AUTOMATICALLY RESETTABLE FAULT INDICATOR

• US 3,676,740 A
• Filed: 06/01/1971
• Issued: 07/11/1972
• Est. Priority Date: 06/01/1971
• Status: Expired due to Term

• Current Assignee: Edmund O. Schweitzer Jr
• Original Assignee: Edmund O. Schweitzer Jr
• Inventors: Schweitzer, Edmund O. Jr.
• Primary Examiner(s): Miller, J. D.
• Assistant Examiner(s): Fendelman, Harvey
• Application Number:
  US05/148,687
• Time in Patent Office: 406 Days
• Field of Search: 324/132,133,127,51 340/253A,255,373 317/22,33SC,33C
• US Class Current: 361/74
• CPC Class Codes: G01R 19/16571 comparing AC or DC current with one threshold, e.g. load current, over-current, surge current or fault current G01R19/16514, G01R19/16519, G01R19/16528, G01R19/16533, G01R19/1659 take precedence; measuring currents by using elements sensitive to the magnetic field generated G01R15/14; measuring earth resistance G01R27/18; testing for leakage or short circuits in electrical apparatus G01R31/52

Abstract

A pair of opposed L-shaped pole pieces of demagnetizable low coercive force material is arranged to embrace an alternating current carrying conductor with the short legs in opposition and the long legs carrying reset windings which are energized with unidirectional current from a capacitor that is charged by a rectifier energized from a capacitor plate electrostatically related to the conductor or a secondary winding of a transformer the primary winding of which is energized from the conductor. A four pole fault indicating rotor is held in a normal position by the magnetic fields from the short legs. A biasing permanent magnet, having magnetic poles of opposite polarity, is offset from the short legs and biases the rotor to fault indicating position when the L-shaped pole pieces are demagnetized by alternating magnetic flux generated by flow of fault current in the conductor. Permanent magnets at the distal ends of the long legs of the L-shaped pole pieces are effective to change the fault current response of the rotor.

Claims

1. Means responsive to flow of alternating fault current in and energization of a conductor comprising:

a magnetic circuit of low coercive force demagnetizable material for embracing said conductor in which alternating demagnetizing flux is induced by alternating current flow in said conductor and having a pair of pole pieces extending toward each other, winding means on said magnetic circuit energized with unidirectional current on energization of said conductor with alternating current to induce poles of the same polarity in said pole pieces, a stationary permanent magnet between and displaced from alignment with said pole pieces and having magnetic poles of opposite polarity on opposite sides for inducing magnetic poles of the same polarity in said pole pieces opposite to said one polarity, and a pivotable fault indicating permanent magnet adjacent said pole pieces and said stationary permanent magnet having diametrical poles of one polarity between diametrical poles of opposite polarity, said fault indicating permanent magnet being biased to a normal position by magnetic flux from said pole pieces induced therein by said winding means and biased to a fault indicating position by magnetic flux from said pole pieces induced therein by said stationary permanent magnet following demagnetization of said pole pieces by flow of fault current in said conductor.

2. Current and energization means according to claim 1 wherein said magnetic circuit includes a pair of L-shaped magnetic members with said pole pieces being formed by the short legs thereof and said winding means being located on the long legs thereof.

3. Current and energization means according to claim 1 wherein capacitor means is connected to be charged on energization of said conductor and is connected to discharge through said winding means to magnetize said pole pieces when the voltAge to which said capacitor means is charged reaches a predetermined value.

4. Current and energization means according to claim 3 wherein rectifier means connected between ground and a capacitor plate electrostatically disposed with respect to said conductor charges said capacitor means.

5. Current and energization means according to claim 3 wherein a transformer has a primary winding connected for energization to said conductor and a secondary winding with secondary terminals and a grounded center tap, and rectifier means connected between ground and one of said secondary terminals charges said capacitor.

6. Current and energization means according to claim 3 wherein gated semiconductor means connected between said capacitor means and said winding means is rendered conducting when said capacitor means is charged to a predetermined unidirectional voltage.

7. Current and energization means according to claim 1 wherein said stationary permanent magnet is positioned on the sides of said pole pieces facing said conductor.

8. Current and energization means according to claim 2 wherein a permanent magnet having magnetic poles of opposite polarity is positioned at the distal end of each of said long legs of said L-shaped magnetic members.

9. Current and energization means according to claim 3 wherein said windings are electrostatically related to said conductor, a counterpoise is spaced from said conductor, and rectifier means connected between said windings and said counterpoise charges said capacitor means.

10. Current and energization means according to claim 3 wherein a counterpoise is spaced from said conductor, and rectifier means connected between said counterpoise and ground charges said capacitor means.