GROUND DETECTION CIRCUIT FOR A D.C. DISTRIBUTION NETWORK

• US 3,668,472 A
• Filed: 05/17/1971
• Issued: 06/06/1972
• Est. Priority Date: 05/17/1971
• Status: Expired due to Term

• Current Assignee: Victor H. Willems, William B. Shields, William F. Sailer
• Original Assignee: Victor H. Willems, William B. Shields, William F. Sailer
• Inventors: Shields, William B., Willems, Victor H., Sailer, William F.
• Primary Examiner(s): Trammell, James D.
• Application Number:
  US05/144,066
• Time in Patent Office: 386 Days
• Field of Search: 317/49,18R,18D,33SC,27R 340/255
• US Class Current: 361/49
• 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

The invention relates to a ground detection circuit for an ungrounded D.C. distribution network. The sensitivity to ground is uniquely independent of polarity of the D.C. bus on which the ground occurs. The occurrence of multiple grounds will cause the ground detection circuit to operate as if all such ground resistances were in parallel with each other. The principle of detection is based on the fact that the algebraic sum of currents flowing through a resistance, having one end connected to ground and the other end being alternately connected to the plus and then to the minus bus of the center tap battery source, is inversely proportional to the '"'"''"'"''"'"''"'"'total resistance'"'"''"'"''"'"''"'"' to ground of the network, where '"'"''"'"''"'"''"'"'total resistance'"'"''"'"''"'"''"'"' is the equivalent of placing all resistances to ground in parallel.

Claims

1. An unground D.C. distribution network including a positive bus, a negative bus and a source of direct current connected across said busses, tap means for said source, a resistance network connected between said busses and ground including a resistor, and switching means for connecting one end of said resistor alternately to said positive and negative busses, and ground detector means responsive to the sum of the currents flowing through said resistor during said alternate connections.

2. A network as recited in claim 1 wherein said resistance network includes a time base and wherein said switching means includes a flip-flop circuit triggered by said time base.

3. A network as recited in claim 2 wherein said flip-flop circuit includes silicon controlled rectifier means for operating said switching means.

4. A network as recited in claim 1 wherein said ground detector includes a diode and a capacitor which is charged to a voltage proportional to the current flowing away from ground through said resistor, said diode preventing the capacitor from discharging its accumulated charge when switching to the opposite polarity bus.

5. A network as recited in claim 4 but with an opposite polarity diode, its capacitor being charged to a voltage proportional to the current flowing towards ground through said resistor.

6. A network as recited in claim 4 wherein said ground detector means also includes a unijunction transistor which controls a thyristor.

7. A network as recited in claim 6 together with a control relay so that upon attainment of a predetermiNed total charge across said capacitors, representative of a predetermined value of ground resistance, said control relay will be operated by the turning on of the thyristor by discharge of said capacitors through said unijunction transistor.

8. The method of detecting a ground in an underground D.C. distribution network including a positive bus, a negative bus, a source of direct current connected across said busses having tap means and a resistance network connected between said busses and said ground, including a resistor;

which method comprises connecting one end of said resistor alternately to said positive and negative busses and detecting the algebraic sum of currents flowing through said resistor during said alternate connections.