Development of a positive creeping discharge along an aerial insulated wire

In high‐voltage aerial distribution systems, the insulated cables are supported by the binding wire with the post insulator at the utility pole. When a lightning strike occurs in the neighborhood of the insulated cable in an aerial power distribution system, inductive lightning surges invade the central line of the cable. Then, creeping discharges develop along the cable surface from the binding wire tip at the same time as flashover of the post insulator at a supporting point of the cable. If the cable insulator has weak points such as pinholes, a malfunction near the cable supporting point may occur, with melting of the wire due to punch‐through breakdown. To prevent such accidents, it is important to clarify the mechanism of the creeping discharge along the insulated cable caused by the lightning strike. The polarity of creeping discharges depends on the polarity of the inductive lightning surges, and the extension length and aspect of the discharge differ greatly depending on the discharge polarity. The development of these creeping discharges is attributed to complicated behavior of the positive and negative electric charges. In the present study, we examined in detail the development of a positive creeping discharge along a wire surface by using a high‐speed image converter camera. This paper describes the mechanism of development of a positive creeping discharge based on the experimental results. 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 173(3): 20–29, 2010; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20997     

Impulse creeping discharge characteristics in insulating oils with EHD function reinforced by added HFC gas components

The basic properties of electrohydrodynamic (EHD) pumping and dielectric strength were examined for two insulating oils, rapeseed ester oil and silicone oil, which were denatured by a bonding of hydrofluorocarbon (HFC)134a gas components decomposed using a barrier discharge reactor. In this work, the mechanism of a pure conduction pumping contributed to the evaluation of the electrical pumping in sample oils. Dielectric strength of oils was evaluated from the impulse creeping discharge characteristics and the 60 Hz breakdown voltage test. Experimental results revealed that the creation of radicals such as C-F and C-H in denatured oils led to a slight deterioration of the insulation ability compared to standard oils, but the pumping ability was reinforced significantly. Such additional EHD function may be utilized as a new cooling method in oil-filled power apparatuses in view of the dielectric strength.     

Characteristics of creeping discharge along aerial insulated wire under impulse voltages with various wave front durations

When lightning occurs in the neighborhood of outdoor high‐voltage distribution lines, creeping discharges propagate along the wire surface from the binding wire tip just after insulator flashover. These discharges give rise to various faults on distribution lines, for instance, disconnection and melting of wire, punch‐through breakdown, and so on. We must clarify the creeping discharge characteristics associated with various inductive lightning surges from the viewpoint of safety in high‐voltage distribution systems. In our previous paper, it was reported that the lengths and aspects of the negative creeping discharges were influenced by the wave front durations of impulse voltages applied to the central line with a grounded binding wire. The present study was performed to obtain more information on such creeping discharges. This paper describes the distinctive characteristics of a creeping discharge along the insulated wire surface when impulse voltages with various wave front durations are applied to the binding wire. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 158(3): 29–37, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20430     

一起110kV户外气体绝缘全封闭组合电器母线气室支撑绝缘子故障分析

本文分析了一起110kV户外气体绝缘全封闭组合电器母线气室导体支撑绝缘子击穿故障,找到了引起故障的原因,提出了解决及处理措施,为户外气体绝缘全封闭组合电器设备类似故障的处理提供了参考.     

聚氯乙烯绝缘电线表面为何有“电”

聚氯乙烯绝缘电线若其表面附着一些导电脏物和在潮湿环境下带电使用时 ,用验电笔接触其表面 ,发现电笔氖管发光闪烁 ,用户认为电线“漏电”,电线质量有问题 ,不能安全使用。该文介绍了针对这情况进行调查及试验 ,认为电线质量并无问题 ,而是由极微量的电容电流引起的 ,并不危及人身安全 ,用户可安心使用。     

500kV气体绝缘金属封闭开关设备盆式绝缘子放电故障原因分析

本文介绍了某±800kV换流站恢复送电过程中发生放电故障的500kV气体绝缘金属封闭开关设备盆式绝缘子现场解体情况,结合继电保护动作分析,追溯设备出厂试验结果,并对盆式绝缘子进行了电场模拟分析,最终确定了盆式绝缘子放电故障原因.     

