Showing papers on "Partial discharge published in 2018"

A review of condition monitoring techniques and diagnostic tests for lifetime estimation of power transformers

Abstract: Power transformers are a key component of electrical networks, and they are both expensive and difficult to upgrade in a live network. Many utilities monitor the condition of the components that make up a power transformer and use this information to minimize the outage and extend the service life. Routine and diagnostic tests are currently used for condition monitoring and appraising the ageing and defects of the core, windings, bushings and tap changers of power transformers. To accurately assess the remaining life and failure probability, methods have been developed to correlate results from different routine and diagnostic tests. This paper reviews established tests such as dissolved gas analysis, oil characteristic tests, dielectric response, frequency response analysis, partial discharge, infrared thermograph test, turns ratio, power factor, transformer contact resistance, and insulation resistance measurements. It also considers the methods widely used for health index, lifetime estimation, and probability of failure. The authors also highlight the strengths and limitations of currently available methods. This paper summarizes a wide range of techniques drawn from industry and academic sources and contrasts them in a unified frame work.

Distributed Partial Discharge Detection in a Power Transformer Based on Phase-Shifted FBG

Abstract: To overcome the low sensitivity of power transformer partial discharge (PD) detection by a lead zirconate titanate (PZT) sensor, we propose a novel PD detection system based on phase-shifted fiber Bragg gratings (PS-FBG). Compared with the conventional method, the proposed sensor can be installed inside the power transformer, which takes the advantage of the optical fiber status as an insulator. Distributed PD detection is achieved using wavelength and time-division multiplexing. Frequency response experiments indicate that the sensitivity of the PS-FBG is 8.46 dB higher than that of the conventional ultrasonic sensor. Moreover, a PD detection experiment shows that the PD sensitivity of the PS-FBG immersed in oil is 17.5 times higher than that of the PZT sensor. Furthermore, the multiplexing and the feasibility of defect localization of the proposed distributed PD detection system are demonstrated.

Critical analysis of partial discharge dynamics in air filled spherical voids

Abstract: In this paper partial discharge (PD) is investigated inside a spherical air filled void at atmospheric pressure using a drift diffusion model. Discharge dynamics consisted of an electron avalanche transitioning into positive streamer, in agreement with earlier work on dielectric barrier discharges. Different model configurations were utilised to test many of the concepts employed in semi-analytical PD activity models, which use simplistic descriptions of the discharge dynamics. The results showed that many of these concepts may be erroneous, with significant discrepancies between the canonical reasoning and the simulation results. For example, the residual electric field, the electric field after a discharge, is significantly lower than the estimates used by classical PD activity models in the literature.

Partial discharge behavior and ground insulation life expectancy under different voltage frequencies

Abstract: Power electronic transformers, namely solid state transformers, have aroused a widespread attention due to the integration issue of large scale renewable energy in modern power system. High frequency power transformer (HFPT) is one of its key components operating at several to tens of kHz. Under such high frequency voltage, accelerated insulation aging and premature insulation failure occur frequently. Partial discharge (PD) is considered as the main cause of electrical performance deterioration in HV systems or LV ones where overvoltage or surge may occur. Therefore, it is necessary to study the PD behavior and insulation life under different voltage frequencies, in order to have a better understanding of premature failure mechanism. In this paper frequency dependence of space charge and PD properties is firstly analyzed theoretically and mathematically, followed by the results of electrical aging tests conducted on polyimide (PI) films that were subjected to surface PDs under 5–30 kHz sinusoidal voltage. Discharge characteristics and lifetime of PI film under different frequencies have been discussed, along with the correlation between lifetime and PD. Both theoretical analyses and experimental results show that average PD amplitude and total PD number per cycle increase first and then decrease afterwards with voltage frequency, which means that the frequency induced inflection phenomenon exists in the tested frequency range. Synergistic action of high frequency induced thermal effect and reduced space charge dissipation time under high frequency is the reason for this novel phenomenon. Besides, strong linear correlation has been found between lifetime and PD characteristic—total PD amplitude per second, which reveals the accelerated aging mechanism under high frequency electrical stress.

