Fault indicator having liquid crystal status display

• US 5,070,301 A
• Filed: 08/31/1990
• Issued: 12/03/1991
• Est. Priority Date: 11/08/1989
• Status: Expired due to Term

• Current Assignee: Edmund O. Schweitzer III, Jean E. Schweitzer, Marilyn L. Schweitzer
• Original Assignee: Edmund O. Schweitzer Jr
• Inventors: Schweitzer, Edmund O. Jr.
• Primary Examiner(s): Harvey, Jack B.
• Application Number:
  US07/577,079
• Time in Patent Office: 459 Days
• Field of Search: 324/96, 324/126, 324/127, 324/133, 324/72, 324/509, 324/539, 324/542, 324/555, 324/556, 350/331 R, 350/332, 350/352, 340/811, 340/784, 340/660, 340/662, 340/664
• US Class Current: 324/509
• CPC Class Codes: G01R 13/404 for discontinuous display, i.e. display of discrete values analogue/digital conversion H03M1/00

Abstract

A fault indicator for indicating the occurrence of a fault current in a monitored electrical conductor of an AC power distribution system utilizes a liquid crystal display having independent "F" and "N" display elements. A rectifier circuit capacatively coupled to the conductor charges a first capacitor in the presence of voltage on the conductor. A second capacitor is connected to the first capacitor by a first reed switch in magnetic communication with the conductor. Upon occurrence of a fault current the reed switch closes and a portion of the charge on the first capacitor is transferred to the second capacitor, which is connected to the "F" display segment electrodes of the liquid crystal display to cause an "F" to be displayed. The fault indication can be reset either by the slow discharge of the second capacitor, or by discharging the second capacitor through a second reed switch manually actuated by a magnetic reset tool from outside the fault indicator housing. The "N" display segment electrodes are capacitively coupled to the monitored conductor and system ground to provide an "N" display indicating that voltage is present on the conductor.

Claims

1. A fault indicator for indicating the occurrence of a fault current in a monitored electrical conductor, comprising:

a housing;

status indicating means within said housing comprising a high impedance display device having at least a pair of display electrodes disposed in operative association with a layer of voltage-responsive light controlling material, the display device providing on the exterior of said housing a first display condition in the absence of an actuating signal applied to said electrodes, and a second display condition in the presence of an actuating signal applied to said electrodes;

a capacitor connected between respective ones of said display electrodes of said display device;

a source of unidirectional current;

switch means responsive to the occurrence of a fault current in the monitored conductor; and

circuit means including said switch means and said current source for applying an actuating signal to said capacitor following occurrence of a fault current in the monitored conductor to condition said display device to said second display condition to indicate the occurrence of said fault current.

2. A fault indicator as defined in claim 1 wherein said switch means are rendered conductive upon the occurrence of a fault current in the monitored conductor for transferring a charge from said current source to said capacitor.

3. A fault indicator as defined in claim 1 wherein the electrical conductor comprises part of an alternating current power distribution system, said current source comprises an additional capacitor, and said circuit means further include rectifier means for applying a unidirectional current derived from the monitored conductor to said additional capacitor.

4. A fault indicator as defined in claim 1 wherein said switch means comprise a reed switch actuated by the magnetic field accompanying the occurrence of the fault current in the monitored conductor.

5. A fault indicator as defined in claims 1, 2 or 3 wherein said high impedance display device includes a second pair of display electrodes, said display device providing a third display condition concurrently with said first or second display condition indicative of the application of an actuating signal to said second pair of display electrodes;

and

wherein said circuit means include means for applying an actuating signal derived from the monitored conductor to said second pair of display electrodes to indicate the presence of voltage on the monitored conductor.

6. A fault indicator as defined in claim 5 wherein the electrical conductor comprises part of an alternating current power distribution system, and said circuit means include means for capacitively coupling respective ones of said second pair of display electrodes to ground and to the monitored conductor.

7. A fault indicator as defined in claim 5 wherein said high impedance display device comprises a liquid crystal display having at least pair of display electrodes each comprising a display element electrode and an associated backplane electrode.

8. A fault indicator as defined in claims 1, 2 or 3 wherein said high impedance display device comprises a liquid crystal display having at least one pair of display electrodes comprising a display element electrode and an associated backplane electrode.

9. A fault indicator as defined in claims 1, 2 or 3 wherein said circuit means further include reset switch means user-actuable from the exterior of said housing for discharging said capacitor to condition said display device to said first display condition.

10. A fault indicator as defined in claim 9 wherein said reset switch means comprise a reed switch magnetically actuable from the exterior of the housing.

11. A fault indicator as defined in claim 10 wherein said reed switch is aligned generally parallel to the monitored conductor.

12. A fault indicator as defined in claims 1, 2 or 3 wherein said circuit means further include a reset circuit for automatically discharging said capacitor upon restoration of voltage in the monitored conductor to condition said display device to said first display condition.

13. A fault indicator as defined in claim 12 wherein said reset circuit comprises transistor switch means having source and drain electrodes connected across said capacitor and a high impedance control electrode responsive to the presence of voltage on the monitored conductor.

