WO2002046730A2 - Systeme et procede servant a mesurer la resistance dielectrique d'un fluide - Google Patents

Systeme et procede servant a mesurer la resistance dielectrique d'un fluide Download PDF

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Publication number
WO2002046730A2
WO2002046730A2 PCT/US2001/046977 US0146977W WO0246730A2 WO 2002046730 A2 WO2002046730 A2 WO 2002046730A2 US 0146977 W US0146977 W US 0146977W WO 0246730 A2 WO0246730 A2 WO 0246730A2
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WO
WIPO (PCT)
Prior art keywords
test
test gap
series
impedance
coupled
Prior art date
Application number
PCT/US2001/046977
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English (en)
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WO2002046730A8 (fr
WO2002046730A3 (fr
Inventor
Timothy L. Cargol
Chathan M. Cooke
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Massachusetts Institute Of Technology
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Publication date
Application filed by Massachusetts Institute Of Technology filed Critical Massachusetts Institute Of Technology
Priority to AU2002225977A priority Critical patent/AU2002225977A1/en
Publication of WO2002046730A2 publication Critical patent/WO2002046730A2/fr
Publication of WO2002046730A8 publication Critical patent/WO2002046730A8/fr
Publication of WO2002046730A3 publication Critical patent/WO2002046730A3/fr

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G01N33/26—Oils; Viscous liquids; Paints; Inks
    • G01N33/28—Oils, i.e. hydrocarbon liquids
    • G01N33/2805—Oils, i.e. hydrocarbon liquids investigating the resistance to heat or oxidation
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
    • G01N27/22—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating capacitance
    • G01N27/221—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating capacitance by investigating the dielectric properties
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G01N33/26—Oils; Viscous liquids; Paints; Inks
    • G01N33/28—Oils, i.e. hydrocarbon liquids
    • G01N33/2888—Lubricating oil characteristics, e.g. deterioration
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/12—Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing
    • G01R31/1227—Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing of components, parts or materials
    • G01R31/1263—Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing of components, parts or materials of solid or fluid materials, e.g. insulation films, bulk material; of semiconductors or LV electronic components or parts; of cable, line or wire insulation
    • G01R31/1281—Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing of components, parts or materials of solid or fluid materials, e.g. insulation films, bulk material; of semiconductors or LV electronic components or parts; of cable, line or wire insulation of liquids or gases

