Partial Discharge Propagation Research Articles

Partial discharge signal propagation characteristics inside the winding of oil-immersed power transformer - using the three-winding transformer model in air

The soundness of a power transformer under an operating voltage is evaluated in partial discharge (PD) test of long-duration ac withstand voltage test. To establish clear control criteria for this PD test, it is necessary to study PD propagation characteristics inside the transformer windings. In this paper, a study was conducted on PD signal propagation characteristics for an oil-immersed transformer. This involved a winding model of a three- winding transformer, or the structure of an actual transformer being produced to investigate the PD signal propagation characteristics relative to the occurrence position, measurement position, and front time of the PD as parameters. Subsequently, since a preceding study on a gas-filled transformer confirmed that an equivalent circuit of the winding could be used for analytical evaluation, an analysis model was also constructed for a three-winding model of the oil-immersed transformer in the present study to investigate the propagation characteristics. Consequently, it emerged that an analysis using an equivalent circuit could also effectively simulate the propagation characteristics, waveform shape, and transmission rate for an oil- immersed transformer. As for the transmission rate, it was found that the signal was detected as significantly damped to a level of several percent depending on the occurrence and measurement positions of the PD, as was also the case for a gas-filled transformer.

Characteristics and Development Mechanisms of Partial Discharge in SF6 Gas Under Impulse Voltages

It is well known that impulse voltages strongly affect the reliability of gas-insulated switchgear (GIS) under actual operational conditions. The alternating-current (ac) withstand voltage test and its corresponding partial discharge (PD) measurement are inadequate for the detection of all the hidden flaws in GIS. Such inadequacy can be compensated by additional impulse withstand voltage test and its PD detection measurement. However, the bulkiness and inefficiency of aperiodic impulse voltage generator make it unsuitable for on-site application. Therefore, in practical tests, oscillating impulse voltage (OIV) is generally adopted instead of aperiodic impulse voltage. In this paper, we measure the PD inception voltage (PDIV) and the breakdown characteristics of a needle-plate gap in SF6 gas under four types of impulse voltages by electrical and optical methods. The 50% probability PDIV is analyzed as a function of gas pressure. The physical mechanisms of the PD under the four impulse voltages are discussed. The PD characteristics under ac voltage are investigated for comparison. Experimental results reveal that the PD development process under the two aperiodic impulse voltages was mainly dominated by the precursor mechanism which consists of streamer and leader stages, while the PD propagation under the two OIVs was affected by the displacement current produced by oscillation. The difference of the PD characteristics under the aperiodic impulse voltage and OIV, and ac voltage are also presented.

Partial discharge characteristics and mechanism in voids at impulse voltages

Partial discharge (PD) characteristics and mechanism in artificial cavities in an epoxy plate have been investigated for different void dimensions and impulse voltage waveforms. A differential measurement system was developed in order to detect PD current pulses effectively. Experimental results showed that the 50% probability PD inception voltage (PDIV50) increases initially as the cavity diameter decreases at constant depth for double exponential impulses as well as oscillating impulses, but after aging, it becomes independent of the cavity diameter. Moreover, some distinctive characteristics of PD (e.g. main discharge and reverse discharge during the rise and fall phases of the applied voltage) were also investigated. The differences of the PD propagation and the mechanism between double exponential impulses and oscillating impulse were discussed.

Time variation of partial discharge activity leading to breakdown of magnet wire under repetitive surge voltage application

This paper discusses partial discharge (PD) propagation, degradation and lifetime characteristics of magnet wires for inverter-fed motor under surge voltage application. Experimental results showed the time variation of PD activity, i.e. intermittent PD, successive PD, critical PD and breakdown (BD), under repetitive surge voltage application with a fixed peak value. Critical PD was a drastic change of PD activity and was identified as the partial BD of magnet wires. Since the final BD was confirmed to be always induced at the critical PD location, the critical PD was regarded as an important indicator to determine the lifetime of magnet wires. The experimental results also clarified that the lifetime of magnet wires could be determined by the total number of PD generation from its inception to breakdown. PD activity was interpreted by the time transition of PD generation frequency, and its mechanisms were discussed.

Partial discharge activity in electrical insulation for high temperature superconducting (HTS) cables

This paper discusses electrical insulation characteristics of liquid nitrogen (LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) / polypropylene (PP) laminated paper composite insulation system for the practical electrical insulation design of high temperature superconducting (HTS) cables. Partial discharge (PD) inception, propagation and breakdown (BD) characteristics under ac voltage application were obtained and discussed at atmospheric and pressurized conditions. Experimental results were analyzed quantitatively and revealed that void- type discharge was categorized as an important form of discharge to characterize the transition of PD activity leading to BD.

