MXPA97005838A

MXPA97005838A - Cable tester of bridge of connection to earth protector better

Info

Publication number: MXPA97005838A
Application number: MXPA/A/1997/005838A
Authority: MX
Inventors: Adelbert Rhein David
Original assignee: Hubbell Incorporated
Priority date: 1996-08-09
Filing date: 1997-07-31
Publication date: 1998-02-01

Abstract

The present invention relates to a protective earthing jumper cable tester basically including a housing, a pair of bridge fixing terminals in the housing for fixing a jumper wire therebetween, a voltage application circuit of cd arranged in the housing and connected to the pair of bridge clamp terminals to apply a direct current through a jumper wire fixed between the bridge clamp terminals, and electronic element in the form of a PC board and microprocessor arranged in the housing and interconnected to the dc voltage circuit to apply a predetermined mathematical relationship to measure a resistance value of at least a portion of the jumper wire fixed between the bridge fastening terminals. The electronic element when applying the predetermined mathematical relationship to measure the resistance value includes elements to take different voltage readings in accordance with the Kelvin measurement procedure and calculate the resistance value of the voltage readings in accordance with the current law from Kircho

Description

CABLE TESTER OF BRIDGE OF CONNECTION TO EARTH PROTECTOR BETTER DO REFERENCE TO RELATED APPLICATION Reference is hereby made to the following United States application which deals with the subject matter relating to the present invention: "Protective Grounding Jumper Cabl Tester and Testing Method" by Clayton C. King, assigned No. US Series 08 / 437,661 and filed on May 9, 1995.

Field of the Invention The present invention relates generally to the test of grounding jumper cables and, more particularly, refers to a grounding jumper cable tester used to determine whether the resistance of a cable-of Grounding bridge to current flow is below a predetermined safe level.

Description of the Prior Art During the maintenance of a power line, it may be activated accidentally due to the inadvertent closing of a breaker or switch or due to the mutual induction of parallel live lines. To protect workers from electric shock in the event of a failure, grounding cables are installed in various configurations to form a bridge system. Grounding jumper cables are conducting wires that have fasteners, such as clamps, at either end. The bridge system provides a path for the current to flow around the worker to a neutral line or to ground. However, in order for the bridge system to adequately protect the worker, it must provide a very low resistance path to the current flow so that the voltage drop across the worker remains within a safe level in case -one fault occurs. The maximum permissible resistance of the bridge system can be determined based on assumptions related to the fault current available at the work site, the duration of the available fault current, and the level of safety to be provided. Once the maximum permissible bridge system resistance is determined, individual ground jumper cables can be selected to form the bridge system. Since the resistance of the bridge system is mainly determined by the resistance of each of the individual bridge cables, it is necessary to determine the resistance of the individual bridge cables. Additionally, since they can be damaged during storage, transport or use, individual jumper cables must be periodically tested to ensure that their resistance remains appropriate for the desired level of protection. There are the grounding jumper cable testers, such as the one manufactured by Hasting's Fibe_ glass Corporation, that are designed to test the resistance of a jumper wire to the current flow. The devices test the resistance of a bridge cable based on Ohm's law that defines the mathematical relationship between voltage, current and resistance. A known channel is applied through the cable and the voltage drop across the cable is measured. With the known current and voltage, the resistance can be determined. However, the prior art jumper cable test device identified above utilizes a current transformer to provide an alternating test current. This presents two significant disadvantages. The first disadvantage is the inductance associated with alternating current. When alternating current flows through the bridge-cable, the inductance can operate in a manner similar to resistance and cause a voltage drop. This induced voltage drop can result in inaccurate determination of high resistance. The effect of the inductance is particularly acute if the cable is wound or on a conductive surface. In this way, when a test current is used, it is critical to take steps to ensure that the jumper wire is properly positioned to minimize the possible effect of the inductance.