A review of partial discharge detection, diagnosis techniques in high voltage power cables

Abstract: Partial discharges (PDs) are the first indication of insulation materials degradation. This paper provides a general review on partial discharge in power cables. It starts with discussing the importance of PD detection and its effect on the continuity of operation and reliability of power systems. It then provides a description of the insulation explaining the process that leads to its breakdown. The stresses on the voids inside the power cable are explained and the equivalent circuit is discussed. The paper then discusses the most common methods to detect the partial discharge off-line and on-line, specifically in power cables. Methods of location of partial discharge inside the power cable are discussed as well. The most common signal de-nosing techniques are also briefly explained. Lastly, a deep insight of the current challenges and difficulties in PD detection and monitoring are provided.

Influence of impulse voltage repetition frequency on RPDIV in partial vacuum

Abstract: The reliability of low-voltage inverter-fed motors is highly dependent on the inception of partial discharges. The effect of impulsive waveform parameters must be investigated to predict the repetitive partial discharge inception voltage (RPDIV) and define test procedures that can indicate properly the behavior in service of the insulation system. This paper focuses on the RPDIV of magnet wires using twisted pairs subjected to repetitive unipolar impulsive voltage waveforms. The effects of supply frequency (5 to 200 kHz) at pressure levels that are typical for aircraft (20 to 100 kPa) is examined. Results show that RPDIV steadily decreases with frequency up to 100 kHz where it reaches a plateau. This behavior is explained as an effect of the oscillations that inevitably exist in the applied voltage waveform. Therefore, a conservative estimate of the RPDIV could be achieved by raising the supply frequency well above the operation frequency. In the experiments, the RPDIV is decreasing linearly with pressure. If this behavior could be confirmed for other insulation systems, the design of systems working at pressures typical of aircraft would result relatively easy.

Measurements on partial discharge in on-site operating power transformer: a case study

Abstract: This study presents the case study of a substation in-service power transformer referred to the on-site partial discharge (PD) detection and evaluation methods. An original methodology for simultaneous application of three methods is proposed: electrical, acoustic and ultra-high frequency. Transformer is powered by the power grid and no external generator is required according to the proposed methodology. Furthermore, several possibilities of applying these concurrent measurements and benefits of such solution in terms of result interpretation, interference resistance and on-site measurement applicability are indicated. The proposed methodology allows for a fast, accurate and secure PD diagnostics in a power transformer under on-site operating conditions. In the described example, a failure as a surface PD in the vicinity of the first phase of high voltage winding output is detected. The research results provide the basis for further works on a diagnostic expert system, which exploits automatic detection and evaluation of the PD phenomenon in power transformers under normal operating conditions.

Application of UHF method for partial discharge source location in power transformers

Abstract: This paper presents a theoretical study relating to partial discharge (PD) source localization in high voltage power transformers using UHF technique. It also includes a brief review of typical PD sources, continuous UHF-based monitoring system, and some suitable UHF sensor types. Using MATLAB calculations and some basic assumptions, the differences in potential accuracy of PD source location are shown for different numbers of sensors, including the influence of sensor position. In addition, in the case of four UHF sensors, other effects were taken into accounts such as background noise sources, signal attenuation, multivariate wavelet denoising and the first peak detection method. By using the programs, at first, it is shown how to find the corresponding loci on which a PD source can be expected to lie by means of two and three UHF sensors in power transformers. Furthermore, using four sensors, it is presented on two different examples how simulated UHF signals, which travel from the partial discharge source to individual UHF sensors, can be used to find a partial discharge source position with sufficient accuracy. Multivariate wavelet transform was applied to the simulated signals in order to remove noise from the signals, and thus to reduce a localization error. The first peak detection method was applied to two various presumed shapes of UHF signal, in order to find time differences of arrival between related signals at the sensors. The corresponding results of partial discharge source location were analyzed and compared.

