Abstract:
A voltage detector that more accurately measures AC voltage of a voltage conductor by correcting the voltage detected directly by the detector&#39;s contact probe to account for the conductor&#39;s size and shape. The housing of the detector has plural non-contact electrode sensors spaced apart over its surface for sensing capacitive charging currents in the detector&#39;s vicinity. By combining voltages sensed by these electrode sensors to the probe&#39;s measured voltage, the detector can correct the contact probe measurement for voltages that bypass the contact probe or other conductors in the vicinity that product their own capacitive charging currents. A microprocessor in the housing of the present detector adds or subtracts sensed voltages depending on whether they are input or output voltages, respectively.

Description:
CROSS REFERENCE TO RELATED PATENTS 
   Not applicable. 
   BACKGROUND OF THE INVENTION 
   The present invention relates to a high voltage measurement and, more particularly, to a high voltage detector that can be used for measuring voltages in high voltage alternating current (AC) circuits or systems with improved accuracy. 
   A voltage detector is a form of voltmeter that measures voltages without the use of a ground lead. The ground lead is avoided in situations where it would present a severe safety risk to the operator of the voltage detector. Typically, voltage detectors are used by those measuring high AC voltages such as electrical power utility linemen. Before the present invention, designers of voltage detectors assumed that the magnitude of the alternating current being measured by a voltage detector was a function of three things: (1) the internal impedance of the device; (2) the external capacitive reactance between the device and electrical ground or nearby electrical grounded conductors and equipment; and (3) the magnitude of the voltage being measured, that is, the voltage carried through the high voltage conductor. See for example, U.S. Pat. No. 6,753,678, which is incorporated herein in its entirety by reference, for further information about voltage detectors. 
   However, even when these three factors are accommodated in the voltage detector design, typical prior art voltage detectors are still not very accurate, ranging from up to 10% below to 50% above the true voltage. Thus there remains a need for a voltage detector having improved accuracy. 
   SUMMARY OF THE INVENTION 
   According to its major aspects and broadly stated, the present invention is a voltage detector that more accurately measures AC voltages. The improvements to the voltage detector are based on the accommodation of an important fourth influence on the accuracy of the voltage measurement, namely, the size and shape of the voltage conductor. In order to correct the voltage measurement for this fourth influence, and achieve significant improvement in accuracy, the present invention uses multiple non-contact input/output sensors deployed over the surface of the detector housing. These sensors evaluate the physical shape and size of the voltage source being measured, and detect nearby electric fields of adjacent phase conductors or ground conductor in a three phase electric system. The voltages these non-contact sensors detect are used to correct the voltage being measured by the direct contact probe to offset the distorting effect of the size and shape of the electrical conductor (and adjacent conductors and grounds) on that direct measurement. 
   The physical shape and size of a voltage source will generally fall into one of three categories: (1) a point source, (2) a long wire, or (3) two-dimensional conductors. A typical point source voltage could be an insulated high voltage bushing protruding from the front portion of an electrically grounded all steel transformer case. A typical long wire could be a bare wire suspended between and insulated from its supporting structures. A two-dimensional conductor could be a large bus-bar suspended between and insulated from its supporting structures. 
   Generally stated, with the physical parameters of a voltage detector remaining constant, the smaller the physical size of an AC voltage source, the greater the current through the voltage detector and the higher and more accurate the apparent voltage indication by the direct contact probe. The reverse is of course also true, namely, the larger the physical size of the AC voltage source, the less current that will pass through the voltage detector probe and the lower will be the voltage indication by the detector. Since no source is a true point source, the present voltage detector uses additional, non-contact electrodes to detect current that is bypassing the detector probe and, with the assistance of a microprocessor, correct the voltage to offset the influence of its size and shape on the measurement. 
   The addition of multiple non-contact input/output sensors supplements the primary probe to detect nearby electric fields that indicate the presence of an adjacent phase conductor or ground conductor, such as would be found in a three phase electric system. 
