Reactive power compensator having a booster transformer

1. A reactive power compensator comprising a power transformer having an AC bus side and a compensator bus side, said power transformer being connectable to an AC grid at said AC bus side, said reactive power compensator further comprising a thyristor-switched capacitor and a thyristor-controlled reactor connected to said compensator bus side, the reactive power compensator being characterized by a booster transformer connected in series with said power transformer and to said compensator bus side; wherein said booster transformer is not active during a period of time before an operating parameter of the thyristor-switched capacitor and/or the thyristor-controlled reactor approaches an end point of its operating area, and said booster transformer is activated after an operating parameter of the thyristor-switched capacitor and/or the thyristor-controlled reactor approaches the end point of its operating area.

2. The reactive power compensator as claimed in claim 1 , wherein said booster transformer comprises a single step tap changer.

3. The reactive power compensator as claimed in claim 1 , further comprising power electronics connected to said booster transformer and arranged to prevent overvoltages.

4. The reactive power compensator as claimed in claim 3 , wherein said power electronics comprises IGBT components, varistors, diodes and/or resistors.

5. The reactive power compensator as claimed in claim 1 , said booster transformer comprising an on-line tap changer.

6. The reactive power compensator as claimed in claim 1 , further comprising a control system arranged to control said booster transformer as well as said thyristor-switched capacitor and said thyristor-controlled reactor.

7. The reactive power compensator as claimed in claim 1 , comprising a static VAr compensator.

8. A computer program stored on a non transitory computer readable medium for controlling a reactive power compensator as claimed in claim 1 , said computer program comprising computer program code which when run on a control system controlling said reactive power compensator causes said control system to activate said booster transformer, thereby to provide voltage support.

9. The computer program as claimed in claim 8 , wherein said booster transformer is activated upon said control system entering an alert operation mode or an emergency operation mode.

10. A computer program product comprising a computer program according to claim 8 and a non transitory computer readable medium on which said computer program is stored.