Portable protective air gap tool and method
AssigneePublic Service Electric and Gas Company
InventorsThomas A. Verdecchio, Raymond Ferraro, George Gela
Life of this patent
Estimating the term…
Abstract
A method for designing and validating a portable protective air gap (PPAG) device for use by workmen doing live-line maintenance on a electrical voltage transmission line network. The method sets out the procedure for optimizing the starting gap distance for a particular PPAG to be used for a given nominal system voltage. Validation testing then follows to achieve final, recommended values. PPAG devices employing axially aligned, hemispherically tipped, first and second electrodes for use on 115/138 kV, 230 kV and 345 kV voltage networks are designed using the methodology of the invention.
Claims36
A method for designing and validating, including testing, a portable protective air gap (PPAG) device including a first and second electrode, suitable for use at a worksite of a particular utility company, the worksite including at least two tower support structures, each at electrical ground potential, for supporting a multiphase, electrical voltage transmission line network used to transmit a known, power frequency system, multiphase voltage of known nominal system voltage, phase to phase, kVrms, ph-ph, the transmission line network including a respective electrical transmission line for at least each phase of the multiphase voltage, each of said transmission lines suspended from a respective segment of the tower support structures by insulating electrodes, the tower support structures having a unique shape based in part on the magnitude of the power frequency system voltage transmitted on the lines of the transmission line network, the PPAG device to be suitable in design to protect a worker positioned at the worksite on or about the tower support structures, and engaged in live-line maintenance, against the possibility of voltage sparkover across one or more of a plurality of air gaps between the worker and each respective electrical transmission line, the method comprising the steps of:
- (b) establishing a set of performance criteria to consider in the design and testing effort including one or more of at least the following,
- (j) the PPAG should not sparkover under nominal maximum, AC system voltage,
- (v) setting a withstand p.u. factor of the PPAG at a predetermined value,
- (vi) setting a breakdown p.u. factor of the PPAG at a predetermined value, and,
- (vii) deciding an expected location for the PPAG, i.e., in the tower support structure or not;
- (b) identifying a set of important parameters that affect the sparkover voltage for a specific air gap of the PPAG design, including,
- (i) the geometry of said first and second electrode,
- (ii) the shape of an applied voltage to be used during the testing phase of the PPAG design,
- (vii) the polarity of said applied voltage,
- (viii) the proximity of the air gap of the PPAG to other objects, including the tower support structure,
- (ix) atmospheric conditions, and,
- (x) the material of the first and second electrodes;
- (c) performing a series of determinations and calculations, including,
- (i) determining a nominal system kilovoltage rating, phase to phase, kVrms ph-ph, of the power frequency system,
- (ii) calculating a nominal maximum system voltage, phase to phase, kVrms ph-ph, by multiplying the value in step (c)(i) by a factor based on the known or anticipated variation in voltage from the nominal system voltage in step(c)(i),
- (iii) calculating a phase-ground, nominal maximum system voltage, kVrms, ph-g, (max), by dividing the result of step (c)(ii), by {square root}3,
- (iv) calculating a peak, phase-ground, nominal maximum system voltage, kVpeak, ph-gr, by multiplying the result of step (c)(iii), by {square root}2,
- (v) stating the withstand p.u. factor, as established by the utility,
- (vi) calculating a required withstand voltage by multiplying the result of step (c)
- (iv) by the p.u. factor stated in step(c)(v),
- (vii) stating an acceptable value of σ, where σ is the standard deviation,
- (viii) calculating a U50 value from the required withstand voltage value by dividing the result of step (c)(vi) by the factor (1−3×σ), where U50 is a peak voltage value where there is a 50% probability of sparkover,
