Discharge Phenomena in SF₆ and SF₆-Air Mixture Gas under Impulse Voltage

The discharge phenomena in pure SF₆ and SF₆-air mixture gas are observed by electrical and optical technics. Current and light pulses accompanied with the corona discharge in pure SF₆ gas have very low peak values and a short duration time compared with those in air. The velocity of the corona development in pure SF₆ gas is about 10⁷cm/s, and is almost the same as that of the leader in air. When the SF₆ density in SF₆-air mixture gas is high, the discharge channel becomes fine and short. The space charge production of l～60 nC is observed for the occurrence of the corona in SF₆-air mixture gas

Asynchronous Operation and Resynchronization of a Synchronous Machine in a Power System

The large signal performance of a multimachine power system is described by a set of differential equations of the form ＝f(x). The system disturbance caused by asynchronous operation of a synchronous machine in a power system was investigated by solving the system equations with the method of Runge-Kutta-Gill and the possibility of the resynchronization of an asynchronously operating machine was studied, using the method of phase plane analysis. The effects of control systems on the resynchronization of a machine were estimated

Reliability Aspect of Application of DDC Computer in Power Plants

The subject of this paper is the reliability aspect of the application of DDC computer systems in thermal and nuclear power plants. The influence of the computer's Mean Time to Failure and Mean Time to Repair on a power plant's economic outage penalty cost has been investigated, and the total economical losses during the economical power plant life have been calculated for various economical factors

Numerical Solution of Three-dimensional Eddy Current Problems

A general numerical method is given for the solution of quasi-stationary electromagnetic field problems. The integral equation-type formulation used permits the elimination of field quantities of inactive regions (air etc.) from the calculation. Some difficulties present in other methods (like surface charges etc.) are also avoided. The use of global variables in connection with the coordinate-independent (tensorial) form of the basic equations is likely to be helpful for an easy definition of a class of practical problems for a general computer program. A numerical example is included

A Network Analogy for Three-dimensional Eddy Current Problems

We present a numerical method for the solution of eeddy current problems arising in the analysis of electric machines. The method is based on a network analogy which is equivalent to a differential-integral equation formulation of Maxwell's equations, using the Biot-Savart Law. The present approach is intended mainly to give an intuitive picture rather than to be used as a general method for solving practical problems. A more effective method is presented in a companion article, where we start from a direct mathematical formulation

An Experimental Study of Flux-Linkage Relations in a Synchronous Generator at Steady States

The inductances of a synchronous generator at a three-phase balanced synchronous operation are discussed experimentally by measuring the air-gap flux-density distributions. The results revealed general aspects of inductances, which depend on the operating conditions of the generator. In particular, the appearance of a unilateral inductance from the armature to the field windings is noteworthy. Special attention is also directed towards the relations between the magnetic flux-linkages and the currents of the armature and the field windings. As a result of this investigation, an alteration is proposed for a conventianal, field flux-linkage relation. The alteration has not been reported hitherto and can not be derived from the conventional theory of synchronous machines

Space Charges Produced in a Rod-to-Plane Gap under Impulse Voltages

The space charges produced in a hemispherical rod-to-plane gap in air are measured under the impulse voltage application by the use of a probe, which is constructed by a sphere near the gap space. The space charges accompanied with the streamer occurrence are about 20～200 nC and 5～60 nC for the positive and negative voltage application, respectively. The maximum space charges over the whole process to the flashover are 20～260 nC and 20～60 nC for the positive and negative voltage application, respectively. After the flashover occurrence, the space charges remain in the gap space, the values being below 200 and 30 nC for the positive and negative voltage application, respectively

Non-Linear Analysis of Sudden 3-Phase Short-Circuit in a Synchronous Generator

The present paper investigates the saturation effect on a sudden 3-phase short-circuit which occurs in a salient-pole synchronous generator used in Kyoto University's model power transmission system. Since the magnetic saturation occurs primarily in the pole-core of the machine, the saturation is taken into account in deriving the directaxis equivalent circuit. First, we make a direct-axis saturation model and then, based upon it, derive a differential equation which regulates flux-linkages under a sudden 3-phase short-circuit condition. With the same degree of accuracy as in the conventional linear theory, this equation can be separated into a set of linear equations which can regulate the armature flux-linkages, and a non-linear differential equation which can regulate the field flux-linkage. By means of such theoretical considerations, simulations and experiments, we clarify how the saturation effects both the amplitudes and the time-constants of the alternating- and the direct-current components of short-circuit currents

Experimental Approach to Shielding and Reducing Effects on Ion Currents and Electric Fields at Earth Level under a DC Transmission Line

Use of a d. c. transmission line to find a way to reduce ion currents and electric fields at earth level is a most important matter for environmental safety. This paper discusses the relation between the ion currents and the electric fields at earth level, measured by using a unipolar d. c. transmission line scale model and a bipolar d. c. transmission line. Electric fields at earth level were calculated by means of the image charge method without taking into consideration the space charge caused by the d. c. line. The middle scale models for the unipolar and the bipolar d. c. lines were set at the height of the d. c. lines at 2m. Both types of scale models were set up in a sufficiently spacious room. Two small scales for the unipolar and the bipolar d. c. lines, with the height of the d. c. lines set at 20cm above the earth and the separating distance between the two d. c. lines set at 35 to 75cm, were placed in a suitable roomo. Both the experimental results are discussed here in comparison with the calculated fields. As a conclusion, in using the model unipolar d. c. line with a shielding wire, the shielding effects for both the electric fields and the ion currents at earth level nearly coincided with the calculated fields. However, in using the model bipolar d. c. lines, the reducing effect for the ion currents dind't coincide with the ealculated fields, actually not quite half of the calculated fields. In particular, the ion currents, at earth level on the positive voltage side were reduced very well, relative to those on the negative voltage side. They were measured in relation to the ratio of the separating distance of the bipolar d. c. lines to the the height of the d.c. line from earth level

Discharge Phenomena of the Insulator Assembly and Occurrence of Critical Cascading Flashover Phenomena

This paper describes conditions for an occurrence of cascading flashover phenomena on the insulator assembly with the use of a high voltage transmission line by experiments in a laboratory room. The 154 kV suspension insulator assembly is employed as testing apparatus which consists of a chain of 9 standard suspension insulators equipped with an arcing horn. In the experiments, the apparatus is separated into two parts consisting of a bare insulator chain and a pair of arcing horns. The lightning impulse with positive polarity or negative are applied to the test pieces, and the over-voltage is used in those tests. Thus, the creeping flashover occurred with short lag time. The V-t curves and the 50% cascading flashover voltage were obtained and the prebreakdown phenomena were observed from the tests, then, it is concluded that the critical cascading flashovers occur with short time lag (T₀＝1.8 μ sec. or less) and a high steepness (1833 kV/μ sec. or more), and corona on the insulator surface starts from negative side electrode