Transformer arrangement

1. A transformer arrangement comprising:

a transformer having a primary side for receiving input voltage and current from a source and a secondary side for providing output voltage and current to a load;

an AC-AC Power Electronic (PE) converter connected to a thyristor used for bypassing the AC-AC PE converter in case of a short-circuit fault in a terminal of the primary side and/or the secondary side;

wherein

the transformer arrangement further comprises a thyristor-based AC-AC PE converter connected to a thyristor-tapped winding and wherein the AC-AC PE converter is connected with the thyristor-tapped winding via the thyristor-based AC-AC PE converter, and wherein the thyristor-based AC-AC PE converter is connected to an impedance to protect the thyristor-tapped winding from short-circuit faults of the thyristor-based AC-AC PE converter, wherein the thyristor-based AC-AC PE converter comprises one or more parallel connected and/or series connected thyristors, and wherein the impedance is a coupled impedance, wherein the coupled impedance is associated to high impedance when a magnetic flux is added when current flows from a top to a bottom terminal of the thyristor-tapped winding and vice versa, and associated to low impedance when the magnetic flux of coupled windings is subtracted when current flows from the top and the bottom terminal of the thyristor-tapped winding to a common terminal of the thyristors and vice versa.

2. The transformer arrangement according to claim 1 , wherein the AC-AC PE converter is connected in series with the thyristor-tapped winding.

3. The transformer arrangement according to claim 1 , wherein the AC-AC PE converter is connected to an auxiliary winding.

4. The transformer arrangement according to claim 3 , wherein the AC-AC PE converter is connected to an impedance to protect the auxiliary winding from a short-circuit fault of the AC-AC PE converter.

5. The transformer arrangement according to claim 3 , wherein the auxiliary winding is tapped.

6. The transformer arrangement according to claim 3 , wherein the auxiliary winding is separate.

7. The transformer arrangement according to claim 3 , wherein the transformer arrangement further comprises a transformer tank, and wherein the AC-AC PE converter, the thyristor-based AC-AC PE converter, and the impedances are installed inside the transformer tank.

8. The transformer arrangement according to claim 3 , wherein the transformer arrangement further comprises a transformer tank and a separate container, wherein the impedances are installed inside the transformer tank and wherein the AC-AC PE converter and the thyristor-based AC-AC PE converter are installed in the separate container.

9. The transformer arrangement according to claim 3 , wherein the transformer arrangement further comprises a separate container, wherein the impedances, the AC-AC PE converter, and the thyristor-based AC-AC PE converter are installed in the separate container.

10. The transformer arrangement according to claim 1 , wherein the impedance is split in two parts, each of which is connected to top and bottom terminals of the thyristor-tapped winding.

11. The transformer arrangement according to claim 1 , wherein an RC snubber network is connected in parallel to each thyristor, wherein the RC snubber network comprises a resistor and a capacitor connected in series and/or in parallel.

12. The transformer arrangement according to claim 11 , wherein a further RC snubber network is a common snubber network for all thyristors which is connected in parallel to the thyristors, wherein the RC snubber network comprises a resistor and a capacitor connected in series and/or in parallel, or a capacitor.