Abstract:
A system and method for monitoring or testing dielectric material nondestructively and in situ within field-based electrical equipment or as samples in a laboratory environment. In exemplary embodiments the use of negative voltage test pulses and a ground plane electrode with a parabolic curve or ogive shape minimizes energy transferred to the dielectric material to avoid or minimize degradation of the material. The disclosed system and method are thus suitable, inter alia, for continuous or near-continuous monitoring of fluid-filled electrical equipment in the field.

Description:
RELATED APPLICATION DATA 
       [0001]    This application claims the benefit of priority of U.S. Provisional Patent Application Ser. No. 61/543,434, filed Oct. 5, 2011, and titled “Dielectric Monitoring System and Method Therefore,” which is incorporated by reference herein in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention generally relates to the field of dielectric material testing and monitoring and more specifically to monitoring of electrical devices containing dielectric material. In particular, embodiments of the present invention are directed to dielectric fluid monitoring systems and methods therefore. 
       BACKGROUND 
       [0003]    Many electrical devices, for example power transformers, use a dielectric material, often a liquid such as silicone, mineral oil, or vegetable oil, to prevent voltage arcing between conductors and to aid in the removal of heat generated by the conductors during operation. In other applications solid or gas dielectric materials may be used. Due to temperature changes within an electrical device, events that occur within the device, e.g., faults, water, oxygen, and other contaminant ingress, etc., the dielectric material may degrade and loses its ability to adequately insulate the voltage and dissipate heat. Moreover, the degradation enhances the risk of an electrical device failure. 
         [0004]    To reduce the possibility of electrical device failure, regular inspections of the dielectric material are typically performed in order to test its dielectric condition. An inspection typically involves the manual extraction of a sample from within the electrical device and subsequent testing with a dielectric strength tester. As regards fluid dielectrics, typical testing apparatus applies an AC voltage stress to an electrode pair immersed in the fluid, with the stress being continuously increased until breakdown occurs, the breakdown being a measure of the ability of the material to perform its dielectric function. Unfortunately, these types of dielectric tests can be destructive to dielectric materials, so much so, that the tests are necessarily performed on a sample external to the electrical device, with the sample being discarded after the test. Additionally, because of the aforementioned laborious testing procedures, electrical device dielectric materials are analyzed on a routine having lengthy intervals between tests (e.g., annual or biannual tests), and generally without regard to the operating history of the electrical device. Thus, degradation may go undetected, resulting in failures of the electrical device. 
       SUMMARY OF DISCLOSURE 
       [0005]    In one implementation, the present disclosure is directed to a system for determining a state of a dielectric material used in dielectric-containing electrical equipment. The system includes a probe defining a gap configured to receive the dielectric material therein; and a pulse generator in electrical communication with the probe, the pulse generator configured to produce a negative voltage pulse at the gap. 
         [0006]    In further embodiments, such a system may also include a control system in electronic communication with the pulse generator, with the control system configured to initiate generation of the negative voltage pulse by the pulse generator and to provide output indicative of the dielectric material state based on a return signal from the probe. The control system may comprise a processor configured to execute instructions to: direct the pulse generator to generate the negative voltage pulse; evaluate a signal from the pulse generator, the signal including information regarding a ground return from the probe resulting from at least a portion of the negative voltage pulse passing across the gap; and determine the dielectric material state including at least a breakdown time based upon the ground return signal. 
         [0007]    In other alternative embodiments, the probe may comprise a needle and a ground plane with the gap defined therebetween. The ground plane may be ogive-shaped with the pointed end toward the gap. The ogive shape may comprise parabolic curves. 
         [0008]    The negative voltage pulse may comprise a substantially square waveform and may be a variable pulse. The negative voltage may be between about −10 kV and about −30 kV or may be between about −15 kV and about −30 kV. 
         [0009]    In further alternatives, the system may be configured to determine the state of a dielectric material that is a fluid and the fluid may be a liquid or gas. The dielectric material also may be a solid. The probe and the gap may be configured and dimensioned to receive a discrete sample of dielectric material, in which case a fluid is contained in a container. 
         [0010]    In yet another alternative, the dielectric-containing electrical equipment comprises fluid-filled equipment and wherein the probe is configured and dimensioned to mount within the fluid-filled equipment in communication with the fluid contained therein. Such fluid-filled equipment may be a power transformer. 
         [0011]    In another implementation, the present disclosure is directed to a system for determining a state of dielectric material in dielectric-containing electrical equipment. The system includes a probe configured and dimensioned to mount within the equipment in communication with the dielectric material contained therein, the probe including a needle and a ground plane; a pulse generator including a voltage multiplier, the voltage multiplier electronically coupled to the probe; and a control system in electronic communication with the pulse generator, wherein the control system includes instructions to direct the pulse generator to generate a substantially square negative voltage pulse; evaluate a signal from the pulse generator, the signal including information regarding a ground return resulting from at least a portion of the substantially square voltage pulse passing from the needle to the ground plane; and determine the dielectric material state including at least a breakdown time based upon the ground return signal. 
