Development of an identification system for location of free metallic particles in GIS based on analysis of Lamb waves

We investigated propagation properties of Lamb waves in a gas‐insulated switchgear (GIS) tank to diagnose insulation performance of GIS. The acoustic signals excited by a free metallic particle colliding with the tank sheath were measured using AE sensors. The wavelet transform was applied to decompose the wave data into its time–frequency components. As a result, difference of propagation properties of Lamb waves is clearly seen with different sizes of GIS tank. Based on the characteristics of Lamb waves, algorithms for location identification of a free metallic particle were examined in model GIS using two AE sensors. Herein, we propose a new system for location identification of a free metallic particle in GIS. Moreover, it is verified that the new identification system is suitable as a diagnostic technique for GIS. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 167(3): 28–35, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20676     

Time–frequency analysis of lamb waves caused by partial discharges and free particles in GIS

We investigated the propagation properties of Lamb waves in a GIS tank, using time–frequency analysis to diagnose the insulation performance of GIS. We measured the acoustic signals excited by metallic particles colliding with the tank sheath, and those emitted by partial discharge in the GIS. The wavelet transform was used to decompose the wave data into its time–frequency components. As a result, it was confirmed that Lamb waves with the dispersive property of the velocity are excited and propagate in a spiral path along the tank wall due to the cylindrical structure of the tank. Taking these results into consideration, we propose a new technique for identification of defect locations in GIS based on time–frequency analysis of acoustic signals with the wavelet transform. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 145(3): 25–32, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10163     

Suppression of Metallic Particle Lift‐Off in GIS by a Nonlinear Resistivity Coating

To suppress metallic particle lift‐off in compact gas‐insulated switchgear (GIS), a coating with nonlinear resistivity characteristics was developed for the inner surface of the GIS tank. An electrical field analysis that measured the current density and electric field (J–E) characteristic indicates that a nonlinear resistivity coating can reduce field intensification at triple junctions between metallic particles and the coating, and can effectively suppress particle lift‐off. The results of experiments using a GIS mock‐up model indicate that a nonlinear resistivity coating increases the lift‐off electric field of metallic particles with less statistical dispersion than a dielectric coating.     

Metallic particle motion and breakdown characteristics in GIS with 0.1‐Hz VLF (very low frequency) high voltage applied

VLF (Very Low Frequency) high voltage with frequency of 0.1 Hz will be utilized for an on‐site test of XLPE underground cables, instead of conventional dc high voltage test. Since XLPE cables are connected to GIS (Gas Insulated Switchgears) in substations, the influence of VLF voltage application to GIS insulation should be investigated. One of the most important characteristics for GIS insulation lies in the metallic particle contamination and its behavior, which may induce breakdown in GIS. From the above viewpoint, this paper discusses the metallic particle behavior and breakdown characteristics under VLF voltage application in GIS. Experimental results revealed that (1) Particle motion under VLF condition was similar to that under dc condition, while specific in the transient behavior at the polarity reversal. (2) Breakdown was induced by particles located in the vicinity of high voltage conductor at the instance of crossing the gap or in the firefly conditions. (3) Breakdown voltage in positive half cycle was higher than that in negative half cycle at the lower gas pressure, while lower at the higher gas pressure, which was attributed to the particle behavior and the breakdown mechanism of SF₆ gas. Consequently, metallic particles in GIS under VLF voltage application exhibited the specific behavior associated with the slow change of instantaneous voltage and polarity, and resulted in the complex pressure dependence of breakdown characteristics. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 139(4): 33–40, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.1166     

Transient response of a grounding system in an underground GIS substation

The transient grounding impedance of a gas‐insulated switchgear (GIS) substation was investigated through measurements on a commercial 300‐kV underground substation. Using the results, the transient impedance of the grounding grid was investigated. The attenuation factor of the propagation line composed of the outer surface of the GIS tank and the concrete floor was also evaluated. The validity of EMTP analysis of surge phenomena in the GIS grounding system was confirmed. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 146(1): 70–77, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10214     

考虑超声波传播特性对GIS内部自由金属粒子的游离尺寸评价

介绍采用电磁波及超声波检测法探讨精确诊断GIS内部是否有金属粒子存在、位置以及绝缘击穿危险程度的诊断检则。以GIS罐内进行的金属粒子自由落下的试验，探计了有关产生超声波波形的衰减、螺旋波以及速度分散等传播特性，根据校正的超声波振幅值评价了GIS内游离的金属粒子的尺寸。     

