Abstract:
A utility power line cable selector system used by a lineman to eliminate guessing which buried cable in a ditch has been de-energized when compared to similar buried cables that are still energized with high voltage 60 Hz. power line current and disposed next to the de-energized cable. The selector system includes a battery operated low power 1 Hz. pulse generator adapted for connecting to a near end of a de-energized cable. The generator is designed to deliver a dc current spike and excite the otherwise de-energized conductor at one second intervals. At a far end of the de-energized cable is connected to a jumper cable. At a location midspan or between the near end and far end of the de-energized cable, the lineman holds a portable hand-held signal pick up clamp and cable detector unit. The signal pick up clamp is placed around a portion of each of the cables in the ditch. The cable detector unit includes an electronic filter, a pulse amplifier and a monstable multivibrator with audio and visual indicators to detect if the cable under test has the dc current spike or the test signal flowing through it&#39;s conductor. The filter is designed to prevent a response from 60 Hz. power line current in the energized cables and responds only to the conductor connected to the output from the pulse generator.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    (a) Field of the Invention  
           [0002]    This invention relates to a power line current test system and more particularly, but not by way of limitation, to a portable utility power line cable selector system for indicating to a power line construction lineman or maintenance crew lineman which buried cable among many buried cables in a ditch has been de-energized. The de-energized buried cable selected for repair work, splicing and/or adding an additional power line or lines thereto.  
           [0003]    (b) Discussion of Prior Art  
           [0004]    Heretofore, power line construction lineman and maintenance utility power lineman have complained for years on why hasn&#39;t a reliable power line cable selector system been developed which can be used with confidence for determining which buried power line cable has been de-energized for working thereon when compared to other energized power line cables.  
           [0005]    Currently, construction and maintenance lineman use an approximate eight foot long insulated pole for turning a threaded spike mounted on a “C” clamp attached to a selected cable. As the spike is rotated on the clamp using the insulated pole, a tip of the spike pierces through the cable&#39;s outside insulation cover, through insulation inside the cover and engages an electric conductor surrounded by the insulation. Hopefully, the conductor has been de-energized and without power. On the other hand, if the crew guesses wrong, the selected cable blows up and the crew is placed in danger, even at the end of the insulated pole. Also, power to electric customers is disrupted for an extended period of time until the cable can be repaired.  
           [0006]    An obvious answer to the proper selection of a de-energized buried cable is to color code each of the buried cables disposed next to each other. But, because of added cost of coloring the outside insulation cover and the added cost of having to inventory large numbers of different colored power line cables, utility companies have opted not to color code power line distribution cables. Therefore, the problem of guessing the correct de-energized cable among many other energized cables in the field remains. Obviously, this problem presents a great safety hazard to lineman and utility companies.  
           [0007]    Tone signal and multiple frequency test equipment can be used for proper cable selection. But, this type of test equipment requires de-energizing all of the buried cables, which can be any number of cables disposed side by side. The de-energizing of all of the buried cables is rarely done since it requires turning off power for an extended period of time to all of the utility power company&#39;s customers being served by the power distributed through the buried cables.  
           [0008]    In U.S. Pat. Nos. 3,924,179 to Dozier and 3,882,287 to Simmonds, methods of certifying dead cables or conductors and detecting faults in multi-conductor cables are disclosed. In U.S. Pat. No. 2,789,268 to Bechtel et al., a method and apparatus is described for identifying electric conductors. In U.S. Pat. No. 5,471,143 to Doany, an apparatus for locating buried conductors is illustrated. In U.S. Pat. No. 4,491,785 to Pecukonis, a signal detection device is disclosed using high frequency loading. The loading is used for tracing and identifying electrical conductors. In U.S. Pat. No. 5,760,591 to Matsuda et al., a method and apparatus for determining an electrical wiring state is described.  