10 kV架空绝缘导线应用中存在的问题及对策

针对10kV架空绝缘导线运行中常见的问题,从设计方面分析了防雷措施不足、线路金具选用不当、档距过大等原因,并提出了对策。从施工方面分析了施工机具不当、施工操作对绝缘破坏严重等原因,提出解决的措施。     

Effects of a barrier on creeping discharge characteristics in SF6 and N2 gases under pulse voltages

This paper describes the effect of a barrier on creeping discharge characteristics in SF₆, N₂, and their mixtures. The barrier height effect on the discharge voltage was investigated under a positive pulse voltage. The discharge voltage increased with increasing barrier height in SF₆ gas. On the other hand, the discharge voltage hardly changed with the barrier height in N₂ gas. In order to clarify the mechanism of the initial creeping corona, it was observed by optical techniques, including an ultra-high-speed electronic imaging system (IMACON 468). The creeping corona path revealed differences in images at various barrier heights. The accumulated charge induced on the barrier by the initial corona in SF₆ gas was able to suppress the development of the later creeping corona, in contrast with N₂ gas. © 1998 Scripta Technica, Electr Eng Jpn, 125(4): 1–8, 1998     

Impulse partial discharge and breakdown characteristics of rod–plane gaps in air and N2 gases

In response to growing environmental concerns, we attempted to develop switchgear without using SF₆ gas. In our research, we used compressed air and pure N₂ as an electrical insulation gas, because of their low global warming potential. In this paper, we examined the impulse breakdown and impulse partial discharge characteristics under various conditions related to nonuniformity of the electric field. The experimental results show that the breakdown voltage (BDV) of air is higher than that of pure N₂ gas under highly nonuniform field conditions in the rod–plane gap. On the other hand, the discharge inception voltage of air and N₂ were almost the same. Furthermore, first partial discharge (PD), leader discharge, and its transition to the breakdown were successfully observed through the measurement of discharge current and light emissions under impulse voltage application. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 148(3): 36–43, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10277     

Effects of ambient humidity and temperature on partial discharge characteristics of conventional and nanocomposite enameled magnet wires

Effects of ambient humidity and temperature on partial discharge (PD) characteristics in twisted pairs with conventional and nanocomposite enameled magnet wires have been investigated. Measurements of the PD inception voltage (PDIV) and the apparent PD charge were performed by applying an ac sinusoidal waveform voltage of 60 Hz to the twisted pair. The observed PDIV in this study can be classified into the following three behaviors. First, the PDIV in both wires decreases with increasing relative humidity (RH) at low temperature. Secondly, the PDIV in both wires slightly increases when increasing the RH at high temperature. Thus, there is a certain value of the absolute humidity to determine the lowest PDIV in both cases with the conventional and nanocomposite enameled wires. Thirdly, the PDIV in the conventional enameled wire significantly decreases at the RH of 95 %, while the decrease rate of that in the nanocomposite enameled wire is relatively small. The observed PD phenomena are discussed in terms of material characterization of the enameled wires such as changes in permittivity due to moisture absorption and wettabilitiy under voltage application.     

Study on mathematical model for VHF partial discharge of typical insulated defects in GIS

Very high frequency (VHF) measurement is a valid technique for partial discharge (PD) detection, and PD mathematical models are very important to study PD denoising and waveshape pattern recognition etc. However, these mathematical models based on the traditional PD measurement have been established according to RC or LCR resistance detection so that they are not suitable for VHF measurements. PD signals are detected based on four typical physical models of defects in gas insulated substation (GIS) using VHF method. The VHF PD mathematical models are established, and the principles and methods of establishment are summarized. Furthermore, the parameters of the mathematical models are given and the validity of PD mathematical model is proved by fitting error, power spectrum and time-frequency analysis. Results show that the VHF PD mathematical models can facilitate theoretical simulation of different insulated defects by using the values of given parameters. In the end, applications of the VHF PD mathematical models and complex wavelet transform for extracting the relevant signals from a white noise background are illustrated     

Impulse partial discharge and breakdown characteristics of rod-plane gaps in N/sub 2//SF/sub 6/ gas mixtures