   These and other features and their advantages will be apparent to those skilled in the art of voltage measurement and detection from a careful reading of the Detailed Description of Preferred Embodiments accompanied by the following drawings. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     In the drawings, 
       FIG. 1  depicts schematically a prior art voltage detector; 
       FIG. 2  illustrates the effects of the electric field of a point source on a prior art voltage detector; 
       FIG. 3  illustrates the effects of the electric field of a long wire on a prior art voltage detector; 
       FIG. 4  illustrates the effects of the electric field of a physically large bus on a voltage detector; 
       FIG. 5A  illustrates an external view of a voltage detector with multiple input electrodes, according to a preferred embodiment of the present invention; 
       FIG. 5B  illustrates a cross sectional, schematic view of the voltage detector of  FIG. 5   a , according to a preferred embodiment of the present invention; 
       FIG. 6  illustrates the effects of the electric field of a point source on a voltage detector, according to a preferred embodiment of the present invention; 
       FIG. 7  illustrates the effects of the electric field of a long wire on a voltage detector, according to a preferred embodiment of the present invention; 
       FIG. 8  illustrates the effects of the electric field of a large bus bar on a voltage detector, according to a preferred embodiment of the present invention; 
       FIG. 9  illustrates the effects of a primary electric field on a voltage detector while being influenced by a second electric field (namely, an adjacent phase long wire) and a third electric field (namely, a neutral conductor long wire), according to a preferred embodiment of the present invention; 
       FIG. 10  illustrates an alternative voltage detector, according to a preferred embodiment of the present invention; and 
       FIG. 11  illustrates a calibrating device for the present voltage detector, according to a preferred embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The present invention is a voltage detector which is a voltage meter without a ground lead. The present voltage detector is an improvement over prior art voltage detectors in that it corrects the apparent voltage of a voltage source for the size and shape of the source as well as the presence of other conductors and grounds in the vicinity of the voltage detector during measurement. 
   Referring now to the figures,  FIGS. 1-4  represent a prior art voltage detector shown in a schematic form and generally indicated by reference number  10 . Detector  10  is shown in  FIG. 1  in partial cross section to reveal its internal components schematically shown. Detector  10  has a housing  12  that is made of a non-conducting material and has electromagnetic shielding  14  inside to protect its internal components from electromagnetic radiation. Detector has an electrode probe  18  with a conducting tip  20  and an opposing handle  24  for use by an operator. Tip  20  is connected electrically through a high voltage dropping resistor  26  to processing circuitry  30  and a display  32 . Processing circuitry is connected electrically to shielding  14 . Dropping resistor is typically rated at about 25 mega-Ohms. 
   When tip  20  of electrode probe  18  is brought into contact with an electrical conductor by an operator using handle  24 , the voltage sensed by tip  20  is reduced by resistor  26  and fed to processing circuitry  30 , which processes the analog signal, conditions it and converts it to a digital signal for display as a digital voltage on display  32 . Detectors generally along the lines described in connection with detector  10  as shown in  FIG. 1  have been in widespread use for well over fifty years. 
     FIGS. 2-4  illustrate the prior art voltage detector of  FIG. 1  being used to detect voltage from three different sources of voltage. These figures include the field lines that run between the detector and various surfaces in its vicinity. For convenience, the structures common to  FIGS. 1-4  use the same reference numbers. In  FIG. 2 , detector  10  is shown detecting voltage from a point source  40 . Electrode probe  18  is in contact with point source  40 . Point source  40  is an insulated bushing protruding from a large electrically grounded all steel transformer case  42 . The direction of the electric field from housing  12  of voltage detector  10  couples to all of its surroundings including grounded transformer case  42 . Since point source  40  is a source of an alternating current electric field and thus surrounded by an electromagnetic field, the AC capacitive charging current emanates from the front portion  44  of voltage detector  10  to grounded transformer case  42  as well as from the back  46  of housing  12  to ground  52 , as shown by field lines in  FIG. 2 . 