Time‐frequency analysis of a pressure wave caused by impulse tree using wavelet transform

This paper describes results of time‐frequency analysis of a pressure wave caused by impulse tree extension using wavelet transform. Pressure waves were measured by a piezo sensor which was located on the back of the plane electrode when high‐voltage nanosecond pulses were applied to a point electrode in a low‐density polyethylene block. Frequency of the pressure wave from induced charges on the plane electrode was higher than that of the pressure wave from tree. In addition, the frequency of the pressure wave from tree tended to decrease with increasing gap length because of the dispersion of the pressure wave during its propagation. When a large tree extension occurred between a 5‐mm gap, pressure waves of about 10 MHz propagated from the tree tip and a pressure wave of 1 MHz propagated from the tree stem. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 142(1): 1–7, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10097     

Consideration of radiated electromagnetic waves from partial discharge based on half‐wave dipole antenna model

Partial discharge (PD) may take place due to residual defects like metallic particles in SF₆ gas‐insulated power apparatus such as GIS. However, the signal of PD occurring in SF₆ gas is very weak and susceptible to external noise in air. Moreover, because of the complicated mechanism of PD, the radiation property of electromagnetic waves from PD has not as yet been clarified. Therefore, it is hard to distinguish the PD signal in SF₆ gas from external noise. From the above points of view, we have been investigating the radiation mechanism of electromagnetic waves from PD. We measured the polarization characteristics of electromagnetic waves radiated from PD in comparison with those of half‐wave dipole antennas. The polarization characteristics of PD were explained by the theory of half‐wave dipole antenna, rather than that of an infinitesimal dipole antenna. Moreover, we compared the power spectrum for PD measured using a biconical antenna with that received from the half‐wave dipole antenna or infinitesimal dipole. It was found that the power spectrum for PD also corresponded to that for the half‐wave dipole antenna with a length of 50 cm. © 1999 Scripta Technica, Electr Eng Jpn, 126(4): 40–47, 1999     

Characteristics of elastic waves caused by corona discharges in anoil-immersed pole transformer

Measurements of elastic waves brought by a pulse of simulated corona discharge in an oil immersed pole transformer and a model tank filled with oil were performed in order to identify the location of insulation deterioration, using an acoustic emission (AE) technique. The detected AE signals were analyzed by means of a fast Fourier transform (FFT), and properties of elastic waves influenced by the existence of insulated windings and magnetic core for power transformation in the transformer were investigated. The result shows that almost all the initial AE signals detected on the-wall of the transformer tank were Lamb waves caused by the oscillation waves passing through the insulating paper and oil with repeating transmission, reflection and refraction. Also, it was possible to recognize whether the measured elastic wave was influenced by windings and their insulating papers or not, by FFT analysis. This suggests that the location accuracy of the corona discharge in the transformers would be improved     

Results of lightning impulse tests for a 275‐kV full GIS substation

This paper describes the outline and results of the lightning impulse tests for a 275‐kV full GIS substation. The behavior of lightning surges is a very important factor for the rational design of substations and low‐voltage and control circuits inside the substations. For the above reason, we carried out lightning impulse tests for a new 275‐kV full GIS substation. In these tests, we measured voltage induced in low‐voltage and control circuits, transient characteristics of grounding grid, injected voltage and current waveforms, and so on. By investigating these data, we confirmed the behavior of lightning surges inside the substation. We also compared simulated waveforms by EMTP analysis with the measured waveforms. The simulated results agreed well with the measured results. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 146(1): 46–58, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10230     

A VHF interferometry system for detecting anomalous propagation of FM radio broadcasting waves related to earthquakes and some preliminary results

Earthquake‐related anomalous electromagnetic phenomena have been reported in various frequency ranges over the past few decades. Investigation of the anomalous propagation of VHF transmitter waves is a promising approach to short‐term prediction and crustal activity monitoring. Anomalous propagation is believed to be generated by disturbances of the atmosphere above the epicenter or along the propagation path prior to large earthquakes. Consequently, over‐the‐horizon propagation has been received. A recent study shows that the appearance of anomalies was signi?cantly enhanced within 5 days of earthquakes with M ≥4.8. However, there is no information on the scattering location, that is, on the direction of wave arrival. Therefore, a simple interferometer system for VHF radio waves to identify the space‐time position of earthquake‐related atmospheric disturbances has been developed and installed at Chiba University. This paper describes the newly developed interferometer system and presents the results of fundamental tests to evaluate the performance of the new interferometer at Chiba. Data on over‐the‐horizon propagation of VHF radio waves obtained from 1‐year continuous measurement at Chiba are described. These are possible radio duct propagations and possible earthquake‐related anomalous propagations. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 183(1): 16–24, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22303     

