Hitachi, Ltd.

The Kansai Electric Power Co., Inc.

Sadahiko Niwa

Kiyoshi Narato

Hiroto Nakagawa

Yasuteru Oono

Keizou Ohtsuka

Osamu Nagura

Yosio Furukawa

Shigehiro Kayukawa

Tadaatsu Kato

Keizo Ohtsuka

A generator/motor system comprises a generator/motor having a primary winding and a secondary winding installed on the motor rotor coupled to a prime mover/load, a main circuit interposed between a power system and the primary winding of the generator/motor, an excitation circuit including a frequency converter inserted between a part of the main circuit and the secondary winding of the generator/motor, a frequency difference detector for determining the difference between the frequency of the power system and a frequency dependent on the rotational speed of the load, and a phase-shift control device for controlling the firing phase of the frequency converter in the excitation circuit by use of a signal from the frequency difference detector as a reference signal. In normal operation, a frequency signal following the frequency of the power system is produced, while at the time of a disturbance of the power system, the same frequency signal of the power system as before the disturbance continues to be produced thereby to keep the system in stable operation. For this purpose, a starting electric machine, a synchronous motor and a synchronous generator are aligned, and an output of the synchronous generator is applied to the frequency difference detector.

Variable-speed generator/motor system

A method and apparatus for diagnosing an overheating of a gas-cooled type electric machine having at least some components coated with an organic insulating material which decomposes into, for example, particles when subjected to high temperatures. The apparatus includes an extracting arrangement for enabling an extraction of gas from any region in an interior space of the electric machine. A device is provided for detecting a density of the particles contained in the gas and an arrangement is provided for analyzing a composition of the decomposed organic insulating material in the coolant gas so that, at first, an overheat region may be found and, secondly, an overheat position in the overheat region can be determined on the basis of the organic composition of the decomposed organic insulating material contained in the coolant gas.

Method and apparatus for diagnosing overheating of an electric machine

In a gas cooled rotary electric machine using insulating coating material which is subjected to thermal-decomposition when the insulating coating material is exposed to high temperatures thereby generating submicron particles, the concentration in the cooling gas of submicron particles generated through thermal-decomposition of the insulating coating material and distributed in the cooling gas is detected and an alarm signal is issued when the time-integration of a signal representing the concentration of the submicron particles exceeds a predetermined reference integration value.

Method and apparatus for diagnosing local overheating in a rotary

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Hitachi, Japan

Sadahiko Niwa