This paper has experimentally investigated transient voltages on floors in an intelligent building due to lightning with special reference to grounding of a lightning rod, the building and the floors by using an 1/10 scaled-down building model. It has been found that the floor voltages are the smallest in the case of the floors bonded to the building structure except the case of the structure being used as a lightning rod. The common grounding of all the floors causes very high floor voltages when the floor grounding is connected to the lightning rod grounding. Individual grounding of the floors, the building and the lightning rod produces rather high voltages on the floors. A voltage difference between the floors is significantly reduced by bonding the floors to the building structure or by the common grounding of the floors.
Partial discharge (PD) characteristics within an artificial air-filled void contained in a solid insulator were experimentally investigated under superimposed sinusoidal voltages of 60 and 600Hz at liquid nitrogen temperature (77K) to find the effects of the waveforms of distorted sinusoidal voltages on PD characteristics at 77K. The results show that PD inception voltage at 77K is independent of the applied voltage waveform. The results also show that, when the 600Hz component of the superimposed voltage is increased with its constant peak value, PD intensity seems to be independent of the voltage waveform, whereas PD pulse number increases. Since PD charge magnitude and pulse number at 77K were remarkably different from those at 298K, their mechanisms are discussed based on the observation results of residual charge distributions remaining on a void surface subjected to PDs under 60Hz ac voltages at both temperatures.
Free wire particle motion behavior and particle triggered breakdown characteristics around different shaped spacers between diverging conducting plane electrodes are studied experimentally in the laboratory air under DC and 60Hz AC voltages. Wire particle motion behavior was observed experimentally and is discussed on the basis of the results of field calculations. Consequently, it was found that a particle around spacer tends to move toward or away from the spacer depending on the field strength around the spacer, under both DC or AC voltages. Moreover, it was observed that a particle can hardly adheres to the spacer in case of corona discharge at wire particle ends under DC voltage and/or an oscillating wire particle in case of AC voltage and viceversa. Also, the wire particle adhesion phenomenon and the characteristics of surface flashover triggered by free conducting wire particle around a simple shaped spacer in quasi uniform field is briefly discussed.
In order to survey the radiation characteristics of pure line noise produced by corona discharge from overhead high voltage transmission lines, a disk type gap noise generator is manufactured. Disk size that decides capacitance between the noise generator and the ground is selected through preliminary indoor experiments and analysis by using charge simulation method. The field experiments are performed with the noise generator hung on the Kochang 765kV full scale test line. As the results, the useful data that can be used to analysis the radiation characteristics of corona noises from transmission lines are obtained. Those data are the directivity of antenna toward the line, lateral profiles, frequency spectra, height pattern and so on.
The behaviors of metal oxide surge arresters installed at substation terminal, generally without spark gaps are well-known by the excellent performances of automatic fault clearance and of reliable overvoltage protection of substation apparatus. As the result of four-year research experiences on the 77kV operating power systems including observed substations T and F halfway between the protection terminals, authors have proved the characterized discharge current of those arresters can be divided into three types of waveforms such as instantaneous heavy pulse, low level lingering continuance and medium continued damping oscillation. The negative lightning discharge with subsequent multiple strokes against de-energized power lines may be the distinct and frequent causes of damping current oscillation of surge arresters. Moreover, the negative discharge current on the sound phase has been encountered not a little in the case of related double-line-to-ground fault. In this paper, the combination of those parameters is clearly expressed through several representing figures of arrester current waveforms together with those of corresponding voltage of surge fronts and 60Hz voltage transients if available.
Lightning protection measures are required for the railway signalling system because suspension and delays of trains due to lightnings may cause social confusion. Therefore, we carried out experiments on propagation characteristics of lightning surges along a rail, and injected a lightning surge current into the rail or wayside ground to raise their potentials, in order to measure the lightning overvoltages on a level crossing for the insulation design. There are no precedents that have carried out these experiments in the field until now. We could obtain the following results. (1) The surge impedance of the rail is 56Ω and the surge propagation velocity in the rail is 55m/μs. (2) The surge attenuation depends only on the duration of wave tail of the traveling lightning surge along the rail and decreases as the duration of wave tail becomes longer. (3) Flashovers may occur at the terminals in the equipment of the level crossing in case 1) a 2kA lightning surge current is directly injected into the rail, or 2) a 10kA lightning surge current is injected into the wayside ground at a vertical distance of 2m from the rail. (4) We can estimate the lightning overvoltages on the terminals in the equipment of the level crossing according to the vertical distance from the rail of the lighting stroke and the level of the stroke current.