         [0012]    In such an implementation, the dielectric material may be a fluid and the dielectric-containing electrical equipment may comprise fluid-filled equipment and the probe may be configured and dimensioned to mount within the fluid-filled equipment in communication with the fluid contained therein. Alternatively, the dielectric material is a solid. 
         [0013]    In further alternatives, the needle and the ground plane may be disposed in an opposing relationship so as to form a gap therebetween. The probe may have an adjustable gap width and the ground plane may have a parabolic shape. The ground plane may comprise a parabolic ogive. In such a system, the pulse generator may sense the ground return via the ground plane. 
         [0014]    In another alternative embodiment, the pulse generator includes a power supply, and the power supply is electronically coupled to the voltage multiplier so as to direct an AC voltage or a pulsed DC voltage to the voltage multiplier. The voltage multiplier may comprise a ladder network of capacitors and diodes. Further, the pulse generator may produce a variable negative voltage pulse, which may be between about −10 kV and about −30 kV or between about −15 kV and about −30 kV. 
         [0015]    In yet another implementation, the present disclosure is directed to a method for testing a dielectric fluid within fluid-filled equipment, wherein the equipment includes a probe having a needle and a ground plane diametrically opposed within so as to form a testing gap. The method includes generating a negative voltage waveform having a substantially square profile; sending the voltage waveform to the needle; monitoring for a ground return of at least a portion of the voltage through the testing gap to the ground plane; determining, when the monitoring indentifies the ground return, a time the ground return occurred. The method may further comprise determining a condition of the dielectric fluid based on said determining a time. 
         [0016]    In yet another implementation, the present disclosure is directed to a method for testing a dielectric fluid within a power transformer. The method includes delivering a negative DC voltage with a predetermined waveform to a probe positioned in the dielectric fluid inside the power transformer; monitoring for a ground return at an electrode disposed in the dielectric fluid in the transformer at a predetermine distance from the probe; and determining, when the monitoring indentifies the ground return, a time the ground return occurred. 
         [0017]    In yet another implementation, the present disclosure is directed to a method for testing dielectric material. The method includes a relatively positioning the dielectric material within a gap formed by a needle electrode and ground plane; generating a negative voltage waveform having a substantially square profile; sending the negative voltage waveform to the needle; monitoring for a ground return of at least a portion of the negative voltage through the gap to the ground plane; measuring, when the monitoring indentifies the ground return, a time the ground return occurred; and determining a condition of the dielectric material based on the measured time. 
         [0018]    In alternative embodiments of such an implementation the needle electrode and ground plane may comprise a probe and the relatively positioning comprise mounting the probe within a dielectric-containing electrical equipment. In such an embodiment, the dielectric material may be a fluid. 
         [0019]    In further alternatives, such a method further comprises forming the ground plane with a parabolic curve, and the parabolic curve may comprise an ogive-shaped electrode. In other alternatives the negative voltage is between about −10 kV and about −30 kV or between about −15 kV and about −30 kV. And in further alternative embodiments the dielectric material may be a fluid or a solid, wherein the fluid may be a liquid or gas. Also, the relatively positioning may comprise placing a discrete sample of dielectric material with the gap. 
         [0020]    In yet another alternative, the adjusting is based on at least one of the type of dielectric material, a type of equipment using the dielectric material, a point in the life-cycle of the equipment and/or the determining comprises correlating the measured time to predetermined dielectric material states. 
         [0021]    In certain embodiments, such a method may comprise a method for monitoring dielectric material state, which would further comprise steps of instructing generation of the negative voltage wave form with a predetermined pulse length, determining if a ground return received in less time than the predetermined pulse length, when no ground return is received, identifying a good state for the dielectric material and instructing a new generation step at a first predetermined frequency interval, when a ground return is received in a time less than the predetermined pulse length but greater than a second time value greater than zero, identifying a caution state for the dielectric material and instructing a new generation step at a second predetermined frequency interval, when a ground return is received in a time less than the second time value, identifying an alert state for the dielectric material. Additionally, the method may comprise, when an alert state is identified, instructing a new generation step at a third predetermined frequency interval. The first predetermined frequency interval may be the same as the second predetermined frequency interval and the first predetermined frequency interval may be greater than the second predetermined frequency interval. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]    For the purpose of illustrating the invention, the drawings show aspects of one or more embodiments of the invention. However, it should be understood that the present invention is not limited to the precise arrangements and instrumentalities shown in the drawings, wherein: 
           [0023]      FIG. 1  is a schematic representation of an exemplary embodiment of a monitoring system used in an electrical device, in this case a power transformer, according to an embodiment of the present invention; 
           [0024]      FIG. 2  is a graph of a voltage versus time for a dielectric material undergoing a breakdown event when using a monitoring system according to an embodiment of the present invention; 
           [0025]      FIGS. 3A and 3B  are graphical representations of two sets of five test pulses transmitted to a dielectric material using an embodiment of the present invention, with time represented on the x axis and voltage represented on the y-axis. 