     FIG. 3  illustrates voltage detector  10  detecting a voltage while being held perpendicular to and touching a long wire  56 . Electrode probe  18  is in contact with long wire  56 . The electric field as indicated by field lines now run both to and from housing  12  of voltage detector  10 . Two lines, one on either side of probe  18 , run to housing; the remainder runs from housing. The electric field from long wire  56  is now coupling directly into front portion  44  of voltage detector  10 , bypassing probe  18  and its dropping resistor  26 , while the electric field from back  46  of voltage detector  10  is coupling to ground  52 . 
     FIG. 4  illustrates voltage detector  10  detecting a voltage while being held perpendicular to a physically large bus bar  60 . Electrode probe  18  is placed in contact with bus bar  60 . The strength of the electric field coupled into front portion  44  of housing  12  is now even greater than that produced by long wire  56  as indicated by additional field lines running to housing  12  of detector  10 . Because bus bar  60  is a source of AC voltage and thus surrounded by an AC electric field, the AC capacitive charging current into front portion  44  of the housing  12  will be broader than that of long wire  56 . The result is that some of the AC capacitive charging current entering front portion  44  of the housing  12  will bypass high voltage dropping resistor  26 , resulting in less current into processing circuitry  30  and a lower voltage indication on display  32 . 
     FIGS. 5A and 5B  illustrate external and cross sectional views of a present voltage detector  80  which represents an improvement over voltage detector  10 . Like voltage detector  10 , it consists of a housing  82  made of a non-electrically conducting material having electromagnetic shielding  84  inside housing  82  to protect the contents of housing  82  from the electromagnetic environment of detector  80 . Housing  82  has a protective, non-conducting shell  86  around it. 
   Detector  80  has a probe  88  with an electrically conducting tip  90  on one end and a handle  94  on the opposing end. Tip  90  is in electrical connection via a high voltage dropping resistor  96  for direct contact with a high voltage source. As with detector  10 , dropping resistor  96  is typically rated at about 25 mega-Ohms. The primary input from tip  90  of probe  88  is fed to a microprocessor  100  wherein the analog signal is conditioned, converted to a digital signal, and then adjusted to compensate for the size and shape of the voltage source, as will be described below, and then displayed on digital display  102 . 
   In addition to these components, detector  80  has plural secondary electrode sensors  106  mounted on support structure  86 . These secondary electrode sensors  106  are deployed below the surface of non-conducting housing  82  but above the shielding so as to purposefully expose the secondary electrode sensors  106  to the external electric fields present. Preferably, housing  82  has a front surface  110  positioned toward the voltage source and a back surface  112  positioned away from the voltage source with plural electrode sensors  106  on front surface  110  and plural electrode sensors  106  on back surface  112 . Electrode sensors  106  are preferably spaced apart over the surface of housing  82  so that they can detect electromagnetic fields about a full 360 spherical degrees of detector  80 . Housing  82  is described as having front surface  110  and back surface  112 . Detector  80  is shown in the figures as having a spherical shape, there is no particular shape that is preferred or required. For example, a rectangular shape will also be suitable and can have electrodes  106  on its lateral faces. 
   Each electrode sensor  106  has its own voltage divider network  104  that is adjustable in order to be able to scale the voltage fed to microprocessor  100 . Electrode sensors  106  are bi-directional and thus capable of input or output signal delivery depending on whether the electromagnetic field in the vicinity of sensors  106  is in phase or is out of phase, respectively, with that of the primary signal being detected by electrode probe  88 . The output of microprocessor  100  is a voltage signal to display  102  that includes the signal from probe  88  corrected by each of the non-contract sensors  106  detecting current. The extent of the correction is related to the strength of the current each detects which in turn is related to the size of the conductor and the presence of other fields. 