The study of surge voltage levels induced in low voltage control or monitoring circuits by lightning surges is very important for the rational design of those circuits in substations. To investigate the induction levels in those circuits, we carried out full-scale lightning impulse tests in a new 275kV full GIS substation. The obtained data clarified that the induced surge levels are under the testing levels of related standards. We analyzed the surge waveforms in the Potential Transformer (PT) secondary circuit by EMTP. The analysis indicated that induced surge levels are almost decided by the ratio of winding and the overvoltage level in a main circuit.
Fundamental characteristics of a 34-m long horizontal conductor buried at a depth of 1m have been studied with an FDTD method. An equivalent radius of a buried thin wire is shown to be 0.23 times the side of cells employed, which is the same as that of an aerial thin wire. The rate of current dissipating from each section of the buried conductor to the injected current is roughly equal to that of the section length to the total length although it is somewhat influenced by the direction of a current lead. As the conductivity of the ground is higher, the wavefronts of a voltage and a current become less steep. The high permittivity distorts wavefronts of a voltage and a current with their propagation. However, its influence appears only initially and the response at the injection point is little influenced by it. The transient grounding resistance at 5μs calculated by the FDTD method is 10 to 20% lower than the resistance calculated by Sunde’s formula.
This paper describes the theoretical calculation and experimental investigation of gas flow in the arc extinguish tube of the model switch. The theoretical calculation discussed here is the second process of the four processes in current interruption. Considering a results of experimental observation on the mass consumption of the tubes to arc energy and the pressure difference of the tube and pressure chambers, the theoretical equations were deduced for the gas flow in the tube during the current interruption process. Using these theoretical equations, the pressure in pressure chamber was calculated, and compared with the experimental results. In spite of adopting many assumptions in the derivation of the theoretical equations, the calculated and experimental values were mostly similar.
In the present work, a high power (30kW), atmospheric pressure inductive thermal plasma has been diagnosed both theoretically and experimentally in pulse amplitude modulation approach with Ar, Ar-CO2, Ar-N2, and Ar-O2 as working gases (100lpm argon and 2.5lpm molecular gas). Simulation has been carried out using a two-dimensional local thermodynamic equilibrium (LTE) code for the same torch and operating conditions as that of experiment. Calculating the so-called response times from both simulated and experimental temporal radiation intensity of ArI at 751nm, a rigorous and comprehensive comparative discussion has been made for a shimmer current level (SCL), the ratio of lower to higher level of current pulse, varying from 40%—100%. The measured temperature is also compared with the calculated apparent temperature. In spite of some discrepancies (at lower SCL) with the magnitude of response times of experimental and simulated plasma at the instant of on-pulsing transition, similar trend of those have been observed. These results will help to clear the understanding of transient performance of the concerned gases and equilibrium phenomena.
This paper surveys disturbances experienced in the low-voltage control circuits of the power stations and the substations of Kansai Electric Power. Induced voltages to an overhead control cable from a grounding mesh were measured when an impulse current was applied to the grounding mesh. A non-metallic sheath cable (CVV cable) and a cable with a metallic sheath (CVV-S cable) were tested to investigate the effect of the metallic sheath on the induced voltage to the cable. Then, a simulation model of the transient induced voltage to the overhead conductor from a counterpoise was proposed. Finally, the simulation results were compared with the measured results to confirm the accuracy of the proposed method.
In this paper we present transient analysis of transformer models by the moment method in frequency domain. The results show that the secondary voltage has the peak which is higher than the voltage calculated by the primary voltage and the winding ratio. The inductance of the winding and the capacitance between windings have an influence on a surge in the transformer winding. In addition to the transient analysis we calculate the inductance from time responses and the impedance in low frequency, and compare them with the analytical equation which is based on Nagaoka factor.
In nowadays deregulated market, available transfer capability (ATC) is a measure of the network capability for further commercial activity above the already committed uses. This paper deals with the development of an interior point nonlinear programming methodology for evaluating dynamic ATC. By establishing a novel method for integrating transient stability constraints into conventional steady-state ATC problem, the dynamic ATC problem is successfully formulated as an OPF-based optimization problem. Then, an interior point nonlinear programming algorithm is used to solve the formed dynamic ATC optimization problem. The method has been implemented and tested on two IEEJ model systems (WEST10 and WEST30). In both systems, satisfactory results are obtained.
The reduction effect of life cycle CO2 emission is examined in case of introducing a PV/solar heat/cogeneration system into public welfare facilities(hotel and hospital). Life cycle CO2 emission is calculated as the sum of that when operating and that when manufacturing equipments. The system is operated with the dynamic programming method, into which hourly data of electric and heat loads, solar insolation, and atmospheric temperature during a year are input. The proposed system is compared with a conventional system and a cogeneration system. The life cycle CO2 emission of the PV/solar heat/cogeneration system is lower than that of the conventional system by 20% in hotel and by 14% in hospital.
