Muneaki Hayashi

Monte Carlo simulation of surface charge on angled insulators in vacuum

A two-dimensional computer analysis of the surface charging on angled insulators has been performed by using the Monte Carlo simulation method. Results are compared to the charge in equilibrium model, originally proposed by C.H. de Tourreil and K.D. Srivastava (1973). >

Transient stability analysis of multimachine power system by Lyapunov's direct method

Practical applications of Lyapunovs direct method to transient stability analyses of multimachine power systems have been obstructed by the well-known conservative nature and the computational difficulty accompanying the usual critical value of Lyapunov function. These problems have been solved in this paper by introducing a new critical value for the first swing stability, and by developing a efficient method of calculating it as well as one of taking account of transfer conductances. These methods have been applied to a transient stability analysis of a 10-machine power system, and yielded results of practical significance.

Effects of spark conditioning, insulator angle and length on surface flashover in vacuum

A flashover test was conducted in a vacuum gap, bridged by an insulator in the shape of a frustum of a cone. The test gap was subjected to a lightning impulse voltage of 2/50 mu s. The flashover voltages were observed for various cone angles and insulator lengths. Traces on the cathode due to flashovers were observed. A spark conditioning using voltage pulses of reverse polarity is shown to reduce the number of shots needed to obtain a stable flashover voltage. The flashover voltages depend strongly on the cone angle even in the case of the lightning impulse. The flashover fields depend strongly on the insulator length. The traces are distributed not only at the triple junction but also over a wide area of the cathode surface when the gap distance is shorter than 15 mm. This fact indicates the existence of two different flashover processes. >

Breakdown process of a rod-to-plane gap in atmospheric air under DC voltage stress

Discharge phenomena were observed under chopped or steady state DC voltage application. A still camera and two photomultipliers were used to record and measure the development of the electrical breakdown in a normal air gap. The breakdown process under both positive and negative DC voltage stress differs from that under impulse voltage. In the case of DC voltage, space charge is produced by corona discharges prior to the complete breakdown, which affects the breakdown process significantly. >

Effect of low-temperature electrode baking on breakdown in vacuum

Effects of electrode baking at a comparatively low temperature in vacuum have been examined. The temperature of the electrode is controlled well below the melting point of organic insulators, if installed. Currents accompanied by the microdischarges and the conditioning process during breakdown test are observed. It is shown that low temperature baking effectively suppresses the microdischarge, and that baking of the anode is more effective than baking of the cathode. It is also shown that baking reduces the number of voltage applications which are necessary for the spark conditioning. >

Studies on Coroaa in Transformer Oil by Measurement of Space Charge

Studies were carried out in needle-plane gaps with a comparatively long separation (50 to 150 mm) in transformer oil. Relations between needle voltages and space charge quantities due to coronas by lightning impulse and ac voltages were obtained. The charge quantities for ac voltage are 2 times larger than those for positive impulse voltage, and 7 times larger than those for negative impulse voltage. The polarity effect on the charge is not observed in case of ac voltages. Back-discharge phenomena take place, accompanied by sudden space charge reductions, at the wave tail of the impulse voltage. The space charge due to initial coronas at the wave front are reduced to 57 to 85% by the phenomena.

Design of Stabilizing Controllers of Power System Using Pole-Assignment Technique

Abstract A method of designing stabilizing controllers is presented in this paper. The controller parameters are determined by pole-assignment technique based on the first and second order eigenvalue sensitivities. The method is applied to a single-machine infinite-bus system and a two-machine infinite-bus system, and the performances of these systems are studied. The results are proved to be very useful for designing decentralized controllers of large-scale power systems and low sensitive controllers to variations of the operating point.

Location of Corona and Measurement of Space Charge in Transformer Oil

An investigation was made in order to develop a location technique of corona discharge in insulating oil, in view of the development of the UHV transformer. This paper describes the principle of analyzing the corona location by making use of electrostatic probes. The corona produces a space charge in the oil, and induces charges on the probes electrostatically. Thus, the location as well as the space charge of the corona can be analyzed.

STABILIZING CONTROL FOR POWER SYSTEMS BY MEANS OF SUPERCONDUCTING MAGNETIC ENERGY STORAGE.

An energy storage for electric power systems using magnetic energy of a superconductive coil has long been proposed and investigated with respect to the conceptual design and the control method. The superconducting magnetic energy storage (SMES) has higher efficiency than the pumped storage, and also, the electric power can be rapidly controlled through the firing angle control of the thyristor bridge of SMES. Therefore, SMES can be used for the stabilization of electric power systems if it is properly controlled. This paper represents the stabilizing control of electric power systems by means of SMES. First, the concept of stabilizaion by an SMES is described. For the system stabilizing control, we propose the control of the firing angle ∝ by the feedback of the angular velocity deviation δω of the generator rotor. We then apply it to a one-machine infinite-bus system to examine its effect. The feedback control has been found very effective for the system stabilization. We also make clear that the optimum location of the SMES for the system stabilization can be determined by means of the participation matrix, using a numerical example on a 10-machine system.