- (ix) for later use, calculating a first breakdown voltage value, from the withstand voltage value by multiplying step (c)(viii) by the factor (1+3×σ),
- (x) for later use, stating the breakdown p.u. factor provided in the performance criteria,
- (xi) for later use, calculating a second breakdown voltage based on the breakdown p.u. factor, by multiplying the result of step (c)(viii) by step (c)(x),
- (xii) stating a first material factor for the material used to form the first and second electrode,
- (xiii) stating a second material factor based on the shape of the first and second electrode,
- (xiv) stating a location factor based on the expected location of the PPAG,
- (xv) calculating a first corrected value for U50 by multiplying step (c)(viii) by each of the above factors, i.e., steps (c)(xii) through (c)(xiv),
- (xvi) using FIG. 14, obtain a first D value for the gap distance between the first and second electrode from the test data for horizontal rod-rod gaps,
- (xvii) using FIG. 15 obtain a second D value for the gap distance between the first and second electrode from the test data for vertical rod-rod gaps,
- (xviii) determining an air saturation factor, a, from graphs available in, at least, IEEE Std 516-1995, “IEEE Guide for Maintenance Methods on Energized Power Lines”,
- (xix) using the formula, D=(C1×C2+a)×(p.u. as stated in step (c)(v))×Vrms,ph-g, to calculate a third D value for the gap distance between the first and second electrode, where C1 and C2 are as identified in, at least, IEEE Std 516-1995, “IEEE Guide for Maintenance Methods on Energized Power Lines”,
- (xx) stating a gap factor, k, to establish a further correction of the value for U50 determined in step (c)(xv), such that the difference in performance of rod-rod and rod-plane gaps is compensated for,
- (xxi) using the formula, U50/k=1080×ln(0.46×D+1), where U50 is the first corrected value for U50 from step (c)(xv), calculate a fourth value of D for the gap distance between the first and second electrode, and, (xxii) using the formula, U50/k=450×D+20, where U50 is the first corrected value for U50 from step (c)(xv), calculate a fifth value of D for the gap distance between the first and second electrode;
- (d) reviewing detailed construction drawings of the tower support structure supporting the line voltages in which the PPAG is to be deployed, such that, at least, the shortest phase-structure distances are determined;
- (e) building a prototype PPAG, PPAGproto, having an initial gap distance, Dinitial, for the gap distance between the first and second electrode, said initial gap distance selected based in part on a review of the range of D values determined in steps (c)(xvi) through (c)(xxii);
- (f) installing the PPAGproto built in step (e), on or off, depending on the choice made in step(a)(iv), a full-scale worksite mockup, the mockup including, at least, the tower support structure supporting at least one phase of the multiphase, electrical voltage transmission line network of known nominal system voltage, and including the shortest phase-structure distance determined in step (d);
- (g) powering said at least one phase of the multiphase, electrical voltage transmission line network of known nominal system voltage, with said known nominal system voltage;
- (h) testing the PPAGproto for its respective breakdown voltage by superimposing a switching impulse voltage source upon said at least one phase, said switching impulse voltage source capable of producing a plurality of peak impulse voltages of known, varying magnitude in combination with a plurality of differing front times of known varying magnitude, the plurality of peak impulse voltages, when added to the calculated peak, phase-ground, nominal maximum system voltage, kVpeak, ph-gr, determined in step(c)(iv), equaling a respective total peak voltage of respective peak magnitude, said respective total peak voltage spanning between values below and above said U50 value determined in step(c)(xv);
- (i) ascertaining the actual breakdown voltage of the PPAGproto under test in step (h);
- and,
- (j) adjusting the gap distance, Dinitial,, if required, and repeat steps (h) and (j), and again, if required, and so forth, until the adjusted gap distance results in an actual breakdown voltage that is acceptably close proximity to the U50 value in step (c)(xv).