           [0009]    None of the above mentioned prior art patents specifically disclose the unique safety features, structure and function of the subject power line midspan cable selector system for correctly identifying a buried de-energized power line cable disposed in a ditch and next to a plurality of energized power line cables carrying high voltage 60 Hz. power line current.  
         SUMMARY OF THE INVENTION  
         [0010]    In view of the foregoing, it is a primary objective of the subject invention to eliminate guessing by a lineman on which buried cable in a ditch has been de-energized when compared to similar buried cables that are still energized with high voltage 60 Hz. power line current and disposed next to the de-energized cable.  
           [0011]    Another object of the subject invention is to eliminate the blowing up of a power line cable in a ditch using a long insulated pole with “C” clamp and spike, since the correct de-energized cable can now be correctly selected among the other energized cables.  
           [0012]    Yet another object of the invention is the power line cable selector system solves the problem of personal safety to lineman who have to try and select a de-energized power line cable from other energized cables. Obviously, with increased safety to lineman, liability risks to a utility company are reduced.  
           [0013]    The power line cable selector system includes a battery operated low power 1 Hz. current pulse generator adapted for connecting to a near end of a de-energized cable at an upstream disconnect station. The generator is connected to one end of the cable&#39;s insulated conductor and connected to a first ground line. The first ground line is connected to the common neutrals of the de-energized cable and the other energized cables. The generator is designed to deliver a de current spike and excite the otherwise de-energized conductor at one second intervals. Obviously, the generator can be designed to deliver different phase current as long as it is not the same as the 60 Hz. power line current flowing through the other buried energized power line cables.  
           [0014]    At a far end of the de-energized cable and at a downstream disconnect station, the selector system includes a jumper cable. The jumper cable is attached to the far end of the insulated conductor and a second ground line connected to common neutrals of the de-energized cable and the other energized cables. The jumper cable connection provides a round trip path from the generator output, through the insulated conductor and a return path via the grounded common neutrals. The length of the de-energized cable and the other cables between the upstream and downstream disconnect stations may be less than 100 feet and up to several miles. The testing to determine which cable is de-energized will always be at a location midspan or somewhere between the two disconnect stations. The disconnect stations may be power line cable switching stations and the like. During the testing for the disconnected or de-energized cable, the other cables may remain energized and they do not interfere with the use of the cable selector system.  
           [0015]    Further, the cable selector system includes a portable hand-held pulse sensing receiver and cable detector unit with a signal pick up clamp. The detector unit and pick up clamp are used between the two disconnect stations and in a ditch where the de-energized cable is to be detected. The signal pick up clamp is placed around a portion of each of the cables in the ditch. The pulse sensing receiver and detector unit includes an electronic parametric filter, a pulse amplifier and a monstable multivibrator with audio and visual indicators to detect if the cable under test has the dc current spike or the test signal flowing through it&#39;s conductor. The audio indicator includes a horn and the visual indicator includes a blinking LED and a current analog meter. The parametric filter is designed to prevent a response from the 60 Hz. power line current in the energized cables and respond only to the conductor connected to the output from the pulse generator. The detector housing unit with signal pick up clamp allows the lineman to check each cable in the trench and determine which cable is de-energized and has the generated test signal running through it&#39;s conductor.  
           [0016]    These and other objects of the present invention will become apparent to those familiar with various power line test systems used with utility power lines when reviewing the following-detailed description, showing novel construction, combination, and elements as herein described, and more particularly defined by the claims, it being understood that changes in the embodiments to the herein disclosed invention are meant to be included as coming within the scope of the claims, except insofar as they may be precluded by the prior art. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]    The accompanying drawings illustrate complete preferred embodiments in the present invention according to the best modes presently devised for the practical application of the principles thereof, and in which:  
         [0018]    [0018]FIG. 1 is a perspective view of a power line construction lineman or maintenance lineman shown in a ditch and using the portable hand-held cable detector unit with signal pick up clamp. The lineman is shown checking one of the buried cables to determine if it is a de-energized cable.  
