Thyristor controlled series capacitor (TCSC) is considered to be effective not only for flow control and stabilization of power systems, but also for mitigation of subsynchronous resonance (SSR). This paper clarifies SSR mitigation mechanism of TCSC. First, we show by time simulations that SSR appears and disappears depending on the firing angle of TCSC. Next, we show that its frequency characteristics varies much with the firing angle. Further, we show that SSR occurs in TCSC-compensated systems as well as in conventional series-capacitor-compensated systems when 60Hz minus an electrical resonance frequency of a transmission system coincides with a tortional oscillation frequency of a generator-turbine shaft. TCSC can avert SSR by changing its firing angle and by shifting the electrical resonance frequency. Next, we propose an equivalent circuit of TCSC which consists of a series capacitor in parallel with a resistor and a reactor. We adjust its parameters so that it shows frequency characteristics same as TCSC. We apply it to time simulations to see if it work equivalently as TCSC. Finally, we do eigenvalue analysis with the equivalent circuit. We can get results corresponding to the time simulations.

View full abstract

The diffusion of power electronics is increasing the harmonic sources like home applications, OA apparatus. and industrial apparatus. They have caused many electrical accidents, such as bunting out, vibration. malfunction and so on. Thus we should take measures to avoid these accidents. As the leading technology of the countermeasure for thus problem we have studied Active Filter (AF) which removes harmonic current by pouring into compensation current to which the quantity of hannonic current with opposite sign is equal. It needs high performance harmonic analyzer to get the quantity of harmonic current.
Recurrent Neural Network (RNN) can detect fundamental current without being affected by harmonic phase changes, It also has the ability to learn how to convert load current to fundamental current by itself. These abilities of RNN fit to apply to harmonic current analyzer of AF. So we suggest to apply RNN as harmonic current analyzer and investigate the ability of RNN to eliminate hannonics. As a result of simulations we have proved that RNN can eliminate harmonic current without being influenced by composition rate and phase of harmonic current and work as a high performance haronic analyzer.

View full abstract

Power resource planning-the decision of construction period of generators-is affected by several uncertainties: load demand, fuel cost, and so on. In order to evaluate power resource planning which necessarily involves several uncertainties, it is usual for planners to prepare many scenarios which consider several uncertainties and to analyze whether the particular resource plan is feasible far every scenario. It is a large computational burden to analyze even one scenario. In order to realize an efficient scenario analysis, several preferable scenarios which can reflect many scenario must be determined. In this paper, in order to create preferable scenarios, we propose a new scenario creation algorithm corresponding to the planner's consideration process. The proposed method employs a combntation of Chaotic Neural Network (CNN) and Genetic Algorithm (GA). CNN is able to carry out a dynamic pattern association function effectively, and GA has an excellent adaptive nature. The effectiveness of the proposed method is demonstrated by numerical results for the actual data of several uncertainties in 1986_??_1990 through comparing these with the decision tree method.

View full abstract

A Superconducting Fault Current Limiter (SFCL) is expected to be very effective to introduce flexibility of power system planning and operation due to its possibility to reduce short circuit current and design criteria of electro-magnetic force and to enhance transient stability and so on.
This paper describes:
(1) Desirable introduction forms of an SFCL into power systems are proposed.
(2) Six specific parameters of an SFCL for power systems application are defined.
(3) Design method of the specific parameters of a resistance type SFCL in overhead transmission lines are proposed and verified considering operation of protective relays.

View full abstract

Recently, there is greater demand for stable supply of electric power as higher level of our living. It becomes the important problem that the cause and the location of ground fault in distribution line is found out in early stage and the bad part is repaired as soon as possible, if once it occurs. Therefore, the unit for recording the waveform Io of ground fault's current and the waveform Vo of its voltage is installed in distribution substations and same data are coming to be gathered and the establishment of the technology to distinguish automatically their fault causes is hastened.
In this paper, a pew classification method of their wavefprms for ground faults. It is the method concerned with phase plane trajectry for the values of current or voltage and their differential values. It is found from the examinations of ground faults waveforms based on the real data that the waveform of current I_o is more suitable than that of voltage V_o for the classification of waveforms at the ground faults and each trajectry of three type waveforms such as sine wave, trapezoidal wave and needle-like wave has each characteristics in its figure. It is also found from the distribution of 167 sampling points on the phase plane that any waveforms at the real ground fault may be classified into three characteristic distribution of the points and it gives the possibility of easy display for the classification of the ground fault causes.

