Patent Description:
Certain barehand or common potential methods of servicing live, or energized, alternating current (AC) power lines are generally known to specially-trained or skilled individuals within the electrical construction and maintenance industry. Generally, barehand and common potential maintenance methods permit maintenance on power lines to be more efficient because electrical power does not need to be shut off to, or routed around, the power line for which maintenance is to be performed. In one instance of performing maintenance on a high voltage AC power line, an aerial lift platform, such as a bucket truck, may be equipped with an insulated, extendable boom to insulate workers in the bucket from ground potential and thus any potential difference with a high voltage AC power line, with which the workers may be in common potential. In conjunction with barehand and common potential methods used on AC power lines, an AC meter may be used to monitor current that passes through the insulated, extendable boom. While using such a meter and method on an AC power line has proven satisfactory, because Direct Current (DC) high voltage and associated current behaves much differently, and an AC meter and techniques are not satisfactory for work on a DC high voltage power line, a new DC meter and method of using the DC meter are desired. <CIT> discloses improvements in or relating to the detection of leakage current. <CIT> discloses a portable current intensity detector for aerial booms. The document "<NPL>discusses history of live-working in France. The Slides "<NPL> live line working techniques. <CIT> discloses a live line tension tool assembly. <CIT> discloses an electrical insulating rod. <CIT> discloses a dead end tool. <CIT> discloses an insulating means suitable for use in handling high voltage power lines.

An apparatus for measuring Direct Current (DC) from an energized DC electrical power line may utilize a DC current measuring device to measure a DC leakage current from the energized DC electrical power line, a DC numerical display that displays the DC leakage current measured by the DC current measuring device, and an audio speaker that sounds upon the DC current measuring device measuring a threshold DC leakage current value. An apparatus may further utilize in some combination, a manual DC voltage class selector switch that is manually adjustable to coincide with a DC voltage of the DC electrical power line, an automatic DC voltage class selector switch that automatically switches to coincide with a DC voltage of the DC electrical power line, a graphical display that visually depicts a level of the DC leakage current measured by the DC current measuring device, an aerial work platform for containing and delivering human workers to a height of an energized DC electrical power line, a chassis, such as a crane chassis, bucket truck chassis, trailer or other chassis. The apparatus may also employ an elongate electrically insulating member having an insulating member first end and an insulating member second end, the insulating member first end connected (e.g. electrically) to the chassis, and the insulating member second end connected (e.g. electrically) to the aerial work platform, a conductive lead having a conductive lead first end and a conductive lead second end, the conductive lead first end contacting the energized DC voltage transmission line, and the conductive lead second end contacting the aerial work platform. A corona ring may be attached proximate to the insulating member first end with an exterior collector band attached proximate the insulating member second end. An internal collector band may be attached proximate to the insulating member second end. A DC input lead having a DC input lead first end and a DC input lead second end may be provided with the DC input lead first end contacting the external collector band and the internal collector band. The DC input lead second end may be an electrical input for the DC measuring device. A DC ground or output lead may be provided and have a DC output lead first end and a DC output lead second end. The DC output lead first end may be attached to an electrical ground point of the DC measuring device and the second end of the DC output lead may contact an Earth ground or potential. A plurality of hydraulic lines may traverse an interior of the elongate insulating member. The hydraulic lines may be electrically connected to the DC measuring device. A plurality of fiber optic lines may traverse an interior of the elongate insulating member. The fiber optic lines may be electrically connected to the DC measuring device. A portable casing to be carried by an individual human may substantially retain the DC current measuring device, the DC numerical display, the graphical display and the audio speaker.

The apparatus and methods of any of the present teachings, may be used in conjunction with, or may include an energized DC electrical power line having a voltage between <NUM>,<NUM> volts and <NUM>,<NUM> volts, inclusive, or between <NUM>,<NUM> volts and <NUM>,<NUM> volts, inclusive, or between <NUM>,<NUM> volts and <NUM>,<NUM> volts, inclusive, or between <NUM>,<NUM> volts and <NUM>,<NUM> volts, inclusive, or a voltage between <NUM>,<NUM> volts and <NUM>,<NUM> volts, inclusive, or between <NUM>,<NUM> volts and <NUM>,<NUM> volts, inclusive.

A portable apparatus for use with an energized DC transmission line may utilize a substantially electrically insulating structure, a DC current measuring device to measure DC current passing through the substantially electrically insulating structure, a DC voltage level switch, a DC display to display a DC current measured by the DC current measuring device at a DC voltage level of the DC voltage level switch, a graphical display to indicate an amperage of the DC current, and an audio speaker to sound at a threshold amperage of the DC current measured by the DC current measuring device. An apparatus may further employ a casing to which the DC current measuring device, the DC voltage level switch, the digital DC display, the graphical display, and the audio speaker, attach. The apparatus may further exhibit a first end of the substantially electrically insulating structure that contacts the energized DC transmission line, and a second end of the substantially electrically insulating structure that contacts an earth ground (i.e. ground voltage, ground potential), an electrical lead having an electrical lead first end and an electrical lead second end, with the electrical lead first end fastened proximate to the second end of the insulating structure and the electrical lead second end fastened to the DC current measuring device. A portable apparatus may also employ a DC ground lead (e.g. an electrically conductive cable) having a DC ground lead first end and a DC ground lead second end, with the DC ground lead first end attached to the DC current measuring device (e.g. an electrical ground point of the DC current measuring device), and the second end of the DC ground lead contacting an Earth ground (e.g. ground voltage or ground potential). The substantially electrically insulating structure may be a ladder, scaffolding, a hydraulic line, a boom (e.g. a crane boom, a bucket truck boom, or an aerial platform device boom), or nearly any fiber reinforced plastic ("FRP") structure used in as an electrically insulating structure.

