Transient protection for multi-terminal HVDC grid

Patent metadata

Field	Value
Publication number	US-10516259-B2
Application number	US-201415321828-A
Country	US
Kind code	B2
Filing date	Jun 27, 2014
Priority date	Jun 27, 2014
Publication date	Dec 24, 2019
Grant date	Dec 24, 2019

Abstract

A method and a device provide protection for a multi-terminal HVDC grid against faults. The method includes measuring a DC displacement voltage having a polarity and a value, determining if a short circuit fault exists by comparing the DC displacement voltage with a threshold displacement voltage and identifying a fault type based on the polarity and the value of the DC displacement voltage. The disclosed device contains a converter having a positive pole and a negative pole, a DC-switch substation, a DC line connecting the converter and the DC-switch substation and a transient fault detector. The transient fault detector contains a positive voltage sensor sensing a positive transient voltage of the positive pole and a negative voltage sensor sensing a negative transient voltage of the negative pole and a control unit which is adapted to derive a DC displacement voltage from the positive and the negative transient voltages.

First claim

The invention claimed is:

1. A method for protecting a multi-terminal HVDC grid against faults, the HVDC grid containing a converter having a positive pole, a negative pole and a neutral pole, a DC-switch substation and a DC line connecting the converter and the DC-switch substation, which method comprises the steps of:
measuring a DC displacement voltage having a polarity and a value;
determining if a fault exists by comparing the DC displacement voltage with a threshold displacement voltage; and
identifying a fault type as a positive to neutral pole short circuit, a negative to neutral pole short circuit or a positive to negative pole short circuit based on the polarity and the value of the DC displacement voltage;
wherein the step of identifying the fault type is executed by measuring the polarity and the value of the DC displacement voltage such that if the polarity of the DC displacement voltage is negative the fault type is identified as the positive to neutral pole short circuit, if the polarity of the DC displacement voltage is positive the fault type is identified as the negative to neutral pole short circuit and if the DC displacement voltage has a greater value than the threshold displacement voltage the fault type is identified as the positive to negative pole short circuit.

2. The method according to claim 1 , which further comprises calculating the DC displacement voltage from a positive transient voltage measured at the positive pole and a negative transient voltage measured at the negative pole.

3. The method according to claim 1 , wherein the step of determining if the fault exists is carried out by assessing if the value of the DC displacement voltage is greater than the threshold displacement voltage.

4. The method according to claim 1 , which further comprises detecting a no fault condition when the value of the DC displacement voltage is lesser than the threshold displacement voltage.

5. The method according to claim 1 , which further comprises detecting a direction of a fault current as towards the converter or the DC line when measured at a converter terminal of the converter based on a polarity of a DC transient current change measured at the converter terminal or, towards the DC-switch substation or the DC line when measured at a DC-switch substation terminal of the DC-switch substation based on the polarity of the DC transient current change measured at the DC-switch substation terminal.

6. The method according to claim 5 , which further comprises calculating the DC transient current change as a difference between a DC transient current and a rated DC current.

7. The method according to claim 5 , wherein the step of detecting the direction of the fault current is executed by sensing the polarity of the DC transient current change such that when the polarity of the DC transient current change at the converter terminal is negative then the direction of the fault current at the converter terminal is towards the DC line, when the polarity of the DC transient current change at the converter terminal is positive then the direction of the fault current is towards the converter, when the polarity of the DC transient current change at the DC-switch substation terminal is positive then the direction of the fault current at the DC-switch substation terminal is towards the DC line and when the polarity of the DC transient current change at the DC-switch substation terminal is negative then the direction of the fault current is towards the DC-switch substation.

8. The method according to claim 5 , which further comprises detecting if the fault is internal or external in respect of the converter by comparing the polarities of the DC transient current change between the converter terminal and the DC-switch substation terminal.

9. The method according to claim 8 , wherein the step of detecting if the fault is internal or external in respect of the converter is carried out such that when the polarity of the DC transient current change at the converter terminal and the polarity of the DC transient current change at the DC-switch substation terminal are different then the fault is internal and when the polarity of the DC transient current change at the converter terminal and the polarity of the DC transient current change at the DC-switch substation terminal are same then the fault is external in respect of the converter.

10. The method according to claim 5 , which further comprises providing a transient busbar differential protection for multiple terminals of the DC-switch substation, wherein when the polarity of the DC transient current change at all the multiple terminals of the DC-switch substation is negative then the fault is internal and when the polarity of the DC transient current change at all the multiple terminals of the DC-switch substation are different then the fault is external, in respect of the DC-switch substation.

11. The method according to claim 1 , which further comprises detecting a transient fault location on the DC line based on a propagation time of travelling waves initiated by the fault.

Assignees

• Siemens Ag

Inventors

• Blug Christian
• Ebner Guenter
• Shang-Jaeger Li
• Trunk Kai
• Wuerflinger Klaus
• Zeller Marcus

Classifications

• H02H7/267

  for parallel lines and wires · CPC title

• H02H7/1255

  responsive to internal faults, e.g. by monitoring ripple in output voltage · CPC title

• H02H7/1257

  responsive to short circuit or wrong polarity in output circuit · CPC title

• H02H3/243

  for DC systems · CPC title

• H02H7/26

  Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured (locating faults in cables G01R31/08) · CPC title