     FIG. 6  represents the present voltage detector  80  with input/output electrode sensors  106 , illustrated here as in  FIGS. 7-9  for convenience as if there were no protective shell  108 , measuring the voltage of point source  40  with probe  88 . Point source  40  is the same as is shown in  FIG. 2 , namely, an insulated bushing protruding from a large electrically grounded all steel transformer case  42 . If the field lines of  FIG. 6  are compared to the field lines of  FIG. 2 , it will be seen that they are similar, namely, some field lines are coupled directly from front surface  110  of shielded housing  82  into steel transformer case  42 . However, other field lines are now coupled from electrode sensors  106  incorporated into front surface  110  of the housing  82  to case  42 . All four input/output electrode sensors  106  on front surface  110  of housing  82  in this situation are acting as output electrode sensors  106  measuring a portion of the AC capacitive charging current going out of front surface  110  of housing  82  to case  42 . The remaining electrode sensors  106  are output sensors as indicated by field lines emanating from housing  82  of detector  80  to ground  52 . 
     FIG. 7  illustrates the present detector  80  with its input/output sensors  106  while being held perpendicular to and measuring the voltage on long wire  56 . A portion of the electric field couples directly from long wire  56  into front surface  110  of housing  82 , including through two of electrodes sensors  106  incorporated into front surface  110  of housing  82 . These two electrode sensors  106  in this illustration are acting as input sensors measuring a portion of the AC capacitive charging current coming into front surface  110  of housing  82 . The remaining two electrode sensors  106  on front surface  110  will still serve as output sensors but at a reduced level when compared to the corresponding two of  FIG. 6 . The remaining field lines couple from back surface  112  of detector  80  to ground  52 . Electrode sensors  106  on back surface  112  are all output sensors as indicated by lead lines that extend to ground  52 . 
     FIG. 8  represents the present invention with additional input/output sensors measuring a voltage while being held perpendicular to a physically large bus bar. Notice a greater portion of the electric field couples directly from the physically large bus into the front portion of the shielded housing and into all four of the electrodes incorporated into the front portion of the housing. All four sensors  106  on front surface  110  of housing  82  in this situation act as input sensors; sensors  106  on back surface  112  of housing continue to act as output sensors as indicated by lead lines that run from housing  82  to ground  52 . Microprocessor can now compensate for the error introduced as a result of the charging current entering front surface  110  of shielded housing  82  and partially bypassing the high voltage dropping resistor  96  in probe  88 . 
     FIG. 9  represents the present voltage detector  80  with eight input/output sensors  106  being held perpendicular to and measuring the voltage on a long wire (B phase) voltage source  120 . The present invention is also being exposed to an adjacent phase (C phase) long wire  122  from the top and rear and a neutral conductor  124  (at near ground potential) from the bottom and rear. The AC charging current sensed in the input/output electrode  106  near the adjacent phase C long wire  122  will be recognized by microprocessor  1  as a different phase and the primary voltage indication adjusted downward accordingly. Likewise the AC charging current sensed by the input/output electrode  106  closest to neutral conductor  124  will be recognized by microprocessor  100  as large when compared to those sensors  106  on the opposing side of housing  82  and the primary voltage indication from contacting probe  80  to long wire  120  is adjusted downward by microprocessor  100  in view of the currents sensed by electrodes  106 . 
     FIG. 10  represents a different embodiment of the present voltage detector  140 . Detector  140  has a housing  142 , a probe  144  with a conducting tip  146  and a handle  148 . Detector  140  also has non-contact electrode sensors  150  that, unlike the “button” shaped sensors  106  shown in  FIGS. 5-9 , are maximized to nearly fill one-eighth of housing  142 . An insulated protective shell  152 , shown partly cut-away in  FIG. 10 , covers sensors  150  Housing  142  does not have to be spherically shaped, of course, but sensors  150  should cover approximately equal areas of its surface, regardless of its shape. Each sensor  150  is electrically isolated and insulated from the others but closely spaced so collectively they form an equivalent electromagnetic shield  84 . Each sensor  150  as before is connected to microprocessor  100 , shown in  FIG. 5   b . Each sensor electrode  150  may be formed by spray painting the inside of the housing with the same type of conductive paint used to form the electrostatic shield in a conventional voltage detector but applied to produce a pattern that leaves insulating strips between each sensor electrode  150 . It may also be accomplished by attaching conductive inserts to the wall of the housing  142  in a pattern that provides an insulating strip between the sections. Each isolated individual electrode sensor  150  is then attached through proper scaling resistors  104  to microprocessor  100 . 