According to the present teachings, an apparatus for use with an energized DC transmission line according to claim <NUM> is defined. The apparatus utilizes an electrically conductive supporting structure of an energized DC electrical power line, an energized DC transmission line located between a surface of Earth and the electrically conductive supporting structure, a first elongate substantially electrically insulating structure contacting each of the electrically conductive supporting structure and the energized DC transmission line, and a DC current measuring device electrically wired in series between the first elongate substantially electrically insulating structure and an electrical ground (e.g. ground potential or ground voltage). A DC current measuring device is electrically wired in series between the first elongate substantially electrically insulating structure, and an electrical ground may be an electrical lead having an electrical lead first end and an electrical lead second end, the electrical lead first end electrically connected to the first elongate substantially electrically insulating structure and proximate to the electrically conductive supporting structure of the energized DC electrical power line. The electrical lead second end may be fastened to the DC current measuring device. A DC ground lead having a DC ground lead first end and a DC ground lead second end, may have the DC ground lead first end attached to an electrical ground point of the DC current measuring device, and the DC ground lead second end in contact with an Earth ground (e.g. ground potential or ground voltage). The structure having Earth potential or Earth ground may be the electrically conductive supporting structure. A second elongate substantially electrically insulating structure contacts each of the electrically conductive supporting structure and the energized DC transmission line. The DC current measuring device may also be electrically connected in series to the second elongate substantially electrically insulating structure.

The DC current measuring device may be electrically connected in series to the second elongate substantially electrically insulating structure to measure a momentary leakage current passing through both the first elongate substantially electrically insulating structure and the second elongate substantially electrically insulating structure, when the first and second structures are electrically connected. The first elongate substantially electrically insulating structure and the second elongate substantially electrically insulating structure are substantially parallel to each other, and are in tension due to a weight of the energized DC electrical power line suspended from the elongate substantially electrically insulating structures. The apparatus may further employ a DC voltage selector switch that adjusts manually or automatically to coincide with a DC voltage level of the energized DC electrical power line, a DC numerical display that displays the DC current measured by the DC current measuring device, an audio speaker that sounds upon the DC current measuring device measuring a threshold DC current value, a graphical display that visually depicts a level of the DC leakage current measured by the DC current measuring device, and a hand-held casing to which the DC current measuring device, the DC voltage selection switch, the digital and graphical display, and the audio speaker are attached or encased.

A process of the teachings of the present invention is defined in claim <NUM>. The process is providing an energized DC electrical line above an Earthen surface (i.e. a surface of the Earth), electrically connecting or electrically bonding a substantially electrically insulating structure against the energized DC electrical line and the Earthen surface (or surface with Earth potential), providing a DC current meter, in series between the insulating member and the Earthen surface, a DC current meter, and measuring a DC momentary leakage current flowing through the insulating member with the DC current meter. DC momentary leakage current is considered to be direct current that flows through, despite how relatively minuscule or not miuscule, a substantially electrically insulating structure (e.g. an FRP or fiber reinforced plastic or other material largely considered to be insulating). Measuring a DC momentary leakage current that passes through the insulating member with the DC current meter, may further entail measuring every <NUM>/<NUM>th or <NUM>/<NUM>th of a second with the DC current meter, the DC momentary leakage current flowing through the insulating member or substantially electrically insulating structure. The process further includes storing in a digital memory, a plurality of momentary leakage current values measured by the DC current meter; and comparing the plurality of momentary leakage current values measured by the DC current meter to a predetermined threshold current value indicative of a DC flashover current value for the substantially electrically insulating structure. Depending upon the comparison of the values, the process may also entail sounding an audible alarm when any of the plurality of momentary leakage current values measured by the DC current meter is larger than the predetermined threshold current value and activating a visible alarm when any of the momentary leakage current values measured by the DC current meter is larger than the predetermined threshold current value. Still yet, the process may include calculating a moving average for the plurality of momentary leakage current values, comparing the moving average to a predetermined threshold current value indicative of a DC current flashover current value for the substantially electrically insulating structure, and sounding an audible alarm when the moving average of the plurality of momentary leakage current values measured by the DC current meter is larger than the predetermined threshold current value.

In another example, a process may include providing an energized DC electrical line above a surface of the Earth, locating a first end of a substantially electrically insulating structure proximate (e.g. near enough to experience circulating current or induction current, or electrically attached with an electrically conductive jumper cable) the energized DC electrical line, locating a second end of a substantially electrically insulating structure proximate an Earthen surface, providing, in series between the insulating member and the Earthen surface, a DC current meter, and measuring a plurality of momentary leakage current values flowing through the substantially electrically insulating structure using the DC current meter. The process may further include measuring every <NUM>/<NUM>th of a second (or other time interval), a DC momentary leakage current flowing through the substantially electrically insulating structure using the DC current meter, calculating a moving average for the plurality of momentary leakage current values, storing in a digital memory, the plurality of momentary leakage current values measured by the DC current meter, and comparing the plurality of momentary leakage current values measured by the DC current meter to a predetermined threshold current value indicative of a DC current flashover current value for the substantially electrically insulating structure, and sounding an audible alarm when any of the plurality of momentary leakage current values measured by the DC current meter is larger than the predetermined threshold current value. The process may also include activating a visible alarm when any of the plurality of momentary leakage current values flowing through the substantially electrically insulating structure measured by the DC current meter is larger than the predetermined threshold current value. The process may further include locating a first end of a substantially electrically insulating structure proximate the energized DC electrical line, electrically connecting a first end of a substantially electrically insulating structure to the energized DC electrical line and the Earthen surface. Locating a second end of a substantially electrically insulating structure proximate an Earthen surface, may further include locating a second end of a substantially electrically insulating structure proximate on a surface that has Ground potential. The process may further include calculating a moving average for the plurality of momentary leakage current values; storing in a digital memory, the plurality of momentary leakage current values measured by the DC current meter, and comparing the plurality of momentary leakage current values measured by the DC current meter to a predetermined threshold current value indicative of a DC current flashover current value for the substantially electrically insulating structure.

