System and method for detecting the presence of an unsafe line condition in a disconnected power meter

• US 20080258709A1
• Filed: 04/01/2008
• Published: 10/23/2008
• Est. Priority Date: 02/26/2007
• Status: Active Grant

• Current Assignee: Elster Electricity LLC (Honeywell International Inc.)
• Original Assignee: Elster Electricity LLC (Honeywell International Inc.)
• Inventors: Shuey, Kenneth C.
• Granted Patent: US 7,746,054 B2
• Time in Patent Office: Days
• US Class Current: 324/110
• CPC Class Codes: G01R 11/25 Arrangements for indicating or signalling faults
• CPC Class Codes: G01R 19/16547 voltage or current in AC supplies switching for protection H02H; circuits for emergency power supply H02J9/00
• CPC Class Codes: G01R 22/10 using digital techniques
• CPC Class Codes: G01R 35/04 of instruments for measuring time integral of power or current

Abstract

A method of detecting the presence of an unsafe line condition at a power metering device is disclosed. The method comprises the steps of determining if a disconnect switch is in the open position, and measuring a first voltage at a first load contact. The method measures a second voltage at a second load contact and determines if the first voltage is greater than a first voltage threshold or less than a second voltage threshold. The method further determines if the second voltage is greater than the first voltage threshold or less than the second voltage threshold. The method indicates that an unsafe condition exists if either the first voltage is greater than the first voltage threshold, or first voltage is less than the second voltage threshold or the second voltage is greater than the first voltage threshold or the second voltage is less than the second voltage threshold, when the disconnect switch is in the open position.

Claims

1. A method for detecting the presence of an unsafe condition at a power metering device comprising:

providing the power metering device, the powering meter device interposed between a voltage source and a load, the voltage source coupled to the power metering device through a first source contact and a second source contact, the power metering device coupled with the load through a first load contact and a second load contact, the power metering device having a disconnect switch positioned between the voltage source and the load, the power metering device having a first bypass resistor and a second bypass resistor, the first bypass resistor coupled between the first source contact and the first load contact, the second bypass resistor coupled between the first source contact and the second load contact,

determining if the disconnect switch is in an open position,

measuring a first voltage at said first load contact;

measuring a second voltage at said second load contact;

determining if the first voltage is greater than a first voltage threshold or less than a second voltage threshold;

determining if the second voltage is greater than a first voltage threshold or less than a second voltage threshold;

indicating that an unsafe condition exists if either;

a) the first voltage is greater than the first voltage threshold;

or,

b) the second voltage is less than the second voltage threshold;

or,

c) the second voltage is greater than the first voltage threshold;

or

d) the first voltage is less than the second voltage threshold; and

,

the disconnect switch is in the open position.

2. The method of claim 1 wherein the first voltage or the second voltage exist due to tapping of the power metering device.

3. The method of claim 1 wherein the first voltage or the second voltage exist due to cross-tapping of the power metering device.

4. The method of claim 1 wherein the first voltage or the second voltage exist due to a portable electric generator.

5. The method of claim 1 wherein a load side voltage sensor is used to measure the first voltage and the second voltage.

6. The method of claim 1 wherein the first voltage threshold is about 170 VAC

7. The method of claim 1 wherein the second voltage threshold is about 50 VAC

8. The method of claim 4 wherein the first voltage exceeds the first voltage threshold for a short a period of time.

9. The method of claim 4 wherein the first voltage is less than the second voltage threshold for a short period of time.

10. A power meter capable of detecting the presence of an unsafe condition, the power meter coupled to a voltage source through a first and second source contacts, the power meter coupled to a load through a first and second load contacts, the power meter measuring power flowing from the voltage source to the load, the power meter comprising:

a disconnect switch, the disconnect switch interposed between the first source contact and the first load contact, and the second source contact and the second load contact, the disconnect switch interrupting the flow of power from the voltage source to the load when the disconnect switch is in an open position;

a first bypass resistor coupled between the first voltage source contact and the first load contact,

a second bypass resistor coupled between the first source contact and the second load contact,

a load side voltage sensing circuit, the load side voltage sensing circuit coupled to the first load contact and a second load contact, the load side voltage sensing circuit measuring a first voltage at the first load contact and measuring a second voltage at the second load contact, the load side voltage sensing circuit determining;

a) if the first voltage is greater than a first voltage threshold or

b) if the first voltage is less than a second voltage threshold, or

c) if the second voltage is greater than a first voltage threshold;

or,

d) if the first voltage is less than a second voltage threshold; and

,

a processing circuit coupled to the disconnect switch and the load side voltage sensing circuit, the processing circuit determining if the disconnect switch is in the open position, the processing circuit indicating that an unsafe condition exists when either the first voltage is greater than the first voltage threshold or, the first voltage is less than the second voltage threshold, or the second voltage is greater than the first voltage threshold or the second voltage is less than the second voltage threshold, and the disconnect switch is in the open position.

11. The power meter of claim 10 wherein the first voltage or the second voltage is caused by tapping the power metering device.

12. The power meter of claim 10 wherein the first voltage or the second voltage is caused by cross-tapping the power metering device.

13. The power meter of claim 10 wherein the first voltage or the second voltage is caused by a portable electric generator.

14. The power meter of claim 10 wherein the first voltage threshold is about 170 VAC.

15. The power meter of claim 10 wherein the second voltage threshold is about 50 VAC.

16. The power meter of claim 10 further comprising a notification circuit, the notification circuit notifying a utility company that the unsafe condition exists.

17. The power meter of claim 13 wherein the first voltage exceeds the first voltage threshold for a short a period of time.

18. The power meter of claim 13 wherein the first voltage is less than the second voltage threshold for a short period of time.

19. The power meter of claim 13 wherein the second voltage exceeds the first voltage threshold for a short a period of time.

20. The power meter of claim 13 wherein the second voltage is less than the second voltage threshold for a short period of time.

21. The power meter of claim 13 wherein the portable electric generator is connected to the first load contact and earth ground.

22. The power meter of claim 13 wherein the portable electric generator is connected to the second load contact and earth ground.

23. The power meter of claim 10 wherein the power meter is a 120/240 VAC split phase watt-hour meter.

24. The power meter of claim 10 wherein the power meter is a 120 VAC single phase—

single element watt-hour meter.

25. The power meter of claim 10 wherein the power meter is a 120/208 dual phase watt-hour meter.