14. A fault indicator as defined in claim 13 wherein said transistor switch means comprise a field effect transistor.

15. A fault indicator for indicating the occurrence of a fault current in a monitored alternating current conductor, comprising:

a housing;

status indicating means within said housing comprising a high impedance display device having at least one pair of display electrodes disposed in operative association with a layer of voltage-responsive light controlling material, the display device providing on the exterior of said housing a first display condition in the absence of an actuating signal applied to said display electrodes, and a second display condition in the presence of an actuating signal applied to said display electrodes;

a first capacitor;

rectifier circuit means operable from the monitored conductor for charging said first capacitor;

a second capacitor having first and second end terminals;

switch means rendered conductive upon the occurrence of a fault current in the monitored conductor for momentarily connecting said first capacitor to said second capacitor to establish a charge in said second capacitor; and

said electrodes of said display device being connected to respective ones of said end terminals of said second capacitor to condition said display device to said second display condition in the presence of said charge.

16. A fault indicator as defined in claim 15 wherein said switch means comprise a reed switch actuated by the magnetic field accompanying the occurrence of a fault current in the monitored conductor.

17. A fault indicator as defined in claim 15 wherein said high impedance display device includes a second pair of display electrodes, said display device providing a third display condition concurrently with said first or second display conditions indicative of the application of an actuating signal to said second pair of display electrodes, and

wherein said fault indicator includes means for applying an actuating signal derived from the monitored conductor to said second pair of display electrodes to indicate the presence of voltage on the monitored conductor.

18. A fault indicator as defined in claim 15 further including reset switch means user-actuable from the exterior of said housing for discharging said second capacitor to condition said display device to said first display condition.

19. A fault indicator as defined in claim 18 wherein said reset switch means comprise a reed switch magnetically actuable from the exterior of the housing.

20. A fault indicator as defined in claim 19 wherein said reed switch is aligned generally parallel to the monitored conductor.

21. A fault indicator as defined in claim 15 further including a reset circuit for automatically discharging said second capacitor upon restoration of voltage in the monitored conductor to condition said display device to said first display condition.

22. A fault indicator as defined in claim 21 wherein said reset circuit comprises transistor switch means having source and drain electrodes connected across said second capacitor and a high impedance gate electrode responsive to the presence of voltage on the monitored conductor.

23. A fault indicator as defined in claim 22 wherein said switch means comprise a field effect transistor.

24. A indicator as defined in claim 15 wherein said high impedance display device comprises a liquid crystal display having at least one pair of display electrodes including a display segment electrode and an associated backplane electrode.

25. A fault indicator for indicating the occurrence of a fault current in a monitored alternating current conductor, comprising:

a housing;

status indicating means within said housing comprising a high impedance display device having at least a pair of display electrodes disposed in operative association with a layer of voltage-responsive light controlling material, the display device providing on the exterior of said housing a first display condition in the absence of an actuating signal applied to said display electrodes, and a second display condition in the presence of an actuating signal applied to said display electrodes;

a first capacitor;

rectifier means for applying a unidirectional current derived from the monitored alternating current conductor to said first capacitor to develop a charge therein;

a second capacitor;

switch means rendered momentarily conductive by the magnetic field accompanying the occurrence of a fault current in the monitored conductor for transferring a portion of the charge on said first capacitor to said second capacitor; and

said display electrodes of said display device being connected to said second capacitor to condition said display device to said second display condition in the presence of said charge.

26. A fault indicator as defined in claim 25 wherein said switch means comprise a reed switch actuated by the magnetic field accompanying the occurrence of the fault current in the monitored conductor.

27. A fault indicator as defined in claim 25 wherein said high impedance display device includes a second pair of display electrodes, said display device providing a third display condition concurrently with said first or second display conditions indicative of the application of an actuating signal to said second pair of display electrodes, and

wherein said fault indicator further includes means for applying an actuating signal derived from the monitored conductor to said second pair of display electrodes to indicate the presence of voltage on the monitored conductor.

28. A fault indicator as defined in claim 27 further including means for capacitively coupling said second pair of display electrodes between the monitored conductor and electrical ground.

29. A fault indicator as defined in claim 25 wherein said high impedance display device comprises a liquid crystal display having at least one pair of display electrodes including display segment electrode and an associated backplane electrode.

30. A fault indicator as defined in claim 25 further including reset switch means user-actuable from the exterior of said housing for discharging said second capacitor to condition said display device to said first display condition.

31. A fault indicator as defined in claim 30 wherein said reset switch means comprise a reed switch magnetically actuable from the exterior of the housing.

32. A fault indicator as defined in claim 31 wherein said reed switch is aligned generally parallel to the monitored conductor.

33. A fault indicator as defined in claim 25 furhter including a reset circuit for automatically discharging said second capacitor upon restoration of voltage in the monitored conductor to condition said display device to said first display condition.

34. A fault indicator as defined in claim 33 wherein said reset circuit comprises transistor switch means having source and drain electrodes connected across said second capacitor and a high impedance gate electrode responsive to the presence of voltage on the monitored conductor.