Time‐domain simulation of power transients in Raman fibre amplifiers

We study power transients in Raman fibre amplifiers (RFA). Transients are defined as the output signal power response to abrupt change in the number of signal channels at the input to the RFA (channel addition/removal). The simulations are based on application of a large signal numerical model which incorporates time variation effects, downstream propagation of multiple signals, upstream propagation of pump and both downstream and upstream propagation of amplified spontaneous emission (ASE). System of coupled non‐linear differential equations describing the propagation of the signal, pump and ASE waves along the RFA and their evolution in time represents a two‐boundary value problem. Due to the backward propagating ASE and counter‐directional pumping, an iterative forward and backward solution of propagation equations must be used in order to achieve a steady‐state distribution of signals, pumps, and ASE powers along the RFA. We have used either the fourth‐order Runge–Kutta routine, or an alternative average power analysis (APA) approach to obtain the steady‐state optical power distribution along the fibre. Direct integration is used to obtain time evolution of optical powers as a response to channel addition/removal. Stability of the numerical solution depends on the relation of discretization steps in space and time. Gain locking of the RFA via electronic feedforward pump control derived from a monitoring channel output power has been introduced in the model to study the possibility of suppressing the surviving channel power fluctuations. Copyright © 2004 John Wiley & Sons, Ltd.     

直流下GIS内运动金属微粒的超声波特性及状态识别

为研究直流电压下气体绝缘开关装置(GIS)内金属微粒处于不同运动状态时的超声波特性,以及基于微粒超声波特性判别运动状态的方法,建立了一套超声波测量系统,设计了GIS内部金属导电微粒的运动状态模型,分别是滚动、非贯穿性跳动和贯穿性跳动。采用该测量系统拾取了在直流电压下微粒运动产生的超声波脉冲信号,并在大量试验数据基础上,提出了基于超声波时间序列(相邻两次超声波脉冲关联)区分微粒运动状态的方法。为进一步量化分析,建立了超声波特征参数(相邻两次脉冲幅值之差-相邻脉冲发生时间间隔,即Δu-Δt)。试验结果分析表明,依据统计分布图谱,可区分金属微粒运动的状态。     

Development and design of DC‐GIS

In order to realize a reliable, compact, and economical converter station for HVDC transmission, applications of gas insulated switchgear (GIS) for dc transmission lines are considered. The characteristics of dc gas insulation differ from those of ac. The behavior of metallic particles left in the enclosure is one of the largest differences. The accumulation of electrical charges on solid insulators is another essential factor in designing a DC‐GIS. Also, degradation of metal oxide arrester blocks under dc stress must be deliberated. Based on the fundamental studies, we developed the components of ± 500‐kV DC‐GIS. Electrical and mechanical performances of these components have been tested and proven to be satisfactory. Finally these components have been assembled into a full DC‐GIS and subjected to a long‐term voltage endurance test. In this paper, the design philosophy of ± 500‐kV DC‐GIS, details of the components, and the test results are described. © 1999 Scripta Technica, Electr Eng Jpn, 129(2): 51–61, 1999     

Estimating the parameters of neural mass models including time delay and nonlinearity using a particle filter: a preliminary study toward model‐based EEG analysis

Electroencephalogram (EEG ) and local field potential (LFP ) signals are measured for both experimental and clinical purposes which include sleep stage analyses, brain–computer interfaces, and disease diagnosis. EEG and LFP data analyses are typically based on models assuming that the measured data is generated from a biological system and estimate the model parameter values that most accurately reproduce the measured data. Thus, use of a biologically plausible model is important for a model‐based analysis. However, analyses using models that include time delay and nonlinearity have not been reported, even though they are biologically important for EEG generation mechanisms. In this study, we developed a parameter estimation method that uses a particle filter for models with time delay and nonlinearity, which was evaluated with simulations. Simulated EEG data were generated from neural mass models (NMMs ). The NMM parameters were estimated from the generated data. Furthermore, parameters for modeling EEG features of patients with Alzheimer's disease were included in the NMM ; the disease parameters were estimated from the simulated EEG data. We observed that NMM parameters, as well as the disease parameters, were accurately estimated from the simulated data. We conclude that the validity of our method for estimating parameters of NMMs including time delay and nonlinearity is confirmed for simulated EEG data, and these results show the possibility of using our method for model‐based analysis with real EEG data. © 2017 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Consideration of Particle Swarm Optimization combined with tabu search