모의 GIS의 전기적 이상에 따른 방사전자파의 특성과 절연진단용 UHF 센서 설계

본 논문에서는 모의 GIS 내부에 도전성 파티클, 미소돌기, 연면방전을 모의함으로 전하의 축적과 전계의 집중이 용이하도록 하여 부분방전을 모의하였다. 이때 부분방전 발생과 진전에 따른 방사전자파를 스펙트럼 분석기와 EMIㆍEMC 측정용 안테나(30~2,000[㎒])를 사용하여 측정ㆍ분석하였다. 이러한 결과를 바탕으로 0.3[㎓]에서 1.7[㎓]대역에서 UHF법을 활용한 절연진단이 가능한 UHF 구형 센서를 설계하였다. 이러한 연구결과는 SF?를 사용하는 실제 GIS 및 전력설비의 UHF 절연진단 시스템에 적용 가능한 UHF 진단센서로 활용할 수 있을 것이다.

모의 GIS 내부에 도전성 이물질 존재시 부분방전 진전에 따른 전자파 측정에 의한 절연진단연구

본 논문에서는 모의 GIS 내부에 도전성 파티클을 놓아둠으로써 전하의 축적과 전계의 집중이 용이하도록 하여 부분방전을 모의하였다. 이때 부분방전 발생과 진전에 따른 방사전자파를 스펙트럼 분석기와 EMIㆍEMC 측정용 안테나(30~2000[㎒])를 사용하여 측정ㆍ분석하였다. 모의 GIS 내부에 도전성 파티클 존재에 따른 부분방전의 검출과 방진전전 과정의 판단을 위한 절연진단의 방법으로써 본 논문에서 제안한 측정 주파수의 대역의 분리와 데이터 측정과 분석법을 이용하면 부분방전의 검출과 방전과정의 판단이 가능함을 확인하였다.

Dispersion and PD detection in shielded power cable [Feature article

Dispersion, the variation in propagation velocity with frequency, is one of those phenomena that people in the field of partial discharge (PD) detection have talked about since at least the early 1980s, but which is lacking a formal treatment in the literature. When one of the authors recently published an analytic theory of PD propagation in shielded power cable, both reviewers said "dispersion, dispersion". They believed that dispersion was important but gave no evidence for that assertion. In fact, as shown below, dispersion in shielded power cable has little if any impact on measurement of PD magnitude because the Fourier components of the pulse attenuate to insignificance before they can disperse to a degree that would cause appreciable change in the peak pulse amplitude or integral of the pulse waveform. However, dispersion does cause some distortion of the pulse shape that has implications for PD location, as it has a second-order effect on the timing of the peak PD amplitude relative to other pulses in the pulse train caused by multiple reflections from the ends of the cable. A Gaussian PD pulse in the time domain will have a Fourier spectrum that is also Gaussian in the frequency domain. If the Fourier components in the frequency domain propagate down the cable at differing velocities, the waveform to which they add will vary as a function of distance propagated, and the energy in the PD pulse is likely to spread out in time, which would have an effect on wide band PD detection no matter what the means of detection.

Technical Development on Partial Discharge Measurement and Electrical Insulation Techniques for Low Voltage Motors Driven by Voltage Inverters

This paper reviews the up-to-date research activities on electrical insulation techniques under repetitive surge voltages with steep wavefront for low voltage inverter-fed motors. Partial discharge (PD) inception, propagation, ageing and breakdown characteristics of magnet wires, including recently developed PD-resistant wires such as nanocomposite enameled wires, are described. PD measurement techniques under the steep-front voltages and IEC activity toward their standardization are also introduced.

Partial Discharge Pulse Propagation in Shielded Power Cable and Implications for Detection Sensitivity

Boggs and Stone (1982) defined the fundamental limits to the electrical detection of corona and partial discharge (PD), i.e., wideband detection of a PD-induced pulse in the presence of thermal noise. This paper treated the effect of frequency-dependent attenuation in shielded power cable in that context. However, most of the plots in that paper were the result of numerical computations. In the same year, Stone and Boggs set out a theory for high-frequency attenuation of shielded power cable. They showed good agreement between attenuation predicted from measured material properties and measured, high-frequency attenuation of shielded power cable. Since 1982, measurements of high-frequency cable attenuation have been reported by a number of authors for a variety of cables. In addition, software tools have become available that facilitate an analytic solution for the parameters of interest. This article summarizes the theory for PD propagation in shielded power cable for both symmetric (Gaussian) and asymmetric PD-pulse waveforms, based on the assumption that the attenuation constant (dB/m or Nepers/m) of the cable is proportional to frequency. This appears to be the most complete possible analytic exposition of PD attenuation in shielded-power cable, which has obvious applications to field PD measurements of such cable.

