Control of high-voltage, direct current systems

Patent metadata

Field	Value
Publication number	US-10680441-B2
Application number	US-201716302314-A
Country	US
Kind code	B2
Filing date	May 9, 2017
Priority date	May 17, 2016
Publication date	Jun 9, 2020
Grant date	Jun 9, 2020

Abstract

The present invention provides methods and apparatus for controlling HVDC power transmission systems so as to increase the effective lifetime of cables carrying the DC power (and particularly the extruded polymer insulation of those cables). The method includes entering a maintenance mode in which the electrical properties applied to the cable are varied so as to facilitate diffusion of space charge accumulation in the extruded polymer insulation.

First claim

The invention claimed is:

1. A method of operating a high-voltage direct-current (HVDC) system, the HVDC system comprising at least one DC link, at least part of the DC link comprising a cable with extruded polymer insulation, the DC link being operable in a maintenance mode and at least one other mode of operation, the method comprising:
entering the maintenance mode, in which the electrical properties applied to the cable are varied so as to facilitate diffusion of space charge accumulation in the extruded polymer insulation; and
measuring an electrical characteristic in the cable, comparing a measured value of the electrical characteristic to a threshold, and entering the maintenance mode based at least in part on the comparison.

2. The method of claim 1 , wherein, in the maintenance mode, the electrical properties applied to the cable are varied so as to induce heating in the cable.

3. The method of claim 1 , wherein, in the maintenance mode, a current applied to the cable is increased relative to the value of the current in the at least one other mode of operation.

4. The method of claim 3 , wherein, in the maintenance mode, the current is increased to its maximum permitted value.

5. The method of claim 1 , wherein, in the maintenance mode, a voltage applied to the cable is decreased relative to the value of the voltage in the at least one other mode of operation.

6. The method of claim 5 , wherein, in the maintenance mode, the voltage is decreased to 0% or more of its maximum permitted value.

7. The method of claim 1 , wherein, in the maintenance mode, a polarity of the voltage applied to the cable is reversed relative to its polarity in the at least one other mode of operation.

8. The method of claim 1 , further comprising entering the maintenance mode periodically.

9. The method of claim 8 , wherein a frequency in which the maintenance mode is entered increases as a function of the lifetime of the cable.

10. The method of claim 1 , further comprising entering the maintenance mode during or after a transition from a first period in which a load on the system is relatively high to a second period in which the load on the system is relatively low.

11. The method of claim 1 , wherein the HVDC system comprises a plurality of DC links, and further comprising, when one DC link of the plurality of DC links is in the maintenance mode, entering a compensatory mode of operation for at least one other DC link of the plurality of DC links in which the power transferred by the at least one other DC link is increased relative to other modes of operation of the DC links.

12. The method of claim 11 , wherein, when one DC link of the plurality of DC links is in the maintenance mode, a compensatory mode of operation is entered for all other DC links of the plurality of DC links.

13. The method of claim 1 , wherein the step of entering the maintenance mode comprises generating control signals for one or more of:
one or more transformers connected to the HVDC system;
one or more voltage converters connected to the HVDC system;
a dynamic braking system (DBS) to the HVDC system; and
a current flow controller (CFC) to the HVDC system,
in order to vary the electrical properties applied to the cable.

14. A control system for a high-voltage, direct-current (HVDC) system, the HVDC system comprising at least one DC link, at least part of the DC link comprising a cable with extruded polymer insulation, the DC link being operable in a maintenance mode and at least one other mode of operation, the control system being configured to:
control the DC link to enter the maintenance mode, in which the electrical properties applied to the cable are varied so as to induce heating in the cable and facilitate diffusion of space charge accumulation in the extruded polymer insulation; and
measure an electrical characteristic in the cable, comparing a measured value of the electrical characteristic to a threshold, and entering the maintenance mode based at least in part on the comparison.

15. The control system of claim 14 , wherein, in order to vary the electrical properties applied to the cable, the control system is configured to generate control signals for one or more of:
one or more transformers connected to the HVDC system;
one or more voltage converters connected to the DC link;
a dynamic braking system connected to the DC link; and
a current flow controller connected to the DC link.

Assignees

• General Electric Technology Gmbh

Inventors

• Tzimas Antonios
• Lucas Guillaume
• Dyke Kevin

Classifications

• Y02E60/60

  Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD] · CPC title

• H02M5/04

  by static converters (controlling transformers, reactors or choke coils, e.g. by tap changing H02P13/00) · CPC title

• H02J3/36 Primary

  Arrangements for transfer of electric power between AC networks via high-voltage DC [HVDC] links; Arrangements for transfer of electric power between generators and networks via HVDC links · CPC title

• H05F3/00

  Carrying-off electrostatic charges ({from shoes A43B7/36}; from living beings A61N1/14; {from tyres B60C19/08; from vehicles B60R16/06; from aircraft B64D45/02; from large containers B65D90/46}) · CPC title