We have carried out analysis of lightning surge on overhead distribution lines by using EMTP. We made a model for electric breakdown of a 14m concrete pole with impulse voltage (rise time: 2μs) applied to the outer surface at the top of the concrete pole. We found that the transient impedance of the breakdown increased linearly before the breakdown and decreased exponentially after the breakdown. The measured voltage and current waveforms correspond to the calculated waveforms by regarding the impedance of the breakdown as resistance. Also we examined the impedance of flashover of an insulator with impulse voltage applied to the lines. The transient impedance of flashover is expressed approximately by the formula: Z(t)=A×exp(-(t-t0)/τ), (A=1500~5000, τ =3×10-8~5×10-8sec, t: time, t0: starting time of flashover).
The present paper describes a prediction method of the dielectric strength of the air in gas temperature range of 300—3500K. First, the equilibrium composition of the air at gas temperatures of 300—3500K was calculated through Saha and Guldburg-Waage equations. Secondly, the electron energy distribution function (EEDF) was calculated by an adoption of the two-term expansion of Boltzmann equation. Finally, the effective ionization coefficient α was derived from the EEDF obtained. The critical reduced electric field strength (E/N)cr, which gives zero effective ionization coefficient α=0, was obtained at gas temperatures of 300—3500K. The result indicates that (E/N)cr decreases as the gas temperature increases from 1500K to 3500K, which is due mainly to an increase in the mole fraction of NO molecule which has a much lower ionization potential compared with N2 and O2. This calculated result fairly agrees with an experimental one.
We have investigated propagation properties of Lamb waves and motion characteristic of free moving metallic particle in gas insulated switchgear (GIS) tank to diagnose insulation performance of GIS. We have proposed a new identification technique of the defect location in GIS based on the time-frequency analysis of the Lamb waves using the Wavelet Transform. In this paper, we measured the acoustic signals excited by a metallic particle colliding with the tank sheath. Furthermore, we measured the moving particle under the high electric field in GIS using a high speed video camera. As a result, it was examined that the relationship between maximum lifting height and the flight time during subsequent impacts of a moving particle. Moreover, we estimated particle size based on propagation properties of Lamb waves.
The present experimental study has aimed the improvement in the performance of a shock-tube driven disk CCMHD generator. For that purpose, an experimental set-up was arranged as follows: (1) An inlet swirl was introduced. (2) An area ratio of the disk generator was small. (3) A cesium seeded helium gas was used as working medium. Not only these factors but also a production of a homogeneous plasma contributed to outstanding performance of an isentropic efficiency of 63% and an enthalpy extraction ratio of 30.8% at a stagnation temperature of 2250K and stagnation pressure of 0.14MPa. Furthermore, a maximum electrical power output of 1.23MW and a maximum power density of 297MW/m3 were obtained.
Superconducting generators have many advantages such as increasing generation efficiency and improving power system stability etc. In Japan, 70MW class superconducting generators have been developed through the national project“Electric Power Application of Superconducting Technologies (1988-1999)”. In this paper, performance evaluation of the rotor damper structure for the 70MW class model generator is discussed. Double-layered damper structure, which consists of a squirrel-cage warm damper and a single-layered cold damper was set as the target. As the first step, basic electromagnetic and thermal performances were obtained through the experimental model. In the following step, the 70MW model rotor damper structure was designed based on the experimental results and the rotor was manufactured. Evaluation of the damper structure of the 70MW rotor was carried out in the verification test from the technical view point of ‘unbalance current capability’, ‘flux shielding’ and ‘generator reactance’ etc. and satisfactory results were obtained. Consequently, it was proven that the damper structure had the performances to satisfy the requirements of the superconducting generators. Performances obtained from the experimental model, design of the 70MW model rotor and evaluation by the verification tests are described in this paper.
In the case of the cable fault that ground fault resistance is less than 10MΩ, Murray Loop Bridge is excellent as a fault locator in location accuracy and the convenience. But, when the induction of several hundred V is taken from the single core cable which adjoins it, a fault location with the high voltage Murray Loop Bridge becomes difficult. Therefore, we developed Murray Loop Bridge, which could be applied even when the induced voltage of several hundred V occurs in the measurement cable. The evaluation of the fault location accuracy was done with the developed prototype by the actual line and the training equipment.
As a weak energy phenomenon by electric field, it is well known that ionic wind is generated by the ionization of gas around the tip of needle electrode in high AC electric field, and the water evaporation is promoted by the wind. This letter presents that the water evaporation is restrained when the tip of needle electrode is in the water.