Calculating a moving average for the plurality of momentary leakage current values may further include calculating a moving average using a predetermined number of momentary leakage current values measured in succession by the DC current meter by excluding the first momentary leakage current value of a series of momentary leakage current values and including the next momentary leakage current value following an immediately prior subset of momentary leakage current values used to calculate an average. The process may further include sounding an audible alarm when any of the plurality of momentary leakage current values measured by the DC current meter is larger than the predetermined threshold current value. The process may further include predicting electrical flashover of the substantially electrically insulating structure from one of the momentary leakage current values that is measured by the DC current meter by comparing the DC momentary leakage current value to a predetermined threshold value indicative of a DC current flashover value of the substantially electrically insulating structure. The process may include displaying on a DC numerical display of the DC current meter, the DC momentary leakage current, sounding an audio alarm upon the DC current measuring device measuring a threshold value of the DC momentary leakage current, displaying on a graphical display, the threshold value for the substantially electrically insulating structure, and displaying on the graphical display, the DC momentary leakage current measured by the DC current meter. The substantially electrically insulating structure may be a hydraulic line, a boom, or any such structure that is made from a fiber reinforced plastic material or other insulating material.

In another example, a process may include measuring direct current (DC) through a material by providing a DC meter capable of measuring amperage at voltages of an electrically energized DC power line, providing an electrically energized DC power line to supply DC through a substantially dielectric material, measuring the DC passing through the substantially dielectric material to determine an instantaneous DC amperage value, comparing the instantaneous DC amperage value to a known DC amperage flashover value for the substantially dielectric material, and activating an alarm when the instantaneous DC amperage value is equal to or greater than the known DC amperage flashover value for the substantially dielectric material. Measuring the DC passing through the substantially dielectric material to determine an instantaneous DC amperage value, may include repeatedly measuring the DC passing through the substantially dielectric material to create a plurality of instantaneous DC amperage values, and calculating a moving average using the plurality of instantaneous DC amperage values. Activating an alarm when the instantaneous DC amperage value is equal to or greater than the known DC amperage flashover value for the substantially dielectric material may further include providing a DC portable meter, and displaying the instantaneous DC amperage value on a visible display of the DC portable meter. The electrically energized DC power line may be between 38kV and 600kV, inclusive.

Turning now to the detailed description of the preferred arrangement or arrangements of the present invention, it should be understood that the inventive features and concepts may be manifested in other arrangements and that the scope of the invention is not limited to the embodiments or examples described or illustrated. The scope of the invention is intended only to be set forth by the scope of the claims that follow. Each embodiment or example is provided by way of explanation of the invention, one of many embodiments of the invention, and the following examples should not be read to limit, or define, the scope of the invention.

<FIG> is a schematic view of components of a DC current meter <NUM> in accordance with teachings of the present invention. DC current meter <NUM> may include an electrically conductive collector <NUM>, an analog front-end <NUM>, which is a current receiver that receives or collects current from electrically conductive collector <NUM> to be measured and used as an input <NUM> for an analog-to-digital converter <NUM>, also known in abbreviated form as "ADC", whose digital output signal <NUM> is used as an input for a micro-controller <NUM>, which is also a computer. With reference including <FIG>, multiple sources of electrical current to be used as input into the analog front end <NUM> of ADC <NUM> may be electrical current from a boom <NUM>, electrical current from one or more of a type of hydraulic line <NUM>, and electrical current from a leveling rod or one or more of a fiber optic cable <NUM>, or both a leveling rod or one or more of a fiber optic cable <NUM>. For example, electrical lines 20a, 20b may carry electrical current from boom <NUM> such that electrical line 20a may carry current from an interior surface or inside diameter surface of boom <NUM>, and electrical line 20b may carry current from an exterior surface or outside diameter surface of boom <NUM>, as depicted, to electrically conductive collector <NUM>. Electrical lines 22a, 22b may each carry electrical current from a single hydraulic line <NUM> or one or more hydraulic lines <NUM> to electrically conductive collector <NUM>. Electrical lines 24a, 24b, may each carry electrical current from fiber optic cable <NUM> to electrically conductive collector <NUM>. In place of, or in additional to fiber optic cable <NUM>, a leveling rod may conduct and carry electricity to electrically conductive collector <NUM>. Although electric lines, fiber optic cables, hydraulic lines, and one or more leveling rods are used as specific examples of structures for which current passing through such structure may be measured, the teachings of the present disclosure may be employed to measure or monitor electrical current for any structure, which may be an insulating structure, if desired.

With reference again to <FIG>, after electrical current from each of boom <NUM>, hydraulic line <NUM>, and fiber optic cable <NUM> passes onto or into electrically conductive collector <NUM>, such electrical current may then pass into analog front end <NUM>. For example, electrical current from boom <NUM> passes through electrical lines 20a, 20b and through a fuse <NUM>, which is an electrical protective device to protect all electrical downstream components from a power surge, before entering analog front-end <NUM>. Electrical current from one or more hydraulic lines <NUM> may pass through electrical lines 22a, 22b, and through a fuse <NUM>, which is an electrical protective device to protect all electrical downstream components from a power surge, before entering analog front-end <NUM>. Electrical current from one or more fiber optic cables <NUM> may pass through electrical lines 24a, 24b, and through a fuse <NUM>, which is an electrical protective device to protect all electrical downstream components from a power surge, before entering analog front-end <NUM>. Instead of a fuse <NUM>, <NUM>, <NUM> which may be a one-time-use type of device when employed for its purpose, a different device with the same current interrupting or stopping purpose may be substituted, such as a circuit breaker, which may be resettable.

Analog front end <NUM> measures the amperage flowing from electrical input collector <NUM> which is a measurement also referred to as "leakage current" because current is flowing through devices such as boom <NUM>, hydraulic line <NUM>, and fiber optic cable <NUM>, which are designed and known to be insulating devices to the extent their materials permit them to be insulating or insulative given the voltage to which boom <NUM>, hydraulic line <NUM>, and fiber optic cable <NUM> that are directly or ultimately connected. Thus, any current that passes through such otherwise insulating devices is known as "leakage current" rather than simply current. Measuring of such leakage current is performed in analog front end <NUM>, which also performs an electrical continuity test on each of any connected boom <NUM>, hydraulic line <NUM>, and fiber optic cable <NUM>. Measuring current or leakage current, such as DC current, through other devices is possible by using the teachings of the present invention.

