Hitachi, Ltd.

The Tokyo Electric Power Company, Incorporated

Chubu Electric Power Company, Inc.

Yoshiaki Matsui

Tokio Yamagiwa

Hiroshi Arita

Kunio Hirasawa

Junzo Kawakami

Junzo Kida

Mitsuyasu Kido

Yoshihiro Sano

Tomio Chiba

Takafumi Maeda

Keizo Inagaki

Shigeyuki Sugimoto

Sadanori Neo

A ground fault current limiter, in which reactors are connected in series to a neutral point for compensating for capacitances to ground of a power switches capable of turning ON/OFF at a high speed are connected in parallel with respective reactors, occurrence of a ground fault is detected from a phase difference between a zero-phase sequence current and a zero-phase sequence voltage at time of sampling, an optimal compensation quantity of capacitances to ground is computed based on the zero-phase sequence current and the zero-phase sequence voltage at time of occurrence of a ground fault, and ON/OFF of the switches are controlled thereby to alter the reactor quantity so as to correspond to the compensation quantity.

Ground fault current limiter and method of limiting ground fault current

In order to control a voltage using e.g. a tap transformer, the difference .DELTA.V between the actual voltage and a reference voltage is obtained and integrated over time. That integral is then modified by at least one parameter generated by fuzzy logic from control conditions of the voltage. In this way the fuzzy logic may find the optimum control strategy which keeps the actual voltage closest to the reference voltage without an excessive number of tap position changes. The reference voltage may vary with time, and therefore the control of the voltage with time may be evaluated, and the control conditions varied accordingly, e.g. by fuzzy logic, so that the control arrangement can exhibit learning. Normally, the integral is modified such that

Voltage or reactive power control method and control device therefor

A method and system of transformer protection in which parallel admittance currents indicative of the apparent excitation state of a transformer to be protected are evaluated from the transformer terminal voltages and currents sampled at a proper interval, and discrimination between an internal defect and excitation inrush is made in response to a magnitude of the parallel admittance current, and a breaker opening command is issued in response to a judgement of internal defect. The method and system enables high-accuracy and high-sensitivity fault detection through a simple computation.

Method and system of transformer protection and method and system of

Growing community of inventors

Katsuta, Japan

Yoshiaki Matsui