, a signal summer, an attenuator assembly, a filter assembly, a transient voltage clamp device, an I/O data acquisition card and software for measuring and analyzing partial discharge under impulse voltage. The partial discharge measurement device suitable for the GIS device on a site can accurately measure pulse current waveforms of partial discharge, can also more actually obtain the discharge amount of a device with an insulation defect, and has a great significance to evaluation on the insulation condition of the device.

Jialin Liu

Papers

Explanation and analysis of oil-paper insulation based on frequency-domain dielectric spectroscopy

Statistical Analysis of Partial Discharges in SF6 Gas via Optical Detection in Various Spectral Ranges

Portable partial discharge detecting and diagnosing device

Partial discharges in void defect of gas insulated switchgear insulator under standard aperiodic and oscillating switching impulses

Partial discharge measurement device for GIS device under site impulse voltage