System and method for determining the impedance of a medium voltage power line

• US 7,714,592 B2
• Filed: 11/07/2007
• Issued: 05/11/2010
• Est. Priority Date: 11/07/2007
• Status: Expired due to Fees

• Current Assignee: Current Technologies LLC (Pattern Inc.)
• Original Assignee: Current Technologies LLC (Pattern Inc.)
• Inventors: Radtke, William O., Kreiss, David G.
• Primary Examiner(s): Dole, Timothy J
• Assistant Examiner(s): Baldridge, Benjamin M
• Application Number:
  US11/936,275
• Publication Number:
  US 20090115427A1
• Time in Patent Office: 916 Days
• Field of Search: 324/629
• US Class Current: 324/629
• CPC Class Codes: G01R 27/16 Measuring impedance of element or network through which a current is passing from another source, e.g. cable, power line
• CPC Class Codes: G01R 31/085 in power transmission or distribution lines, e.g. overhead
• CPC Class Codes: H02H 3/40 responsive to ratio of voltage and current
• CPC Class Codes: H02H 3/44 responsive to the rate of change of electrical quantities

Abstract

A system and method of detecting changes in the impedance of a segment of medium voltage power line is provided. In one embodiment, the method comprises receiving voltage data comprising data of the voltage of the power lines at locations at a plurality of different points in time, receiving current data that comprises data of the current flowing between adjacent locations at the plurality of points in time, intermittently determining an impedance of the power lines between adjacent locations based on the voltage data and current data, monitoring the impedance of the power lines between adjacent locations over time, and providing a notification of a change in the impedance of a power line between adjacent locations upon detection of a change in the impedance beyond a threshold change.

Claims

1. A method of determining an impedance of a medium voltage power line having a finite characteristic impedance, comprising:

determining a first voltage comprising the voltage of the power line at a first location at a first time;

determining a second voltage comprising the voltage of the power line at a second location at the first time;

determining a first current comprising the current flowing between the first location and the second location of the power line at the first time;

determining a third voltage comprising the voltage of the power line at the first location at a second time;

determining a fourth voltage comprising the voltage of the power line at the second location at the second time;

determining a second current comprising the current flowing between the first location and the second location of the power line at the second time;

determining a first voltage change comprising the difference between the first voltage and the third voltage;

determining a second voltage change comprising the difference between the second voltage and the fourth voltage;

determining a current change comprising the difference between the first current and the second current;

determining the impedance by dividing the difference between the first voltage change and the second voltage change by the current change; and

outputting data of the determined impedance.

2. The method according to claim 1, further comprising:

storing one or more distribution transformer turns ratios in a memory; and

wherein;

said determining a first voltage comprises multiplying voltage data of a first low voltage power line by a turns ratio of a first distribution transformer; and

said determining a second voltage comprises multiplying voltage data of a second low voltage power line by a turns ratio of a second distribution transformer.

3. A method of determining an impedance of a medium voltage power line having a finite characteristic impedance, comprising:

determining a first voltage change comprising data of a change in a voltage at a first location of the power line between a first time and a second time;

determining a second voltage change comprising data of a change in a voltage at a second location of the power line between the first time and the second time;

determining a current change comprising a change in the current flowing between the first location and the second location of the power line between the first time and the second time;

determining the impedance by dividing the difference between the first voltage change and the second voltage change by the current change; and

outputting data of the determined impedance.

4. The method according to claim 3, further comprising:

detecting a change in the impedance of the power line above a predetermined threshold; and

providing a notification of the change in the impedance.

5. The method according to claim 3, wherein the data of a change in a voltage at the first location comprises data of a change in a voltage of a low voltage power line.

6. The method according to claim 3, wherein the data of a change in a voltage at the first location comprises data of a change in a voltage of the medium voltage power line.

