Device and method for increasing fault clearing time

Abstract

A device for increasing fault clearing time is provided having a component part designed to identify a short circuit event and load resistors connectable in the event of a fault such that the turbine power transmitted to the shaft is electrically absorbed by the generator and converted into heat until the grid comes back online.

Claims

1. An apparatus for extending the fault clearing time comprising: an electrical generator; electrical loads formed with switches arranged in parallel; a transformer, which is connected to the electrical generator; and a component part designed to identify a short circuit event, wherein the apparatus is designed in such a way that, in the event of a short circuit, the electrical loads are connected to the electrical generator, the electrical loads are arranged in series with the short circuit path at the transformer neutral point on the high voltage side, and the switches are opened.

2. The apparatus as claimed in claim 1, wherein the electrical loads are in the form of load resistors.

3. The apparatus as claimed in claim 1, wherein the electrical loads are connected in parallel with the transformer.

4. The apparatus as claimed in claim 1, wherein the electrical generator has three phases.

5. The apparatus as claimed in claim 1, wherein electrical generator comprises a synchronous generator.

6. A method for extending the fault clearing time in the case of an electrical generator, which is connected to an electrical consumer grid, the method comprising: in the event of a short circuit, connecting additional electrical loads to the electrical generator; wherein the electrical loads are arranged in series with the short circuit path at a transformer neutral point and, in the event of a short circuit, switches arranged in parallel with the electrical loads are opened.

7. The method as claimed in claim 6, wherein the electrical loads are in the form of load resistors.

8. The method as claimed in claim 6, wherein the electrical loads are in parallel with a transformer, which is connected to the electrical generator.

9. The apparatus as claimed in claim 4, wherein electrical generator comprises a synchronous generator.

10. The method as claimed in claim 6, wherein electrical generator comprises a synchronous generator.

11. The method as claimed in claim 8, wherein electrical generator comprises a synchronous generator.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will now be explained in more detail with reference to an exemplary embodiment. FIGS. 2 and 3 show, schematically:

(2) FIG. 1 shows several grid code requirements as detailed in the background.

(3) FIG. 2 a first embodiment of the apparatus according to the invention;

(4) FIG. 3 a second embodiment of the apparatus according to the invention.

DETAILED DESCRIPTION OF INVENTION

(5) FIG. 2 shows a three-phase electrical generator 5, in particular synchronous generator, wherein a first phase 6, a second phase 7 and a third phase 8 are formed at the output. The first phase 6, the second phase 7 and the third phase 8 are connected to a transformer 9. The secondary side 10 of the transformer 9 is connected to an electrical grid 11. In the first phase 6, a first outgoing line 12 is provided, by means of which a first switch 13 and electrical loads 14 are connected to ground 15. The second phase 7 comprises a second outgoing line 16 and a second switch 17, which is connected to the second outgoing line 16, and a load 18, which is connected to ground 15. The third phase 8 comprises a third outgoing line 19 and correspondingly a third switch 20 and a load 21, which in turn is connected to ground 15.

(6) The phases 6, 7 and 8 are in this case connected to the transformer 9 via the generator switch 25.

(7) FIG. 3 shows an alternative embodiment of the invention. The difference over FIG. 2 is that the loads 14, 18 and 21 are in series with the short-circuit path at the transformer neutral point on the high-voltage side. In each case one switch 22, 23 and 24 is arranged in parallel with the loads 14, 18 and 21, respectively.

(8) The electrical generator 5 is driven via a turbine (not illustrated). In the event of a fault, the turbine power impressed onto the shaft is connected by the generator 5 via connectable loads 14, 18, 21 until grid recovery and is converted into heat. In other words: in the event of a fault, the turbine power impressed onto the shaft is taken off electrically from the generator 5 and converted into heat via connectable loads 14, 18, 21 until grid recovery. During the fault time, the electrical generator 5 remains connected to the electrical grid 11. Grid resynchronization is therefore not required and a higher degree of power station availability can be achieved. The critical fault clearing time T.sub.Ku for the respective assembly without additional loads can generally be determined analytically corresponding to the following formula:

(9) $T_{\mathrm{Ku}}=\sqrt{\frac{2.Math.{}_0.Math.J}{P_r}.Math.\left({}_{\mathrm{Ku}}^{}-{}_0^{}\right)},$

(10) where

(11) .sub.0 denotes the rated circuit frequency

(12) J denotes the moment of inertia of the entire assembly

(13) .sub.Ku denotes the maximum transient voltage angle until stability of the turbo set is obtained

(14) .sub.0 denotes the transient voltage angle prior to the onset of a short circuit

(15) P.sub.T denotes the turbine power.

(16) The loads 14, 18 and 21, which can be in the form of electrical resistors, dissipate the turbine power contributing to the shaft acceleration in the event of a fault, as a result of which the critical fault clearing time is considerably extended and, as a result, there is an increase in the transient stability of the electrical generator 5, in particular synchronous generator, via loading resistors 14, 18 and 21 connectable in the event of a short circuit. The load resistors 14, 18 and 21 illustrated in FIG. 2 are in parallel with the transformer 9 on the transformer low-voltage side in order to make use of the short-circuit residual voltage present in the event of a short circuit over the transformer series impedance. The additional use of adjustable reactances can improve the reactivity of the circuit even more.

(17) FIG. 2 shows the topology for this first embodiment of the invention.

(18) The topology of the second embodiment is shown in FIG. 3. The load resistors 14, 18 and 21 are in series with the short-circuit path at the transformer neutral point on the high-voltage side. They are connected into the short circuit by opening of the parallel switches 22, 23, 24.

(19) Thus, advantageously the critical fault clearing time for electrical generators 5 in the event of a fault is increased, both on the transformer low-voltage side and on the transformer high-voltage side. An expansion of the circuit topology with switchable or adjustable reactances can increase the fault clearing time further still.

(20) In accordance with the invention, therefore, the critical fault clearing time can be considerably extended without needing to make any design changes to the turbine and generator 5, which results in an inexpensive measure of the invention illustrated here. In addition, no grid isolation during the temporally limited short circuit is required, so that permanent availability of the electrical generator 5 without resynchronization can be achieved.