View full abstract

Large capacity adjustable speed machines (ASMs) at pumped storage power station have been put into full operation and the operating characteristics of ASM have been highly evaluated from the view point of power system operation. The output power (input power) of ASM can be controlled very quickly by applying a vector control scheme to the excitation control. This quick responsive feature of ASM can make it possible to improve the stability of the neighbor sub-power system.
For improvement of transient stability, the output power of ASM is reduced very quickly in order to control the acceleration of neighbor generators during and after transmission line faults. For improvement of dynamic stability, the output power of ASM is modulated in accordance with the stabilizing signals detected from the swing of generator rotor or the power flow fluctuation on the transmission line.
This paper describes the design concepts and method of control system for improving the transient and dynamic stability and proposes a power system stabilizing control system. The effects of the proposed stabilizing control system have been verified by a power system simulator.

View full abstract

In order to discuss the reliability of a gas insulated switchgear (GIS) insulation under the operating conditions, the deterioration characteristics (V-t characteristics) of GIS insulating spacer model was studied by AC voltage application. The deterioration factor n which indicates the decrease of breakdown voltage under the application up to 1000 hours was found to change at the two grade with the lapse. And, the relation between partial discharge (PD) inception voltage and breakdown voltage was studied after 1000 hours applications. As the result, it was found that both voltage (V₅₀) at a 50% cumulative probability were equal to the initial values. But, dispersion of PD inception and breakdown voltage have a tendency to be larger than initial values.
Moreover, in oder to make the deterioration phenomenon clear, the relation between the ratio of applied voltage (Va) and the initial PD inception voltage (Vp) and lifetime was obtained. The inclination of curve indicated at the minimum value in VaJVp-t characteristics has similar tendency with V-t characteristics and the minimum value of Va/Vp is 0.4. This value corresponds to deterioration of 3.4 σ (σ is standard deviation) from V₅₀ of PD inception. From the above characteristics, the threshold value of dielectric strength for V-t characteristics on GIS insulating spacer model is assumed to be a 4 σ from V₅₀ of PD inception.

View full abstract

The object of the numerical investigations is the effect of gasdynamic fluctuations of plasma flow, under the assumption of fully developed turbulence, on the performances of the ideal non-equilibrium MHD-generator. The numerical investigations are carried out on the basis of the quasi-one-dimensional timedependent numerical model, which takes into account turbulent effects. Because of the comparatively high Reynolds number, all of the relevant scales of motion cannot be captured by the numerical grid scheme, and the effect of small scale eddies (less than the mesh size) is accounted by the subgrid-scale eddy turbulent viscosity model. The direct numerical simulation is used for large scale eddies (larger than the mesh size). Mainly, the investigations were conducted in the interval of middle and low values of external load resistances, which corresponds to the stable and the unstable areas on the Voltage-Current characteristic. The results of the numerical simulations show the development of the additional MHD viscosity in unstable regions on the Voltage-Current characteristic.

View full abstract

This paper presents a new system for detecting electromagnetic waves emitted from a partial discharge (PD) due to a material defect in a high-voltage electric machinery and apparatus. PD is a symptom and/or a direct cause of the deterioration of the insulation used in the high-voltage stator coil. This system can detect PD by using the spatial phase information of the microwave emitted from PD which is very short duration voltage pulse. We describe the properties of this system, which is composed of two double-ridge-guidehorn-antennas, a GHz-2ch-down-converter (originally designed and produced), two A/D converters and a computer, and experimentally show that this system is able to apply to detection of the microwave emitted from PD of the stator coil in this paper. The result of this work is the development of new non-contact PD detection system for the generator which can be performed by station personnel.

View full abstract

The small capacitive current switching by the vacuum switch is simulated using Electromagnetic Transients Program (EMTP) into which Mayr's equation is combined through the function of TAGS. Mayr's equation to describe the dynamic behavior of an arc in vacuum switches is a function of arc conductance, arc time constant and arc energy loss. The arc time constant and the arc energy loss are assumed as a function of arc conductance.
To obtain the arc parameters experimentally, a resonant high frequency circuit constructed by a capacitor and a reactor is added to the test circuit. The arc parameters are obtained by the resonant high frequency component of the arc current and the arc conductance.
While the arc current becomes small, the spike voltages appear on the average arc voltage. The spike voltage stimulates arc current to generate the resonant high frequency current component. The resonant high frequency current component becomes larger with the passing of the time, then the current chopping occurs when the resonant high frequency current passes through zero.
The arc current is simulated by the reproduction of the spike voltages according to the measured arc voltage waveform in simulating processes. The simulation of the spike voltages are realized by a small resistance and two current sources. The result of the simulation of the switching arc phenomena by the vacuum switches gave good agreement with the result of the measured arc current near the current chopping. In consequence of this simulation, the small capacitive current interruption by vacuum switches is closely influenced by the spike voltages.