Analog front end <NUM> is an electrical circuit and may employ high precision shunt resistors for each channel creating a path to ground. Alternatively, a Hall effect sensor can be used instead of one or more shunt resistors. A Hall effect sensor may be arranged in any necessary position relative to the device from which to measure magnetic current. As an example, the Hall effect sensor may be arranged parallel to, or otherwise proximate to, a capacitor or other electric circuit component, with a lead to ground. The Hall effect sensor may be used to detect a magnetic field that translates to a current, such as direct current. The shunt resistors are monitored by high bandwidth and high gain amplifiers for potential difference (i.e. voltage) across them, induced by current (also known as leakage current) flowing to ground. Its resistor and amplifier design will allow for bi-directional leakage current detection for a scale of +/- <NUM> to <NUM> microamperes or single-ended +/- <NUM> to <NUM> microamperes range. The output of an amplifier may be amplified again (e.g. once more) before being input into analog to digital converter <NUM> as input <NUM>. The amplifier output, which is input <NUM>, will go to analog to digital converter <NUM> employing a precision high-speed ADC chip. Alternatively input <NUM> may be directed directly to microcontroller <NUM> and thereby bypass a separate ADC <NUM> if microcontroller <NUM> is equipped with its own built-in ADC, which may depend upon specific application requirements. The specific application requirements that may dictate whether a separate ADC is used, or input signal <NUM> goes directly in microcontroller <NUM> may be the bandwidth of the input signal, and the accuracy and precision of the detected current. The operation or functionality is such that leakage current passing through the internal shunt resistors from the test insulation connections of the boom equipment, will create a potential difference across the resistor with reference to ground. Any analog-to-digital converter, whether it is a separate ADC outside of microcontroller <NUM> or within microcontroller <NUM>, converts the analog voltage level to a digital representation, which can then be processed by microcontroller <NUM> to perform various outputs such as an audible trigger alarm(s) from speaker <NUM>, a readable display on an LCD display <NUM>, a graphical display such as a momentary leakage current graphical display <NUM>, and then store or log all output or results to memory <NUM>, which may be an external memory device as a separate component from microcontroller <NUM>.

With continued reference to <FIG>, other components of the teachings of the present invention will be explained. <FIG> depicts one or more function buttons <NUM>. Function buttons may be input controls to control functions of the microcontroller in accordance with the present invention. For instance, one function may be an on and off switch to supply or electricity or power to, and prevent power or electricity from flowing to microcontroller <NUM>. Another function button <NUM> may be a continuity test button, also known as a self-test button. Such a test when initiated by pressing such a button, permits the microcontroller to cause electricity to test the continuity of each of the electrical wires 20a, 20b, 22a, 22b, 24a, 24b to ensure that no electrical open circuits or breaks in continuity in any of the leakage current electrical wires 20a, 20b, 22a, 22b, 24a, 24b exists. Other functions to invoke with a function button <NUM> are possible. A voltage class selector <NUM> may function to permit a user to manually select a voltage class, range or upper limit at which a voltage meter, such as DC voltage meter <NUM>, may properly function. Alternatively, voltage class selection may be performed automatically, and internally within DC voltage meter <NUM> upon DC voltage meter <NUM> sensing or measuring voltage. Thus, no manual voltage selection need be performed with a switch such as voltage class selector <NUM>. Examples of voltage classes are: from <NUM>-<NUM> kV, <NUM>-<NUM> kV, and <NUM>-600kV. Other DC voltage classes are possible. This, in accordance with the present teachings, voltage class selector <NUM> could have three distinct positions, or more. A ground wire <NUM> that creates an electrical path to Earth permits functions, such as test functions and current monitoring within microcontroller <NUM>, and functioning of current meter <NUM> itself, to properly work.

<FIG> is an external view of DC current meter <NUM> with most of the operative components enclosed within a casing <NUM>. By enclosing the components of DC current meter <NUM> within casing <NUM>, the portability of the teachings of the present invention are enhanced. <FIG> is one example of how an instantaneous reading or readout, such as an LCD display <NUM>, an audio speaker <NUM>, a voltage class selector switch <NUM> and an accumulated momentary leakage current graphical display <NUM>, may be arranged or positioned within and around a surface of casing <NUM>.

<FIG> depicts DC current meter <NUM> in an in-use position with an aerial lift device <NUM> equipped with a bucket <NUM> for human occupants. The aerial lift device <NUM> may be mounted to a truck, vehicle, or trailer chassis <NUM>, or similar platform, the chassis <NUM> may or may not have wheels. When DC current meter <NUM> is in use, a boom <NUM>, which may be a fixed length, or extendable in a telescoping fashion, may be extended such that bucket <NUM> resides beside an energized (i.e. live) high voltage direct current power line <NUM> so that human occupants within bucket <NUM> can perform maintenance on, or further construct, high voltage direct current power line <NUM>. When current meter <NUM> is in use, bucket <NUM>, which may be constructed with metallic components, is placed at the same potential (i.e. voltage) as DC power line <NUM>. Similarly, a human occupant within bucket <NUM> is also placed at the same potential as DC power line <NUM>. In order place bucket <NUM> and any human occupant within the bucket <NUM> at the same potential as DC power line <NUM>, a bonding clamp <NUM> is used. Bonding clamp <NUM> provides an electrical link to bucket <NUM> and human occupants to achieve a common potential for the DC power line <NUM>, bonding clamp <NUM> and bucket <NUM>. Bucket <NUM> is pivotably attached to telescoping boom <NUM> to permit relative motion between bucket <NUM> and telescoping boom <NUM>. Telescoping boom <NUM> is an electrically insulating member made from fiberglass, or fiberglass and other non-conductive materials, which may include plastics and other materials.