A method for designing and validating, including testing, a portable protective air gap (PPAG) device including a first and second electrode, suitable for use at a worksite of a particular utility company, the worksite including at least two tower support structures, each at electrical ground potential, for supporting a multiphase, electrical voltage transmission line network used to transmit a known, power frequency system, multiphase voltage of known nominal system voltage, phase to phase, kVrms, ph-ph, the transmission line network including a respective electrical transmission line for at least each phase of the multiphase voltage, each of said transmission lines suspended from a respective segment of the tower support structures by insulating electrodes, the tower support structures having a unique shape based in part on the magnitude of the power frequency system voltage transmitted on the lines of the transmission line network, the PPAG device to be suitable in design to protect a worker positioned at the worksite on or about the tower support structures, and engaged in live-line maintenance, against the possibility of voltage sparkover across one or more of a plurality of air gaps between the worker and each respective electrical transmission line, the method comprising the steps of:
- (a) establishing a set of performance criteria to consider in the design and testing effort including one or more of at least the following,
- (i) the PPAG should not sparkover under nominal maximum, AC system voltage,
- (ii) setting a withstand p.u. factor of the PPAG at a predetermined value,
- (iii) setting a breakdown p.u. factor of the PPAG at a predetermined value, and,
- (iv) deciding that the PPAG is to be located in the tower support structure;
- (b) identifying a set of important parameters that affect the sparkover voltage for a specific air gap of the PPAG design, including,
- (i) the geometry of said first and second electrode,
- (ii) the shape of an applied voltage to be used during the testing phase of the PPAG design,
- (iii) the polarity of said applied voltage,
- (iv) the proximity of the air gap of the PPAG to other objects, including the tower support structure,
- (v) atmospheric conditions, and,
- (vi) the material of the first and second electrodes;
- (c) performing a series of determinations and calculations, including,
- (i) determining a nominal system kilovoltage rating, phase to phase, kVrms ph-ph, of the power frequency system,
- (ii) calculating a nominal maximum system voltage, phase to phase, kVrms ph-ph, by multiplying the value in step (c)(i) by a factor based on the known or anticipated variation in voltage from the nominal system voltage in step(c)(i),
- (iii) calculating a phase-ground, nominal maximum system voltage, kVrms, ph-g, (max), by dividing the result of step (c)(ii), by {square root}3,
- (iv) calculating a peak, phase-ground, nominal maximum system voltage, kVpeak, ph-gr, by multiplying the result of step (c)(iii), by {square root}2,
- (v) stating the withstand p.u. factor, as 1.3,
- (vi) calculating a required withstand voltage by multiplying the result of step(c)
- (iv) by the p.u. factor stated in step (c)(v),
- (vii) stating 5% (i.e.,0.05) as an acceptable value of σ, where σ is the standard deviation,
- (viii) calculating a U50 value from the required withstand voltage value by dividing the result of step (c)(vi) by the factor (1−3×σ)(i.e.,0.85), where U50 is a peak voltage value where there is a 50% probability of sparkover,
- (ix) for later use, calculating a first breakdown voltage value, from the withstand voltage value by multiplying step (c)(viii) by the factor (1+3×σ)(i.e., 1.15),
- (x) for later use, stating the breakdown p.u. factor provided in the performance criteria, as 1.7,
- (xi) for later use, calculating a second breakdown voltage based on the breakdown p.u. factor, by multiplying the result of step (c)(viii) by step (c)(x),
- (xii) calculating the ratio of step (c)(ix) to step (c)(xi),
- (xiii) stating a first material factor of 1.0 for the material used to form the first and second electrode, where said material is steel,
- (xiv) stating a second material factor of 1.0 based on the shape of the first and second electrode, where each of said first and second electrodes is a ½″ round rod with a hemispherical tip,
- (xv) stating a location factor of 1.1 for location of the PPAG in the tower,
- (xvi) calculating a first corrected value for U50 by multiplying step (c)(viii) by each of the above factors, i.e., steps (c)(xiii) through (c)(xv),
- (xvii) using FIG. 14, obtain a first D value for the gap distance between the first and second electrode from the test data for horizontal rod-rod gaps,
- (xviii) using FIG. 15 obtain a second D value for the gap distance between the first and second electrode from the test data for vertical rod-rod gaps,
