Means and method for measuring electrical-ground resistance between earth-separated locations

• US 3,913,010 A
• Filed: 04/30/1974
• Issued: 10/14/1975
• Est. Priority Date: 07/16/1973
• Status: Expired due to Term

• Current Assignee: Leopoldo Scarpino
• Original Assignee: Leopoldo Scarpino
• Inventors: Scarpino, Leopoldo
• Primary Examiner(s): Strecker, Gerard R.
• Application Number:
  US05/465,591
• Time in Patent Office: 532 Days
• Field of Search: 324/51,52,62 317/18R,18B 340/255
• US Class Current: 324/509
• CPC Class Codes: G01R 27/20 Measuring earth resistance; Measuring contact resistance, e.g. of earth connections, e.g. plates
• CPC Class Codes: H02H 11/001 in case of incorrect or interrupted earth connection disconnection by breaking of earth connection H02H5/105
• CPC Class Codes: H02H 7/226 for wires or cables, e.g. heating wires

Abstract

The invention contemplates safety monitoring by measuring the electrical-resistance condition of a remote electrical ground with reference to a given base end, as in application to elongate flexible trailing cable of the character used to supply large quantities of electrical power from a base or source-connection end to a movable load-connection end, which may be as much as several miles remote from the base end. The measurement involves a relatively simple set of electrical components whereby a Wheatstone bridge may be defined using the unknown earth resistance as one arm of the bridge; two flexible conductors connect the set (at the base end) to the remote ground.

Claims

1. As an article of manufacture, a unitary ground-resistance measuring set adapted for use with a local earth-ground connection at one end of an elongate electrical multipleconductor cable the other end of which includes at least two conductor connections to a remote ground to earth;

said set comprising resistance-bridge elements consisting of elements of two conjugate arms for connection between opposed first diagonal bridge terminals, one of which terminals is said remote ground and the other of which is contained in said set;

a monitoring variable resistor connected at one end to the first diagonal bridge terminal of said set and having means at its other end for connection to said local earth-ground connection, whereby said monitoring resistor may be connected in series with the earth between cable ends to define one of the conjugate arms, and whereby the local earth-ground connection may be one terminal of the second diagonal of the bridge;

two series-interconnected resistance members forming elements of the other conjugate arm and connected at one end to the first diagonal bridge terminal of said set and having means at its other end for connection to one of the remote-grounding conductors of said cable, the point of interconnection of said resistance members of said other conjugate arm defining the other terminal of the second diagonal of the bridge;

d-c source supporting means at said set and having first and second pole connections to the terminals of one bridge diagonal; and

voltage-responsive means at said set and interconnecting the terminals of the second bridge diagonal;

the diagonal connection to said remote-ground terminal being via the other remote-grounding conductor of said cable.

2. The article according to claim 1, wherein the said resistance members in said other conjugate arm are each of substantially greater ohmic value than said variable resistor.

3. As an article of manufacture, a ground-resistance bridge measuring set comprising two elongate flexible conductors connected to each other only at the end remote from said set and having connectable means at said one end for detachable connection to a first earth-bound ground, said bridge set including first bridge-diagonal arm elements with means for series-accommodation of a voltage source and second bridge-diagonal arm elements with means for series-accommodation of a voltage-responsive device, said first earth-bound ground being a first corner of said bridge, resistance-bridge elements consisting of elements of two conjugate arms connected to said first corner and across one of said bridge diagonals, two series-interconnected resistance members forming elements of one conjugate arm and defining at their interconnection one terminal of the other bridge diagonal, means including second earth-bound ground-connectable means local to the set and including a further resistor member in the set for establishing said further resistor member and the earth-ground resistance as the other conjugate arm, said second earth-bound ground-connectable means defining the other terminal of the other bridge diagonal, the bridge diagonal to said first earth-bound ground being via one of said conductors and that part of said first conjugate arm which is to be connected to the first earth-bound ground being via the other of said conductors, one of the resistor members of said bridge being variable, whereby upon bridge balance the adjustment of the variable reSistor member is indicative of earth resistance between said earth-bound system grounds, plus resistance indicative of the degree of fidelity of connection of said grounds to earth.