           [0026]      FIG. 4  is a flow chart illustrating an exemplary process for monitoring a dielectric material according to an embodiment of the present invention; and 
           [0027]      FIG. 5  is a block diagram of a control system for use with a monitoring system according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0028]    Referring now to the drawings,  FIG. 1  illustrates an exemplary monitoring system  100  in accordance with certain aspects of the present invention for use with a dielectric-containing electronic device, such as, but not limited to, fluid-filled power transformers, on-load tap changers, circuit breakers, and regulators. For ease of discussion,  FIG. 1  illustrates an exemplary embodiment of the invention in terms of one such device, power transformer  104 , that includes monitoring system  100 . 
         [0029]    As discussed more fully below, monitoring system  100  includes components necessary to directly measure and electronically communicate to a utility or other entity, information related to the condition of a dielectric material contained within the device without having to manually remove and test the dielectric material. This information may be used to determine where dielectric material is along its life-cycle, its current condition, and if precautionary or corrective actions should be taken in a way that minimizes operational risk, avoids costs associated with forced power outages, and increases the useful life of the transformer. 
         [0030]    In the exemplary embodiment shown in  FIG.1 , monitoring system  100 , using control system  112  and pulse generator  116 , generates and transmits a precise voltage for a precise amount of time to a probe  120  within any dielectric material containing electrical equipment, such as power transformer  104 , and reports the condition of the dielectric material, including whether and when a breakdown of dielectric material occurs. 
         [0031]    As shown in  FIG. 1 , exemplary power transformer  104  includes a transformer tank  124 , into which a winding assembly  128  is positioned. Transformer tank  124  is typically a water resistant container that, in certain embodiments of power transformer  104 , holds a dielectric material, in this case a fluid/liquid, which may be, but is not limited to, mineral oil, silicon, vegetable oils, or other fluids suitable for insulating the conductors within the transformer, dissipating heat generated during the operation of the transformer, and mitigating water migration toward winding assembly  128 . 
         [0032]    Winding assembly  128  includes a pair of end blocks  132 , i.e., end blocks  132 A-B, with a plurality of windings  136  and a plurality of insulation assemblies  152  disposed between the end blocks. End blocks  132 A-B are positioned in opposing relationship and are sized and configured to evenly distribute a clamping force from clamping assembly  144  along longitudinal axis  148  of power transformer  104 . Windings  136  are typically formed around at least a portion of a magnetic core (not shown) and include multiple turns of a metal conductor, such as copper or aluminum. Each winding  136  may be wrapped around the magnetic core in a circular disc, helical, or layered pattern, or other wrapping pattern known in the art. Each winding  136  may be spaced apart by one or more radially arranged and circumferentially spaced insulation assemblies  152 . 
         [0033]    Insulation assemblies  152  may include one or more insulation plates  156  stacked on top of one another. Insulation assemblies  152  are sized and configured so as to aid in the distribution of the clamping force from end block  132 A, through windings  136 , to end block  132 B. Insulation assemblies  152  also provide dielectric distance between windings  136  to prevent short circuits, to maintain the mechanical integrity of winding assembly  128  during random (non-spontaneous) short circuit events, and to provide a path between the windings that allows a sufficient amount of dielectric fluid to circulate and remove heat from the windings. Insulation assemblies  152  are typically spaced equidistantly around the circumference of windings  136 , extending radially from the center of power transformer  104 . In the exemplary power transformer shown in  FIG. 1 , six insulation assemblies  152  are located between each of windings  136  and are spaced about 60 degrees apart ( FIG. 1  shows three of these insulation assemblies, i.e., assemblies  152 A,  152 B and  152 C). As will be understood by persons of ordinary skill in the art, the number and positioning of insulation assemblies  152  may be chosen so as to appropriately distribute the clamping force throughout winding assembly  128 . 
         [0034]    Insulation plates  156  as used in a power transformer of the type exemplified in  FIG. 1  are often constructed of cellulose, and are typically capable of absorbing dielectric fluid when placed in a dielectric fluid bath. Insulation plates  156  may also be a fiber composite having a combination of fibrous reinforcement, aramid fibers, polymers, and additives, which may give the insulation plates superior resistance to corrosion, chemicals, and high temperatures. In an embodiment, insulation assembly  152  includes a number of insulation plates  156  that is sufficient in number to prevent short circuiting of power transformer  104  during a fault event within an expected range. It will, however, be appreciated by persons of ordinary skill in the art that the power transformer illustrated in  FIG. 1  is but one of many types of dielectric containing electrical equipment for which embodiments of the present invention may be employed. 
         [0035]    As shown in  FIG. 1 , the electrical device (exemplary power transformer  104 ) includes a portion of monitoring system  100 , probe  120 , within the device itself, in this case within transformer tank  124 . Probe  120  may generally be placed anywhere within an electrical device so as to be in proper communication with and to measure the condition of dielectric material contained therein. In an exemplary embodiment, the placement of probe  120  is determined based upon an analysis of where dielectric material is most likely to be contaminated or to suffer degradation and based upon the proximity of other high voltage components within the device. 