View full abstract

Two-dimensional stability analyses for open-cycle supersonic disk MHD generators are carried out which take into account electrical boundary conditions. A method of γ-θ two-dimensional linear stability analysis for supersonic disk MHD generator is proposed, which examines the time growth rate of perturbations. The growth rate is determined by the characteristic equation which is derived from the electrical boundary condition. Whether the perturbations grow or decay is judged diagramatically in a way similar to the Nyquist's method. A coal-fired outflow supersonic disk MHD generator of commercial scale is analyzed under several types of boundary conditions. The stability is much affected by the electrical boundary condition and also by the azimuthal wavenumber of disturbance. The two-dimensional analysis has revealed an azimuthally nonuniform instability in one of the load sections of the generator, where no instability is found in the one-dimensional analysis. The analysis also shows that the instability can be suppressed by subdividing the load section with some control electrodes.

View full abstract

The influence of water vapor contained in working gas on the discharge structure and performance in a closed cycle disk MHD generator is examined numerically. A model of the energy loss process due to inelastic collisions of electrons with water molecules is proposed. The contamination of water vapor is found to narrow the stable region in electron temperature where the fully ionized seed plasma is realized. It is confirmed from γ-θ two dimensional numerical simulations with the present model that water vapor contamination causes the strong nonuniform plasma and reduces the generator performance.

View full abstract

There is a few data of contamination characteristics of HVDC porcelain type surge arresters. Therefore, this paper describes contamination withstand characteristics of DC 250kV porcelain type surge arresters with special sheds and nominal sheds. Uniform pollution and non uniform pollution (partial wetting) slurry methods have been applied to contamination evaluations. This DC 250kV porcelain type surge arrester with special sheds can withstand on slurry pollution tests at equivalent salt deposit density 0.01-0.03mg/cm².

View full abstract

In the technical report relating to the insulation design of overhead transmission lines published by The Institute of Electrical Engineers of Japan⁽¹⁾, two calculation methods are indicated with respect to a distance between two circuits in overhead transmission lines.
One of the methods is an empirical formula, while another is intended to determine the range of fluctuation in swinging motion when the wind having a specific spectrum and spatial structure has acted on a conductor. The author has given additional development to the latter method, thus successfully establishing a more rational method to determine a necessary distance between two circuits.
That is to say, in the conventional method, it was presumed that the wind having identical characteristics and structure would act upon the conductor on the windward side, differently from that on the leeward side. In practice, however, the wind which has acted upon the conductor on the windward side acts upon the conductor on the leeward side with a certain time lag, so both motions are not an independent phenomenon. As a result of making studies considering this point, the author has found that the fluctuation in distance becomes far smaller than the value calculated by the conventional method, consequently making it clear that the width under transmission lines can be much reduced.

View full abstract

Lightning strokes with high energy sometimes occur on the Japan Sea Coast. In this area, not a few surge arresters on power distribution lines have been damaged by lightning. Therefore, it is very important to study the method to reduce the number of failure of surge arresters.
This paper describes the effect of lightning protection method on the failure rates of surge arresters on power distribution lines due to direct lightning hits. The analysis shows that: (1) the failure rates of surge arresters without an overhead ground wire are about 3_??_5 times larger than those with one, and (2) when surge arresters with higher withstand capabilities are adopted, it is effective to give priority to the installation of surge arresters at the open-termination of a line.

View full abstract

Ablation arcs in a cylindrical tube which has a pressure chamber at one end of it are investigated experimentally and theoretically. The experimental data are interpreted by an arc model consisting of four processes which describe the relationship among the pressure distribution in the tube, gas flow in the tube and the pressure in the pressure chamber.
Ablative gas ejected from the tube under the heat of the arc raises the pressure in the chamber in the 1st and the 2nd processes. The pressure in the chamber diminishes in the 3rd process, because of both its excessive high pressure and relatively low power of the arc, i.e. the gas in the chamber flows out through the gap between the arc column and the tube wall. After current zero, or in the 4th process, the gas in the chamber blows out through the tube with no disturbance. The 3rd and the 4th processes are mainly treated in this study.
The well-known quasi-steady-state theoretical solution is applied to the analysis of thermodynamical parameters in the pressure chamber in the 4th process. The same parameters in the 3rd process are described by a new quasi-steady-state theoretical equation which considers the balance between pressure of the arc and pressure in the chamber. Calculated and measured pressures in the chamber are in good agreement under a suitable initial condition of temperature in the chamber. Calculated effective diameter of the arc column and optically observed diameter of the bright region corresponding to the arc column show similar contractive characteristics.

View full abstract