Fault detection system and method, and power system for subsea pipeline direct electrical heating cables

Patent metadata

Field	Value
Publication number	US-9151794-B2
Application number	US-201214130494-A
Country	US
Kind code	B2
Filing date	Jun 20, 2012
Priority date	Jan 7, 2011
Publication date	Oct 6, 2015
Grant date	Oct 6, 2015

Abstract

A fault detection system for subsea pipeline direct electrical heating cables is provided. The fault detection system includes a first ammeter for measuring a first phase current, a second ammeter for measuring a second phase current, and a third ammeter for measuring a third phase current. The fault detection system also includes a first calculation unit for calculating a negative sequence current from the first phase current, the second phase current, and the third phase current, and a first detection unit for detecting a change in the negative sequence current.

First claim

The invention claimed is:

1. A fault detection system for subsea pipeline direct electrical heating cables, the fault detection system comprising:
a first ammeter that measures a first phase current in the subsea pipeline direct electrical heating cables;
a second ammeter that measures a second phase current in the subsea pipeline direct electrical heating cables;
a third ammeter that measures a third phase current in the subsea pipeline direct electrical heating cables;
a first calculation unit that calculates a negative sequence current from the first phase current, the second phase current, and the third phase current; and
a first detection unit that detects a change in the negative sequence current, wherein the change in the negative sequence current indicates a fault in the subsea pipeline direct electrical heating cables.

2. The fault detection system of claim 1 , further comprising:
a second calculation unit that calculates a positive sequence current from the first phase current, the second phase current, and the third phase current; and
a third calculation unit that divides the negative sequence current by the positive sequence current to obtain a relative negative sequence current, wherein the first detection unit detects a change in the relative negative sequence current.

3. The fault detection system of claim 2 , further comprising:
a fourth calculation unit that calculates a sequence impedance matrix.

4. The fault detection system of claim 3 , further comprising:
a second detection unit that receives a signal indicating a malfunctioning of a symmetrizing unit.

5. The fault detection system of claim 4 , further comprising:
a third detection unit that receives a signal indicating a malfunctioning of a balancing unit.

6. The fault detection system of claim 1 , further comprising:
a second detection unit that receives a signal indicating a malfunctioning of a symmetrizing unit.

7. The fault detection system of claim 6 , further comprising:
a third detection unit that receives a signal indicating a malfunctioning of a balancing unit.

8. A power supply for subsea pipeline direct electrical heating cables, the power supply comprising:
a symmetrizing unit that symmetrizes a load; and
a fault detection system comprising:
a first ammeter that measures a first phase current in the subsea pipeline direct electrical heating cables;
a second ammeter that measures a second phase current in the subsea pipeline direct electrical heating cables;
a third ammeter that measures a third phase current in the subsea pipeline direct electrical heating cables;
a first calculation unit that calculates a negative sequence current from the first phase current, the second phase current, and the third phase current; and
a first detection unit that detects a change in the negative sequence current, wherein the change in the negative sequence current indicates a fault in the subsea pipeline direct electrical heating cables.

9. The power supply of claim 8 , further comprising:
a balancing unit that balances the load.

10. The power supply of claim 9 , further comprising:
a local fault detection device that detects a malfunctioning of the symmetrizing unit, the balancing unit, or the symmetrizing unit and the balancing unit.

11. The power supply of claim 9 , further comprising:
a three-phase transformer.

12. The power supply of claim 8 , further comprising:
a local fault detection device that detects a malfunctioning of the symmetrizing unit, the balancing unit, or the symmetrizing unit and the balancing unit.

13. The power supply of claim 12 , further comprising:
a three-phase transformer.

14. The power supply of claim 8 , further comprising:
a three-phase transformer.

15. A fault detection method for subsea pipeline direct electrical heating cables, the fault detection method comprising:
measuring a first phase current in the subsea pipeline direct electrical heating cables;
measuring a second phase current in the subsea pipeline direct electrical heating cables;
measuring a third phase current in the subsea pipeline direct electrical heating cables;
calculating a negative sequence current from the first phase current, the second phase current, and the third phase current; and
detecting a change in the negative sequence current that indicates a fault in the subsea pipeline direct electrical heating cables.

16. The fault detection method of claim 15 , further comprising:
calculating a positive sequence current from the first phase current, the second phase current, and the third phase current;
dividing the negative sequence current by the positive sequence current to obtain a relative negative sequence current; and
detecting a change in the negative sequence current by detecting a change in the relative negative sequence current.

17. The fault detection method of claim 16 further comprising:
calculating a sequence impedance matrix from the first phase current, the second phase current, and the third phase current;
calculating a change of sequence voltages based on the sequence impedance matrix; and
calculating a load impedance change based on the change of sequence voltages.

18. The fault detection method of claim 15 , further comprising:
calculating a sequence impedance matrix from the first phase current, the second phase current, and the third phase current;
calculating a change of sequence voltages based on the sequence impedance matrix; and
calculating a load impedance change based on the change of sequence voltages.

19. A non-transitory computer-readable medium on which a computer program for processing a physical object is stored, the computer program, when executed by a data processor, causes the fault detection system for subsea pipeline direct electrical heating cables to:
measure a first phase current in the subsea pipeline direct electrical heating cables;
measure a second phase current in the subsea pipeline direct electrical heating cables;
measure a third phase current in the subsea pipeline direct electrical heating cables;
calculate a negative sequence current from the first phase current, the second phase current, and the third phase current; and
detect a change in the negative sequence current that indicates a fault in the subsea pipeline direct electrical heating cables.

Assignees

• Radan Damir
• Siemens Ag

Inventors

• Radan Damir

Classifications

• G01R31/52

  Testing for short-circuits, leakage current or ground faults · CPC title

• G01R25/00

  Arrangements for measuring phase angle between a voltage and a current or between voltages or currents · CPC title

• G01R31/083

  in cables, e.g. underground · CPC title

• H05B2214/03

  Heating of hydrocarbons · CPC title

• G01R31/02 Primary

  Physics · mapped topic