4. The method of using Wheatstone-bridge elements at one end of an elongate multiple-conductor cable to check the instantaneous true-resistance status end-to-end of a conductive path via earth ground between the ends of said cable, which comprises interconnecting two of said conductors to each other and to a first earth-ground connection of said path at the other end of said cable to define one of two bridge-excitation terminals;

serially connecting a voltage source in one of said two conductors to thereby define the other of said bridge-excitation terminals at the one end of said one conductor;

forming two conjugate arms extending between said opposed bridge-excitation terminals by (1) selecting and serially interconnecting two resistors of relatively high ohmic value and serially connecting the same with the other of said conductors at said one end, thereby defining one of said arms, and (2) selecting a variable resistor of relatively low ohmic value and serially interconnecting the same with a second earth-ground connection of said path at said one end; and

varying said resistance until substantially zero voltage is observed between the point of interconnection of said fixed resistors and the point of interconnection of said variable resistor with said earth-ground path.

5. The method of using Wheatstone-bridge elements at one end of an elongate multiple-conductor cable to check the instantaneous true-resistance status end-to-end of a conductive path via earth ground between the ends of said cable, which comprises interconnecting two of said conductors to each other and to a first earth-ground connection of said path at the other end of said cable to define one of two bridge-excitation terminals;

serially connecting a voltage source in one of said two conductors to thereby define the other of said bridge-excitation terminals at the one end of said one conductor;

forming two conjugate arms extending between said opposed bridge-excitation terminals by (1) selecting and serially interconnecting two resistors of relatively high ohmic value and serially connecting the same with the other of said conductors at said one end, thereby defining one of said arms, and (2) selecting a variable resistor of relatively low ohmic value and serially interconnecting the same with a second earth-ground connection of said path at said one end;

setting the resistance of said variable resistor to an ohmic value which is predetermined to represent a threshold of tolerable resistance above a normal resistance in said earth-ground path, and observing for reduction to substantially zero the voltage between the point of interconnection of said fixed resistors and the point of interconnection of said variable resistor with said earth-ground path.

6. The method of using Wheatstone-bridge elements at one end of an elongate multiple-conductor cable to check the instantaneous true-resistance status end-to-end of a conductive path via earth ground between the ends of said cable, which comprises interconnecting two of said conductors to each other and to a first earth-ground connection of said path at the other end of said cable to define one of two bridge-excitation terminals;

serially connecting a voltage source in one of said two conductors to thereby define the other of said bridge-excitation terminals at the one end of said one conductor;

forming two conjugate arms extending between said opposed bridge-excitation terminals by (1) selecting and serially interconnecting two resistors of relatively high ohmic value and serially connecting the same with the other of said conductors at said one end, thereby defining one of said arms, and (2) selecting a variable resistor of relatively low ohmic value and serially interconnecting the same with a second earth-ground connection of said pAth at said one end;

setting the resistance of said variable resistor to an ohmic value which is predetermined to represent a threshold of tolerable resistance above a normal resistance in said earth-ground path, and observing for change in polarity the voltage between the point of interconnection of said fixed resistors and the point of interconnection of said variable resistor with said path.

7. The method of using Wheatstone-bridge elements at one end of an elongate multiple-conductor cable to check the instantaneous true-resistance status end-to-end of a conductive path via earth ground between the ends of said cable, which comprises interconnecting two of said conductors to each other and to a first earth-ground connection of said path at the other end of said cable to define one corner of the bridge;

selecting and serially connecting two resistances of ohmic value much higher than that of the path to be checked, thereby defining a second bridge corner at the interconnection of said resistances;

selecting and connecting in series with the free end of one of said high resistances a low resistance of ohmic magnitude comparable to that for which observation is to be made in said path, thereby defining a third bridge corner at said interconnection of high and low resistances, and thereby also leaving an available free end of a high resistance and an available free end of the low resistance;

connecting one of said available free ends to said one end of a first cable conductor; and

connecting the other available free end to a second earth-ground connection of said one end of said path, thereby defining the fourth bridge corner, and thereby establishing the series loop-connection of all four bridge corners wherein said earth-ground path is the arm between said first and fourth corners;

selecting and diagonally connecting a voltage-excitation source between a first two opposite bridge corners; and

selecting and diagonally connecting a voltage-responsive device between the remaining two opposite bridge corners;

locating the voltage-excitation source and the voltage-responsive device at said one end of the cable, and using a second cable conductor to complete the requisite one of the diagonal connections to said first-defined bridge corner.

