This application claims priority to EP/01120357.7 filed Aug. 24, 2001 under the European Patent Convention and which is incorporated by reference herein in its entirety.
The invention relates to a method of running up a turboset having a gas turbine and a three-phase generator excited with a brushless rotating rectifier exciter. It also relates to an apparatus for carrying out the method.
A turboset, in particular having a three-phase synchronous generator, is normally used for the generation of electrical energy in a power plant. The turboset comprises a gas turbine, the three-phase synchronous generator and an excitation current device. The three-phase current generated is tapped at the stator winding of the generator, while the rotor winding for generating a magnetic field is excited with direct current. The direct current is provided by a brushless rotating rectifier exciter or by a static thyristor-controlled excitation device via slip rings. A brushless rectifier exciter with stationary poles is coupled to the generator in such a way that its rotor rotates with the generator shaft. In this case, the three-phase current generated at first in the exciter can be rectified by means of rectifiers rotating with the rotor shaft of the exciter. The direct current generated by such a rectifier exciter can be passed directly, without slip rings, to the rotor of the generator.
In contrast to a turboset having a steam turbine as drive, a gas turbine cannot run up the turboset independently. The turboset is generally run up from the xe2x80x9cturning operationxe2x80x9d with a speed of about 100 rev/min to 200 rev/min, for which an oil-hydraulic drive is usually used. As is well known, it is not until a gas turbine is at a sufficient speed of about 1000 rev/min that it can be ignited and assume the further run-up to the rated speed. In order to reach this limit speed, a separate xe2x80x9cstarting motorxe2x80x9d or the generator, as frequency-controlled motor, may be used for the run-up.
If a starting motor is used, it is mechanically connected to the turboset via a clutch and runs the turboset up to the requisite limit speed. If the gas turbine assumes the further run-up, the motor is uncoupled. For this arrangement, the type of excitation of the generator is unimportant if the design of the xe2x80x9cfree shaft endxe2x80x9d on the excitation side of the generator is disregarded.
For the run-up with a frequency-controlled generator, for which a thyristor-controlled starting device is required, which feeds current into the armature winding of the generator, a brief speed-dependent excitation of the rotor winding of the generator is required. In a generator having slip rings, this feeding is effected from a static rectifier station. Disadvantages associated with this are in particular wear and other disturbances with regard to the slip rings and/or carbon brushes, which have to be designed for the continuous operation of the generator. If the turboset has a rotating brushless exciter set attached to the generator shaft or if this exciter set is directly coupled electrically and mechanically, frequency-controlled run-up is not readily possible, since the requisite excitation of the field winding of the generator is absent. Intermediate excitation for the run-up operation via auxiliary slip rings is certainly conceivable but likewise entails disadvantages associated with the slip rings.
The object of the invention is therefore to specify a method of running up a turboset having a gas turbine and a brushless rotating rectifier, in which method efficient utilization of components which are necessary for the generator operation is achieved. Furthermore, an apparatus especially suitable for carrying out the method is to be specified.
With regard to the method, said object is achieved according to the invention by the features of the claims. Advantageous developments are the subject matter of the claims.
In the method according to the invention, a three-phase current is supplied to a stator winding (field winding) of a rectifier exciter arranged on a shaft together with a generator and a turbine, this three-phase current producing a rotary field, the rotary speed of which differs from that of the shaft and induces a three-phase voltage in the rotor winding. The current generated in the rotor winding by the induced voltage is rectified by a rectifier rotating with the rotor winding and is supplied as direct current to a rotor winding of the generator, through the stator winding of which a frequency-controlled three-phase current is passed.
With regard to the apparatus, the object is achieved by the features of the claims. To this end, the excitation winding in the stator of the rectifier, through which excitation winding direct current flows during generator operation of the turboset, is changed in its function and used as a three-phase excitation winding. So that the excitation flux is large enough at all speeds, the exciter is operated as an asynchronous generator with reverse field. By the interposition of a three-phase AC power controller in the three-phase circuit feeding into the stator winding of the exciter, the excitation flux can be controlled in accordance with the run-up. Via this rectifier exciter changed in its function, the current can be passed to the generator rotor without slip rings. The generator, which is not equipped with slip rings, i.e. it is free of slip rings, can therefore work as a converter-fed motor, so that no separate starting motor is required.
The feeding in three-phase circuit of the field winding of the rectifier exciter is switched off as soon as the limit speed has been reached, starting from which the turbine, driven at first by the generator acting as motor, runs up independently. After the run-up operation has been completed, the rectifier exciter can be used in a function known per se, direct current being fed into the stator winding. Alternatively, three-phase current may be fed into the stator winding of the rectifier exciter, this three-phase current being asynchronous relative to the constant rated speed of the turboset. A voltage regulator circuit for the turbogenerator can be constructed via the three-phase AC power controller.