Abstract:
An apparatus and method for identifying the presence of high conductivity or permittivity conditions in a wide range of electrically insulating materials is disclosed. The apparatus includes a grounded enclosure containing electronics for controlling measurement and communication processes and first and second spaced-apart electrode assemblies for engaging an insulator to be tested. The first and second electrode assemblies are mounted in the enclosure for linear movement such that pressing of the first and second electrodes against an insulator causes the electronics to initiate a measurement.

Description:
This application claims the benefit of Provisional Application No. 61/525,781 filed on Aug. 21, 2011. 
    
    
     BACKGROUND OF THE INVENTION 
     This application relates to an apparatus and method for identifying the presence of high conductivity or permittivity conditions in a wide range of electrically insulating materials and, more particularly, to a detector to assess the electrical integrity of a polymer insulator. 
     Insulators are utilized in many applications on transmission and distribution systems. The main application of an insulator is to mechanically attach current carrying conductors to support grounded structures while electrically insulating the conductors from the grounded structures. 
     Non-ceramic insulators (NCI) (also called polymer or composite insulators) are considered high risk if they contain internal or external defects of conductive or high permittivity. An example of a conductive defect would include internal carbonization of the fiberglass rod due to discharge activity, and an example of a high permittivity defect would be water internal to the insulator. 
     A requirement for ensuring worker safety when performing live work (LW) with polymer insulators is to confirm the short-term (i.e. for the duration of the work) electrical and mechanical integrity of both the installed and the replacement polymer units. Currently there are no generally accepted and easily applied procedures to accomplish this. Consequently, some utilities have opted not to use polymer insulators. In addition, a number of utilities that do use polymer insulators avoid live work on structures on which these insulators have been installed. 
     Accordingly, there is a need for an apparatus and method that can identify electrical and mechanical integrity of both installed and replacement polymer insulators. 
     BRIEF SUMMARY OF THE INVENTION 
     These and other shortcomings of the prior art are addressed by the present invention, which provides an apparatus for identifying high risk insulators with conductive or high permittivity defects. The apparatus includes a metallic enclosure containing electronics for controlling measurement and communication processes, and first and second spaced-apart electrode assemblies for engaging an insulator to be tested. The first and second electrode assemblies are mounted in the enclosure for linear movement such that pressing of the first and second electrodes against an insulator causes the electronics to initiate a measurement. 
     According to an aspect of the invention, an apparatus for identifying high risk insulators with conductive or high permittivity defects includes a chassis having a plurality of apertures and first and second rails, electronics mounted to the metallic chassis which is electrically grounded to the metallic enclosure for controlling measurement and communication processes, a high voltage electrode assembly connected to the chassis by a spring loaded mechanism to allow the high voltage electrode assembly to move linearly in and out from the chassis, and a grounded electrode assembly connected to the metallic chassis by a moveable plate and to the moveable plate by a spring loaded mechanism. The moveable plate is adapted to move along the first and second rails to position the grounded electrode at a pre-determined spacing from the high voltage electrode assembly and the spring loaded mechanism is adapted to allow the grounded electrode assembly to move linearly in and out from the chassis. When the high voltage electrode assembly and grounded electrode assembly are pushed against an insulator, the electrode assemblies move linearly inward towards the chassis, thereby causing the electronics to initiate a test. 
     According to another aspect of the invention, a method of evaluating insulators for defects includes the steps of providing an apparatus for identifying high risk insulators having a microprocessor, a high voltage electrode assembly, and a grounded electrode assembly. The method further includes the steps of engaging the high voltage electrode assembly and grounded electrode assembly with an insulator to be tested, submitting the insulator to a high voltage at various frequencies to determine a resonance frequency of the insulator, submitting the insulator to a high voltage at the resonance frequency for a pre-determined amount of time, and conducting measurements during the pre-determined amount of time for comparison to a calibration result set. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The subject matter that is regarded as the invention may be best understood by reference to the following description taken in conjunction with the accompanying drawing figures in which: 
         FIG. 1  is a perspective view of an apparatus according to an embodiment of the invention; 
         FIG. 2  is a rear perspective view of the apparatus of  FIG. 1 ; 
         FIG. 3  shows the apparatus of  FIG. 1  being installed on an insulator; 
         FIG. 4  shows the apparatus of  FIG. 2  with a casing removed; 
         FIG. 5  shows a chassis of the apparatus of  FIG. 1 ; 
         FIG. 6  shows a travelling plate for interaction with the chassis of  FIG. 5 ; 
         FIG. 7  shows electronics of the apparatus of  FIG. 1 ; and 
       FIGS.  8  and  9 A- 9 C show electrode assemblies of the apparatus of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to the drawings, an exemplary apparatus in form of a detector according to an embodiment of the invention is illustrated in  FIGS. 1 and 2  and shown generally at reference numeral  10 . 
     The detector  10  has the capacity to identify conductive, semi-conductive or high permittivity conditions, both internal and external without physical contact with internal conductive defects. The detector  10  is able to identify conductive, semi-conductive and high permittivity internal conditions which occur in service and are small in dimension electrically. 