High sensitivity detection of partial discharge acoustic emission within power transformer by sagnac fiber optic sensor

Abstract: Partial discharge acoustic detection is an important monitoring tool for power transformer diagnosis, which was traditionally performed by mounting the piezoelectric transducers on the oil tank surface. The disadvantage of partial discharge acoustic detection is its low sensitivity when partial discharge occurs inside the winding, which greatly compromises the value of partial discharge acoustic detection. Fiber optic sensors that can be deployed within power transformer are expected to be a potential solution. In this research, we used a Sagnac fiber sensor system built in lab to investigate the benefits of using fiber optic sensor for partial discharge acoustic detection. Acoustic pulses were induced in oil outside the winding and in oil duct inside the winding of a single phase 50 kV transformer. Although both fiber optic sensor and piezoelectric sensor can effectively detect the acoustic pulses outside the winding, fiber optic sensor gained a much better sensitivity over piezoelectric transducer to detect the acoustic pulses originated inside the winding. We envisage that the proposed fiber sensor can be deployed in power transformers to significantly enhance the detection performance of acoustic emission induced by partial discharge.

Recognition of multiple partial discharge patterns by multi-class support vector machine using fractal image processing technique

Abstract: Partial discharge (PD) measurement is an efficient method for condition monitoring of insulation in high-voltage (HV) power apparatus. Generally, phase-resolved PD (PRPD) patterns are commonly used to identify the PD sources. It is clearly recognised that there is a correlation between the PD patterns and the insulation quality. However, in the case of multiple PDs, the PRPD patterns partially overlapped in nature, which results in difficult to identify the types of partial discharges. In this proposed methodology, a combined algorithm of different edge detection methods with box-counting fractal image compression technique is used for fractal feature extraction. The extracted features used as the input vector for the classifiers for PD recognition. To evaluate the performance of the proposed methodology, artificially multiple PD sources are simulated in HV laboratory. The result of this proposed work shows better recognition for canny edge detected fractal features implemented with user define kernel multi-class nonlinear support vector machine which can be further used to assess the insulation properties for practical implementation in power industry.

Electrical tree growth and partial discharge in epoxy resin under combined AC and DC voltage waveforms

Abstract: The effect of DC bias on electrical tree growth and partial discharge (PD) characteristics in epoxy resin (Araldite LY® 5052/Aradur® HY 5052 supplied by Huntsman) is investigated using three waveforms: AC, AC with positive DC bias, and AC with negative DC bias. Needle-plane samples are used. Tree growth is shown to be accelerated by the combined effect of DC and 50 Hz AC, beyond the AC growth rate. Positive and negative DC biased tests result in 62% and 54% reductions in average time to breakdown, respectively. Different tree structures and stages of development are associated with different partial discharge characteristics, with thick dark tree branches associated with high PD magnitudes, whereas fine tree channel growth is linked with PD magnitudes below 1 pC. AC tests showed five distinct stages of tree growth compared to four stages seen in DC biased tests. In particular, trees growing in the ‘reverse direction’ from the planar to the point electrode, which is observed in the latter stages of AC tests, is not seen in the DC biased tests. It is concluded that for composite voltages, the AC component is the essential driver of tree growth but the DC component can accelerate propagation. AC noise may therefore compromise the reliability of insulation in HVDC networks.

Localization of partial discharge in transformer oil using Fabry-Pérot optical fiber sensor array

Abstract: Partial discharge is the main reason for insulation deterioration and failure of high voltage electrical asset. Thus, the online detection and localization of partial discharge can provide the information on the equipment degradation characteristics, and moreover, is of great value for improving the safe operation of the power grid and the developing of optimal maintenance. Accounting for the good sensitivity, the high immunity to electromagnetic interference, the compact size with outstanding insulation level, the Fabry-Perot optical fiber sensor is attracting increasing attention as a promising way for online acoustic partial discharge localization. In this study, the partial discharge localization in the transformer oil is realized by an ultrasonic detection system, which is consisting of 2×2 Fabry-Perot optical fiber sensor array with steered response power algorithm. In general, the Fabry-Perot optical fiber acoustic sensor array shows good direction sharpness, and achieves accurate localization. This detection and localization system is further applied to a 35 kV transformer single-phase winding and verified with partial discharges on the outer winding.

Partial Discharge Ultrasound Detection Using the Sagnac Interferometer System.