Continuing with <FIG>, mounted to telescoping boom <NUM> proximate to bucket <NUM> is a corona ring <NUM>. Corona ring <NUM> may be mounted within three meters or within three yards of the junction of boom <NUM> and bucket <NUM>, or where most electrically advantageous. At an opposite end of boom <NUM>, proximate a truck chassis <NUM>, other mounting platform or lowest pivot point of boom <NUM>, an outer collector band <NUM> and an inner collector band <NUM> may be mounted to and against, an exterior and an interior, respectively of boom <NUM>. Boom <NUM> may be hollow and used as a conduit or passageway for components depicted on <FIG>, such as one or more hydraulic lines <NUM>, electric lines 22a, 22b, and one or more fiber optic cables <NUM>, and electric lines 24a, 24b. As also depicted in <FIG>, electric lines 20a, 20b are attached to boom <NUM>, and at least electric line 20a may traverse boom interior <NUM>, while electric line 20b may traverse or run along some length of an exterior surface or interior surface of boom <NUM>. At a base of boom <NUM>, an electrical collection point exists for all structures being monitored for current flow, which may be an input for meter <NUM>. Each of hydraulic lines <NUM>, fiber optic cables <NUM>, and boom <NUM> are made of a dielectric material and have electrical insulating qualities; however, even dielectric and insulating materials will permit some relative quantity of current to pass, and the teachings of the present invention including voltage meter <NUM>, are designed to detect that level of current and alert a user of the invention.

<FIG> is a graph of current measurements versus time <NUM> in an example measuring scenario using current meter <NUM> in accordance with teachings of the present invention. The zones within the graph of <FIG> will be explained later during a presentation of operation of the teachings of the present invention.

<FIG>, not falling within the subject-matter for which protection is sought, depicts an insulating ladder <NUM> arranged in contact with an energized electrical conductor <NUM> at contact points <NUM>, <NUM>, and a current meter <NUM> electrically connected to insulating ladder <NUM>. At the opposite end of insulating ladder <NUM>, a first electrically conductive clamping ring <NUM> surrounds and contacts a first ladder leg <NUM>, and a second electrically conductive clamping ring <NUM> surrounds and contacts a second ladder leg <NUM>. A clamp ring jumper wire <NUM> electrically connects to each of first electrically conductive clamping ring <NUM> and second electrically conductive clamping ring <NUM>. Although either electrically conductive clamping ring <NUM>, <NUM> may be used, <FIG> depicts a meter lead in wire <NUM> conduct electricity from each of first electrically conductive clamping ring <NUM> and second electrically conductive clamping ring <NUM> and to current meter <NUM>. Current meter <NUM> is the same current meter <NUM> depicted in <FIG> and <FIG>, although in the arrangement depicted in <FIG>, meter lead in wire <NUM> is a single conductive wire. The arrangement of <FIG> permits current meter <NUM> to detect leakage current passing from DC power line through the insulating ladder and to ground <NUM>.

In <FIG>, not falling within the subject-matter for which protection is sought, an insulating scaffolding <NUM> is arranged in physical and electrical contact with an energized DC conductor <NUM>, such as with electrical jumper <NUM>. When a human worker is resident upon horizontal platform <NUM>, DC current meter <NUM> may be electrically connected to insulating scaffolding <NUM> to monitor the leakage current through insulating scaffolding <NUM>. More specifically, in a given horizontal plane at some distance from either an Earthen surface <NUM> upon which insulating scaffolding <NUM> may reside, or at some distance from energized DC conductor <NUM>, each of vertical posts <NUM> passing through such horizontal plane are electrically connected with an electrically conductive wire <NUM> or multiple pieces of electrically conductive wire <NUM>. Electrically conductive wire <NUM> may be secured against each vertical post <NUM> by an electrically conductive clamp ring <NUM> to permit a continuous electrical loop of electrically conductive wire <NUM>, which securely holds electrically conductive clamp ring <NUM> and electrically conductive wire <NUM>. Thus, a continuous loop from vertical pole to vertical pole around insulating scaffolding <NUM> is created. From one of electrically conductive wire <NUM>, meter lead in wire is connected to create an electrically conductive link from electrically conductive wire <NUM> to current meter <NUM>. The arrangement of <FIG> will measure DC current passage through the insulating scaffolding and into ground via ground wire <NUM>.

<FIG> depicts a first insulating hot stick <NUM> and a second insulting hot stick <NUM> used during a replacement of an insulator <NUM> on a DC power line <NUM>, and placement of current meter <NUM> during use of such replacement, in accordance with teachings of the present invention. A hot stick is a name used by professionals engaged in the trade of maintaining, constructing and reconstructing energized, or live, DC power lines, for specific types of insulated poles, which are also tools, and usually made of fiberglass, or fiberglass and other insulating material(s). The insulating materials prevent, for practical purposes, electrical current from traveling from DC power line <NUM> to ground <NUM>.

Continuing with <FIG>, use of current meter <NUM> during a typical scenario involving replacement of an aged or otherwise compromised insulator <NUM> may involve a conductor supporting structure <NUM>, such as part of a lattice tower or any powerline supporting structure that is grounded and thus at the potential of ground <NUM> (i.e. in the industry known as ground potential). As part of conductor supporting structure <NUM>, <FIG> depicts an approximately horizontal, or horizontal beam <NUM>, with, relative to horizontal beam <NUM>, an angled beam <NUM>. Horizontal beam <NUM> and angled beam are joined by connective structures <NUM> to increase strength. With first insulating hot stick <NUM> and second insulting hot stick <NUM> attached to conductor supporting structure <NUM>, such as to horizontal beam <NUM>, first insulating hot stick <NUM> and second insulting hot stick <NUM> hang to the same or approximately the same length as insulator <NUM>. First insulating hot stick <NUM> and second insulting hot stick <NUM> may be separated at a specified distance by a limiting bracket <NUM>. Each of first insulating hot stick <NUM> and a second insulting hot stick <NUM> is affixed to energized DC power line <NUM> by clamping or some suitable device, and similarly each of first insulating hot stick <NUM> and a second insulting hot stick <NUM> is affixed to horizontal beam <NUM> by clamping or some suitable device. Limiting bracket <NUM> may be located proximate energized DC power line <NUM>. When first insulating hot stick <NUM> and second insulting hot stick <NUM> are in place as depicted in <FIG>, insulator <NUM> may be removed and instead of insulator <NUM>, before removal, bearing the tensile load due to gravity of energized DC power line <NUM>, each of first insulating hot stick <NUM> and second insulting hot stick <NUM> bears half the tensile load of energized DC power line <NUM>.