   Each electrode sensor  106 ,  150 , has its own scaling voltage divider network  104 . Each input from a sensor  106 ,  150 , is scaled and then fed to microprocessor  100  through an analog-to-digital converter  108  where the individual signals are conditioned and converted to digital signal for combining. Because each electrode sensor  106 ,  150  is an input/output, bi-directional electrode, the digital signals can add or subtract to the signal from probe  88 ,  144 , depending on whether the AC input signal from any particular auxiliary electrode sensor  106 ,  150 , is in phase with the AC signal on probe  88 ,  144  or our of phase. If charging current is going into sensor  106 ,  150 , it is acting as an input sensor. If the AC input signal on the same electrode is 180 degrees out of phase with the AC signal on probe  88 ,  144 , charging current is going out of sensor  106 ,  150  and it is then acting as an output sensor. The direction of the arrows on the electric force lines in the figures indicates whether sensors  106  are acting as input or output sensors. 
   In phase or 180 degrees out of phase indicates the auxiliary electrode is being acted upon by either the same source voltage (long wire or large flat bus) or a ground, respectively. If the phase angle of the AC voltage signal on the auxiliary electrode is either 120 degrees or 240 degrees removed from the AC voltage signal on main probe, the auxiliary electrode is sensing another phase. 
   Once calibrated, the voltages sensed by sensors  106 ,  150  contribute to the voltage sensed by probe  88 ,  144 . Assume the voltage detected by probe  88 ,  144 , is displayed in a range of 0 to 140 volts and each of the auxiliary electrode sensors  106 ,  150 , can raise or lower probe  88 ,  144 , input by up to +/−10 volts. If probe  88 ,  144 , detector  80 ,  140 , is put in contact with and held perpendicular to an energized long wire and the correct voltage should be indicated as 100 volts on the display but the effect of the long wire is to reduce the indication to 90 volts, then any two electrode sensors  106 ,  150 , in alignment with the conductor would each raise the input by 5 volts each for a total of 100 volts. If none of the four electrode sensors  106 ,  150 , are in alignment with the long wire, each would ideally add two and one half volts for a total of 100 volts. 
   If probe  88 ,  144 , of detector  80 ,  140 , is placed in contact with but not perpendicular to the energized long wire, say, at an angle of 45 degrees, the effect would be to reduce the voltage indication to an even lower value of say 84 volts. The electrode sensor  106 ,  150 , in alignment with and closest to the long wire would now add ten volts to the voltage indication and electrodes  106 ,  150 , above and below but not in alignment would add 3 volts each because of their closer proximity to the conductor, and the voltage indication would remain at 100 volts. 
   The worse case condition would be a large flat bus. If probe  88 ,  144 , is held perpendicular to and put in contact with an energized large flat surface, the effect would be to reduce the voltage to say 80 volts. Each of the four electrode sensors  106 ,  150 , would add 5 volts each for a total of 100 volts. 
   If probe  88 ,  144 , is held at 45 degrees from an energized flat surface, the effect would be to reduce the voltage indication even further to, say, 74 volts. The electrode sensor  106 ,  150 , closest to the flat surface would add 10 volts and the next two closest electrode sensors  106 ,  150 , would add eight volts each for a total of 100 volts. 
   In all of the foregoing examples, the auxiliary electrode sensors  106 ,  150 , closest to the source are sensing input AC charging current from a conductor of the same phase as the AC signal on the main probe. Any grounded conductor or surface brought into close proximity of detector  80 ,  140 , would cause the reverse of this to happen. For example, a grounded conductor or surface can cause a voltage of 100 volts to indicate 110 volts on detector  140 . In this situation the auxiliary electrode sensors  106 ,  150 , closest to the grounded conductor or surface would now sense an output charging current 180 degrees out of phase with that detected by probe  80 ,  140 , and adjust the indicated voltage down to 100 volts. 