         [0019]    [0019]FIG. 2 is a cross section of a typical high voltage power line cable.  
         [0020]    [0020]FIG. 3 is a schematic drawing of three power line cables. One of the cables is shown as an isolated and de-energized cable for performing repair work thereon and/or splicing additional cables thereto. The other two cables remain energized.  
         [0021]    [0021]FIG. 4 is a general electrical diagram of the current pulse generator attached to a near end of the de-energized cable and generating a low voltage dc current spike and used as a test signal.  
         [0022]    [0022]FIG. 5 is a general electrical diagram of the pulse sensing and cable detector unit with signal pick up clamp. The pick up clamp is used for receipt around a portion of each power line cable in the ditch.  
         [0023]    [0023]FIG. 6 is a detailed electrical diagram illustrating all of the individual electrical components connected together and making up the current pulse generator.  
         [0024]    [0024]FIG. 6A a test signal sent from the pulse generator and received by the pulse sensing and cable detector unit.  
         [0025]    [0025]FIG. 7 is a detailed electrical diagram illustrating all of the individual electrical components connected together and making up the pulse sensing receiver and cable detector unit with the signal pick up clamp.  
         [0026]    [0026]FIG. 8 is a detailed electrical diagram of an alternate embodiment of the pulse signal filter as a high pass filter. The high pass filter can be used as part of the cable detector unit.  
         [0027]    [0027]FIG. 9 illustrates the response of the two filter configurations described and illustrated in FIGS. 7 and 8.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0028]    In FIG. 1, a perspective view of a power line construction lineman or maintenance lineman  10  shown in a ditch  12  and using the portable hand-held pulse sensing receiver and cable detector unit. The detector unit has a general reference numeral  14 . The detector unit  14  includes a signal pick up clamp  16  used for receipt around a portion of a first buried cable  18  to determine if it is a de-energized cable. The buried cable  18  is disposed next to a second buried cable  20  and a third buried cable  22 .  
         [0029]    The ditch  12  can include any number of buried cables that need to be tested to determine the de-energized cable. The detector unit  14  with the signal pick up clamp  16  are one part of the overall cable selector system and are described in greater detail in FIGS. 5 and 7.  
         [0030]    In FIG. 2, a cross section of the high voltage power line cable  18  is illustrated. The cable  18  includes an outer insulation cover  24 , concentric neutrals  26  and inside insulation  28  surrounding a stranded high voltage conductor  30 , which typically in the United States distributes 60 Hz. power line current.  
         [0031]    In FIG. 3, a schematic drawing of the three power line cables  18 ,  20  and  22  are shown. In this example, cable  18  has been isolated and de-energized for performing repair work thereon or splicing additional cables thereto. At a near end  32  of the cable  18 , the cable has been disconnected at an upstream disconnect station, shown as square  34 . Also, at a far end  36  of the cable  18 , the cable has been disconnected at a downstream disconnect station, shown as a square  38 . As mentioned above, the distance between the two disconnect stations  34  and  38  or the length of the disconnected cable  18  may vary from less than 100 feet and up to several miles.  
         [0032]    A battery operated, low power current pulse generator, having a general reference numeral  40 , is connected at the near end  32  to the conductor  30  of the cable  18 . Also, the generator  40  is connected to a first ground line  42 . The first ground line  42  is connected to each of the neutrals  26  in the cables  18 ,  20  and  22  and a ground  43 . The pulse generator  40  is another part of the cable selector system and is described in greater detail in FIGS. 4 and 6. The generator  40  provides a low power current test signal with a 1 Hz repetition rate, shown as arrow  44 .  
         [0033]    A jumper cable  46  is shown connected at the far end  36  to the conductor  30  of the cable  18 . The jumper cable  46  is also shown connected to a second ground line  48 . The second ground line  48  is connected to each of the neutrals  26  in the cables  18 ,  20  and  22  at the downstream disconnect station  38  and to a ground  49 . The jumper cable  46  is another part of the cable selector system.  
