Apparatus and method for optimization of power flow control between different paths of a high voltage network in dependence of a disturbance in the network

1. A method for controlling a power flow in a high voltage ac transmission system comprising a phase shifting transformer comprising a tap changer, a controlled series compensator having a controllable reactance element comprising one or several capacitive reactance units and a control unit for controlling the phase shifting transformer and the controlled series compensator in coordination, the method comprising:

prior to a disturbance, operating the phase shifting transformer and the controlled series compensator to achieve system loss minimization,

after a disturbance, operating the controlled series compensator to achieve voltage recovery support, and

after voltage recovery, operating at least one of the phase shifting transformer and the controlled series compensator to handle thermal constraints.

2. The method according to claim 1 , wherein operating the controlled series compensator to achieve voltage recovery support comprises switching in capacitive reactance steps.

3. The method according to claim 1 , wherein operating the phase shifting transformer and the controlled series compensator to handle thermal constraints is performed during a period of more than 1 minute after operating the controlled series compensator to achieve voltage recovery support is initiated and until operation is returned to system loss minimization.

4. The method according to claim 1 , wherein operating the controlled series compensator to achieve voltage recovery support is initiated within a fraction of a second after a disturbance.

5. The method according to claim 1 , wherein operating the phase shifting transformer and the controlled series compensator to handle thermal constraints is performed during a period of about 15-30minutes after operating the controlled series compensator to achieve voltage recovery support is initiated and until operation is returned to system loss minimization.

6. 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 performing a method for controlling power flow in a high voltage ac transmission system comprising a phase shifting transformer comprising a tap changer, a controlled series compensator having a controllable reactance element comprising one or several capacitive reactance units, and a control unit for controlling the phase shifting transformer and the controlled series compensator in coordination, the method comprising

prior to a disturbance, operating the phase shifting transformer and the controlled series compensator to achieve system loss minimization,

after a disturbance, operating the controlled series compensator to achieve voltage recovery support, and

after voltage recovery, operating at least one of the phase shifting transformer and the controlled series compensator to handle thermal constraints.

7. A high voltage ac transmission system, comprising:

at least two parallel lines, and

an apparatus comprising a phase shifting transformer comprising a tap changer, a controlled series compensator comprising a controllable reactance element comprising at least one capacitive unit, and a control unit for controlling the phase shifting transformer and the controlled series compensator in coordination, wherein the control unit is arranged to perform a method comprising prior to a disturbance, operating the phase shifting transformer and the controlled series compensator to achieve system loss minimization, after a disturbance, operating the controlled series compensator to achieve voltage recovery support, and after voltage recovery, operating at least one of the phase shifting transformer and the controlled series compensator to handle thermal constraints arranged in one of said at least two parallel lines.

8. The system according to claim 7 , wherein the apparatus is installed in the line with the largest remaining thermal margin.

9. The system according to claim 8 , wherein the apparatus is installed in the line with the largest inductive reactance in the transmission interface between remote production sources and a load.

10. The system according to claim 8 , wherein the load comprises a city.

11. An apparatus for controlling the power flow in a high voltage ac transmission system, the apparatus comprising:

a phase shifting transformer comprising a tap changer,

a controlled series compensator comprising a controllable reactance element comprising at least one capacitive unit,

a control unit for controlling the phase shifting transformer and the controlled series compensator in coordination, wherein the control unit is arranged to perform a method comprising prior to a disturbance, operating the phase shifting transformer and the controlled series compensator to achieve system loss minimization, after a disturbance, operating the controlled series compensator to achieve voltage recovery support, and after voltage recovery, operating at least one of the phase shifting transformer and the controlled series compensator to handle thermal constraints.

12. The apparatus according to claim 11 , wherein one or several of the capacitive units will be equipped with low boost capability.