- (xix) determining an air saturation factor, a, from graphs available in, at least, IEEE Std 516-1995, “IEEE Guide for Maintenance Methods on Energized Power Lines”,
- (xx) using the formula, D=(C1×C2+a)×(p.u. as stated in step (c)(v))×Vrms,ph-g, to calculate a third D value for the gap distance between the first and second electrode, where C1 and C2 are as identified in, at least, IEEE Std 516-1995, “IEEE Guide for Maintenance Methods on Energized Power Lines”,
- (xxi) stating a gap factor, k, to establish a further correction of the value for U50 determined in step (c)(xvi), such that the difference in performance of rod-rod and rod-plane gaps is compensated for,
- (xxii) using the formula, U50/k=1080×ln(0.46×D+1), where U50 is the first corrected value for U50 from step (c)(xvi), calculate a fourth value of D for the gap distance between the first and second electrode, and,
- (xxiii) using the formula, U50/k=450×D+20, where U50 is the first corrected value for U50 from step (c)(xvi), to calculate a fifth value of D for the gap distance between the first and second electrode;
- (d) reviewing detailed construction drawings of the tower support structure supporting the line voltages in which the PPAG is to be deployed, such that, at least, the shortest phase-structure distances are determined;
- (e) building a prototype PPAG, PPAGproto, having an initial gap distance, Dinitial, for the gap distance between the first and second electrode, said initial gap distance selected based in part on a review of the range of D values determined in steps (c)(xvii) through (c)(xxiii);
- (f) installing the PPAGproto built in step (e), on a full-scale worksite mockup, the mockup including, at least, the tower support structure supporting at least one phase of the multiphase, electrical voltage transmission line network of known nominal system voltage, and including the shortest phase-structure distance determined in step (d);
- (g) powering said at least one phase of the multiphase, electrical voltage transmission line network of known nominal system voltage, with said known nominal system voltage;
- (h) testing the PPAGproto for its respective breakdown voltage by superimposing a switching impulse voltage source upon said at least one phase, said switching impulse voltage source capable of producing a plurality of peak impulse voltages of known, varying magnitude in combination with a plurality of differing front times of known varying magnitude, the plurality of peak impulse voltages, when added to the calculated peak, phase-ground, nominal maximum system voltage, kVpeak, ph-gr, determined in step(c)(iv) , equaling a respective total peak voltage of respective peak magnitude, said respective total peak voltage spanning between values below and above said U50 value determined in step(c)(xvi);
- (i) ascertaining the actual breakdown voltage of the PPAGproto under test in step (h);
- and,
- (j) adjusting the gap distance, Dinitial,, if required, and repeat steps (h) and (i), and again, if required, and so forth, until the adjusted gap distance results in an actual breakdown voltage that is acceptably close proximity to the value in step (c)(xvi).
A universal portable protective air gap (PPAG) device including a first and second electrode, suitable for use at a worksite of a particular utility company, the worksite including at least two tower support structures, each at electrical ground potential, for supporting a multiphase, electrical voltage transmission line network used to transmit a known, power frequency system, multiphase voltage of known nominal system voltage, phase to phase, kVrms, ph-ph, the transmission line network including a respective electrical transmission line for at least each phase of the multiphase voltage, each of said transmission lines suspended from a respective segment of the tower support structures by insulating electrodes, the tower support structures having a unique shape based in part on the magnitude of the power frequency system voltage transmitted on the lines of the transmission line network, the PPAG device to be suitable in design to protect a worker positioned at the worksite on or about the tower support structures, and engaged in live-line maintenance, against the possibility of voltage sparkover across one or more of a plurality of air gaps between the worker and each respective electrical transmission line, the PPAG for actual use by placement at a worksite, in one of the tower support structures, wherein each of said first and second electrodes are round rods, each said electrode having a hemispherical tip, said first and second electrodes coaxially aligned with each other such that said respective hemispherical tips are axially distant from each other by a gap distance, Dactual, and disposed facing each other, said gap distance, Dactual, a function, at least, of the known, nominal system voltage for the particular, multiphase, electrical voltage network supported by the at least two tower support structures.