         [0034]    The jumper cable connection provides a round trip path from the generator&#39;s test signal  44 , through the insulated conductor  30  of the cable  18  and a return signal, shown as arrows  50 , via the grounded common neutrals  26  connected to the ground lines  42  and  48 . As mentioned above, the testing to determine which cable is de-energized will always be at a location midspan or somewhere between the two disconnect stations  34  and  38 . The disconnect stations  34  and  38  may be power line cable switching stations and the like. During the testing for the disconnected or de-energized cable  18 , the other cables  20  and  22  may remain energized and they do not interfere with the use of the cable selector system.  
         [0035]    [0035]FIG. 4 is a general electrical diagram of the current pulse generator  40 . It is shown attached to the near end  32  of the de-energized cable  18 . The pulse generator  40  is illustrated broadly including a battery powered free running multivibrator  52  for charging and discharging a capacitor  54 . The multivibrator  52  combined with the capacitor  54  make up a 1 Hz pulse generator. The electrical components of the multivibrator  52  connected to the capacitor  54  are shown in detail in FIG. 6 and making up the pulse generator  40  for creating the low voltage test signal  44 .  
         [0036]    In FIG. 5, a general electrical diagram of the cable detector unit  14  and signal pick up clamp  16  is shown. The key components making up the detector unit  14  include a parametric filter, having general reference numeral  56 , a pulse amplifier, having general reference numeral  58  and a monostable multivibrator indicator, having general reference numeral  60 . The electrical components making up the filter  56 , the amplifier  58  and the indicator  60  are shown in detail in FIG. 7.  
         [0037]    In FIG. 6, a detailed electrical diagram illustrating the individual electrical components of the free running multivibrator  52  making up the current pulse generator  40  are shown. The electrical components include a pair of 9 volt batteries  62  connected to a 9 volt line  64 , an 18-volt line  66  with a switch double throw  68  and a zero volt line  70  via the other half of the switch  68 . The other half of the switch  68  is connected to ground  74 . Resistor  77  is connected to a transistor  78  and resistor  82  is connected to a transistor  84 .  
         [0038]    An operational amplifier  86  is connected to the 18-volt line  66  by a capacitor  80  and with a resistor  81 , a resistor  75  and a resistor  76  comprise a free running multivibrator. A transistor  88  is connected to the 18-volt line  66  and the transistor  84  is connected via a resistor  89  to a transistor  88 . The transistor  88  is connected to the capacitor  54  via a diode  90  and resistor  91 , The capacitor  54  is connected to the zero volt ground line  70 . The transistor  88  is also connected to the zero volt line  70  via resistor  92 . The capacitor  54  is also connected to a SCR  94 , a resistor  95  and an adjustable resistor  96  prior to outputting the test signal  44 .  
         [0039]    The output of the multivibrator  52  is illustrated as a square waveform “A”, shown in FIG. 6A. When waveform “A” is positive, transistor  84  is turned “on”, which activates transistor  88 . When transistor  88  is turned “on”, capacitor  54  is charged. The actual current pulse delivered to the conductor  30  is the discharge current of the capacitor  54  initiated at the time of the negative transition of the 1 Hz waveform “A”.  
         [0040]    A current pulse waveform “C”, shown in FIG. 6A, or test signal  44  coincides with a gate pulse waveform “B” as shown in FIG. 6A and from the SCR  94 . When waveform A, shown in FIG. 6A, swings negative, resistor  77  switches the transistor  78  “on” and turning transistor  98  “on”. Resistor  99  in turn switches transistor  100  “on”. The transistor  100  then turns the SCR  94  “on”, which discharges the capacitor  54 . The SCR  94  stays “on” until the capacitor  54  is discharged. The peak current is limited by the resistor  95 . A resistor  101 , connected to the zero volt line  70 , inhibits ringing in the conductor  30  of the cable  18 . It should be mentioned that any significant ringing anywhere in the cable detector unit  14  can cause a false signal indication. A capacitor  102  by passes a resistor  103  for allowing a larger initial turn on pulse to the SCR  94 . The capacitor  102  is connected to the zero volt line  70  via a resistor  104 . Resistor  104  develops the waveform “B”, shown in FIG. 6A, which turns on the SCR  94 .  