The second disadvantage is the low test voltage. MJJ chos jumper cables have aluminum clamps. A thin aluminum oxide coating is formed over the clamps. This coating is highly resistant to current flow but breaks easily when a sufficient voltage level is applied, in the range of 5 to 10 volts. The voltage levels found at work sites are more than sufficient to interrupt any aluminum oxide coating on the clamps making the coating resistance irrelevant. However, if insufficient voltage is applied during the test the thin coating of aluminum oxide can Raise the resistance of the bridge cable and result in unnecessary rejection of the bridge cable. While the current transformer used in the above known devices provides a sufficiently high alternating test current, it does so at the cost of the voltage. The voltage drop created by the above positive alternating current cable test dies is often inadequate to interrupt the aluminum oxide coating, resulting in a determination of imprecise resistance and unnecessary rejection of the jumper wire. The invention described and claimed in the above-identified patent application, which is assigned to the assignee of the present invention, addressed to the disadvantages associated with the prior art devices by providing a grounding bridge cable test device. and test method that avoided the inductance problem associated with the alternating current and provided a sufficient voltage drop to interrupt any aluminum oxide coating on the cable clamps. In this prior device, an operator had to first adjust the amount of current flowing through the jumper wire to a pre-selected amount and then take a pair of test probes and contact them with the jumper cable to perceive the amount of cable resistance between the probe contact points and compare it with a safe, predetermined resistance level. If the cable passed the initial test, then repeated tests were performed at different current levels having predetermined threshold resistance values to ensure that the cable was safe to use for its intended application. The multiple test steps and adjustment operations not only conserve time, but also have the potential for operator error. Consequently, there is a need for a ground bridge jumper test device that is more automatic in operation in order to reduce the number of steps in the test procedure and the time required to carry out the test operation and a test device that not only produces very accurate and safe test results but also one that substantially reduces the possibilities of operator error.

SUMMARY OF THE INVENTION The present invention provides a protective grounding cable tester designed to meet the above mentioned needs avoiding the disadvantages of the prior art without introducing other disadvantages. Accordingly, the present invention is directed to a protective grounding cable tester used to determine whether a grounding bridge has an adequately low resistance to current flow so that it can be safely used in a bridge system. The inventor of the present invention uses direct current to measure the resistance in the jumper wire and the output current of the cable can be limited to a maximum amount specified by an internal current limiting resistor. The ground connection bridge tester p tector of the present invention basically includes: (a) an assembly that can be portable for field use of the tester; (b) one oar of bridge fixing terminals in the housing (c) a dc voltage applying circuit disposed in the housing and connected to the pair of bracket clamping terminals to apply a direct current through a jumper wire fixed between the bridge clamping terminals; and (d) electronic means disposed in the housing and interconnected to the dc voltage circuit to apply a predetermined mathematical relationship to measure a resistance value of at least a portion of the bridge cable set between the bridge fastening terminals. The dc voltage circuit includes a DC power supply, preferably 5 volts, which has first and second terminals. The first terminal of the power supply is interconnected by a first wire-to-first conductor of the wall-fixing terminals and the second terminal of the power supply is interconnected by a second wire-to-wire conductor. second of the pair of bridge fixing terminals. A known resistance, preferably having a value of 5 ohms, is connected in series in the first wire conductor and is arranged between the first terminal of the power supply and the first bridge clamping terminal to limit the amount of current ( 10 ampere rating) flowing through the circuit when a bridge cable is to be tested is fixed between the first and second bridge clamping terminals. Preferably, the electronic element is in the form of a PC board with a microprocessor. It will automatically and reliably measure the resistance value of at least a portion of the Duente cable fixed between the terminals - of the Duente's fixation. . By applying the predetermined mathematical relationship to measure the resistance value of the jumper cable, the electronic element includes means. It will take different readings of assembly in accordance with the Kelvin measurement procedure and calculate the resistance value from the readings. voltage conditions in accordance with the Kirchoff current law. The electronic element also includes indicating means to indicate to an operator whether the measured resistance value of the cable is greater or less than a preselected resistance value for a cable of a certain size. And for problem tripping operations, to place different portions of the jumper cable that may have a high resistance value, the tester further includes a pair of Drueba probe terminals interconnected to the electrode element and dissolves in the housing for connection to A pair of test leads will give you the resistance of a portion of the jumper wire between the contact points of the selected probe. A switch, connected to the electronic element, is provided for selection between a fixed mode to take a voltage reading through the bridge clamp terminals and a probe mode to take a voltage reading across the contact points. of probe. These and other features and advantages of the present invention will become apparent to those skilled in the art following a reading of the following detailed description when taken in conjunction with the drawings in which an illustrative embodiment of the invention is shown and described. the invention.

