Utility ground detection

Patent metadata

Field	Value
Publication number	US-9915692-B2
Application number	US-201213690946-A
Country	US
Kind code	B2
Filing date	Nov 30, 2012
Priority date	Jun 1, 2010
Publication date	Mar 13, 2018
Grant date	Mar 13, 2018

Abstract

In an embodiment, a missing utility ground detection circuit includes a pair of balanced resistors each connected to receive utility voltage from a different one of a pair of utility power lines, the balanced resistors being connected together at a summing node to be capable of summing the voltages from the pair of utility power lines. It includes an unbalance resistor connected to shunt voltage from one of the utility power lines. It has a summing amplifier with an input coupled to the summing node and to a reference voltage, and an input coupled to a second reference voltage. It has an averaging circuit connected at the output of the summing amplifier. A comparator is provided having an input connected to the averaging circuit an input connected to a threshold voltage.

First claim

What is claimed is:

1. A missing utility ground detection circuit comprising:
a) a pair of balanced resistors each connected to receive utility power from a different one of a pair of utility power lines, the balanced resistors being connected together at a summing node to be capable of summing a utility voltage from the pair of utility power lines;
b) an unbalance resistor connected so as to shunt voltage from only one line of the pair of utility power lines so as to unbalance the pair of utility power lines to allow detection of a missing utility ground when a utility ground is not present;
c) a summing amplifier comprising:
1) a first input coupled to the summing node;
2) a second input coupled to a second reference voltage; and
3) an output;

d) an averaging circuit connected at the output of the summing amplifier; and
e) a comparator comprising a first input connected to the averaging circuit a second input connected to a threshold voltage.

2. The circuit of claim 1 , wherein the first input of the summing amplifier is further connected to a reference voltage.

3. The circuit of claim 2 , wherein the unbalance resistor is connected between the only one line of the pair of utility power lines input and ground.

4. The circuit of claim 2 , wherein the first input of the summing amplifier is connected to the reference voltage via an offset resistor.

5. The circuit of claim 2 , wherein the second input of the comparator is connected between threshold resistors, the threshold resistors being connected to each other in series, the threshold resistors being connected between ground and a reference voltage.

6. The circuit of claim 5 further comprising a feedback resistor connected between the second input of the comparator and an output of the comparator.

7. The circuit of claim 2 further comprising a feedback resistor connected between the second input of the comparator and an output of the comparator.

8. The circuit of claim 2 , wherein the second input of the summing amplifier is connected to ground, and wherein the first input of the summing amplifier is connected to receive a positive reference voltage via an offset resistor.

9. The circuit of claim 1 further comprising a diode connected between the first input of the summing amplifier and the balanced resistors.

10. The circuit of claim 9 , wherein the diode is a Zener diode.

11. The circuit of claim 9 , wherein the unbalance resistor is connected between the only one of the pair of utility power line and ground.

12. The circuit of claim 9 , wherein the second input of the comparator is connected between threshold resistors, the threshold resistors being connected to each other in series, the threshold resistors being connected between ground and a reference voltage.

13. The circuit of claim 12 further comprising a feedback resistor connected between the second input of the comparator and an output of the comparator.

14. The circuit of claim 9 further comprising a feedback resistor connected between the second input of the comparator and an output of the comparator.

15. A missing utility ground detection circuit comprising:
a) a summing amplifier comprising:
(i) an inverting input connected to receive a utility voltage via balanced resistors and a first reference voltage via a shunt connected offset resistor;
(ii) a non-inverting input connected to receive a second reference voltage;
(iii) an output;

b) an unbalance resistor connected in shunt between only one utility power line input and a third reference voltage;
c) a filter having an input connected to the output of the summing amplifier;
d) a comparator comprising:
(i) an inverting input connected to an output of the filter; and
(ii) a non-inverting input connected to receive a threshold voltage; and

e) wherein the unbalance resistor is connected so as to pull the voltage at the inverting input of the summing amplifier if a utility ground is not tied to ground such that the unbalance resistor causes the output of the summing amplifier to pulse if the utility ground is not tied to ground.

16. The circuit of claim 15 , a feedback resistor connected between the non-inverting input of the comparator and an output of the comparator.

17. The circuit of claim 15 , wherein the non-inverting input of the summing amplifier is connected to ground, and wherein the inverting input of the summing amplifier is connected to receive a positive reference voltage via the shunt connected offset resistor.

18. The circuit of claim 15 , wherein the unbalance resistor is connected between the only one utility power line input and ground.

19. The circuit of claim 15 , wherein the non-inverting input of the comparator is connected between threshold resistors, the threshold resistors being connected to each other in series, the threshold resistors being connected between ground and a threshold resistor reference voltage.

20. A missing utility ground detection circuit comprising:
a) a summing amplifier comprising:
(i) an inverting input connected to received utility voltage via a Zener diode connected in series with parallel connected balanced resistors each connected to a utility power input;
(ii) a non-inverting input connected to a first reference voltage;
(iii) an output;

b) an unbalance resistor connected between only one utility power line input and a second reference voltage so as to unbalance the utility power inputs to allow detection of a missing utility ground when a utility ground is not present;
c) a filter having an input connected to the output of the summing amplifier;
d) a comparator comprising:
(i) an inverting input connected to an output of the filter; and
(ii) a non-inverting input connected to receive a threshold voltage.

21. The circuit of claim 20 further comprising a feedback resistor connected between the non-inverting input of the comparator and an output of the comparator.

22. The circuit of claim 20 , wherein the non-inverting input of the summing amplifier is connected to ground.

23. The circuit of claim 20 , wherein the unbalance resistor is connected between the only one utility power line input and ground.

24. The circuit of claim 20 , wherein the non-inverting input of the comparator is connected between threshold resistors, the threshold resistors being connected to each other in series, the threshold resistors being connected between ground and a threshold resistor reference voltage.

25. A method for detecting a missing utility ground in utility voltage inputs, the method comprising:
a) unbalancing only one of the utility voltage inputs so as to allow detection of a missing utility ground when a utility ground is not present;
b) sensing and summing the unbalanced only one of the utility voltage inputs and an other of the utility voltage inputs;
c) comparing the summed voltages to a reference threshold voltage to provide a compared output;
d) averaging the compared output to provide an averaged output; and
e) comparing the averaged output to a fault threshold voltage to provide a ground fault signal.

26. The method of claim 25 , further comprising feeding back a portion of ground fault signal and combining the feedback portion with the fault threshold voltage such that the averaged output is compared to a combined signal comprising the fault threshold voltage and the feedback portion to provide the ground fault signal.

Assignees

• Flack Albert
• Berman Scott Garret
• Aerovironment Inc

Inventors

• Flack Albert
• Berman Scott Garret

Classifications

• H02H5/105

  responsive to deterioration or interruption of earth connection (for preventing switching-on H02H11/001) · CPC title

• H02H3/00 Primary

  Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection (specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems H02H7/00; systems for change-over to standby supply H02J9/00 ){; integrated protection (for motors H02H7/0822)} · CPC title

• G01R31/025 Primary

  Physics · mapped topic

• G01R31/52 Primary

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