         [0036]    In the exemplary embodiment shown in  FIG. 1 , probe  120  includes needle  160  and ground plane  164 , with the needle and the ground plane being separated by gap  168 . Needle  160  can facilitate the delivery of a high voltage charge to the dielectric material at a precise location and may be made of several materials and by methodologies known in the art. In an exemplary embodiment, needle  160  has point  172  with a diameter about 50 to about 100 microns and is made from tungsten carbide. In an alternative embodiment, needle  160  is made from hardened steel. 
         [0037]    Ground plane  164  serves to receive the voltage transmitted by needle  160 . In an exemplary embodiment, ground plane  164  is ogive-shaped, with narrowed end  176  directed toward point  172 . The ogive shape of ground plane  164  provides a specifically, curved-shaped ground plane electrode to create focused electrical field. In a preferred embodiment, the curved shape is parabolic, or based on a parabolic ogive. The needle to parabolic ground plane electrode assembly creates a focused electric field, localizing breakdowns to a high field and medium voltage region. This allows for increased sensitivity and with reduced energy delivered to the test material upon breakdown, thus further reducing degradation as a result of testing. As with needle  160 , ground plane  164  may be made from tungsten carbide, harden steel, or other metals suitable for withstanding the high voltage operating environment used with monitoring system  100 . 
         [0038]    The design of probe  120  is such that dielectric material is received within gap  168 ; in the case of a fluid dielectric, flows through gap  168 . The size of gap  168  is dependent upon, among other things, the type of dielectric material used with the equipment, the type of equipment and the amount of voltage to be supplied to the dielectric material. In exemplary embodiments, gap  168  is sized such that a dielectric breakdown of the material does not occur when the dielectric material is known to be in a good condition (e.g., when the dielectric material is new or otherwise confirmed to be in good condition). In one exemplary embodiment, for a power transformer as shown in  FIG. 1 , using mineral oil as the dielectric material, gap  168  may be about 0.1 to about 0.4 mm. In alternative embodiments, depending on device parameters as may be determined by persons of ordinary skill in the art, gap  168  may be less than about 0.1 mm, but generally will not be less than about 0.08 mm, or in an overall range of about 0.08 mm to about 0.4 mm. In another alternative embodiment, probe  120  may be configured such that gap  168  has an adjustable width, which can be adjusted to a specific width based on the nature of the particular equipment to be monitored and the material to be tested. Factors such as different points within the life-cycle of the equipment being monitored may also be considered in selecting a specific gap width. Preferably the gap may be locked in place upon installation. Such adjustment may be achieved by providing for movement and locking of either or both of ground plane  164  and needle  160 . 
         [0039]    Pulse generator  116  provides a voltage to probe  120  via voltage input line  180 . Pulse generator  116  receives power from a voltage source (not shown) and multiplies the voltage to a desired level for output to probe  120 . In an exemplary embodiment, pulse generator  116  produces a negative voltage having a square waveform of a predetermined duration. As shown in  FIG. 1 , pulse generator  116  can include a power supply  184  and a voltage multiplier  188 . Power supply  184  is suitable for providing conditioned low level AC power or pulsed DC power, e.g., 110 volts AC or DC, to voltage multiplier  188  and is typically connectable to an external power source (not shown). 
         [0040]    Voltage multiplier  188  generates high DC voltage from the low voltage provide by power supply  184 . In one exemplary embodiment, as will be appreciated by persons of ordinary skill in the art, voltage multiplier  188  may be made up of a voltage multiplier ladder network of capacitors and diodes. Using only capacitors and diodes, voltage multiplier  188  can step up relatively low voltages to the high values required for testing dielectric strength of the dielectric material. In an exemplary embodiment, voltage multiplier  188  provides an output voltage of between about −10 kV and about −30 kV, in some embodiments between about −15 kV and about −30 kV. Among other advantages, variable pulse magnitude capability permits testing and monitoring of multiple materials in multiple applications or equipment using the same system. 
         [0041]    A negative square pulse as used in exemplary embodiments of the present invention helps to keep the plus signal as clean as possible. Negative pulses across the needle-to-plane electrode configuration demonstrate a pulse free mode that helps prevent energy being released into the system prior to breakdown. The square pulse is used to quickly expose the oil to a preset voltage and quickly turn it off in case of a breakdown avoiding any overshoot voltages. 
         [0042]    Power supply  184  and voltage multiplier  188  both get instructions from control system  112 . Control system  112  is configured to instruct pulse generator  116  to generate an output voltage pulse as described above with a certain magnitude for a certain amount of time, for example, 500 nanoseconds. In general the pulse length will be a positive time greater than zero and equal to or less than about 500 nanoseconds. In an exemplary embodiment, control system  112  receives instructions (discussed in more detail below) regarding the desired output voltage and pulse length and directs power supply  184  to provide a square voltage waveform of that magnitude and duration to voltage multiplier  188 . The output of voltage multiplier  188  is transmitted on voltage input line  180  for use by probe  120 . In some embodiments, the control system may instruct the pulse generator to generate a pulse with a length between about 100 and 500 nanoseconds. However, while the system may permit selection of different pulse lengths, the pulse length will most typically be fixed at a specific time for a particular equipment monitoring or test routine. 