This paper presents a new form of Particle Swarm Optimization (PSO) based on the concept of tabu search (TS). In PSO, when a particle finds a local optimal solution, all of the particles gather around that one, and cannot escape from it. On the other hand, TS can escape from the local optimal solution by moving away from the best present solution. The proposed Tabu List PSO (TL‐PSO) is a method for combining the strong points of PSO and TS. This method stores the history of pbest in a tabu list. When a particle has a reduced searching ability, it selects a pbest of the past from the historical values, which is used for the update. This makes each particle active, and the searching ability of the swarm makes progress. The proposed method was validated by numerical simulations with several functions that are well known as optimization benchmark problems for comparison to the conventional PSO method. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 172(4): 31–37, 2010; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20966     

Development of 72‐kV high‐pressure air‐insulated GIS with vacuum circuit breaker

SF₆ gas has excellent dielectric strength and interruption performance. For these reasons, it has been widely used for gas‐insulated switchgear (GIS). However, use of SF₆ gas has become regulated under agreements set at the 1997 COP3. Thus, investigation and development for GIS with a lower amount of SF₆ gas are being carried out worldwide. Presently, SF₆‐free GIS has been commercialized for the 24‐kV class. Air or N₂ gas is used as the insulation gas for this GIS. On the other hand, SF₆‐free GIS has not been commercialized for the 72‐kV‐class GIS. The dielectric strengths of air and N₂ gas are approximately one‐third that of SF₆ gas. To enhance the insulation performance of air and N₂ we have investigated a hybrid gas insulation system which has the combined features of providing an insulation coating and suitable insulation gas. We have developed the world's first 72‐kV SF₆‐free GIS. This paper deals with key technologies for SF₆‐free GIS, such as the hybrid insulation structure, a bellows for the high‐pressure vacuum circuit breaker, a newly designed disconnector and spacer, and prevention of particle levitation. Test results of the 72‐kV high‐pressure air‐insulated GIS with the vacuum circuit breaker are described. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 157(4): 13–23, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20451     

Discharges from moving particles in GIS [gas-insulated switchgear]

The study of the motion of moving metallic particles in GIS requires a good knowledge of the carried charge of the particle. In this paper, measurements of the charging process of a moving particle, performed in a realistic single-phase GIS, are presented. By measuring the charge impulses and the voltage phase at consecutive impacts, it is possible to estimate the carried charge and then compare the results with the existing models of the particle charge. Also, besides the discharges from in-flight corona reported by several authors, it is shown that, for higher voltage levels, several discharges between the particle and the enclosure (outer electrode) can occur as the particle impacts with the enclosure     

Insulation resistance under DC stress and electrification characteristics of GIS epoxy insulator

Gas‐insulated switchgear (GIS) has widely been used for AC power distribution because of its high reliability and compactness. Recently, DC GIS has been developed with various investigations for dielectric breakdown characteristics of DC gas insulation. GIS insulation is composed of SF₆ gas and solid spacers, and it has been recognized that the dielectric performance of DC GIS is mainly influenced by solid spacers. Under DC stress, the electric field is directed one way, the effect of electrification for charges to be accumulated in the spacer must be taken into account and also the effect exists in AC GIS because the switching operations may leave the remnant DC charge on the AC GIS spacer. This paper first describes the effective resistivity (the bulk or the surface) of the solid spacer under the DC stress from the experimental investigation, and the critical factor on the solid spacer that causes reduced dielectric performance of the GIS insulation is studied. Second, the present paper deals with the electrification on the GIS with various levels of surface roughness of the epoxy insulator and metallic electrode. Finally, the DC insulation characteristics of GIS insulator are investigated based on the experimental results. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 168(4): 6–13, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20788     

Multiresolution model of electromagnetic wave propagation in dispersive materials

A multiresolution time‐domain (MRTD) technique based on Haar wavelets has been applied to model the propagation of waves in dispersive materials, using a discretization of the convolution equation that governs the behaviour of the media. To validate the method, the reflection coefficient at the interface between air and several different linear dispersive media, as well as the propagation of a plane wave towards a non‐linear dispersive medium have been calculated and compared with other numerical techniques and theoretical results. Copyright © 2003 John Wiley & Sons, Ltd.