   A device for calibrating probe  80 ,  140 , is illustrated in  FIG. 11 . Device  160  is a large, rectangular conductive surface  162  having an area extending over several square feet with a hole  164  formed therein. A conductor  168  not larger than the end of an electrically conductive wire, that is, smaller in diameter than said probe is positioned in the center of hole  164  so that it is not touching surface  162 . Surface  162  is insulated from ground and other sources of electricity and electric fields but is connected to a switch  172  having a first position that connects surface  162  to ground and a second position that connects surface  162  to the same voltage as conductor  168 . 
   A probe  180  of a detector  182  produces an output that is scaled to produce an arbitrary range of voltages such as 60 to 140 volts AC as input to microprocessor  100  when 100 volts AC is applied to the tip of the main probe. The actual voltage produced will depend on the proximity of voltage detector  182  to ground or other sources of voltage. Each electrode sensor  184  is also scaled to produce a range of voltages representing +/−10 volts AC. The actual voltage produced by each electrode sensor  184  will also depend on its proximity to ground or sources of voltage. 
   Step  1  of the calibration process is performed as follows. Surface  162  is grounded and probe  180  of voltage detector  182  is brought into contact with conductor  168 . Electrode sensors  184  are now at higher potential than their surroundings and surface  162 . Therefore, the direction of the AC charging current is from the front portion four electrodes to surface  162 . 
   The probe  180  output is scaled to represent 120 volts on display  188  after processing by the microprocessor (not shown in  FIG. 11 ) in detector  182 . Each of the four electrode sensors  184  on a front portion  190  of detector  182  are then scaled to represent −5 volts, using a feature of display  188  that allows individual sensor  184  voltages to be seen. When the voltages of sensors  184  on front portion  190  of detector  182  are added to the 120 volts of probe  180 , the result is 100 volts as displayed. 
   Next, in step  2 , switch  172  is moved to the position that connects it to a source of voltage, namely 100 volts, the same as produced by conductor  168 . Electrode sensors  184  on front portion  190  are now at lower potential than surface  162  so the direction of the AC charging current is from surface  162  to electrode sensors  184  on front portion  190 . 
   Probe  180  should now be delivering approximately 80 volts into the microprocessor. Accordingly, each of the four sensors  184  on front portion  190  of detector  182  are adjusted to +5 volts, so that the display of detector  182  reads 100 volts. 
   In step three, electrode sensors  184  on back portion  192  are adjusted switching switch  172  to ground and by then removing the microprocessor inputs for each of the four sensors  184  on front portion  190  and replacing them with the four inputs for sensors  184  on back portion  192 . Sensors  184  are now at a higher potential than surface  162 . The charging current then flows from sensors  184  on rear  192  to the grounded surface  162 . With source  168  are 100 volts, probe  180  of detector  182  should read approximately 120, so each sensor  184  is adjusted to −5 volts so that voltage detector  182  reads 100 volts. 
   In step  4 , switch  172  is moved from ground to 100 volts AC, which drops the voltage sensed by probe  180  to 80 volts. After adjusting the four electrode sensors  184  to +5 volts, the detector will read 100 volts. Then the inputs for sensors  184  from back portion  192  of detector  180  to the microprocessor are returned to their previous locations and the inputs for sensors  184  from front portion  190  are reattached. 
   The ratio of 100 volts on the contract electrode to plus or minus 10% of that voltage on the non-contact electrodes used in the calibration examples is representative, with the exact ratio depending on the size of the detector and the spacing of the terminals on the detector, among other factors. Regardless of the ratio, the principal and the calibration procedure remains the same. 
   It is intended that the scope of the present invention include all modifications that incorporate its principal design features, and that the scope and limitations of the present invention are to be determined by the scope of the appended claims and their equivalents. It also should be understood, therefore, that the inventive concepts herein described are interchangeable and/or they can be used together in still other permutations of the present invention, and that other modifications and substitutions will be apparent to those skilled in the art from the foregoing description of the preferred embodiments without departing from the spirit or scope of the present invention.