         [0043]    Control system  112  also receives one or more signals containing information related to breakdown events that occur across gap  168 . In an exemplary embodiment, control system  112  senses for a ground return, which is the passage of voltage from needle  160 , across gap  168 , to ground plane  164 . The sensing by control system  112  may occur continuously or nearly continuously thereby improving the accuracy of identifying the beginning of a breakdown event (e.g., initial breakdown time  212 ,  FIG. 2 , discussed in detail below). 
         [0044]    In an exemplary embodiment, pulse generator  116  may be encased in a protective box suitable for containing a high voltage device. The components of pulse generator  116  may also be immersed in a high voltage potting compound. Exemplary potting compounds include resins, including, but not limited to, epoxies and silicones. 
         [0045]    As noted above, control system  112  provides instructions to pulse generator  116  regarding the magnitude and duration of the voltage to be delivered to probe  120 . The instructions delivered by control system  112  can be based on inputs by a user, from preprogrammed instructions, and/or based upon feedback received from pulse generator  116 . For example, control system  112  may receive a signal from pulse generator  116  indicating a breakdown event occurred at a certain time. If the certain time is within a determined timeframe, control system  112  may increase the frequency of testing of the dielectric material so as to more closely monitor the condition of the material. 
         [0046]    In an exemplary embodiment, control system  112  can also include, among other things, one or more filters  194  for conditioning the incoming information from pulse generator  116 , and processor  198 . In an alternative embodiment, some or all of control system  112  may be combined with pulse generator  116 . More details of an exemplary control system are discussed below in connection with  FIG. 5 . 
         [0047]    Processor  198  is capable of receiving breakdown information from pulse generator  116 . In an exemplary embodiment, the pulse generator provides a digital signal and an analog signal, the signals containing information related to the breakdown event. In such an embodiment, processor  198  compares the two signals. Comparing the two signals can lead to increased accuracy in determining the time of dielectric breakdown. From the information contained on one or both of the signals, processor  198  then determines a breakdown time, which is the length of time the voltage coming from pulse generator  116  has been applied to dielectric material before the pulse generator sensed a ground fault return (i.e., voltage passing across gap  168  via the dielectric material to ground plane  164 ). The length of time to breakdown is an indicator of dielectric material condition in so far as dielectric material in poorer condition will break down earlier than dielectric material in better condition. The length of time to breakdown of dielectric material may be reported to an operator or may be part of an alert system, such as the alert system described below. 
         [0048]    A test sequence in accordance with embodiments of the present invention, and resulting breakdown event if it occurs, may be represented in a graph of applied voltage over time, as shown in  FIG. 2 . In this example, voltage from pulse generator  116  is delivered to needle point  172  at time  204 . Due primarily to the square waveform, the voltage delivered to the needle point at time  204  is about an instantaneously maximum voltage, Vm, corresponding to the minimum dielectric material breakdown voltage chosen for the given material. If there is no breakdown of dielectric material, the voltage at the needle point would be maintained to end time  208 . However, in the example illustrated in  FIG. 2 , a breakdown of dielectric material begins at an initial breakdown time  212  and reduces the voltage potential across gap  168  to zero (0) at time  216  via a non-linear voltage reduction represented by breakdown line  220 . 
         [0049]    It should be noted that in contrast to prior art ASTM dielectric testing, which significantly degrades the oil sample, monitoring system  100 , because of the extremely small quantity of electrical energy delivered to the material, due to the square waveform and the short duration of the voltage pulse does not degrade the dielectric material when the material is in good condition and minimizes the degradation of the dielectric material when a breakdown occurs. Thus, when a breakdown event occurs at the beginning of the pulse, the total pulse time will be less than pulse time instructed by the control system. Additionally, depending on the impedances used to generate the pulse, the overall energy available to be dissipated in the test cell can be less than 1 μJ, which is an amount that minimizes dissolved gas and does not appreciably reduce dielectric strength. 
         [0050]    Although Vm in  FIG. 2  is shown as constant, in some instances it may vary. To avoid false indications of dielectric breakdown that could occur as a result of identifying any deviation from Vm, the breakdown time of dielectric material can be determined at the time when breakdown line  220  crosses a threshold voltage value, Vth, which, in this embodiment, occurs at time  224 . In an exemplary embodiment, threshold voltage value is equal to about 70 to 90% of Vm. In another embodiment it may be about 80% of Vm. Other values of Vth may be chosen depending on the desired sensitivity of monitoring system  100  to breakdowns of dielectric material. 