In accordance with the present invention, <FIG> also depicts current meter <NUM> affixed in some fashion to conductor supporting structure <NUM>. Additionally, an electrically conductive jumper <NUM> located between first insulating hot stick <NUM> and second insulting hot stick <NUM>, creates an electrical path between the two sticks <NUM>, <NUM>. Electrically conductive jumper <NUM> is securely fastened to each of first insulating hot stick <NUM> and second insulting hot stick <NUM> by an electrically conductive clamp <NUM> that is consistent to each junction. From one of electrically conductive clamp <NUM> to current meter <NUM>, a meter electrical lead wire <NUM> permits leakage current to flow to current meter <NUM>. A conductive ground lead <NUM>, clamped to conductor supporting structure <NUM> with clamp <NUM>, completes an electrical current path via conductor supporting structure <NUM> to Earth ground <NUM>.

<FIG> is a perspective view of how hydraulic lines <NUM> and fiber optic cables <NUM> may reside within boom <NUM>. Additionally, <FIG> shows how electric lines 22a, 22b, 24a, 24b may conduct current which is directed to meter <NUM> as part of the monitoring of any leakage current in accordance with teachings of the present invention. Collector block <NUM> is electrically conductive and may be the transition point at which hydraulic lines <NUM> transition from their needing to be insulating part to not needing to be an electrically insulating part. Collector block <NUM> is electrically conductive and may be the transition point at which fiber optic lines <NUM> transition from their needing to be an electrically insulating part to not needing to be a an electrically insulating part. <FIG> also depicts fiber optic cables <NUM>, which may be gathered with an electrically conductive clamp <NUM> from which electric lines 24a, 24b transmit current to meter <NUM>. Electrically conductive clamp <NUM> has dual electric lines 24a, 24b running from it for the same reason that hydraulic collector block <NUM> has dual electric lines 22a, 22b running from it, which is to easily permit an electrical continuity test from meter <NUM> (e.g. as another <FIG> function button <NUM>) to ensure there are no breaks or interruptions in the electrical continuity of such an electrical circuit.

During one example operation of the present invention, and with initial reference to <FIG>, when bucket <NUM> of aerial lift device <NUM> is electrically bonded to energized DC power line <NUM>, with bonding clamp <NUM>, also a conductive lead, contacting each of energized DC power line <NUM> and bucket <NUM>, bucket <NUM> and any human occupants will reach the same potential or voltage as energized DC power line <NUM>. With such an energized arrangement, DC current passing through boom <NUM>, DC current passing through hydraulic lines <NUM>, and DC current passing through fiber optic cables <NUM>, which individually and collectively are referred to as "leakage current" must be monitored as it moves through these structures to ground <NUM>. Current meter <NUM> will monitor this DC leakage current, as depicted in <FIG>, which is an example graph of DC current in microamps versus microseconds, shows leakage current measurements within a specific DC voltage class. DC current measurements may be taken or measured at almost any frequency, such as from <NUM> measurements per second to <NUM> or more measurements per second, and as previously stated, within a particular DC voltage class for a particular energized DC power line <NUM>. All current measurements may be performed by microcontroller <NUM>, or an average current calculated after a predetermined number of measurements, such as after <NUM> or <NUM>, or some other quantity, and then stored in a memory such as external memory <NUM>. An average of some quantity of the current measurements may be displayed on graphical display <NUM>, which may be a color display, and on an LCD display <NUM>, which may be a numerical display. Because over time, electrical charge may build on insulating components such as boom <NUM>, hydraulic lines <NUM> and fiber optic cables <NUM>, and as a result, an average current value for the total of current measurements, or some predetermined quantity of current measurement values, may increase from a first or safe current zone <NUM> to current zone <NUM>, which may be a caution zone. In caution zone <NUM>, some current measurement values, such as current measurement value <NUM> are greater than others, such as current measurement value <NUM>. Zone <NUM> of <FIG> depicts a zone of highest current measurement values, which are also know as current spikes and may indicate an instance of, or impending, flash-over. A flashover is an event in which the DC leakage current exceeds the highest permissible value for a particular voltage class.

With continued reference to <FIG>, zone <NUM> represents an impermissible zone within which if DC leakage current reaches for a particular voltage class or range, some intervention or preventive steps need to be taken to stop or reduce the amount of leakage current passing to ground <NUM>. Within impermissible zone <NUM>, microamp levels for current measurements <NUM>, <NUM> and <NUM> represent the highest levels of leakage current.

A graph such as the graph depicted with <FIG>, could be plotted for many different pieces of insulating equipment for which leakage current needs to be monitored. For example, as depicted in <FIG>, the leakage current passing through insulating ladder <NUM> could be monitored and plotted for a selected voltage class of an energized DC power line <NUM> if insulating ladder <NUM> is in contact with energized DC power line <NUM>. Similarly, as depicted in <FIG>, the leakage current passing through insulating scaffolding could be monitored and plotted for a selected voltage class of an energized DC power line <NUM> with which insulating scaffolding <NUM> is in contact.

Alternatively, an array of information could be compiled and stored, such as in a database in memory <NUM> of meter <NUM>. An array of information may include columns of information including, but not limited to, time (e.g. seconds ), amperage reading (e.g. micro amps) at a time interval (e.g. every <NUM>/<NUM> of a second, every <NUM>/<NUM>th of a second, every <NUM>/<NUM>th of a second), and average amperage value for a predetermined number of amperage readings (e.g. every <NUM> reading, every <NUM> readings), or over a predetermined time period (e.g. every second, every ten seconds). As an example, an average amperage value for a predetermined number of amperage readings, or an average amperage value over a predetermined time period may be displayed on LCD display <NUM> or other display, such as display <NUM>, on meter <NUM> for visual inspection by viewer or user of meter <NUM>. Still yet, instead of displaying a numerical value on a display, a graphical representation may simultaneously be displayed or instead be displayed. A graphical representation may be a continuously changing bar graph that graphically displays an average amperage value for a predetermined number of amperage readings, or an average amperage value over a predetermined time period.

