COUPLING A GAS TURBINE AND A STEAM TURBINE WITH A TARGET COUPLING ANGLE BY ADJUSTING THE POLAR WHEEL ANGLE

Abstract

A method for coupling a gas turbine connected to a generator and a steam turbine, wherein the generator has an excitation winding, the excitation of which can be changed by changing an excitation current flowing through the excitation winding, the method having the following steps: a) accelerating and/or decelerating the steam turbine in such a way that the coupling takes place with a target coupling angle; b) if necessary, changing the excitation current such that the excitation of the excitation winding changed in this way leads to a changed polar wheel angle, wherein the polar wheel angle is changed in such a way that the achieving of the target coupling angle is supported. In an analogous method, the polar wheel angle is changed for the purposes of improved decoupling. A corresponding control device is for coupling a gas turbine connected to a generator.

Claims

1. A method for coupling a gas turbine connected to a generator and a steam turbine, the generator having an excitation winding, the excitation of which is changed by changing an excitation current flowing through the excitation winding, the method comprising: a) accelerating and/or decelerating the steam turbine in such a way that the coupling takes place with a target coupling angle; b) when necessary, changing the excitation current, so that the thus-changed excitation of the excitation winding leads to a changed polar wheel angle, wherein the polar wheel angle being changed in such a way as to be conducive to achieving the target coupling angle.

2. The method as claimed in claim 1, wherein when the gas turbine is leading with respect to the target coupling angle, the excitation current is raised and, when the gas turbine is lagging, the excitation current is lowered.

3. The method as claimed in claim 1, wherein the changing of the excitation current is used to compensate for fluctuations of the grid frequency that make it more difficult for the target coupling angle to be achieved.

4. The method as claimed in claim 1, wherein the changing of the excitation current allows the angle of the gas turbine to be variable by up to 5°.

5. The method as claimed in claim 1, wherein the excitation voltage is changed to change the excitation current.

6. A method for uncoupling a steam turbine and a gas turbine connected to a generator, the generator having an excitation winding, the excitation of which can be changed by changing an excitation current flowing through the excitation winding, the method comprising: changing the excitation current in such a way that the thus-changed excitation of the excitation winding leads to a changed polar wheel angle, which facilitates uncoupling.

7. A control device for a single-shaft turbo set with a gas turbine, a steam turbine and a generator, wherein the control device is adapted to carry out a method as claimed in claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Further details are to be described on the basis of FIG. 1, which shows a power diagram in which the interrelationships between the reactive power, the effective power and the polar wheel angle are represented.

DETAILED DESCRIPTION OF INVENTION

[0017] The effective power in MW is plotted on the abscissa of FIG. 1. The reactive power in Mvar is plotted on the ordinate. For the reactive power, the line 1 passes through 0. For the operating points lying on the line 1, therefore, only effective power is provided. For the operating points lying under the line 1, the reactive power is negative, for those lying above it is positive. The straight lines ending at the edge stand for certain values of cos phi, phi being the angle between the voltage induced in the generator and the resultant current in the phasor diagram.

[0018] The arrows 3, 4 and 5 extending from an origin 2 lying at the bottom left are significant in the present case. As can be seen, these end at operating points with the same effective power, but different reactive power. The line 6 that joins the two end points of the arrows 3 and 5 is a typical range in which the reactive power can be adjusted while the effective power remains the same.

[0019] The angle between the arrows 3, 4 and 5 and the ordinate is the respective polar wheel angle. The position of the origin 2 is determined by the measurement technology. Generally, the polar wheel angle can be read off in the power diagram by taking an arrow from the origin 2 to the respective operating point and determining the angle of this arrow in relation to the ordinate.

[0020] If for instance coupling is performed at the operating point that lies at the end of arrow 4 and it is established by the control that, for coupling with the target coupling angle, the gas turbine is leading by 2°, it is then appropriate to lower the polar wheel angle by 2°. As can be seen in the power diagram that is shown in FIG. 1, for this purpose the reactive power has to be increased. This requires that the excitation, that is to say the excitation voltage and consequently the excitation current, have to be lowered until the polar wheel angle is 42°. It is therefore possible in an easy way, by changing the reactive power that can be brought about by changed excitation, to influence the polar wheel angle, and consequently to influence the target coupling angle in an improved way.