BRIEF DESCRIPTION OF THE DRAWINGS In the following detailed description, reference will be made to the appended drawings in which: Figure 1 is a top plan view of a protective cable bridge grounding bridge protector. invention, with its upper casing cover being removed and with a typical grounding jumper cable having clamps at each end that are fixed to the bridge clamping terminals of the tester to begin a cable test. Figure 2 is an elevation view of a removable terminal post that is threadedly attached to. the tester bridge fixing terminal. Figure 3 is an electrical block diagram illustrating the functional operations of the tester shown in Figure 1 to test the strength of a bridge cable in accordance with the invention., the Dropler being shown in fixed mode to take a voltage line through the bridge clamp terminals. Figure 4 is a view identical to Figure 3 but-with the Drover being shown in the probe mode to take a vot- ing reading through the contact points of son.

DETAILED DESCRIPTION OF THE INVENTION In the following description, similar reference characters designate equal or corresponding parts in all the various views. Likewise, in the following description, it should be understood that terms such as "for", "back", "left", "right", "ups", "tos ab_a jo", and the like, are words of convenience and should not be considered as limiting terms. Referring now to the drawings, and particularly to Figure 1, there is illustrated a protective grounding jumper cable tester of the present invention, which is generally designated 10. The tester 10 includes a housing -12 that preferably , although not necessarily, it is portable to be easily accommodated to field use of the tester. The tester 10 also has a cover (not shown) attached to the housing 12 by a pair of joints (not shown) to pivotally close the cover during periods of non-use and open the cover to access the components therein. which are described below, to use the tester 10. The basic components of the tester 10 include a pair of bridge fixing terminals 14, 16; a cd voltage application circuit 18; and an electronic element 20 for automatically measuring the resistance valve of at least a portion of a bridge cable 22 fixed between the bridge fixing terminals 14, 16, applying a predetermined mathematical relationship. The bridge fixing terminals 14, 16 are mounted on the upper panel 12A of the housing 12 adjacent to the rear corners thereof, and preferably, each fixing end 14, 16 is internally threaded to receive a portion 24 of extension extension of threaded terminal, such as that shown in Figure 2, which threaded hia and from terminal 14, 16 to respectively deploy the post for use and removal of the post for storage in the attachment 12 The posts 24 having different sizes and configurations can be provided to facilitate the clamping of the bridge clamps 22A having clamps of different sizes and shapes. The dc voltage applying circuit 18, as shown diagramatically in Figures 3 and 4, is housing 12 and connected to the pair of bridge and operable terminals 14, 16 to apply a direct current through of the bridge cable 22 fixed between the bridge fixing terminals 14, 1. More particularly, the dc voltage applying circuit 18 includes a cd power supply 26 having first and second terminals 26A, 27B; a first wire conductor 28 interconnecting the first terminal 26 of the power supply 26 and first one of the pair of bridge fixing terminals 14, 16; a second power conductor 30 interconnects the second terminal 26B of the power supply 26 and a second 16 of the pair of the bridge terminals 14, 16; and a known resistor 32 (R.) connected in series in the first wire conductor 28 and disposed between the first terminal 26A of the power supply 26 and the first bridge fixing terminal 14 to limit the amount of current flowing through