A portable protective air gap (PPAG) device including a first and second electrode, suitable for use at a worksite of a particular utility company, the worksite including at least two tower support structures, each at electrical ground potential, for supporting a multiphase, electrical voltage transmission line network used to transmit a known, power frequency system, multiphase voltage of known nominal system voltage, phase to phase, kVrms, ph-ph, the transmission line network including a respective electrical transmission line for at least each phase of the multiphase voltage, each of said transmission lines suspended from a respective segment of the tower support structures by insulating electrodes, the tower support structures having a unique shape based in part on the magnitude of the power frequency system voltage transmitted on the lines of the transmission line network, the PPAG device to be suitable in design to protect a worker positioned at the worksite on or about the tower support structures, and engaged in live-line maintenance, against the possibility of voltage sparkover across one or more of a plurality of air gaps between the worker and each respective electrical transmission line, the PPAG for actual use by placement at a worksite, in one of the tower support structures, wherein each of said first and second electrodes are round rods, each said electrode having a hemispherical tip, said first and second electrodes coaxially aligned with each other such that said respective hemispherical tips are axially distant from each other by a gap distance, Dactual, and disposed facing each other, said gap distance, Dactual, a function, at least, of the known, nominal system voltage for the particular, multiphase, electrical voltage network supported by the at least two tower support structures, wherein the known nominal system voltage is 115/138 kV, and, wherein said gap distance, Dactual, falls in the range between 9.5 inches and 12.5 inches.
A portable protective air gap (PPAG) device including a first and second electrode, suitable for use at a worksite of a particular utility company, the worksite including at least two tower support structures, each at electrical ground potential, for supporting a multiphase, electrical voltage transmission line network used to transmit a known, power frequency system, multiphase voltage of known nominal system voltage, phase to phase, kVrms, ph-ph, the transmission line network including a respective electrical transmission line for at least each phase of the multiphase voltage, each of said transmission lines suspended from a respective segment of the tower support structures by insulating electrodes, the tower support structures having a unique shape based in part on the magnitude of the power frequency system voltage transmitted on the lines of the transmission line network, the PPAG device to be suitable in design to protect a worker positioned at the worksite on or about the tower support structures, and engaged in live-line maintenance, against the possibility of voltage sparkover across one or more of a plurality of air gaps between the worker and each respective electrical transmission line, the PPAG for actual use by placement at a worksite, in one of the tower support structures, wherein each of said first and second electrodes are round rods, each said electrode having a hemispherical tip, said first and second electrodes coaxially aligned with each other such that said respective hemispherical tips are axially distant from each other by a gap distance, Dactual, and disposed facing each other, said gap distance, Dactual, a function, at least, of the known, nominal system voltage for the particular, multiphase, electrical voltage network supported by the at least two tower support structures, wherein the known nominal system voltage is 230 kV, and, wherein said gap distance, Dactual, falls in the range between 17 inches and 21 inches.
A portable protective air gap (PPAG) device including a first and second electrode, suitable for use at a worksite of a particular utility company, the worksite including at least two tower support structures, each at electrical ground potential, for supporting a multiphase, electrical voltage transmission line network used to transmit a known, power frequency system, multiphase voltage of known nominal system voltage, phase to phase, kVrms, ph-ph, the transmission line network including a respective electrical transmission line for at least each phase of the multiphase voltage, each of said transmission lines suspended from a respective segment of the tower support structures by insulating electrodes, the tower support structures having a unique shape based in part on the magnitude of the power frequency system voltage transmitted on the lines of the transmission line network, the PPAG device to be suitable in design to protect a worker positioned at the worksite on or about the tower support structures, and engaged in live-line maintenance, against the possibility of voltage sparkover across one or more of a plurality of air gaps between the worker and each respective electrical transmission line, the PPAG for actual use by placement at a worksite, in one of the tower support structures, wherein each of said first and second electrodes are round rods, each said electrode having a hemispherical tip, said first and second electrodes coaxially aligned with each other such that said respective hemispherical tips are axially distant from each other by a gap distance, Dactual, and disposed facing each other, said gap distance, Dactual, a function, at least, of the known, nominal system voltage for the particular, multiphase, electrical voltage network supported by the at least two tower support structures, wherein the known nominal system voltage is 345 kV, and, wherein said gap distance, Dactual, falls in the range between 29 inches and 33 inches.
Dependencies are inferred from the claim text.