Method and a device for selecting and dimensioning measures in a case of instability in an electrical power system

1. A method for determining/dimensioning measures for restoring an electrical power system, which experiences or is heading for a voltage collapse, to a normal condition, the method comprising:

determining an actual voltage/phase angle in the electrical power system,

determining a power unbalance within at least one sub-area in the electrical power system,

determining suitable power-balancing measures,

dimensioning an extent of the respective measure, and

carrying out the power-balancing measures.

2. The method according to claim 1 , wherein the determination of the actual voltage/phase angle is performed by measuring in at least one node in the sub-area.

3. The method according to claim 1 , wherein the determination of the actual voltage/phase angle in the electrical power system is performed by measuring in at least one node and by calculation.

4. The method according to claim 1 , wherein the power unbalance is determined based on the actual voltage/phase angle and a desired voltage/phase angle.

5. The method according to claim 1 , wherein the power unbalance is determined starting from a circuit calculation based on the actual and a desired voltage/phase angle.

6. The method according to claim 4 , wherein the power unbalance is determined starting from a comparison of the actual voltage, the voltage drop across a magnitude related to the source impedance, and the equivalent voltage of the source.

7. The method according to claim 6 , wherein the magnitude related to the source impedance is source impedance, source admittance, short-circuit power or short-circuit current.

8. The method according to claim 1 , further comprising:

disconnecting a load corresponding to the determined power unbalance, such that the voltage/phase angle returns to a desired/predetermined level.

9. The method according to claim 1 , further comprising:

supplying power, corresponding to the determined power unbalance, to the electrical power system such that the voltage/phase angle returns to a desired/pre-determined level.

10. The method according to claim 1 , further comprising:

redistributing power, corresponding to the determined power unbalance, within the electrical power system by controlling reactive power resources such that the voltage/phase angle returns to the desired level.

11. The method according to claim 1 , wherein the power unbalance is determined based on a simultaneous comparison of the actual phase angle and a desired phase angle and of an actual voltage and a desired voltage.

12. The method according to claim 1 , wherein determination/dimensioning of measures is based on the magnitude of the detected power unbalance and possible power-balancing means in an area.

13. The method according to claim 1 , further comprising:

addition of power to the electrical power system and disconnection of loads from the electrical power system are combined such that the power-balancing measures together correspond to the determined power unbalance.

14. The method according to claim 1 , further comprising:

performing disconnection of loads in a predetermined order of priority.

15. The method according to claim 1 , further comprising:

stating the order of priority in a table.

16. The method according to claim 15 , wherein the table contains information about which switching members are available within the area.

17. The method according to claim 15 , wherein the table contains information about what power change is caused by activation of respective switching members.

18. The method according to claim 15 , further comprising:

selecting a required number of switching members based on the information in the table, such that the necessary power change is achieved.

19. The method according to claim 15 , wherein the table is regularly updated.

20. The method according to claim 8 , wherein the load disconnection is executed manually.

21. The method according to claim 8 , wherein the load disconnection is executed automatically.

22. A device for determining/dimensioning measures for restoring an electrical power system, which experiences or is heading for a voltage collapse, to a normal condition, the device comprising:

actual voltage/phase angle determining means arranged for determining an actual voltage/phase angle in the electrical power system,

power unbalance determining means arranged for determining a power unbalance within at least one sub-area in the electrical power system,

power-balance measure determining means arranged for determining suitable power-balancing measures,

dimensioning means arranged for dimensioning the extent of the respective measures, and

restoring means arranged such that the selected measures can enable the electrical power system to be restored to a stable condition.

23. The device according to claim 22 , further comprising:

actual power balance determining means arranged to determine the actual power unbalance starting from a circuit calculation based on the actual voltage/phase angle and the desired voltage/phase angle.

24. A computer program product, comprising:

a computer readable medium; and

computer program instructions recorded on the computer readable medium and executable by a processor for carrying out a method comprising

determining an actual voltage/phase angle in the electrical power system,

determining a power unbalance within at least one sub-area in the electrical power system,

determining suitable power-balancing measures,

dimensioning an extent of the respective measure, and

carrying out the power-balancing measures.

25. The computer program product according to claim 24 , wherein the computer program instructions are at least partly transferred via a network.

26. The computer program product according to claim 25 , wherein the network is the Internet.