         [0051]      FIGS. 3A and 3B  illustrate voltage over time based on data generated by an exemplary dielectric monitoring system as described using material samples with different contaminants. The data presented in  FIG. 3A  shows a measurable shift in damping coefficient as metallic particles are introduced into the test sample, in this case mineral oil. The data presented in  FIG. 3B  shows a subtle, but measurable shift in frequency as moisture is added to a separate test sample, again mineral oil. These graphs not only show the flatness of the square pulse and the rapidity of voltage fall and rise, but also resonant ringing after breakdown. 
         [0052]    Mathematically, the resonant ringing frequency of the probe circuit can be stated by the equation: 
         [0000]      ω 0 =1/√( L C )   [1]
 
         [0053]    Where L is the inductance of gap  168  and C is the capacitance of gap  168 . The damping of the ringing of the circuit is given by the equation: 
         [0000]      γ=(1/(2  R ))√( L/C )   [2]
 
         [0054]    Where R is the resistance of gap  168 . As various contaminants present in the dielectric material may possess varying levels of electrical resistance, capacitance, and inductance, it is possible to relate the measured frequency and damping coefficient of periodic ringing after a breakdown with general categories of contaminants present near the probe. For example, certain metallic contaminants are known to have a higher inductance than water, as well as a lower resistance and lower capacitance. The higher inductance may cause a higher damping coefficient to be observed if certain metallic contaminants are responsible for the breakdown, in comparison with water contamination resulting in the loss of material insulating quality. 
         [0055]      FIG. 4  shows an exemplary process  300  for monitoring a dielectric material according to embodiments of the present invention. Such a process may be based on a system including related hardware and software that provides instructions to a grid or other operator based on dielectric force breakdown measurements. Software or firmware instructions for implementing the process illustrated in  FIG. 4  may be executed by control system  112 , described more below and illustrated in  FIG. 5 . Turning to  FIG. 4 , at step  304 , parameters such as a maximum voltage value corresponding to the desired minimum dielectric breakdown resistance value, an indicator of dielectric material condition, are determined. The minimum dielectric breakdown value will vary by kind of dielectric material used within any piece of equipment, such as electrical device  104 . 
         [0056]    At step  308 , the voltage determined in step  304  is delivered to a probe, such as probe  120 , within the transformer. As discussed above, delivery of the voltage is initiated by control system  112 , which directs a pulse generator, such as pulse generator  116  to produce a voltage of a certain magnitude for a certain duration. 
         [0057]    At step  312 , a determination is made as to whether a dielectric material breakdown occurred. If not, the system will report a “Green” status (“good state”) and wait until the predetermined test protocol requires further testing to be performed. If a breakdown is detected to have occurred, the system proceeds to step  316 . 
         [0058]    At step  316 , the time at which the breakdown occurred is determined. In an exemplary embodiment, the time to breakdown is determined through the consistent reporting of whether a ground return is sensed by pulse generator  116 , which indicates that the voltage potential across gap  168  is decreasing and thus the dielectric material is experiencing a breakdown. Depending on the time to the breakdown, the monitoring system may indicate the dielectric material condition by providing a status of the material. In the exemplary embodiment of process  300  shown in  FIG. 4 , if the breakdown of dielectric material occurs after a predetermined time X, which depends on the type of equipment tested and the nature of the dielectric material, the process can proceed to step  320  where the system is placed on “Green” status. After setting the system on “Green” status, the process returns to step  308  or  336  (alternative discussed later) for continued measurement of the dielectric material breakdown times. In an alternative embodiment, after setting the system on “Green” status after an earlier “Yellow” (“caution state”) or “Red” status (“alert state”) indication, the monitoring system may less frequently test the dielectric material. If the breakdown of the dielectric material occurs prior to X, indicating a more degraded condition of the dielectric material, the process continues to step  324 . 
         [0059]    At step  324 , the time to breakdown of the dielectric material is evaluated to determine extent of degradation, as quicker breakdown times may require different responses by an operator. Depending on the speed of the breakdown of the dielectric material, the system may be placed in a “Yellow” status at step  328  or a “Red” status at step  332 . “Yellow” status can indicate, among other things, that precautionary measures should be taken, such as scheduling an outage for the transformer in order to replace dielectric material. “Red” status can indicate, among other things, that the condition of dielectric material has decreased below a predetermined level and/or that the condition of the dielectric material has increased the probability of failure of the transformer. In one exemplary embodiment of process  300 , the system is set to “Red” status if, at step  324 , the time to breakdown is less than a time X, but greater than an earlier time Y. In an exemplary embodiment, X and Y are parameters determined in accordance to the nature of the electrical equipment and the nature of the dielectric material. 
         [0060]    Regardless of the parameters such as X and Y employed, after placing the system in a “Yellow” status, the process returns to step  308  or  336  (alternative discussed later) to continue measuring the condition of dielectric. The system may also be placed in “Yellow” status based on predefined criteria. For example, the system may also be placed in “Yellow” status when the time to breakdown has decreased by a certain amount of time over a certain period, e.g., one month. As a result of being placed in a “Yellow” status, in an embodiment, process  300  may increase the frequency of testing of dielectric material. Upon being placed in a “Yellow” status, the frequency of testing may be increased or decreased to provide higher resolution of historical data, particularly in the latter example, when the quality of the dielectric material is believed to be changing more rapidly. 
