Hitachi, Ltd.

Hitachi Engineering Co., Ltd.

Yasushi Momochi

Masuo Goto

Akira Isono

Takaaki Kai

Koichi Kimura

Hiroaki Aotsu

Akihisa Kaihara

Satoshi Kitamura

Takeshi Matuzaki

Hirosi Okada

A field control apparatus for a generator having a field winding comprises a terminal voltage control unit for controlling a field current of the generator in accordance with a difference between a terminal voltage signal of the generator and a reference voltage signal, which control unit has at least one of a line drop compensation function, an under-excitation limitation function, an over-excitation limitation function, a power factor regulation function, an armature winding over-current compensation function and a cross-current compensation function. The field control apparatus includes a detector as a common signal source for detecting active power and reactive power components at an output terminal of the generator and means responsive to the output of the detector for performing scalar operation in accordance with a function of the added compensation/control function described above. An output of the operating means is added to the differential signal as an added function signal to control the field current for excitation of the field winding.

Excitation control apparatus for a generator

Disclosed is an apparatus for carrying out normal stop of a synchronous generator in an advantageous manner without use of a field breaker. The apparatus comprises a six-phase thyristor converter for controlling field excitation of the synchronous generator in dependence upon terminal voltage thereof, which converter exhibits not only a forward conversion function (power rectifier) but also backward conversion function (power inverter). When a generator operation stop command is produced, the operation of the converter in power rectifier mode is changed over to power inverter mode. During the inverter mode operation, when the terminal voltage of the synchronous generator becomes lower than a preset value, a pair of counter part thyristors among the thyristors constituting the converter are simultaneously fired to bring about a short-circuited state in the excitation circuit with all the firing pulses supplied to the other thyristors being suppressed, thereby to complete the stopping operation for the synchronous generator.

Excitation control apparatus suited for normal stop operation of

An apparatus for protecting a synchronous machine from a field overvoltage is disclosed. The apparatus comprises a field excitation control circuit which is impressed with the armature voltage of the synchronous machine so as to provide a DC power supply for producing a DC output to excite the field winding of the synchronous machine, a first discharge circuit which is adapted to discharge the stored energy of the field winding when the synchronous machine is to be tripped under predetermined conditions, and a second discharge circuit for reducing the field voltage by allowing a field current to flow therethrough in response to generation of an overvoltage whose absolute value is higher than a predetermined level, across the field winding. The resistance of the second discharge circuit is selected to be higher than that of the first discharge circuit so that even in the presence of an overvoltage across the field winding, the overvoltage is suppressed by the second discharge circuit thereby to prevent frequent tripping of the synchronous machine due to overvoltage.

Field overvoltage protecting apparatus for synchronous machine

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Hitachiota, Japan

Yasushi Momochi