Abstract: Partial discharge detection is crucial for electrical cable safety evaluation. The ultrasonic signals frequently generated in the partial discharge process contains important characteristic information. However, traditional ultrasonic transducers are easily subject to strong electromagnetic interference in environments with high voltages and strong magnetic fields. In order to overcome this problem, an optical fiber Sagnac interferometer system is proposed for partial discharge ultrasound detection. Optical fiber sensing and time-frequency analysis of the ultrasonic signals excited by the piezoelectric ultrasonic transducer is realized for the first time. The effective frequency band of the Sagnac interferometer system was up to 175 kHz with the help of a designed 10 kV partial discharge simulator device. Using the cumulative histogram method, the characteristic ultrasonic frequency band of the partial discharges was between 28.9 kHz and 57.6 kHz for this optical fiber partial discharge detection system. This new ultrasound sensor can be used as an ideal ultrasonic source for the intrinsically safe detection of partial discharges in an explosive environment.

A new approach to partial discharge detection under DC voltage

Abstract: The continuing development of HVDC power transmission systems presents many problems related to evaluation of the reliability of power system assets [1]-[5]. In this context the identification of insulation defects plays a key role in preventing unexpected failures of electrical components. Partial discharge (PD) measurement is a useful approach to assessing the condition of HV power apparatus and cables. Such measurements are also widely employed for HVAC systems. The inception mechanisms of PD in AC systems are well-known, and measurements are usually performed following the IEC 60270 standard [6]. PD measurements under DC voltage present complexities related to the nature of the phenomenon and the supply conditions [7]. In AC systems phase-resolved-partial-discharge (PRPD) patterns allow assessment of the insulation condition, and provide information on the types of defect present [8]. Such analysis cannot be performed under DC voltage, since each discharge event cannot be related to a phase value. The interpretation of the acquired data therefore requires a different approach.

Localization of Partial Discharges Inside a Transformer Winding Using a Ladder Network Constructed From Terminal Measurements

Abstract: Precise localization of partial discharge (PD) inside a power transformer winding is a challenging task. Previously, researchers have used internal calibration or reference signals to locate the PD source. The location of any arbitrary (test) PD source is ascertained from the maximum correlation between reference and test signals. However, in practical transformer windings, internal tappings or design details are usually unavailable to generate reference signals. The proposed work employs terminal measurements to construct a physically realizable ladder network. Simulated responses obtained from the ladder network for signals of known pulse-widths at all locations are used as reference data. The terminal responses of the test PD signals are obtained from a laboratory-scale winding by applying signals of arbitrary pulse-widths and shapes at various locations. The PD test signals are generated using a function generator, a PD calibrator, and real discharges. To predict the location of the PD source, the simulated reference data are then correlated with the test data. The position corresponding to the maximum correlation indicates the PD location. The proposed methodology is verified using experimental investigations carried out on two different laboratory-scale transformer windings.

Mapping of discharge channels in void creating effective partial discharge area

Abstract: This paper describes a novel approach to understanding partial discharge (PD) dynamics and mapping of the discharge channels in a void. During long term PD exposure, discharges develop inside channels within a void, leading to a variation in the discharge area on the void wall as well as a clustering effect. In this paper, the development of a method for identifying localized changes in the dielectric structure, through the detection of dispersed channels with reduced resistivity which occur due to multichannel discharges, is described. Discharge spots in selected ranges of surface resistivity, occurring due to the energetic impact of PD, are mapped. This mapping shows both the distribution of local centers on the surface of the specimen, characterized by a reduced value of surface resistivity. Furthermore, during aging tests this surface resistivity exhibited a progressive reduction by four orders of magnitude, justifying the occurrence of an effective discharge area in the void source. This additionally impacts PD pattern modulation and can be a possible initiation of the formation of cross channels in the bulk isolation which, in the long term, can lead to complete discharge.

Optical Partial Discharge Diagnosis in SF 6 Gas-Insulated System With SiPM-Based Sensor Array

Abstract: This paper aims to promote optical partial discharge (PD) detection from laboratory scale to practical application for sulfur hexafluoride (SF6)-insulated power equipment. First, a micro silicon photomultiplier (SiPM)-based PD sensor is evaluated for detecting PDs in SF6 gas and is proven to have the equivalent properties with pulse current acquisition and vacuum photomultiplier tube in terms of the signal-to-noise ratio, pulse resolution, and linearity. Then, a double-spectral PD sensor based on SiPM is first proposed and developed to realize a more specific PD diagnosis. It is demonstrated that by using the double-spectral PD sensor not only stochastic PD patterns can be obtained for PD recognition, but PD severity can be estimated as well.