         [0041]    In FIG. 7, a detailed electrical diagram is shown illustrating all of the individual electrical components making up the cable detector unit  14  connected to the signal pick up clamp  16 . The clamp  16  is a current transformer similar to those used with clamps for current meters. The size of the clamp is determined by the diameter of the cables being tested.  
         [0042]    The clamp  16  is connected to the parametric filter  56 . The filter  56  is designed to reject a signal developed across the resistor  105  resulting from any 60 Hz current from the energized cables, while the filter passes the high frequency components of the 1 Hz test signal  44 . The clamp  16  will respond to the magnetic field that accompanies any current flowing through the conductor  30 .  
         [0043]    The output of the clamp  16  is connected to a resistor  105 , which develops an input signal voltage processed first by the filter  56 . The output of the clamp  16  is also connected to resistors  106 ,  107 ,  108 ,  109 ,  110  and capacitor  112 . Between the resistors  106  and  107  are connected a resistor  114  and an amplifier  116 . The resistor  114  is connected to a resistor  118 , a capacitor  120  and an amplifier  122 . Between the resistors  108  and  109  and resistors  109  and  110  is connected an amplifier  124 . Between the resistor  110  and the capacitor  112  and the resistor  114  is connected an amplifier  126 . The amplifier  124  is connected to the input of an amplifier  128  via resistors  127  and  129 . The amplifier  116  is also connected to the input and output of amplifier  128  via resistors  130  and  131 .  
         [0044]    The parametric filter  56  exhibits two feedback loops. Both loops stabilize the dc voltage at the output of the operational amplifier  126  at zero volts. At the 60 Hz frequency, the signal at the output of operational amplifiers  116  and  122  is equal in amplitude and 180 degrees out of phase. These two signals delivered to the summing amplifier  128  result in zero output voltage at the 60 Hz frequency, while the test signal  44  is passed on to input the pulse amplifier  58 .  
         [0045]    The pulse amplifier  58  comprises an input capacitor  132  and a gain control pot  134  connected to a non-inverting operational amplifier  136 . The amplifier  136  is connected between resistors  137  and  138  and between resistors  138  and  139 . An inverting amplifier  140  is connected between resistors  139  and  141  and resistor  141  and a capacitor  142 . The capacitor  142  is connected between the resistor  141  and a resistor  143 . Another inverting amplifier  144  is connected between resistor  143  and a resistor  145 . The amplifier  144  is connected between the resistor  145  and a capacitor  146 . The output of the capacitor  146  is connected to a resistor  147 , a diode  148  and resistor  150 .  
         [0046]    The input capacitor  132  and the capacitors  142  and  146  between the inverting amplifiers  140  and  142  block any dc offset that would accumulate if the amplifiers were directly coupled. The overall maximum gain of the amplifiers  136 ,  140  and  144  is 1000 determined by the resistors  137 ,  138 ,  139 ,  141 ,  143  and  145 . The arrangement of the non-inverting amplifier and the inverting amplifiers are such that a positive signal pulse voltage at the input to the resistor  105  of the filter  56  coincides with a positive pulse voltage at the output of the operational amplifier  144  of the pulse amplifier  58 .  
         [0047]    The pulse output of the amplifier  58  is delivered to an input of the multivibrator indicator  60 . The purpose of the “one shot” multivibrator is to stretch a very narrow 1 Hz pulse signal into a 1 Hz rectangular wave, as illustrated as waveform “D” and shown in FIG. 6A. The waveform “D” is delivered to provide an output indication, which is easy to recognize and without confusion relative to any possible false signal received through the cable&#39;s conductor  30 .  
