Method and device for determining an input voltage on a transforming station of a power network

1. A method for determining an input voltage of a transformer in a transforming station, the method comprising:

measuring an input current of the transformer, an output current of the transformer, an output voltage of the transformer and a phase angle between the output current and the output voltage of the transformer;

determining, by a processor of a computing device, a transformation ratio and complex admittances of parallel elements of the transformer in the transforming station based on the measured input current, the measured output current, the measured output voltage and the measured phase angle between the output current and the output voltage; and

determining, by the processor of a computing device, the input voltage of the transformer in the transforming station based on the determined transformation ratio and the determined admittances of the parallel elements.

2. The method as claimed in claim 1 , wherein the transformation ratio and the admittances of the parallel elements are determined by means of statements relating to at least one of a rated voltage on a high-voltage side of the transformer, a relative short-circuit voltage and a rated current on the high-voltage side.

3. The method as claimed in claim 1 , wherein the transformation ratio and the admittances are determined by solving an equation system,

wherein the equation system is solved using a transformation matrix of a p-equivalent circuit of the transformer.

4. The method as claimed in claim 3 , wherein the equation system is overdefined, and is solved using a non-linear state estimation.

5. The method as claimed in claim 4 , comprising:

determining a plurality of measured-value sets of the input current of the transformer, of the output current of the transformer and of the output voltage of the transformer are determined, to increase the overdefinition of the equation system.

6. The method as claimed in claim 3 , wherein the p-equivalent circuit provides two parallel elements with admittances, between which a series element with an impedance is arranged in series, and

wherein an imaginary part of the impedance is determined approximately by determining a magnitude of the impedance.

7. The method as claimed in claim 3 , wherein the p-equivalent circuit provides two parallel elements with admittances, between which a series element with an impedance is arranged in series, and

wherein the impedance is determined from the relative or absolute short-circuit voltage and copper losses.

8. A measurement and monitoring unit for determining an input voltage of a transformer in a transforming station, comprising:

a voltage measurement unit configured to measure an output voltage of the transformer;

at least one current measurement unit configured to measure an input current of the transformer and an output current of the transformer;

a phase difference unit configured to determine a phase angle between the output current and the output voltage; and

a calculation unit configured to determine a transformation ratio and an admittance of parallel elements of the transformer in the transforming station based on the measured input current, the measured output current, the measured output voltage and the phase angle between the output current and the output voltage, and to determine an input voltage of the transformer in the transforming station based on the determined transformation ratio and the determined admittance of the parallel elements.

9. The method as claimed in claim 2 , wherein the transformation ratio and the admittances are determined by solving an equation system,

wherein the equation system is solved using a transformation matrix of a p-equivalent circuit of the transformer.

10. The method as claimed in claim 9 , wherein the equation system is overdefined, and is solved using a non-linear state estimation.

11. The method as claimed in claim 10 , comprising:

determining a plurality of measured-value sets of the input current of the transformer, of the output current of the transformer and of the output voltage of the transformer are determined, to increase the overdefinition of the equation system.

12. The method as claimed in claim 4 , wherein the p-equivalent circuit provides two parallel elements with admittances, between which a series element with an impedance is arranged in series, and

wherein an imaginary part of the impedance is determined approximately by determining a magnitude of the impedance.

13. The method as claimed in claim 4 , wherein the p-equivalent circuit provides two parallel elements with admittances, between which a series element with an impedance is arranged in series, and

wherein the impedance is determined from the relative or absolute short-circuit voltage and copper losses.

14. The method as claimed in claim 1 , wherein the determining of the transformation ratio and the admittances of parallel elements includes determining the transformation ratio and the admittances of a p-equivalent circuit of the transformer.

15. The measurement and monitoring unit as claimed in claim 8 , wherein the calculation unit is configured to determine the transformation ratio and admittance of a p-equivalent circuit of the transformer, and to determine the input voltage of the transformer based on the determined transformation ratio and the determined admittance of the p-equivalent circuit.