Insulation characteristics of fluoronitriles / CO 2 gas mixture under DC electric field

Abstract: Environmentally friendly DC gas insulated transmission line (GIL) is currently one of the hot topics in advanced electric power equipment. Recently, fluoronitriles have been widely studied and considered to replace SF6 in GILs. In this paper, the breakdown voltage, insulator flashover voltage, and the partial discharge inception voltage of fluoronitriles/CO 2 gas mixtures are reported in a DC electric field. The mole ratio of the mixed gases are 4 : 96 % and 8 : 92 %, and the gas pressure is in the range 304.7 to 717.83 kPa. Based on the results, the breakdown field strength of fluoronitriles/CO 2 gas mixture shows a growth tendency with increasing gas pressure in a uniform electric field. At 717.83 kPa, the positive breakdown field strength is higher than the negative and reached a maximum. In a non-uniform electric field, the negative breakdown voltage of fluoronitriles/CO 2 gas mixture increases with increasing gas pressure. In the contrast, the positive breakdown voltage decreases with the rise of gas pressure, which exhibits a significant polarity effect. The flashover voltage of fluoronitriles/CO 2 gas mixture increases with increasing gas pressure. At the same gas pressure, the negative flashover voltage is slightly higher than the positive. The negative flashover voltage of fluoronitriles/CO 2 gas mixture at 717.83 kPa is equal to 96.06 % of SF6 gas at 0.5 MPa abs. The negative partial discharge inception voltage (PDIV) of the fluoronitriles/CO 2 gas mixture is greater than the positive, and both 4 : 96 % and 8 : 92 % gas mixtures showed higher PDIV than the SF6. Considering the insulation characteristics, the fluoronitriles/CO 2 mixture has the potential to replace SF6 in DC gas insulated transmission lines.

A Partial Discharge Detection Method for SF 6 Insulated Inverted Current Transformers Adopting Inner Shield Case as UHF Sensor

Abstract: A partial discharge (PD) detection method for SF6 insulated inverted current transformers (SIICTs) adopting an inner shield case as an ultra-high frequency (UHF) sensor is proposed in this paper. The inner shield case is a component of the SIICT. Its structure is similar to that of an antenna and can be used as a UHF sensor to measure the PD UHF signal. A 110 kV current transformer is used as an experimental object and the voltage standing-wave ratio of the inner shield case is calculated. The validity and sensitivity of this method are proved by experiments with ac voltage. This PD detection method solves the problem that the UHF sensor is difficult to mount inside current transformers and provides a novel method for PD detection of SIICTs.

Investigating the effect of cavity size within medium-voltage power cable on partial discharge behaviour

Abstract: One of the common causes of cross-linked polyethylene (XLPE) insulation ageing and finally cable failure is the presence of a cavity within cable insulation. Gas filled cavities can be initiated in XLPE cables during its manufacturing, installing and operating conditions. Once the size of the cavity reaches the critical limit, noticeable partial discharge (PD) activity develops. Therefore, the size of the cavity is one of the important factors that considered when investigating the PD activity in power cable. This work studies the effect of cavity size on PD behaviour within insulation layer of an 18/30 kV XLPE cable specimen; the changing in an artificial spherical cavity depths and diameters is investigated in the laboratory. In addition, 2D model geometry of a cable insulation having an artificial cavity is also developed using COMSOL software and MATLAB program to simulate the PD measurements from the laboratory experiments to imitate the conditions found during measurements, hence interpreting the obtained experimental results and determining the significant parameters influencing PD activity; hence, more a fuller understanding of PD phenomena within a cavity. The results show good coincidence between experimental and simulated data, in terms of PD magnitude and PD inception voltage.

Partial discharge measurement at DC voltage — Evaluation and characterization by NoDi∗ pattern

Abstract: In this paper the requirements on PD measurement systems for DC voltage are summarized and the experience gained about the PD behavior of some typical defects in HVDC GIS and GIL are discussed. Some physical effects at different voltage levels are shown and a method for the representation and characterization of the PD pulse sequences is introduced. Special test cells with different types of defects such as a protrusion, a floating electrode, a free moving particle and a void are used for the investigations. The procedure for PD measurement at DC voltage is improved and PD pulse sequences at different gas pressures and voltage levels were recorded. In a further step the PD behavior up to the breakdown voltage was determined. The NoDi∗ pattern was developed for the visualization and interpretation of the measured PD pulse sequences. This pattern supports the visualization and the physical interpretation of the pulse sequences and may allow the characterization of the typical defects in HVDC GIS and GIL by a human expert.