Before presenting details of a process or routine that meter <NUM>, and more specifically microcontroller <NUM> within meter <NUM>, may employ in accordance with the present teachings, further details on measurement by meter <NUM> of direct current will be presented. When a fully insulating body is exposed to a voltage source (e.g. either AC or DC) no current will pass through it regardless of the voltage or potential difference experienced by the insulating body. However, in reality a fully insulating body or "perfect insulator" does not exist, and all insulators to some degree respond or perform as resistors and therefore are subject to Ohms law for current passing through the insulting body. This is known as resistive current. Thus, in the present teachings, resistive current is passing through the insulating body, such as insulating boom <NUM>, insulating ladder <NUM>, hot sticks <NUM>, <NUM>, etc. to which meter <NUM> is connected. In addition to resistive current passing through such insulating bodies, another type of current passes through the insulating bodies. This current is known as capacitive current.

A capacitor in its simplest form is essentially two conductive objects separated by an electrically insulating medium. When DC voltage is applied to one of the conductive objects no current will flow from one object to the other, if the insulating medium is perfectly insulating. Regarding AC voltage (time varying voltage), when voltage is applied to the same capacitor, a displacement current passes through the non-perfectly insulating medium. This "capacitive" effect actually occurs when DC voltage is applied as well and is known as a transient voltage and is a result of the lack of a perfect insulator between the conductive objects and the presence of charge carriers in same. Current, known as momentary current, will flow for a short period of time and then stop as the electrical charge between the energized source and the insulating medium reach parity. However this electrical charge is released when this current flows to ground and the cycle repeats. Comparing the preceding explanation to teachings of the present disclosure, a boom <NUM> of a bucket truck, or other live line tool such as an insulating ladder <NUM> is an electrically insulating medium. Conductive objects may be DC power line <NUM> and ground <NUM>, such as Earth.

With reference to <FIG>, when bucket <NUM> is electrically bonded (i.e. at the same electrical potential) to DC power line <NUM>, boom <NUM>, because it is physically connected to bucket <NUM>, will still experience a very small current flow to ground <NUM>. The current flow is the sum of the capacitive and resistive currents explained above. The sum of these two types of current is greater with insulating devices, such as boom <NUM>, used in conjunction with AC voltage/ AC current power lines than with DC voltage/DC current power lines. Moreover, measuring DC current, such as with meter <NUM>, is different than measuring AC current, especially when DC voltages range from <NUM> kV to 500KV, which may be measured with teachings of the present disclosure. As discovered during testing in conjunction with the present teachings, in direct current situations as the electrical resistance of some insulating materials of insulators begins to degrade or lose their insulating properties, either from contamination or when the voltage applied across an insulator increases relative to the resistance of the insulator, the resistive current will remain relatively unchanged. However, during this time of relatively consistent resistive current, "pulses" or "momentary current spikes" or "short duration spikes," which are increases of capacitive current, which may be many orders of magnitude greater than the relatively stable resistive current, will begin to move through the insulator with increasing intensity and frequency as the resistive threshold (i.e. breakdown) of the insulator is approached. Theses "pulses" of current may last for only a few milliseconds as they discharge to ground and therefore must be measured in small time intervals by equipment sensitive enough to detect and monitor any pulses. Traditional analog meters or any presently known current measuring devices that display measured current are insufficient at least because an analog needle will not react quickly enough to notify one of impending dielectric breakdown, and a digital LCD display will not register the measured current value and display it for a long enough period of time to be of benefit to a user. Regardless, voltages in the DC voltage range from <NUM> kV to 500KV are extraordinarily high for known meters and proper notification of a dielectric failure.

Thus, teachings of the present disclosure may employ an analog to digital converter <NUM> or other device within meter <NUM> that is capable of detecting short-lasting current changes for a predetermined number of times in a minute, detecting what that current is, detecting how long each current change or increase lasts, recording them, and displaying such information so that a user can understand what stresses or potential dielectric breakdown a particular insulator is experiencing. The time scale or number of times that a current measurement may be measured may be in the range of 100ths of a second (milliseconds) to 1000ths of a second (microseconds). Durations of an electrical pulse may be in the range from approximately <NUM>/10th of a second to approximately <NUM>/60th of a second. Each current measurement may be in 100ths of an amp (milliamps) to 1000ths of an amp (micro amps), or larger or smaller. In accordance with the present teachings, each current measurement is displayed graphically to allow a user, such as an electrical worker or lineman, to interpret a current measurement, but such measurements are also recorded by the method or process of software within meter <NUM> by a memory <NUM>, such as a hard drive or similar data memory device. The measurements of current and their duration may be stored in memory <NUM> of the meter <NUM> as a series of integers (or values) over a given time period. As measurements of current are recorded by an analog current sensor within ADC <NUM> and digitally converted, a process or method of software analyzes the current value or reading of the electrical pulses and tracks both, the frequency and intensity. The frequency may be the number of current spikes for a given period of time, and the intensity may be the amplitude or current value. These values are logged (e.g. stored) by the software. The time scale of the frequency of the pulses is not displayed to the worker but is tracked by the software. The worker is only shown the amplitude (the electrical current value) of the pulses. For a voltage of a DC power line <NUM> applied to a given insulator (e.g. boom <NUM> of bucket truck , ladder <NUM>, or other live line tool) a known, safe threshold value has been determined through experimentation.

