DC BUS RESISTIVE PATH TO GROUND FAULT DETECTOR

• US 3,801,898 A
• Filed: 03/22/1972
• Issued: 04/02/1974
• Est. Priority Date: 06/16/1971
• Status: Expired due to Term

• Current Assignee: John A. Young
• Original Assignee: John A. Young
• Inventors: Young, John A.
• Primary Examiner(s): Strecker, Gerard R.
• Application Number:
  US05/236,940
• Time in Patent Office: 741 Days
• Field of Search: 324/51,133 340/248,253,255 307/236
• US Class Current: 340/651
• CPC Class Codes: G01R 27/18 Measuring resistance to earth , i.e. line to ground
• CPC Class Codes: H02H 3/16 responsive to fault current to earth, frame or mass with balanced or differential arrangement H02H3/26 ; monitoring earth connection H02H5/105

Abstract

A detector for indicating a resistive path to ground fault on either bus of a pair of ungrounded DC buses conducting electric power to a load. The detector includes one gate circuit for each bus. A positive DC bias signal applied to the gate circuit for the positive bus maintains this circuit in one mode of operation during the absence of a fault on either bus; a negative DC bias signal applied to the gate circuit for the negative bus maintains this circuit in a second mode of operation during the absence of a fault on either bus. The voltages on the buses are compared in a simple resistor network. Whenever these voltages become imbalanced because of a resistive path to ground fault on either bus, a signal from the network, proportional to the imbalance and applied to the gate circuits, will switch the circuit for the faulted bus to the other mode of operation. This switching is annunciated to indicate a fault occurrence as well as the faulted bus.

Claims

1. A detector for indicating a resistive path to ground fault on either bus of a pair of ungrounded buses conducting electric power to a load, said detector comprising:

a. a gate circuit for each of said buses, each gate circuit being capable of operation in either of two modes of operation;

b. input bias means for each gate circuit for normally operating each circuit in a different one of said modes;

c. input control means for said gate circuits for comparing the voltages on said buses and applying a signed signal to both of said circuits whenever said voltages become imbalanced as a result of said fault, said signal switching the gate circuit for the faulted bus to the other one of said modes; and

, d. monitoring means for said gate circuits for annunciating said switching.

2. The detector in accordance with claim 1 in which said input control means comprises a resistor network including a resistor connected between each of said buses and each of said gate circuits.

3. The invention in accordance with claim 1 wherein said input control means includes an operational amplifier the output of which varies in accordance with the nature of said ground fault.

4. A detector for indicating a resistive path to ground fault on either bus of a pair of ungrounded DC buses conducting electric power to a load, said pair comprising a positive and a negative bus, said detector comprising:

a. a first and a second gate circuiT for the positive and negative bus respectively, said circuits being capable of operation in either of two modes of operation;

b. input bias means for each circuit for normally operating each in a different one of said modes, one bias means inputting a positive DC signal to said first circuit and the other inputting a negative DC signal to said second circuit;

c. input control means for said gate circuits for comparing the voltages on said buses and applying an additional signal to both of said circuits whenever said voltages become imbalanced as a result of a fault, a negative additional signal indicative of said fault on said positive bus switching said first circuit to the other one of said modes and a positive additional signal indicative of said fault on said negative bus switching said second circuit to the other one of said modes; and

, d. monitoring means for said circuits for annunciating said switching.

5. The detector in accordance with claim 4 in which said input control means comprises a resistor network including a resistor connected between each of said buses and each of said gate circuits.

6. The invention in accordance with claim 4 wherein said input control means includes an operational amplifier the output of which varies in accordance with the nature of said ground fault.