7. A method of determining an impedance of a medium voltage power line having a finite characteristic impedance, comprising:

a. receiving, from a first device, first voltage data comprising data of the voltage of the power line at a first location at a first time;

b. receiving, from a second device, second voltage data comprising data of the voltage of the power line at a second location at the first time;

c. receiving first current data comprising data of the current flowing between the first location and the second location of the power line at the first time;

d. receiving, from the first device, third voltage data comprising data of the voltage of the power line at the first location at a second time;

e. receiving, from the second device, fourth voltage data comprising data of the voltage of the power line at the second location at the second time;

f. receiving second current data comprising data of the current flowing between the first location and the second location of the power line at the second time;

g. determining a first voltage change that comprises a difference between the first voltage data and the third voltage data;

h. determining a second voltage change that comprises a difference between the second voltage data and the fourth voltage data;

i. determining a current change that comprises a difference between the first current data and the second current data;

j. determining an impedance of the power line between the first location and the second location by dividing the difference between the first voltage change and the second voltage change by the current change; and

outputting data of the determined impedance.

8. The method according to claim 7, further comprising:

storing one or more distribution transformer turns ratios in a memory;

determining a voltage of the medium voltage power line at the first location by multiplying the first voltage data by a turns ratio of a first distribution transformer; and

determining a voltage of the medium voltage power line at the second location by multiplying the second voltage data by a turns ratio of a second distribution transformer.

9. The method according to claim 7, further comprising:

repeating steps a through j;

determining the impedance determined by step j differs from a previously determined impedance by a predetermined amount; and

providing a notification of a change in impedance.

10. A method of detecting changes in an impedance of a plurality of medium voltage power lines, each having a finite characteristic impedance, comprising:

receiving voltage data comprising data of the voltage of the power lines at each of a plurality of locations at a plurality of different points in time;

receiving current data comprising data of the current flowing between adjacent locations of the plurality of locations at each of the plurality of points in time;

repeatedly determining the impedance of the power lines between each of the plurality of adjacent;

detecting a change in the impedance of the power lines between one or more of the plurality of adjacent locations;

providing a notification of the detection of the one or more changes in impedance; and

wherein said determining the impedance of the rower lines between each of the plurality of adjacent locations comprises;

determining a voltage change at each location over time;

determining a current change comprising a change in the current flowing between adjacent locations over time; and

dividing a difference between the voltage changes of adjacent locations by the current change between the adjacent locations.

11. The method according to claim 10, wherein the voltage data comprises data of the voltage of a low voltage power line, the method further comprising:

storing one or more distribution transformer turns ratios in a memory; and

determining a medium voltage by multiplying the voltage data of each of the plurality of locations with a turns ratio of a distribution transformer.

12. The method according to claim 10, further comprising for the impedance between each of the plurality of adjacent locations, comparing a determined impedance with one or more previously determined impedances.

13. A method of detecting changes in the impedance of a plurality of medium voltage power lines, each having a finite characteristic impedance, comprising:

receiving voltage data comprising data of the voltage of the power lines at each of a plurality of locations at a plurality of different points in time;

receiving current data comprising data of the current flowing between adjacent locations of the plurality of locations at the plurality of points in time;

repeatedly determining information of an impedance of the power lines between a plurality of adjacent locations based on the voltage data and current data;

detecting a change in the impedance of a power line between adjacent locations;

providing a notification of a change in the impedance of a power line between adjacent locations upon detection of a change in the information of the impedance beyond a threshold change; and

wherein said determining information of the impedance of the rower lines comprises;

determining a voltage change at each location over time;

determining a current change comprising a change in the current flowing between adjacent locations over time; and

dividing a difference between the voltage changes of adjacent locations by the current change between the adjacent locations.

14. The method according to claim 13, wherein the voltage data comprises data of the voltage of a low voltage power line, the method further comprising:

storing one or more distribution transformer turns ratios in a memory; and

determining a medium voltage by multiplying the voltage data of each of the plurality of locations with a turns ratio of a distribution transformer.

15. The method according to claim 13, wherein said detecting comprises comparing determined impedances of the power lines between the plurality of locations with previously determined impedances.

16. The method according to claim 13, wherein:

a characteristic of a change in the impedance is detected that corresponds to one or more types of power line events; and

said notification includes information of the one or more types of power line events corresponding to the detected change in impedance.

17. The method according to claim 16, wherein the notification includes data indicating that a change in impedance comprises one of an increase in impedance and a decrease in impedance.

18. The method according to claim 13, wherein the information of the impedance comprises a value proportional to the impedance of the power line between adjacent locations.

19. The method according to claim 13, wherein the information of the impedance comprises a value of the impedance of the power line between adjacent locations.