Partial discharge and breakdown characteristics of moving transformer oil contaminated by metallic particles

Abstract: The presence of metallic particles in oil insulation degrades the performance of power transformers. At present, a large amount of research has focused on PD and breakdown characteristics initiated by particles in stationary transformer oil. However, in actual use, transformer oil flows which affect the movement of particles, and hence PD and breakdown characteristics change. In order to clarify these, PD parameters and breakdown voltage were measured in moving transformer oil in the presence of metallic particles, and the effects of flow velocity, particle size and concentration were investigated. It is found that as the oil flow velocity increased, PDIV became higher, whereas the discharge magnitude and frequency decreased. On the contrary, the discharge magnitude and frequency increased with particle size and concentration. Besides, the breakdown voltage increased with the circulation of oil, but it became lower with increasing particle size and concentration. A simulation model including electric field and fluid field was employed to study the moving trajectory of particles in flowing transformer oil. When the oil flow velocity increased, the collision number between particles and electrodes decreased and it became larger with particle size and number. In terms of the simulation results, the variation of PD characteristics could be interpreted. The breakdown voltage, as affected by oil flow velocity, particle size and concentration were discussed.

Noniterative Method for Combined Acoustic-Electrical Partial Discharge Source Localization

Abstract: The combined acoustic-electrical system is used in the factory or plant environment for the partial discharge (PD) source localization in power transformers. A noniterative method for this combined acoustic-electrical PD-locator-system is devised and presented in this paper for the first time. It employs three acoustic emission (AE) sensors. The proposed method is compared with the existing noniterative method used in the all-acoustic system, which employs four AE sensors. The comparative study shows that the proposed method can locate the PD source irrespective of its position within the tank, whereas the prevailing noniterative method for the all-acoustic system fails to locate the PD source at certain positions within the tank. The effect of the sensor positioning on the performance of the method is studied, and some guidelines for the sensor placement on the transformers tank wall in a factory or plant environment are suggested. The proposed method is also applied to the data taken from the published literature. The localization results are compared with those of an existing iterative method (Newton's method) to prove its superiority in terms of computational time.

Partial discharge detection on 320 kV VSC-HVDC XLPE cable with artificial defects under DC voltage

Abstract: VSC-HVDC power transmission systems based on extruded cables are being commissioned with higher rated voltages and longer distances in recent years. In China, the rated voltage of commissioned VSC-HVDC cable projects has been increased from 160 to 200 kV, and then to 320 kV in the past 5 years. To investigate the feasibility of discovering insulation defects of an XLPE HVDC cable system using partial discharge detection under DC voltage, a test cable loop was built using the same batch of 320 kV HVDC XLPE cable used to construct the Xiamen ± 320 kV VSC-HVDC project. Artificial defects of insulation wound and semi-conductive layer tips were designed and constructed at the joint. The two types of defects were effectively detected by the HVDC partial discharge test, and the measured results show distinguished discharge characteristics. Suggestions for determining trigger level and partial discharge inception voltage under DC voltage for partial discharge detection of extruded HVDC cables are given.

Graphic approaches for faults diagnosis for Camellia insulating liquid filled transformers based on dissolved gas analysis