8. As an article of manufacture, a unitary ground-resistance measuring set adapted for use with a local earth-ground conductor at one end of an elongate electrical multiple-conductor cable the remote end of which includes an earth-ground connection of at least a pair of conductors of said cable;

said set comprising Wheatstone-bridge elements, d-c source supporting and connecting means, and voltage-responsive means;

said set further comprising ground-connection means for making an earth-ground connection local to said set, and first and second terminals for connection at said one end to the respective two cable conductors which are remotely earth-grounded, whereby the point of remote earth-grounding may constitute a first bridge corner and the earth path between remote and local earth grounds may be one of the arms of a completed bridge;

said bridge elements at said set comprising two serially connected resistance arms of ohmic value much higher than that of the earth-ground path to be measured, thereby defining a second bridge corner at the interconnection of said high-resistance arms, a low-resistance arm of ohmic value comparable to that of the earth-ground path to be measured, said low-resistance arm being connected to the otherwise-free end of one of the high-resistance arms, thereby defining a third bridge corner at interconnection of high and low-resistance arms, and thereby also defining first and second otherwise-available free ends of a high-resistance arm and of the low-resistance arm respectively, said otherwise-available free ends being respectively connected to said first terminal and to the ground-connection means of said set, thereby defining the fourth bridge corner at the ground-connection means of said set, and therEby establishing the series-loop connection of all four bridge corners via said arms when said set is cable-connected as aforesaid;

said d-c source connecting means comprising opposite-pole connections for a first two diagonally opposite bridge corners, and voltage-responsive means for diagonally connecting the remaining two opposite bridge corners, the one of said diagonal connections which is to include the first-defined bridge corner being connected to the second of said terminals, so that the second remotely-grounded cable conductor may be the means of completing the diagonal connection to the first-defined bridge corner.

9. The article of claim 8, in which said low-resistance arm is selectively variable, whereby measured earth-path resistance is a function of the adjusted ohmic value of the low-resistance arm at bridge balance.

10. As an article of manufacture, a Wheatstone-bridge ground-resistance measuring set comprising a pair of elongate flexible conductors connected to each other at one end only and having means at said one end for detachable connection to a first earth-bound ground, thereby defining at said detachable connection a first bridge corner;

said set further comprising d-c source-supporting and connecting means, voltage-responsive means, and second-ground means for detachable connection to a second earth-bound ground;

thereby defining, electrically adjacent to said first bridge corner, a second bridge corner at said second-ground means and establishing an earth-resistance bridge arm between said corners;

said bridge elements of said set comprising two serially connected resistance arms of ohmic value much higher than that of the earth-ground path to be measured, thereby defining a third bridge corner at the interconnection of said high-resistance arms, a low-resistance arm of ohmic value comparable to that of the earth-ground path to be measured, said low-resistance arm being connected to the otherwise-free end of one of the high-resistance arms, thereby defining a fourth bridge corner at interconnection of high and low-resistance arms, and thereby also defining first and second otherwise-available free ends of a high-resistance arm and of the low-resistance arm respectively, said otherwise-available free ends being respectively connected to the other end of one flexible conductor and to said second bridge corner respectively, thereby establishing the series-loop connection of all four bridge corners via said arms when said set is detachably ground-connected as aforesaid;

said d-c source-connecting means comprising opposite-pole connections to a first two diagonally opposite bridge corners, and voltage-responsive means for diagonally connecting the remaining two opposite bridge corners, the one of said diagonal connections which is to include the first-defined bridge corner being connected to the other end of the other flexible conductor, whereby said other flexible conductor is the means of completing the diagonal connection to the first-defined bridge corner.