Bandwidth and sensitivity issues in PD detection in power cables

An investigation on partial discharge (PD) propagation in power cables is carried out in this paper with the aim of inferring limits for PD detection as a function of the distance between PD source and detector. Although this problem has not an exact solution unless noise levels are not specified, useful information concerning detectability and error in estimates are provided in this paper for both medium and high voltage polymeric cables. The issue of calibrator characteristics with respect to sensitivity detection is also tackled.

Determination of Partial Discharge Propagation and Location in Transformer Windings Using a Hybrid Transformer Model

Experimental experiences prove that partial discharge (PD) is a major source of inner insulation system failure in power transformers. If the deterioration of the insulation system caused by PD activity can be detected at an early stage, preventive maintenance measures may be taken. Due to the complex structure of the transformer, accurate determination of PD location is one of the major challenges in front of power utilities. This problem comes to be vital in open access systems. A hybrid transformer model and its application for locating partial discharge and studying its propagation along the transformer windings are proposed in this article. It is based on the structural data of the transformer for equivalent model parameters determination. The lumped parameter equivalent model for winding sections is constructed satisfying the quasi-static condition. Then an algorithm is developed to use the constructed matrices for PD propagation and location studies by application of the multi-conductor transmission line equivalent model. The results of the study are presented for a 66 kV/25 MVA transformer with fully interleaved winding.

Partial discharge inception and propagation characteristics of magnet wire for inverter-fed motor under surge voltage application

In this paper, we investigated the PD generation, propagation, degradation and breakdown (BD) characteristics of magnet wire for inverter-fed motor under surge voltage application. Experimental results revealed the transition of PD activity, i.e. intermittent PD, successive PD, critical PD and BD, under repetitive surge voltage application with a fixed peak value. The transition from intermittent PD to successive PD was associated with the PD propagation along the enamel surface into the lower electric field region. Critical PD was a drastic change of PD activity and identified as the local BD of magnet wire. Since the final BD was confirmed to be always induced at the critical PD location, critical PD was regarded as an important indicator to determine the life of magnet wire for inverter-fed motor.

Streamer and leader discharge propagation characteristics leading to breakdown in electronegative gases

This paper describes the propagation characteristics and mechanisms of partial discharge (PD) leading to breakdown (BD) in electronegative gases such as SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> /N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2 </sub> F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> /N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> gas mixtures for AC voltage application. An established PD measuring system of highly time-resolved PD current and light intensity waveforms, streak and light emission images enabled us to discuss the physical mechanisms of PD generation and propagation in terms of space charge behavior. Experimental results revealed that the time-resolved PD generation was divided into different groups composed of the first large PD and the subsequent small PDs; the former was identified as the leader discharge, and the latter corresponded to the streamer discharges. The successive generation of the streamer and leader discharges was interpreted by the change of critical volume size. The time-resolved PD generation characteristics leading to BD were also measured and discussed. The leader discharge would be obliged to take a detour along the periphery of the positive space charge area in the vicinity of the needle electrode, and finally result in BD in electronegative gases

The Study of PD Propagation Phenomenon in Power Network

This paper presents the measured and analyzed responses of the partial discharge (PD) when it propagates in a power network from its origin to the measuring nodes. On and offline measurements are done in a power network consisting of a 16.5-kV/250-MVA-rated power generator, busbar, and step-up transformer. The simultaneously measured PD at two ends of the busbar indicated that the intensity of PD decreased as it traveled a longer distance and the time interval of its occurrence had a finite delay indicating the dominant mode of PD propagation as a transmission line. Frequency-domain analysis indicated the presence of characteristic resonance frequencies and the number increased as the measuring node moved away from the PD origin. The offline measurement by injecting an exponential PD signal at the neutral indicated that the signal will be absorbed in the generator, and the signal at the measuring node will be attenuated by 50 times and will be distorted. Pspice simulation is used to develop the network model for the propagation path. The Pspice analysis indicated that the distributed models of generator, busbar, and lumped parameter models of a transformer can be used to match the offline measurement. The model showed that each model can have the characteristic resonant peaks depending on the selected parameters and it can distort the simultaneously observed PD at two different nodes.