Continuing with <FIG>, various zones are evident on graphical display <NUM> to display current values. For example, a safe (e.g. green) level of current is graphically displayed by a series of green bars on the meter with a given value. Such a green zone is predetermined by the DC voltage class (e.g. a DC voltage range) of DC power line <NUM>. Thus, safe zones of measured current by meter <NUM> will vary based upon the DC voltage range or precise DC voltage of a power line to which meter <NUM> is connected for measuring current values "leaking" through insulating tools. Thus, any current values or pulses below a predetermined value are shown graphically with green bars on a lighted vertical intensity graph. This could also be displayed through colored lights, a physical graph, or any other graphical display of intensity. Yellow zone (i.e. caution) or red zone (i.e. danger and stop working on DC power line <NUM>) current threshold values are also displayed, but these may be accompanied by an audible or visual warning signal of some type to alert the operator to the presence of increasing intensity of these current pulses. Yellow zone current pulses are of value because changes in the physical positioning of the bucket, insulating properties or momentary voltage increases on DC power line <NUM> may cause transient current spikes to be measured by meter <NUM>. These must be noted and a user or worker must be alerted to yellow zone current pulses but they do not necessarily constitute a dangerous situation. Red zone current pulses indicate that a safe current threshold of the insulation integrity has been exceeded or is imminent and any workers must remove themselves or the live line tool (e.g. boom <NUM>) from the energized source, such as DC power line <NUM>. Any red zone current pulses would be several orders of magnitude below the actual flashover threshold of the insulating live line tool (e.g. boom <NUM>) to provide additional warning time and an adequate safety factor. A flashover is a dielectric failure of a device such as an insulating live line tool (e.g. boom <NUM>) that can also be thought of as the creation of an instantaneous conductive path for discharge of current, or electrons, through the insulated device.

Because of the relatively large quantities of data the software will generate, in the form of current measurements or calculations, any "old" recoded and displayed current spikes may be constantly deleted from the memory in order to provide the user or worker with newer, more relevant data as to the present or instantaneous insulating properties or condition of an insulating live line tool (e.g. boom <NUM>). As an example, a timescale of one minute may be used such that the software would count the current spikes for a given value of time, say <NUM> recorded current values per second, or <NUM>,<NUM> per minute. As the meter continues operation for however many minutes or hours the meter is employed for a given time of monitoring current, the oldest values of current measured or recorded may be deleted and the graphical display may be reset to show the corresponding lack of incidents, in the current time scale.

As an example, at time <NUM>, which may be a first measurement of a current through a boom <NUM> or other live line tool, a yellow zone current measurement was recorded and displayed on the graphical display. Subsequently, the next <NUM>,<NUM> instances of current measurements through the boom <NUM> or other live line tool, no other yellow zone current spikes are measured. As a result, the software may be written to delete the <NUM> measurements, and the measurement at time <NUM>, from memory <NUM>. Moreover, the corresponding graphical representation on graphical display <NUM> of this current spike may be removed. If results are being displayed on LCD display <NUM> in a continuous fashion, such display on LCD display <NUM> may be removed. With memory deleted, the process may begin again. Memory <NUM> may be used to plot graphs of current measurements over time for specific DC voltages and each of the variety of insulating devices with which meter <NUM> will be used. Alternatively, no memory may be utilized, and one or more of graphical display <NUM>, LCD display <NUM>, and an audible alarm for a yellow zone or red zone event may be utilized.

<FIG> depicts a flowchart <NUM> of an example routine controlled by software within microcontroller <NUM>, for example, to monitor current through an insulating body such as boom <NUM>, hot stick <NUM>, <NUM>, or ladder <NUM>, as examples, using meter <NUM> in accordance with the present teachings. What is being monitored by the routine of flowchart <NUM> is the flow of current, such as capacitive current. At step <NUM>, the routine may include providing a direct current (DC) power line to supply direct current to a dielectric material. At step <NUM>, the routine may include detecting a direct current amperage value passing through the dielectric material. At step <NUM>, the routine may include measuring the direct current amperage passing through the dielectric material to determine an instantaneous direct current amperage value. At step <NUM>, the routine may include comparing the instantaneous direct current amperage value to a known acceptable direct current amperage amplitude value. At step <NUM>, the routine may include sounding an audio alarm when the instantaneous direct current amperage value is greater than the known acceptable direct current amperage amplitude value. At step <NUM>, the routine may include repeating, for a predetermined number of times, measuring the direct current amperage passing through the dielectric material to determine ongoing instantaneous direct current amperage values. At step <NUM>, the routine may include averaging the ongoing instantaneous direct current amperage values to determine an average value of the instantaneous direct current amperage value for a predetermined period of time. At step <NUM>, the routine may include comparing the average value of the instantaneous direct current amperage values for a predetermined period of time, to a predetermined threshold value of the instantaneous direct current amperage values indicative of a direct current flashover value for the material. At step <NUM>, the routine may include displaying the instantaneous direct current amperage value for a predetermined period of time on a visible readout of a direct current portable meter. At step <NUM>, the routine may include selecting by hand, a DC voltage class using a DC voltage class switch on the direct current portable meter. Additional steps of the routine of flowchart <NUM> are envisioned, including intervening steps of those steps depicted in <FIG>.

The discussion of any reference is not an admission that it is prior art to the present invention, especially any reference that may have a publication date after the priority date of this application. At the same time, each and every claim below is hereby incorporated into this detailed description or specification as an additional embodiment(s) of the present invention.

Claim 1:
An apparatus comprising:
a first elongate substantially electrically insulating structure (<NUM>) arranged to contact, when the apparatus is in use, each of an electrically conductive supporting structure (<NUM>) and an energized DC transmission line (<NUM>), the electrically conductive supporting structure supporting the energized DC transmission line which is located between a surface of Earth and the electrically conductive supporting structure; the apparatus further comprising a DC current measuring device (<NUM>) electrically wired in series between the first elongate substantially electrically insulating structure and an electrical ground (<NUM>); and
a second elongate substantially electrically insulating structure (<NUM>) arranged to contact, when the apparatus is in use, each of the electrically conductive supporting structure and the energized DC transmission line,
wherein the first elongate substantially electrically insulating structure and the second elongate substantially electrically insulating structure are substantially parallel to each other and, when the apparatus is in use, are positionable on opposite sides of an insulator that is about to be replaced (<NUM>) and are in tension due to a weight of the energized DC transmission line, and wherein, during replacement of the insulator, the DC current measuring device is configured to measure a momentary DC leakage current of a momentary current spike from the energized DC transmission line passing through at least the first elongate substantially electrically insulating structure in millisecond time intervals, to store in a digital memory, a plurality of the momentary DC leakage currents measured by the DC current measuring device (<NUM>) and to deliver a warning if the momentary DC leakage current reaches a threshold DC current value, wherein the threshold DC current value is indicative of a DC current flashover current value for at least the first elongate substantially electrically insulating structure (<NUM>).