         [0061]    The system may be placed in “Red” status based on several different criteria. For example, and as shown in  FIG. 4 , if the time to breakdown of the dielectric material has fallen to less than earlier time Y, the system may be placed in “Red” status at step  332 . As another example, the system may be placed in “Red” status if the measured time to breakdown between sequential measurements has fallen by more than a predetermined value over a predetermined period. Notably a steep reduction in a relatively short amount of time may suggest to the operator that the reduction in the dielectric material condition may have occurred because of an ingress of contamination, such as water, and further investigation may be justified to determine if there are further problems with the transformer. As a result of being placed in a “Red” status, in an embodiment, process  300  may increase the frequency of testing of the dielectric material when placed in “Red” status. 
         [0062]    An alternative embodiment of process  300  includes step  336 , which determines the frequency of testing of the dielectric material. The frequency of testing can be based, at least in part, on the results of the previously performed testing. For example, if the system has been placed in a “Yellow” status, the process may increase the frequency of measurements of dielectric material so as to provide the utility or operator with more frequent status updates of the condition of the dielectric material. Changes in the frequency of monitoring of the dielectric material may be automated, for example, any frequency increases may be proportional to the time to breakdown measured or may be a step function. Changes in the frequency of monitoring may also be manual. For example, after the system status is updated, a user is prompted to enter the frequency of testing going forward. 
         [0063]    It is to be noted that any one or more of the aspects and embodiments of process  300  and/or monitoring system  100 , as described herein, may be conveniently implemented using one or more machines (e.g., one or more computing devices that are utilized as a user computing device) programmed according to the teachings of the present specification, as will be apparent to those of ordinary skill in the computer art. Aspects and implementations of monitoring system  100 , discussed above, employing software and/or software modules may also include appropriate hardware for assisting in the implementation of the machine executable instructions of the software and/or software module. 
         [0064]    Such software may be a computer program product that employs a machine-readable storage medium. A machine-readable storage medium may be any medium that is capable of storing and/or encoding a sequence of instructions for execution by a machine (e.g., a computing device, control system  112 ) or a portion of the machine (e.g., processor  198 ) and that causes the machine to perform any one of the methodologies and/or embodiments described herein. Examples of a machine-readable storage medium include, but are not limited to, a magnetic disk, an optical disk, a magneto-optical disk, a read-only memory “ROM” device, a random access memory “RAM” device, a magnetic card, an optical card, a solid-state memory device (e.g., a flash memory), an EPROM, an EEPROM, and any combinations thereof. A machine-readable medium, as used herein, is intended to include a single medium as well as a collection of physically separate media, such as, for example, a collection of compact disks or one or more hard disk drives in combination with a computer memory. As used herein, a machine-readable storage medium does not include a signal. 
         [0065]    Such software may also include information (e.g., data) carried as a data signal on a data carrier, such as a carrier wave. For example, machine-executable information may be included as a data-carrying signal embodied in a data carrier in which the signal encodes a sequence of instruction, or portion thereof, for execution by a machine (e.g., a computing device) and any related information (e.g., data structures and data) that causes the machine to perform any one of the methodologies and/or embodiments described herein. 
         [0066]      FIG. 5  shows a diagrammatic representation of one exemplary embodiment of control system  112 , within which a set of instructions for causing a processor  198  to perform any one or more of the aspects and/or methodologies of the present disclosure. It is also contemplated that multiple computing devices may be utilized to implement a specially configured set of instructions for causing monitoring system  100  to perform any one or more of the aspects and/or methodologies of the present disclosure. 
         [0067]    Control system  112  can also include a memory  408  that communicates with processor  198 , and with other components, via a bus  412 . Bus  412  may include any of several types of bus structures including, but not limited to, a memory bus, a memory controller, a peripheral bus, a local bus, and any combinations thereof, using any of a variety of bus architectures. 
         [0068]    Memory  408  may include various components (e.g., machine readable media) including, but not limited to, a random access memory component (e.g., a static RAM “SRAM”, a dynamic RAM “DRAM”, etc.), a read only component, and any combinations thereof. In one example, a basic input/output system  416  (BIOS), including basic routines that help to transfer information between elements within control system  112 , such as during start-up, may be stored in memory  408 . Memory  408  may also include (e.g., stored on one or more machine-readable media) instructions (e.g., software)  420  embodying any one or more of the aspects and/or methodologies of the present disclosure. In another example, memory  408  may further include any number of program modules including, but not limited to, an operating system, one or more application programs, other program modules, program data, and any combinations thereof. 