Rigidité diélectrique d'un interface gaz–support avec contaminant métallique dans l'air sec et ses mélanges avec le SF6

In this paper, we conduct a series of experiments aimed at analysing the dielectric properties of compressed dry air, and some SF6–air mixtures up to 700 kPa, under application of AC 50 Hz and lightning impulse (LI) 1.2 μs/50 μs voltage. The investigations were carried out by using a cylindrical spacer model with an adhering particle on the surface under homogenous field conditions. We measure the partial discharges (PD) propagation characteristics under LI voltage stress, as well as the PD inception voltage and the flashover voltage for the contaminated particle. We also investigate the surface charge accumulation on the spacer surface under contaminated particle conditions. The results of the experiments reveal the influence a conducting particle has on the determined flashover field strength, for SF6–air mixtures compared with pure, compressed dry air. This influence is discussed for different particle lengths, but also for three different particle positions in the gap. Pure dry air achieves a higher dielectric strength when the particle gets into contact with the high voltage electrode, under negative LI voltage stress. The same result is obtained for the SF6–air mixtures, when the particle is located in the middle of the gap, as floating electrode on the spacer surface. The reported results contribute to the improvement of the models of breakdown through the interface gas–solid isolator. The application of these models should offer the possibility for considering the use of dry air, or its mixtures with SF6 which, normally have a lower relative global warming potential than pure SF6.[Traduit par la Rédaction]

Impulse partial discharge characteristics and their mechanisms under non-uniform electric field in N/sub 2//SF/sub 6/ gas mixtures

We have investigated impulse partial discharge (PD) and breakdown (BD) characteristics of a needle-plane gap in N/sub 2//SF/sub 6/ gas mixtures under positive lightning impulse voltage application, and discussed their physical mechanisms. The 50% probability PD inception voltage (PDIV/sub 50/), leader discharge onset voltage (LOV) and BD voltage (BDV/sub 50/) were measured and analyzed as a function of gas pressure and SF/sub 6/ content. Experimental results revealed the stepwise propagation process of the impulse PD and enabled us to classify the impulse PD in N/sub 2//SF/sub 6/ gas mixtures into two types, the streamer discharge and the leader discharge. We also discussed the impulse PD propagation mechanisms in terms of PD parameters such as propagation length, time interval and current pulse magnitude, and suggested a sequential relationship in the PD propagation process under non-uniform electric field.

모의 GIS 내부에 유전체 파티클 존재시 부분방전 진전에 따른 방사전자파의 특성

In this paper partial discharge were simulated by insulation particle which could be easy accumulated charge and concentrated electric field in the model GIS. In this times this paper measured and analyzed the radiated electromagnetic waves by using spectrum analyzer and antenna for measurement of in accordance with occurrence and propagation of partial discharge. This paper suggested the other method of detecting and estimating of partial discharge for insulation diagnosis of GIS being insulation particle by measurement and analysis of radiated electromagnetic waves. From results of this study, it was confirmed that if the suggested method should be used for the diagnosis of insulation in the model GIS being insulation particle, detecting partial discharge and estimating discharge propagation will be possible.

Investigation of propagation of partial discharges in power transformers and techniques for locating the discharge

The location of partial discharges in a power transformer can be determined based on the characteristics of the transfer function from the discharge source to the measuring terminal. Previous studies partially validated the technique using computer simulation and practical experiments based on a PD calibrator to represent a discharge signal. 'Real' discharges produced by insulation defect models were used to study how discharges propagate in an 11 kV plain-disc-type transformer winding: A corona model and a 'floating objects in oil' model produced discharge signals with different durations at various locations along the winding. Measurements were taken at the tap of the bushing capacitance through a conventional discharge detector. The signals were filtered, amplified and fed into a digital storage oscilloscope. The frequency spectra of the measured signals showed significant similarities irrespective of the type of discharge source. The characteristic of the transfer functions, i.e. the crests and troughs in the spectra, could be used for locating the source of the discharge. Energising the transformer increased the level of electric noise, which did affect the low frequency end of the spectra, but did not have any impact on the characteristics used for location.

The contribution of discharge area variation to partial discharge patterns in disc-voids

Experimental ac partial discharge (PD) patterns are presented for a disc-void (area greater than length) with metal surfaces, one metal and one insulating surface, and with both surfaces insulating. These patterns indicate that the portion of the surface over which the charge is deposited (discharge area) plays an important role in producing the fluctuations in discharge magnitude commonly observed for such voids. A simulation model for PD patterns in voids is presented, which expressly includes the effects of the charge distribution left on the void surface by consecutive PDs. This model defines two factors that control the PD propagation. These are: a minimum field required to maintain the discharge within an existing surface path Ein and a minimum peripheral field required to extend the discharge path Ep. There is also one other factor, the occurrence probability that controls the incidence of the PD. It is shown that the model gives a variation in PD magnitude throughout the active region of phase without any stochastic factors, i.e. when only variations in the discharge areas are allowed for, but that in order to reproduce the typical (turtle-like) PD patterns observed for the disc-void with insulating interfaces the occurrence probability and surface conductivity have to be included. The current model is compared to previous models and the relationship of the model factors to the change of PD patterns with ageing is briefly discussed.