Method and device for monitoring an electric network in a rail vehicle and rail vehicle

1. A method for monitoring an electric network in a rail vehicle, wherein the electric network comprises at least one power converter, at least one permanent magnet machine, and at least one phase line for an electrical connection of the at least one power converter and the at least one permanent magnet machine, the method comprising:

determining a potential difference between a machine-side part of the at least one phase line and a reference potential;

determining a potential-difference-dependent variable based on the potential difference;

determining a speed of the permanent magnet machine;

determining, as a function of the speed, a speed-dependent reference variable;

determining a deviation of the potential-difference-dependent variable from the speed-dependent reference variable; and

detecting a network fault if the deviation is greater than a predetermined threshold value.

2. The method as claimed in claim 1 , wherein upon detection of a network fault, a speed of the permanent magnet machine is reduced and/or a further interruption of the machine-side part of the phase line is carried out.

3. The method as claimed in claim 1 , wherein an accuracy of the determination of the potential difference is checked in that at least one normal operating potential difference is determined in the case of an uninterrupted phase line, wherein a deviation of the normal operating potential difference from a normal operating reference value is determined, wherein a sufficient accuracy if the deviation is less than or equal to a predetermined threshold value and/or in that a standstill of the permanent magnet machine is detected, wherein at least one standstill potential difference is detected in the case of an interrupted phase line, wherein a deviation of the standstill potential difference from a standstill reference value is determined, wherein a sufficient accuracy if the deviation is less than or equal to a predetermined threshold value.

4. The method as claimed in claim 1 , wherein the speed is assigned to one speed interval of multiple speed intervals, wherein an interval-dependent reference variable is assigned to one speed interval, wherein the speed-dependent reference variable is determined as the interval-dependent reference variable.

5. The method as claimed in claim 1 , wherein the potential difference is assigned to one potential difference interval of multiple potential difference intervals, wherein an interval-dependent potential difference value is assigned to one potential difference interval, wherein the potential-difference-dependent variable is determined as a function of the interval-dependent potential difference value.

6. The method as claimed in claim 1 , wherein a potential difference between a machine-side part of the phase line and a reference potential and a potential-difference-dependent variable is determined for each phase line, wherein a combined output signal is formed, wherein the combined output signal comprises a first bit sequence, which codes the potential-difference-dependent variable formed from the minimum potential difference, wherein the combined output signal comprises a further bit sequence, which codes an equality of all potential differences.

7. The method as claimed in claim 1 , wherein the potential-difference-dependent variable is a maximum amplitude or an RMS value of the potential difference during a predetermined determination duration.

8. The method of claim 1 , wherein the electric network comprises three phase lines, the method further comprising:

determining a potential difference between a machine-side part of a phase line and a reference potential for each phase line;

determining a speed of the permanent magnet machine and, as a function of the speed of the permanent magnet machine, a speed-dependent reference variable for each phase line;

determining a potential-difference-dependent variable; and

determining a deviation of the potential-difference-dependent variable from the speed-dependent reference variable for each phase line.

9. The method of claim 8 further comprising:

detecting a network fault based on at least one of the deviations of the potential-difference-dependent variable from the speed-dependent reference variable for each phase line being greater than a second predetermined threshold value.

10. The method of claim 8 further comprising:

determining a minimum potential difference of all potential differences and a variable dependent on the minimum potential difference,

determining a deviation of the variable dependent on the minimum potential difference from the speed-dependent reference variable for each phase line; and

detecting a network fault based on the deviation of the variable dependent on the minimum potential difference from the speed-dependent reference variable being greater than a second predetermined threshold value.

11. The method of claim 10 further comprising:

detecting a two-phase network fault or a three-phase network fault as a function of the potential differences and/or the deviation of the variable dependent on the minimum potential difference from the speed-dependent reference variable for each phase line.

12. A device for monitoring an electric network in a rail vehicle,

wherein the device comprises:

at least one evaluation unit,

at least one determination unit, and

at least one interruption unit,

wherein at least one phase line of the electric network is interruptible by the at least one interruption unit,

wherein a potential difference between a machine-side part of the at least one phase line and a reference potential is determinable by the determination unit,

wherein a potential-difference-dependent variable is determinable by the determination unit or the evaluation unit,

wherein a speed of a permanent magnet machine of the electric network is determinable by the determination unit and, as a function of the speed, a speed-dependent reference variable is determinable by the determination unit or the evaluation unit,

wherein a deviation of the potential-difference-dependent variable from the speed-dependent reference variable is determinable by the evaluation unit, and

wherein a network fault is detectable by the evaluation unit if the deviation of the potential-difference-dependent variable from the speed-dependent reference variable is greater than a predetermined threshold value.

13. The device as claimed in claim 12 , wherein the potential difference between the machine-side part of the at least one phase line and the reference potential is determined close to a motor.

14. A rail vehicle comprising a device as claimed in claim 13 .

15. A rail vehicle comprising a device as claimed in claim 12 .

16. The device of claim 12 , wherein a potential difference between a machine-side part of each phase line of the electric network and a reference potential is determinable by the determination unit for each phase line of the electric network;

wherein a speed-dependent reference variable is determinable by the determination unit for each phase line of the electric network;

wherein a potential-difference-dependent variable and a deviation of the potential-difference-dependent variable from the speed-dependent reference variable are determinable by the determination unit for each phase line; and

wherein a network fault is detectable by the determination unit if at least one of the deviations is greater than a second predetermined threshold value.

17. The device of claim 16 , wherein the predetermined threshold value and the second predetermined threshold value are equal.

18. The device of claim 12 , wherein a minimum potential difference of all potential differences and a variable dependent on the minimum potential difference are determinable by the determination unit;

wherein a deviation of the variable dependent on the minimum potential difference from the speed-dependent reference variable is determinable by the determination unit; and

wherein a network fault is detectable by the determination unit if the deviation of the variable dependent on the minimum potential difference from the speed-dependent reference variable is greater than a second predetermined threshold value.

19. The device of claim 18 , wherein a two-phase network fault or a three-phase network fault is detectable by the determination unit as a function of the potential differences and/or the deviation of the variable dependent on the minimum potential difference from the speed-dependent reference variable.

20. The device of claim 18 , wherein the predetermined threshold value and the second predetermined threshold value are equal.