Abstract: As vegetable insulating liquids have different chemical compositions from mineral oils, dissolved gas characteristics under thermal and electrical faults have differences; thus fault diagnostic methods based on dissolved gas analysis (DGA) used for mineral oil-filled transformers may not be suitable to vegetable oil-filled transformers. This paper presents experimental results of dissolved gases in Camellia insulating liquid under typical thermal and electrical faults in transformers. Thermal fault simulation experiments include three parts, which are low temperature, medium temperature and high temperature faults, and the electrical fault simulation experiments also include three parts, which are partial discharge, breakdown discharge and arc discharge. Experimental results show that apart from CO and CO 2 , H 2 and C 2 H 6 are the main characteristic gases under thermal faults, and the percentage of H 2 decreases while CH 4 , C 2 H 4 and C 2 H 6 increases with temperature. In addition, H 2 and CH 4 are the main characteristic gases under partial discharge faults; C2H2 is the main characteristic gas under breakdown faults, and C2H2 and C2H4 are the main characteristic gases under arc discharge faults. Furthermore, graphic fault diagnostic methods based on DGA of Camellia insulating liquid including Triangle and Pentagon diagnostic methods are proposed. Compared with the current diagnostic method, the proposed methods in this paper have higher diagnostic accuracy.

Partial discharge detection for characterizing cable insulation under low and medium vacuum conditions

Abstract: Design of cables for operation in a low pressure environment is challenging, when applications also demand lightweight and flexibility, and material choice is restricted. The operating pressures in combination with relevant distances, can be situated near gas breakdown and cause partial discharges, making long-term damage conceivable. An experimental setup is developed, based on partial discharge detection in a vacuum system, to characterize the partial discharge inception voltage of three coaxial cable designs in an argon and nitrogen environment at controllable pressure. In order to cope with outgassing behavior, a lumped element model is presented to simulate the internal pressure distribution along the cable as a function of settling time. Microscopic cross sections of the cables are analysed with electrostatic voltage simulations. Using scaled Paschen curves, expected partial discharge inception is determined and compared with measurements. Quantifying cable performance, in terms of minimum PD inception voltage and pressure, in relation to its design is feasible, but also deviations occur which are discussed.

Study on the Dielectric Properties of C 4 F 7 N/N 2 Mixture Under Highly Non-Uniform Electric Field

Abstract: As an environment-friendly gas insulating medium, C4F7N has attracted great attention in recent years due to its excellent environmental protection and insulation performance However, studies on the insulation performance of C4F7N/N2 gas mixture are not comprehensive at present In this paper, the breakdown and partial discharge characteristics of the C4F7N/N2 gas mixture under highly non-uniform field were tested using the gas insulation performance test platform The effects of gas pressure and mixing ratio on the negative partial discharge inception voltage (PDIV±), positive PDIV (PDIV−), and breakdown voltage of the gas mixture were analyzed The engineering application potential of the C4F7N/N2 gas mixture was also discussed considering the limitation of liquefaction temperature It is found that an increasing gas pressure or a mixing ratio can effectively improve the insulation performance of the C4F7N/N2 gas mixture The breakdown properties of a gas mixture for a minimum operating temperature of x00B1;%at 03, 04, 05, and 06MPa can reach 634%, 546%, 49%, and 564% of pure SF6, respectively, and the PDIVx00B1; can reach 804%, 669%, 628%, and 688% of pure SF6, respectively Relevant results not only reveal the influence of the mixing ratio and pressure on insulation performance of the C4F7N/N2 gas mixture, but also provide significant guidance for its engineering application

A Novel Approach for Partial Discharge Measurements on GIS Using HFCT Sensors.

Abstract: This paper presents a novel measuring system for partial discharge (PD) measurements in Gas Insulated Systems (GIS) using high frequency current transformers (HFCT). The system is based on the measurement of the induced PD currents in the GIS enclosure. In opposition to the existing antenna technologies that measure the radiated energy in the very high frequency/ultra-high frequency (VHF/UHF) range, the proposed system measures the PD conducted currents in the high frequency (HF) range and below. The foundation of the measurements together with a detailed explanation of the sensor installed conveniently at the bolts of the GIS spacer are presented. An experimental study on the current distribution in the GIS enclosure is described to evaluate the impact of the sensor on the measurements. Laboratory experiments have been performed that show the suitability of this method to properly measure particle discharges caused by corona, surface and free moving particle discharges in SF₆. Discharges in the range of 1 to 4 pC have been properly measured. An analysis to evaluate the performance of the method is shown, in comparison to VHF/UHF antenna measurements. The potential benefits of this novel technique rely on the small attenuation of PD signals in the GIS components in the HF range and sample rate reductions. Finally, a discussion on the potential applicability of present cluster and charge calculation techniques to the proposed PD GIS measurement using HFCT is presented.