Electrical generator or motor structure – Dynamoelectric – Rotary
Patent
1995-10-23
1998-07-21
Dougerty, Thomas M.
Electrical generator or motor structure
Dynamoelectric
Rotary
322 68, 322 59, 310179, 310182, 310210, H02K 1926
Patent
active
057838917
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a brushless synchronous machine having an exciter, whose field excitation winding is powered via a regulator connected to a separate multi-phase designed auxiliary winding in the stator of the main machine.
2. Discussion of the Prior Art
The German Laid Open Application 27 14 188 discloses a synchronous machine that is used as a generator.
In the case of a synchronous generator of the type shown in the German Application above, a problem arises in supplying the field excitation winding of the exciter with sufficient energy in all operating states. This can be done by providing an auxiliary exciter with a permanent-magnet rotor to supply the exciter. Moreover, to reduce the outlay for supplying the exciter, it is possible to power the field excitation winding of the exciter from the main machine. For this purpose, voltages are diverted from the winding of the main machine, for example, and in addition, current transformers are connected, which are fed with the load current of the main machine. A circuit arrangement of this type enables the exciter to be supplied with energy during no load running, as well as in the case of normal load, and in the event of a short-circuit.
German Laid Open Application No. 27 14 188 discloses configuring an additional auxiliary winding in the stator of the main machine and of supplying the exciter with the energy gained from this, via a regulator.
However, a problem occurs in the arrangement described above, particularly in the event of a short-circuit, when the terminal voltage of the generator and the fundamental wave of the field in the air gap nearly disappear. In that case, the residual magnetic field permeating the air gap of the main machine is essentially made up of odd-order harmonic components, of which, for example, the component of the third harmonic wave, given The usual formation of the poles, is normally quite large.
When an auxiliary winding is used, however, depending on its design, not all harmonic waves are able to be effectively utilized to energize the excitation winding. For example, the relative phase relation of the a.c. voltages induced in the individual phases can be so unfavorable for certain harmonic waves that, on the whole, the phase-to-phase voltage is too low for powering the exciter.
U.S. Pat. No. 3,479,543 discloses an electrical machine having an auxiliary winding for excitation, whose design is directed to the effective utilization of the magnetic cross-field of the machine.
Great Britain Parent No. 2,011,186 discloses an auxiliary winding, which is designed as a multi-phase winding and operated as a single-phase winding, with which a third harmonic wave is supposed to be utilized. However, the single-phase operation of that device results in such a strong pulsation or ripple factor of the supply voltage that this voltage is not utilized very effectively.
The object of the present invention is to create a simple auxiliary winding, which will enable the largest possible component of the energy-rich, low-order harmonic waves, in particular the third harmonic wave, to be effectively utilized to generate a supply voltage for the exciter.
The object of the present invention is solved by providing an auxiliary winding with a number of phases that differ from the harmonic number of the harmonic wave of the field of the main machine that is the most salient in the event of a short circuit.
For a conventionally designed pole formation for a 3-phase synchronous generator of a few MVA power output, in a four- or five-phase auxiliary winding, comprised of only one or two turns, an a.c. voltage is induced in each phase by the normally heavily salient third harmonic wave, whose phase-to-phase voltage suffices to adequately supply the exciter in the event of a short circuit. Thus, as the result of the design in accordance with the present invention, a minimum outlay results for the auxiliary winding as a means for supplying energy to the exciter system.
One advantageou
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Auinger Herbert
Bredthauer Jurgen
Wachta Bernhard
Dougerty Thomas M.
Mullins B.
Siemens Aktiengesellschaft
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