         [0069]    Control system  112  may also include a storage device  424 , such as, but not limited to, the machine readable storage medium described above. Storage device  424  may be connected to bus  412  by an appropriate interface (not shown). Example interfaces include, but are not limited to, SCSI, advanced technology attachment (ATA), serial ATA, universal serial bus (USB), IEEE 1394 (FIREWIRE), and any combinations thereof. In one example, storage device  424  (or one or more components thereof) may be removably interfaced with control system  112  (e.g., via an external port connector (not shown)). Particularly, storage device  424  and an associated machine-readable medium  428  may provide nonvolatile and/or volatile storage of machine-readable instructions, data structures, program modules, and/or other data for control system  112 . In one example, software  420  may reside, completely or partially, within machine-readable medium  428 . In another example, software  420  may reside, completely or partially, within processor  198 . 
         [0070]    Control system  112  may also include an input device  432 . In one example, a user of control system  112  may enter commands and/or other information into computer system  112  via input device  432 . Examples of an input device  432  include, but are not limited to, an alpha-numeric input device (e.g., a keyboard), a pointing device, a joystick, a gamepad, an audio input device (e.g., a microphone, a voice response system, etc.), a cursor control device (e.g., a mouse), a touchpad, an optical scanner, a video capture device (e.g., a still camera, a video camera), touch screen, and any combinations thereof. Input device  432  may be interfaced to bus  412  via any of a variety of interfaces (not shown) including, but not limited to, a serial interface, a parallel interface, a game port, a USB interface, a FIREWIRE interface, a direct interface to bus  412 , and any combinations thereof. Input device  432  may include a touch screen interface that may be a part of or separate from display  436 , discussed further below. Input device  432  may be utilized as a user selection device for selecting one or more graphical representations in a graphical interface as described above. 
         [0071]    Input device  432  may also include a sensor assembly or other suitable communications interface  433  for communicating with external sensors or inputs. In one exemplary embodiment, sensor assembly includes communications interface with probe  120  and/or pulse generator  116  to provide feedback as described herein regarding the sensed ground return indicative of dielectric material breakdown and related parameters. The output of probe  120  and/or pulse generator  116  can be stored, for example, in storage device  424  and can be further processed to provide, for example, an analysis of the time to breakdown of the dielectric material over time, by processor  198 . 
         [0072]    A user may also input commands and/or other information to control system  112  via storage device  424  (e.g., a removable disk drive, a flash drive, etc.) and/or network interface device  440 . A network interface device, such as network interface device  440  may be utilized for connecting control system  112  to one or more of a variety of networks, such as network  444 , and one or more remote devices  448  connected thereto. Examples of a network interface device include, but are not limited to, a network interface card (e.g., a mobile network interface card, a LAN card), a modem, and any combination thereof. Examples of a network include, but are not limited to, a wide area network (e.g., the Internet, an enterprise network), a local area network, a telephone network, a data network associated with a telephone/voice provider, a direct connection between two computing devices, and any combinations thereof. A network, such as network  444 , may employ a wired and/or a wireless mode of communication. In general, any network topology may be used. Information (e.g., data, software  420 , etc.) may be communicated to and/or from control system  112  via network interface device  440 . 
         [0073]    Control system  112  may further include a video display adapter  452  for communicating a displayable image to a display device, such as display device  436 . Examples of a display device include, but are not limited to, a liquid crystal display (LCD), a cathode ray tube (CRT), a plasma display, a light emitting diode (LED) display, and any combinations thereof. Display adapter  452  and display device  436  may be utilized in combination with processor  198  to provide a graphical representation of a utility resource, a location of a land parcel, and/or a location of an easement to a user. In addition to a display device, control system  112  may include one or more other peripheral output devices including, but not limited to, an audio speaker, a printer, and any combinations thereof. Such peripheral output devices may be connected to bus  412  via a peripheral interface  456 . Examples of a peripheral interface include, but are not limited to, a serial port, a USB connection, a FIREWIRE connection, a parallel connection, and any combinations thereof. 
         [0074]    Persons of ordinary skill in the art will appreciate that the present invention and its application are not limited to the specific embodiments described above for purposes of exemplifying embodiments of the invention. For example, while liquid dielectrics such as mineral oil are commonly selected as a dielectric material, persons of ordinary skill in the art will appreciate based on the teachings set forth herein that embodiments of the present invention are not limited to use with liquid dielectrics. Dielectric fluids comprising gas, or dielectric solid materials also may be monitored and tested via embodiments of the present invention. Additionally, while field monitoring of in-service equipment is an area of important need for the present invention, embodiments of the invention may also be used for non-destructive testing of dielectric material samples, for example in a bench-top or laboratory setting. Persons of ordinary skill in the art will recognize that in the case of such testing, embodiments of the present invention may be utilized essentially unchanged from the description above other than the probe element being removed from specific equipment and configured to hold a material sample within the gap as is otherwise known in the art. Fluid samples in this regard may be contained in a suitable container between the needle and ground plane (parabolic-shaped) electrodes. 
         [0075]    Exemplary embodiments have been disclosed above and illustrated in the accompanying drawings. It will be understood by those skilled in the art that various changes, omissions and additions may be made to that which is specifically disclosed herein without departing from the spirit and scope of the present invention.