         [0048]    The input to the indicator  60  is received by a transistor  152  via resistors  153  and  154 , which momentarily turns the transistor  152  “on”. The transistor  152  is connected to diodes  156  and  158  and resistor  159 . A transistor  160  is connected between the diodes  156  and  158  and connected to a transistor  162  via a resistor  163 . A negative transition of the collector of the transistor  152  is passed via the diodes  156  and  158  to a resistor  154  and via a charged capacitor  166  to the transistor  162 . During a steady state and while waiting for a pulse signal, the resistor  154  keeps transistor  162  “on”. This keeps the collector voltage of the transistor  162  low and transistor  160  “off”. An incoming pulse signal turns transistor  152  “on” via the resistor  154 . The “on” state of transistor  152  drives its collector low, which via diodes  156  and  158  holds the resistor  164  low. Transistor  160  stays “on” until capacitor  166  discharges and returns to a steady state with the transistor  162  “on” and the transistor  152  “off”. The “one shot” then waits for the next pulse signal. The values of capacitor  166  and resistor  167  are selected to keep transistor  160  “on” for approximately ½ second. This feature allows a horn  168  to beep, an analog meter  170  to respond and register and an LED  172  to light up for providing the lineman  10  both visual and audio indicators that the cable  18  is de-energized and the cable detection unit  14  is receiving the test signal  44 .  
         [0049]    In FIG. 8, a second embodiment of the cable detector unit&#39;s filter is described as a high pass filter having a general reference numeral  174 . The high pass filter  174  is used in place of the parametric filter  56 . A graph of the output voltage versus log frequency of the filter  174  is illustrated as waveform B shown in FIG. 9.  
         [0050]    The input from the clamp  16  is connected to a resistor  176  and an amplifier  178 . The output of the amplifier  178  is connected to resistors  180 ,  182 ,  184  and  186 . An amplifier  188  is connected between the two resistors  180  and  182  and between a resistor  190  and a capacitor  192 . The output of the amplifier  178  is also connected to resistor  194  and a capacitor  198 . The capacitor  198  is connected between the resistor  194  and to an amplifier  202 . The output of the amplifier  202  is connected to resistors  204 ,  206  and adjustable resistor  208 . An amplifier  210  is connected between the resistors  204  and  206  and between resistors  184  and  186 .  
         [0051]    The output circuit of the high pass filter  174  or the amplifier  210  is a balanced differential amplifier. This type of amplifier inherently rejects common mode signals. Common mode signals are identical in amplitude shape and relative phase at the inverting and non-inverting inputs. The effectiveness of the high pass filter  174  is a result of relative phase shift tracking of the amplifiers  188  and  202 . This phase shift tracking occurs when the value of the resistor  190  and capacitor  192  is equal to the value of the resistor  194  and capacitor  198 . The values of this resistor and capacitor combination are selected for a crossover frequency near 3 KHz and shown as waveform B in FIG. 9. Under this condition, the output of the amplifier  188  and the amplifier  202  over a range of frequencies from below 60 Hz to well above 60 Hz will track in relative phase shift and amplitude.  
         [0052]    At a frequency well above 60 Hz, the amplitude of the filter  174  will begin to roll off, but the relative phase will continue to track. A high common mode rejection of the differential amplifier  210 , which is adjustable by adjustable resistor  208 , exhibits very good rejection of the 60 Hz frequencies. However, as waveform B in FIG. 9 illustrates, the high frequency components of the pulses are passed. The resistor  176  develops the signal voltage from the clamp  16  and the amplifier  178  insures a good equal low impedance source for the amplifier  202  and the amplifier  188 .  
         [0053]    While the invention has been particularly shown, described and illustrated in detail with reference to the preferred embodiments and modifications thereof, it should be understood by those skilled in the art that equivalent changes in form and detail may be made therein without departing from the true spirit and scope of the invention as claimed except as precluded by the prior art.