of the circuit 18 when the bridge cable 22 is fixed between the first and second terminals 14, 16 of the bridge fixation. Preferably, the cd power supply 26 is a 5 volt supply and the known resistor 32 has a value 0.5 ohms so that the maximum current flowing through the circuit 18 is limited to 10 amperes. In the preferred embodiment, the known resistor 32 takes the form of two separate resistors, a 0.2-ohm resistor and a 0.3-ohm resistor, connected in series in the first -28-open conductor to reduce the wattage requirement. of each resistor 32. Still referring to Figures 3 and 4, the electronic element 20, which is illustrated in block diagram form, takes the form of a PC board 34 with a microprocessor 36 for measuring the resistance value of the bridge cable 22 by taking different voltage readings in accordance with the well-known Kelvin measurement procedure and then calculating the resistance value from these voltage readings in accordance with Kirchoff's current law, also a principle well known to those experienced in the field. Even when taking two voltage readings is sufficient for this calculation, the tester 10, in accordance with the preferred mode, uses a voltage measurement of four the two singles to obtain accurate resistance measurements. When the full length of the cable 22 is being tested, as illustrated in Figure 3, the four kelvin voltage readings are as follows: (1) a first voltage reading V. is taken between the terminals 26A, 26B first and Second of the 26 power supply:; (2) a second voltage reading V is taken between the second terminal 26B of the power supply 26 and a first location 38 in the first wire conductor 28 positioned between the known resistor 32 and the first bridge fixing terminal 14; (3) a third voltage reading V3 is taken between the second terminal 26B of the power supply 26 and the first bridge-terminating terminal 14; and (4) a fourth voltage reading V4 is taken between the second terminal 26B of the power supply 26 and the second bridge fixing terminal 16. Of these four readings V, _. of voltage, the microprocessor 36 calculates the resistance value R for the test bridge cable 22 in accordance with the Kirchoff current law as follows: R = (v ~ vl ^ divided by (V -V) by the resistor C. Known R. (known resistance) In other words, subtract the second voltage reading V2 from the first voltage reading V. to obtain a first difference, subtract the fourth reading V. voltage from the third reading V3 To obtain a second difference, divide the first difference between the second difference to obtain a quotient, and then multiply the quotient by the known resistance Rk (32) for this way obtain the resistance R measured. R value of measured resistance of the bridge cabling 22 has been calculated as described above, the micro switch 36 compared to a preselected resistance value (threshold) for a cable of a given diameter size, the measured r value of resistance is greater than the preselected residence value, the tester 10 through a red indicator light 10, mounted on the upper panel 12A of the housing 12 and electrically connected (not shown) to the electronic element 20 activates the light to notify an operator that the jumper wire 22 failed the test and thus must be inspected and tested again as set forth in the test and inspection section of the aforementioned application, on the other hand, in case the R value of the measured resistance of the cable 22 If the bridge is less than the preselected resistance value, a green indicator light 42 mounted adjacent to the lumen 40 ja in the upper panel 12A of the housing 12 and connected electrically (not shown) to the electronic element 20 is activated to notify the operator that the bridge wire 22 has passed the test and that the tested bridge wire 22 is safe for its intended purpose.