     The detector  10  is portable, self-contained, lightweight, able to be used on energized installed insulators, may be installed on the end of a “hotstick” ( FIG. 3 ) or held by hand, and provides a simple Go/No-Go output. The detector  10  is not only applicable to polymer insulators, but also to other insulating components such as fiberglass hot sticks, guy strain insulators, fiberglass cross-arms, composite poles, and the like. Thus, the technology incorporated in the detector  10  does not necessarily need to be utilized to evaluate components that fill an electrical function; rather, it is applicable to any component which is manufactured from a material having insulating properties and the internal or external condition being sought is conductive, semi-conductive, or has a high permittivity. 
     As shown, the detector  10  includes a Faraday cage  11  (also called a guard electrode), a tuning forks  12  and  13 , bunny ears  14  and  15 , a grounded enclosure  16 , a universal hotstick receiver  17 , a high voltage electrode assembly  18 , and a grounded electrode assembly  19 . The cage  11  houses the enclosure  16  and ensures that measurements taken by the detector  10  are not impacted by the presence of nearby conductive objects. The cage  11  also reduces high electric field and arcing effects on the detector  10  when it is in energized environments. The enclosure  16  may be bonded to the cage  11  or floating with respect to the cage  11 . As shown, the enclosure  16  is floating and houses all of the electronics needed for the detector  10  to operate, including circuit boards, batteries, and power supplies to shield the electronics from electrical disturbances, electric fields, and arcing. 
     The tuning forks  12 ,  13  and bunny ears  14 ,  15  extend the Faraday cage  11  around the electrode assemblies  18  and  19 . The tuning forks  12  and  13  are designed such that they make mechanical and electrical contact with end fittings of an insulator ( FIG. 3 ) to prevent arcing to the detector  10  when measurements are being made close to energized and grounded end fittings of an insulator. 
     The receiver  17  is connected to the enclosure  16  and is bonded to the cage  11 . The receiver  17  is adapted to receive and connect to a hotstick to allow the detector  10  to be placed on an energized insulator. The receiver  17  includes a slot  20  for receiving a connector of a hotstick and a plurality of blocks  21  to form a castellated end  22  that meshes with a castellated end of the hotstick, thereby preventing the detector from rotating with respect to the hotstick during installation. The castellated end  22  also allows the hotstick to be secured to the detector  10  at various angles relative to the hotstick to allow for easier installation. 
     Referring to  FIG. 4 , the electrode assemblies  18  and  19  are attached to spring loaded mechanisms  26  and  26 ′ so that they can move linearly in and out from the enclosure  16 . Electrode assembly  18  is connected to mechanism  26  and electrode assembly  19  is connected to mechanism  26 ′. The mechanisms  26  and  26 ′ include bushings  27  and  27 ′ and springs  28  and  28 ′ to aid in the linear movement of the electrode assemblies  18  and  19 . Mechanism  26  is connected to a chassis  29  ( FIG. 5 ) and mechanism  26 ′ is connected to both the chassis  29  and a travelling plate  30  ( FIG. 6 ) which is adapted to move along rails  31  and  32  to allow the distance between the electrode assemblies  18  and  19  to be adjusted relative to each other to allow for different designs of insulators to be accounted for. As shown, the traveling plate  30  and mechanism  26 ′ are secured in position to the chassis  29  by a spring loaded connector  33 ,  FIG. 6 , which pushes a spring-biased pin through the travelling plate  30  and into apertures  34  of the chassis  29  to prevent movement of the plate  30  along the rails  31 ,  32 . 
     To move the plate  30  along the rails  31  and  32  and adjust the distance between electrode assemblies  18  and  19 , a user pulls on a handle  36  of the connector  33  which moves the pin against the bias of the spring and disengages the pin from an aperture  34  of the chassis  29  to allow the plate  30  to move. Once the plate  30  and electrode  19  is in position, the user releases the handle  36  and the spring forces the pin into an aperture  34  of the chassis  29 . 
     Micro-switches  38  and  38 ′ are also attached to the chassis  29  and are operably connected to the electrode assemblies  18  and  19  and electrically attached to electronics  39  to tell the electronics  39 ,  FIG. 7 , that a user has pushed the electrodes against an insulator and it is engaged. The micro-switches  38  and  38 ′ are engaged when the electrodes have linearly moved into a predefined range (nominally between 0.75 inches and 1.0 inch). The detector  10  will only initiate a measurement when the micro-switches inform the electronics  39  that both electrode assemblies  18  and  19  are fully engaged. LEDs  40  communicate to a user whether and which electrode is engaged. If during a measurement process, one electrode is disengaged the user is informed by LED  41  that the measurement is not valid. In addition, audible beeping tones are used to communicate the engagement of the electrodes in the event that the user cannot see LEDs  40 . The tones are activated when an electrode is engaged. A slow tone indicates that the grounded electrode is engaged and a fast tone indicates that the high voltage electrode is engaged. The tones are particularly useful in allowing a user to manipulate the detector  10  at the end of the hotstick to make sure both electrodes are engaged at the same time. When both electrodes are engaged, a solid tone is emitted to indicate that a measurement is taking place. 
