Faulted current indicator with protection against temporary overloads and transients

• US 5,136,456 A
• Filed: 11/17/1989
• Issued: 08/04/1992
• Est. Priority Date: 11/17/1989
• Status: Expired due to Fees

• Current Assignee: Sigma Instruments, Inc. (Inficon Holding AG)
• Original Assignee: Sigma Instruments, Inc. (Inficon Holding AG)
• Inventors: Yeh, Thomas
• Primary Examiner(s): DEBOER, TODD
• Application Number:
  US07/438,631
• Time in Patent Office: 991 Days
• Field of Search: 361/86, 361/87, 361/92, 361/93, 361/94, 361/95, 361/96, 361/68, 361/59, 361/3, 361/2, 361/55, 361/63, 361/94, 340/650, 340/664
• US Class Current: 361/63
• CPC Class Codes: H02H 1/04 Arrangements for preventing response to transient abnormal conditions, e.g. to lightning or to short duration over voltage or oscillations; Damping the influence of dc component by short circuits in ac networks
• CPC Class Codes: H02H 3/042 combined with means for locating the fault locating faults in cables G01R31/08

Abstract

The disclosed faulted current indicator ignores temporary overloads and transients by inhibiting any trip resulting from an overcurrent signal until a disabling circuit senses that a fuse or circuit breaker has reduced the line current to zero.

Claims

1. A faulted current indicator, comprising:

reset means for producing a reset signal in response to a first current value in a cable;

trip means for producing a trip signal in response to a second current value higher than the first current value in the cable;

disabling means coupled to said trip means for producing a signal to enable said trip means to produce the trip signal when the current in the cable drops below the first current value within a given time after reaching the second current value and disable the trip signal otherwise.

2. An indicator as in claim 1, wherein:

said trip means includes means to maintain the trip signal longer than the time the current drops from above the second current value to below the first current value.

3. An indicator as in claim 1, wherein:

said disabling means enables said trip means to produce the trip signal when the current in the cable drops from the second value to a value substantially zero within the given time.

4. A faulted current indicator as in claim 1, wherein:

said disabling means includes inrush restraint means for disabling said trip means in response to current inrushes.

5. A faulted current indicator, comprising:

reset means for producing a reset signal in response to a first current value in a cable;

signal producing means for producing a signal in response to the cable exceeding a second current value higher than the first current value in the cable;

distinguishing means coupled to said indicting means and current in the cable for distinguishing between the indications followed by current in the cable dropping below the first current value within a given time and indications followed by current in the cable failing to drop below the first current value within the given time;

and trip signal means responsive to said distinguishing means for producing trip signals only in response to indications followed by cable currents dropping below the first current value within the given time, and for disabling the trip signals at all other times.

6. A faulted current indicator as in claim 5 wherein:

said distinguishing means further includes inrush restraint means for preventing said trip signal means from producing a trip signal when said indicating means responds to current inrushes.

7. An indicator as in claim 5, wherein:

said indicating means includes means to maintain the indication longer than the time the current drops from above the second current value to below the first current value.