To investigate faults, by identifying which portions of the bridge cable 22 components can be a high strength area, the tester 10 further includes a pair of test probe terminals interconnected to the electronic element 20 mounted on the top panel 12A of the housing 12 for c) with a pair of test probes (not shown) for sensing the resistance of a portion of the bridge cable between selected probe contact pins 44A, 44B in the cable 22 A selector input switch 46, mounted on the upper pan 12A of the housing 12, is connected to the electronic element 20 to interrupt between a "fixed mode" where the voltage readings V- and V. above described are taken through the bridge fixing terminals 14, 16 and a "sond mode for taking V, and 4 voltage readings through probe contact points 44A, 44B placed in a portion of the bridge cage, as illustrated in Figure 4. The illustration n of Figure 4 is identical to the illustration of Figure 3, except in Figure 3, the respective voltage readings are taken through the bridge fixing terminals 14, 16, while in Figure 4, the readings of corresponding voltages s taken through the probe contact points 44A, 44B representing a portion of the bridge cable 22, such as d the clamps 22A at the opposite ends of the cable, or one the ferrules 22B used to fix a clamp As can be seen, when the resistance value R is calculated from the four voltage readings as described above, the readings V ~ and V are replaced by the VV readings when the input selector switch 46 is in the probe mode and the test probes (not shown) a portion of the cable is used for p bar. Referring again to Figure 1, as well as Figures 3 and 4, the tester 10 includes an energy module 48 having a receptacle for receiving a plug (not shown) of an energy cord (not shown). for connecting the power supply 26 and the board 34 PC, through the wire conductors 48a, 48b, 48c, 48d, to an alternate power source, such as a sixty-cycle conventional appliance power receptacle. As is known, the power supply 26 receives alternating current and converts it into direct current. Likewise, the board 34 PC is interconnected to the power supply 26 through the wire conductors 50a, 50b to automatically connect and disconnect the power supply 26. The power module 48 is mounted on the upper panel 1 of the housing 12 and includes a main power switch 52 which illuminates when the power to the tester 10 is connected and a fuse 54 to protect the circuit from the test 10. Also mounted on the Upper panel 12A of the housing 12 is a switch 56, wire size indicator, a continuous test switch 58, a single test switch 60, and a visual display unit 62 all being operatively connected to the electronic element 20. The cable switch 56 allows an operator to select the size of the cable to be tested, whose size is displayed in the display window of the display unit 62 together with the preset resistance threshold value of the particular size cable. what is being tested. Also displayed in the display unit 62 is the measured resistance value of the full length bridge wire 22 between the fixed bridge terminals 14, 16 when the input selector switch 46 is in a fixed mode and exhibits the tested resistance of the bridge cable portion between the probe contact points 44A, 44B when the input switch 46 is in the probe mode. The single test switch 60 allows the tester 10 to make a single resistance measurement and then retains this value, after the continuous test switch 58When connected, it allows the tester 10 to continually measure at the rate of one per second and when in the disconnected position, the tester 10 will retain the last measurement made. Briefly, the method of using the tester 10 is as follows: First the fixing extension posts 24 are screwed to the respective bridge fixing terminals 14, 16 and the cable 22 is fixed to the fixed terminals 14, 16. bridge connection as shown in Figure 1. The power switch 52 is then connected to activate the various components described above. The size of the cable to be tested is then selected by using the cable size switch 56 which exludes the size in the display unit 62 as well as the threshold value of the cable of particular size. The interlock 46 input selector moves to the fixed position and the continuous test switch 58 is placed in the disconnected position. The single test switch 60 is then depressed to complete the test and the tested resistance R value is displayed in the display unit 62. The red indicator light 40 will illuminate if the tested resistance is above the preset threshold: do shown in the display and the green light 42 will illuminate if the tested resistance is below the preset threshold. It should be noted that the jumper wire 22 being tested is always connected between the bridge clamp terminals 14, 16 independently of the test mode, in the fixed mode or the probe mode. In case a cable fails the above test initially, the operator can use the tester 10 easily to identify the high resistance areas of the cable by switching from fixed mode to probe mode and connecting a set of probes (not shown) to the probe terminals 44. The continuous test switch 58 is switched to the connected position so that the tester 10 repeatedly makes measurements at a rate of one per second until the high resistance area is located. In this probe mode, the display unit 62 will display the resistance through the portion of the bridge cable 22 to which the probe ends contact. The display unit 62 will display the measured resistance from a probe contact point 44A to another probe contact point 44B, as s illustrated in Figure 4. As above, the red light 40 will illuminate if the value The measured resistance is greater than the preset resistance value, while the green light 42 will illuminate if the measured resistance value is less than the preset threshold value. It is considered that the present invention and its advantages will be understood from the foregoing description and it will be evident that various changes may be made to it without abandoning the spirit and scope of the invention or sacrificing all its material advantages, as described above. which precedes being only preferred or exemplary as a modality thereof.