     Referring to  FIGS. 8 and 9 , electrode assembly  18  includes a high voltage electrode  43  connected to a metallic shaft  44  by a insulating (in this case it is fiberglass but it could be any suitable insulating material) fiberglass rod  46 . The fiberglass rod  46  electrically insulates the electrode  43  from the metallic shaft  44 . The metallic shaft  44  connects the electrode assembly  18  to mechanism  26 . Electrode assembly  19  includes a grounded electrode  43 ′ connected to a metallic shaft  44 ′. The shaft  44 ′ connects the electrode assembly  19  to mechanism  26 ′. The grounded electrode  43 ′ and mechanisms  26  and  26 ′ are grounded electrically to the chassis  29 . Electrodes  43  and  43 ′ may be “Y”, “Hook”, “Pincer”, or any other suitable shape. 
     As illustrated in  FIGS. 9A-C , the grounded electrode  43 ′ includes a sensing probe or probes  50  attached to an end of the electrode  43 ′. The sensing probes are electrical conductors that are insulated from the electrode  43 ′. In the illustrated implementation, probes  50  include two flat strips of flexible circuit boards and are installed in cavities  51  of the electrode  43 ′. The implementation prevents the probes  50  from picking up stray electric fields from the high voltage electrode  43 . A insulation strip  52  of insulating material, such as rubber, is placed on top of and in contact with the probe  50 . The strip  52  has a pre-determined thickness and can deform to allow the probe  50  to be in contact with as much of the insulator under test as possible. It should be appreciated that the greater number of probes, the more sensitive the detector  10 . 
     Referring to  FIG. 7 , the electronics  39  include a microprocessor which controls all of the measurement and communication processes. Once the electrodes are adjusted to the desired spacing, the user calibrates the device either with “nothing” between the electrodes or a “known” good section of insulator. LED  60  provides the calibration status. The electronics  39  use this against which to compare values. In performing measurements, the detector  10  is pushed against a good section of insulator until the micro-switches  38  and  38 ′ provide an electrical signal to the LEDs  40  (one for each electrode assemblies, i.e., grounded and HV) to indicate that the electrodes are engaged or until a command is received by an RF receiver  56  from an RF control device. When LEDs  40  are lit, a measurement takes place. 
     Once the detector is engaged, a high voltage resonant voltage supply  61  sweeps through a frequency range and determines the resonance of the insulator. A high voltage at the resonant frequency is then supplied for a pre-determined amount of time, for example, 10 seconds. During this time, the current in HV supply, the drive level from power electronics to supply, the resonant frequency, and the measurements from sensing probes  50  are measured. The results are then compared against the “calibration” values. Depending whether the results are within some “predefined band” from the initial calibration, LED  57  or LED  58  is provided to the user. The results may also be sent to an RF enabled wireless device and/or via buzzer  59 . Through the measurement process the buzzer  59  sounds so that the user knows a measurement is being made. The high voltage supply  61  is a custom high frequency (in the implementation 1-2 MHZ) high voltage supply (in the implementation 1-3 kV) that uses a custom ferrite transformer and power electronics to create the voltage. 
     The RF receiver  56  allows the unit to be remotely controlled and to provide results to an RF enabled device. In the implementation, WiFi is used and the device hosts an HTML interface (web page) which allows a laptop, phone or tablet to control the device and report results. This option is not always used—the user may also simply use LEDs  40 ,  41 ,  57 ,  58  together with the buzzer  59 . 
     The detector  10  may also be battery powered. The battery may be rechargeable, such as a special lithium polymer battery which requires special charging. The electronics  39  contain charging intelligence and is capable of receiving power from an 8-14V DC source, e.g. from a car. 
     In operation, a test sequence is initiated by either the operator pushing the electrodes against the insulator or a remote RF enabled device (in this case any WiFi enabled computer, phone or tablet). A high frequency (in the implementation 1-2 MHZ) high voltage (in the implementation 1-3 kV) is placed across a section of the insulator, and the sensing probe  50  integrated into the grounded electrode  43 ′ measures the capacitive and resistive currents. LED  57  indicates whether there is a condition based on (a) the sensing probe measurement, (b) the current drawn by the high voltage supply  61 , and (c) the resonant frequency of the high voltage supply. LED  41  provides an indication of any erroneous measurement such as (a) the measurements do not fit the expected profile, (b) contact is lost with the insulator, (c) the on-board battery voltage is low, and (d) self diagnostics of the electronics. The remote RF enabled device also provides these indications plus more detailed information. It also keeps a history of the measurements and provides a graph of measurements along the insulator. 
     The foregoing has described an apparatus and method for identifying the presence of high conductivity or permittivity conditions in a wide range of electrically insulating materials. While specific embodiments of the present invention have been described, it will be apparent to those skilled in the art that various modifications thereto can be made without departing from the spirit and scope of the invention. Accordingly, the foregoing description of the preferred embodiment of the invention and the best mode for practicing the invention are provided for the purpose of illustration only and not for the purpose of limitation.