Impulse partial discharge (PD) and breakdown (BD) characteristics of rod-plane gaps in N/sub 2//SF/sub 6/ gas mixtures were investigated for different gap geometry, gas pressure and SF/sub 6/ gas content. Experimental results revealed that the 50% probability breakdown voltage increased with gas pressure, which agreed with the theoretical values with consideration of discharge time lag for impulse voltage application. For the calculation of discharge inception voltage, the volume-time theory was successfully applied to the N/sub 2//SF/sub 6/ gas mixture. Furthermore, impulse PD light emission image was observed together with PD current pulse and light intensity waveforms. The long discharge with stepwise propagation and double-peak PD pulses could be observed, which corresponded to the streamer/leader transition leading to breakdown.     

Characteristics of creeping discharge developed in a narrow gap between insulators and effect of a backside electrode

Discharge characteristics have been investigated for a needle–plane electrode configuration containing insulating barriers with a narrow gap which has been placed between the needle and the plane. The characteristics of creeping discharge developed in the narrow gap of the barrier filled with SF₆ are especially considered. In the case of a configuration with a backside electrode below the needle, the corona generated from the needle easily extended to the gap. On the other hand, for a configuration without a backside electrode, the corona has hardly extended to the gap, and on increasing the applied voltage the corona developed greatly in the gap. This difference in corona extension should affect the flashover characteristics in the present system. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 146(2): 27–36, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10248     

Laser-guided discharge characteristics of long air gaps and observation of the discharge process

Laser-guided discharge is promising for protection of power transmission systems against lightning. Several experiments concerning the laser-induced electrical discharge have been performed up to now. However, it is necessary to understand the mechanism of the laser-induced electrical discharge to achieve the laser-triggered lightning. When a high-power laser beam is focused in air, a high degree of ionization is produced as brilliant beams near the focus. In this paper, the electrical discharge induced up to 2-meters with a high-power CO₂ laser focused by a 10-meter focal length mirror is described. Experiments of the laser-guided discharge were carried out by application of an impulse voltage to a rod-rod gap after laser radiation. This paper deals with the effects of delay times and polarity of the impulse voltage on 50 percent flashover voltage characteristics and the observation results of discharge phenomena taken by a still camera, a special camera named ALPS (Automatic Lightning Discharge Progressing Feature Observation System) and an image converter camera.     

Charging characteristics of a solid insulator in vacuum under AC voltage excitation

We have investigated charging and flashover characteristics of a polymeric or glass insulator exposed to AC voltage in vacuum in order to develop compact and reliable high voltage VCBs (vacuum circuit breakers). This paper focuses on charging characteristics of a cylindrical model insulator. The charging of an insulator is investigated using an electrostatic probe that measures the electric field near the triple junction on the grounded electrode. This method allows a time-resolved measurement of the charging process. The insulator was made of borosilicate, fused quartz or polymetyl methacrylate, and was in the shape of a right cylinder with 10 mm in thickness. It has been clarified that the charging is characterized by three sequential states; initiation, quasi-stable and stable states, and that the polarity of the charge is positive for these states irrespective of the voltage phase. The charging characteristics with AC voltage are compared to our previous results with DC voltage excitation. We find that the charge magnitude at the stable state coincides with that obtained by DC. The electric field on the grounded electrode, and therefore the charge magnitude, decreases with the surface roughness, and decreases as the insulation strength is increased. A computer simulation has been conducted to investigate the quasi-stable state, which clarifies that the transition in surface charge distribution being synchronous to the voltage phase is responsible for causing the quasi-stable state.     

Partial discharge pattern recognition by neuro-fuzzy networks in heat-shrinkable joints and terminations of XLPE insulated distribution cables

An identification technique is described, based on a developed adaptive fuzzy logic network, that enables the recognition of partial discharges (PD) generated by different defects in heat-shrinkable joints and terminations of XLPE insulated power distribution cables. It is shown that different sources of PD can be identified on the basis of fuzzy rules applied to a selection of parameters derived from PD-pulse phase and amplitude distributions. A comparison with other PD pattern recognition techniques based on traditional neural networks is presented and discussed.