Claims

1. - A protector cable bridge tester, which comrpenses: (a) a housing; (b) a pair of bridge fixing terminals in the -location for fixing a bridge cable between them; (c) a cd voltage application circuit disposed in the housing and connected to the pair of bridge clamp terminals to apply a direct current through a bridge wire fixed between the bridge clamp terminals; and > (d) electronic elements arranged in the housing and interconnected to the dc voltage circuit to apply a predetermined mathematical relationship to measure a resistance value of at least a portion of the bridge cable fixed between the bridge fastening terminals. 2. The tester as described in the claim 1, wherein the electronic element when applying the predetermined mathematical relationship to measure the resistance value includes means for taking different voltage readings in accordance with the Kelvin measurement procedure and calculating the resistance value of the voltage readings of compliance with the law

«Kirchoff current.

3. The tester as described in the claim 2, wherein the electronic element further includes indicating means to indicate to an operator whether the measured resistance value is greater or less than a preselected resistance value.

4. - The tester as described in claim 1, wherein the dc voltage circuit includes a DC power supply and a predetermined resistance interposed from the circuit in order to limit the amount of current flowing through the circuit when applied the voltage.

5. The tester as described in claim 4, wherein the cd power supply is a supply of volts and the predetermined resistance has a value of 0.5 ohms so that the maximum current flowing through the circuit is limited at 10 amps.

6. The tester as described in claim 1, wherein the voltage circuit includes: a power supply of cd having first and second terminals; a first wire conductor that interconnects the first terminal of the power supply to a first of the pair bridge clamping terminals; a second wire conductor interconnecting the second terminal of the power supply and a second one of the pair of bridge fixing terminals; and a known resistor connected in series in the first wire conductor and disposed between the first terminal the power supply and the first bridge clamping terminal to limit the amount of current flowing through the circuit when a bridge cable is going to be tested f between the first and second bridge fixing terminals.

7. The tester as described in claim 6, wherein the cd power supply is a supply of volts and the known resistance has a value of 0.5 ohms so that the maximum current flowing through the circuit is limited. at 10 amps.

8. The tester as described in claim 6, wherein the electronic element when applying the predetermined matic ratio to measure the resistance value includes elements to take: a first voltage line between the simple and second terminals of the power supply. Energy; a second voltage reading between the second end of the power supply and a first location on the first wire conductor positioned between the known resistance of the first bridge clamping terminal; a third voltage line between the second terminal and the power supply and a first location on the bridge between the first and second locking terminals; and a fourth voltage reading between the second terminal of the power supply and a second location on the bridge cable placed between the first and second bridge fastening terminals, one of the first and second locations on the bridge cable being closer to the known resistance than the other of the first and second locations on the bridge cable.

9. The tester as described in claim 8, wherein the electronic element when applying the predetermined math ratio to measure the resistance value further includes an element for calculating the resistance value of at least a portion of the bridge cable Fixed between the bridge clamp terminals subtracting the second voltage reading from the first voltage reading to obtain a first difference, subtracting the fourth voltage reading from the third voltage reading to obtain a second difference, dividing by first difference by the second difference to obtain a -cociente, and then multiplying the quotient by the known resistance to obtain in this way the resistance value.

10. The tester as described in claim 2, further comprising: a pair of test probe terminals interconnected to the electronic element and arranged in the housing for connection to a pair of test probes to sense the strength of a portion of the bridge cable between the selected probe-contact points; and a switch connected to the electronic element switchable between a fixed mode to take a voltage reading through the bridge clamp terminals and a probe mode to take a voltage reading through the probe cont. points. .