Definitions

  • the present invention generally relates to the field of electric power transformer systems, and particularly relates to such systems that use an internal fluid, such as oil, for dielectric and/or heat transfer purposes.
  • Oil is used extensively as an internal fluid in modern electric power apparatus, for example in power transformers of most transmission systems. Oil generally serves two necessary functions; to insulate voltage between metallic conductors at close clearances, and to aid in the removal of heat generated by losses in the conductors. Unfortunately, oil can degrade and loose it's ability to adequately insulate voltage and thereby enhance the risk of a dielectric failure; this in-turn can lead to a forced outage and/or catastrophic failure. The direct dollar cost of a single failure may be very expensive (possibly exceeding ten million dollars) and may further cause adverse implications for safety and the environment. It is known to employ regular inspection of transformer oil condition, often on an annual basis and especially in oil insulated tap changer compartments.
  • Such inspections typically involve careful manual extraction of an oil sample and subsequent testing in a dielectric strength tester.
  • the dielectric strength test is typically made in accordance with a recognized standard procedure and apparatus, typically via standards such as the American Society of Testing Materials (ASTM) D-877 or D- 1816 or certain international standards such as provided by IEC/VDE authorities.
  • ASTM American Society of Testing Materials
  • Such tests apply an AC voltage stress to an electrode pair immersed in the subject oil, the stress is continuously increased until breakdown occurs.
  • the voltage at breakdown is the measure of insulating ability.
  • These standard tests employ defined electrodes, defined applied AC high voltage at fixed rates of rise until breakdown, and a statistical method for interpreting the results of a few repeated tests.
  • NDBD Non-Destructive Breakdown method
  • the oil condition is assessed from the NDBD breakdown activity. Three major differences that distinguish the NDBD measurement from the ASTM - type dielectric strength tests are
  • BD uses a short (submicrosecond) duration constant pulse voltage from a pulser
  • the ASTM test specifies repeated measurements under fixed conditions to more clearly distinguish degradation. Because of changes to the oil due to damage induced by the breakdowns in the test itself however, there is typically a limit of 5 breakdowns maximum on any oil sample. In contrast, the NDBD test allows many more repeated measurements and thus greater accuracy of the measurement. It is important to recognize that in the NDBD approach the test induces no breakdown events in clean (or good) oil and hence no damage to the oil is possible when the oil is clean. However, when the oil does degrade, detection is achieved by the onset of breakdown activity of the NDBD test events. The occurrence of repeated breakdowns is one signature of a degraded oil condition.
  • the NDBD test will exhibit progressively greater probability of breakdown in any series of tests as the oil condition significantly degrades.
  • the NDBD test breakdowns must, therefore, not themselves be the cause of significant degradation to the oil, especially for the NDBD test to be acceptable as a measurement performed on oil inside a power apparatus, without oil extraction.
  • conventional NDBD tests on samples yield improvements in reduced oil degradation compared to the ASTM-type tests, the NDBD tests are not suitable for in-service testing, i.e., during operation of the electric power apparatus.
  • the difficultly with performing in-service tests is that some degradation of the oil may result from the testing itself. Such damage is related to the currents in the oil during breakdown.
  • the characteristic surge impedance of the pulser voltage acts to provide an inherent limit to the current and thereby possible damage to the oil under test. For example, for a 20kN pulse voltage and a 50 ohm line impedance, a current limit of 400 amperes is achieved for the very short duration of the pulse, e.g. , up to 0.3 microseconds. The charge transfer could therefore attain a value of about 120 microcoulombs for this case.
  • the integral of current squared times time is another measure used to quantify the activity of a discharge and for this case amounts to about 5 x 10- 2 amps 2 -seconds. These values are typically ten times or more smaller than breakdown events from a classical ASTM type test, but still provide conditions in which damage to the oil may result. There remains a need, therefore, for a system and method for achieving in-service measurement of the dielectric strength of oil in an electric power apparatus.
  • a system for monitoring the quality of an internal fluid contained in an apparatus.
  • the system includes a pulse input port, a test gap unit, and a reactive impedance unit.
  • the pulse input port receives a test pulse input signal from a pulse source.
  • the test gap unit provides a test voltage across a test gap while the test gap unit is immersed in the internal fluid within the apparatus.
  • the test gap means has an inherent capacitance.
  • the reactive impedance unit provides an impedance in series with the inherent capacitance of the test gap unit that restricts transfer of current to the test gap, and is coupled to the pulse input port and coupled to the test gap unit.
  • FIG. 1 shows an illustrative view of a circuit in accordance with an embodiment of the invention
  • FIG. 2 shows an illustrative view of the circuit of Figure 1 in a test system that is coupled to an electrical power apparatus in accordance with an embodiment of the invention
  • FIG. 3 shows an illustrative view of a circuit in accordance with a further embodiment of the invention.
  • FIG. 4 A shows an illustrative graphical view of gap voltage (N gap ) versus time for a test system in accordance an embodiment of the invention.
  • FIG. 4b shows an illustrative graphical view of gap current (I gap ) versus time for a test system in accordance an embodiment of the invention.
  • the invention provides a system and method for measuring oil dielectric strength within a power apparatus.
  • This disclosed apparatus improves the NDBD test so as to be suitable for use directly in a power apparatus without oil extraction and hence may be performed in-service, i.e., while the apparatus is energized in-service.
  • the invention provides that the need for and cost of manual oil extraction for dielectric strength evaluation may be eliminated, and enables early detection of oil degradation by more frequent and automated dielectric strength tests.
  • the operation of the test in accordance with the invention may be performed selectively on-site, and may even be automated if desired. An automated system for performing such in-service tests enables the opportunity for remote control and access to the test so that manual activity at the site for such oil condition tests is eliminated.
  • a system of the invention provides a special apparatus that enhances the usefulness of the NDBD type oil dielectric strength test.
  • the basic NDBD test method acts to greatly reduce the energy delivered and the amount of damage to the oil compared to traditional tests.
  • substantial further improvements to the NDBD test performance and reduced discharge effects on the oil have been demonstrated and achieved with a system of the invention as disclosed below.
  • a system 10 of the invention includes a series impedance 12 that is coupled between a pulse input port 14 and a gap device port 16.
  • the series impedance 12 is added to directly control the pulse currents in the test gap so as to reduce the impact of the NDBD test on the oil and thereby make the test more suitable for in-service application, while at the same time permitting reliable breakdown measurements.
  • the test reliability and performance of the point to plane gap which is driven by a pulse voltage in the NDBD test method, is greatly improved by an added series impedance which acts to further control the pulse currents during an NDBD test event.
  • the effect of the added series impedance is to cause the NDBD discharge events to be micro-discharge events with greatly reduced energy deposited into the oil and reduced wear of the point test electrode tip.
  • the added series impedance is introduced intentionally to greatly reduce the total amount of current that is available at the test gap from the pulser, typically by factors of 10 or more.
  • a preferred embodiment for this series impedance is a high- voltage capacitor, C s , in parallel with a high-voltage resistor, R s , as shown in Figure 1.
  • the resistance, R s preferably of more than 10 kilohms and less than 10 megohms is used to dissipate any residual charge or voltage accumulated on the series capacitor after a test event.
  • this series impedance is in series with the output of a pulser 18, and pulser 18 has an inherent resistance R P that is shown diagrammatically in Figure 2.
  • the test gap equivalent circuit is also shown in Figure 2, and includes an inherent capacitance C g that is in parallel with a switch 20.
  • the switch 20 represents the spark event when it closes.
  • the series impedance may be physically located on either the 'high-side' as depicted in the figure or on the 'return-ground lead' side of the test gap with essentially the same effect, except for possible small differences due to the effects of stray capacitances.
  • the added capacitance of the example series impedance, C s is selected to be large compared to the effective series capacitance of the test gap itself so that most of the pulse voltage appears across the test gap. It is also selected to be small to restrict the currents through the test gap. Examples include a 100 pF added series capacitance, C s , for a test gap capacitance, C g . of lOpF. These two capacitors in series form a capacitive voltage divider, and with these illustrative values essentially 90% of the pulser voltage is still applied to the test gap. R s is much greater than the pulser source resistance R P so as to influence the steady current after breakdown.
  • the circuit charges with a time constant of essentially R P Cg since C g is in series with C s and C s is greater than C g . At the above values the time constant is 5ns, neglecting stray capacitances that may increase the time.
  • the voltage on the test gap equalizes at about 90% of the pulser voltage, according to the capacitor divider action of C g and C s . In the condition where the pulser is on and breakdown occurs, the gap-switch 20 is closed.
  • the charge on the gap capacitance C g is dissipated in the closed switch 20 and the gap voltage becomes very small. Now current from the pulser is fed into the closed test gap via the added series circuit.
  • the added series capacitance then charges with a time constant of approximately R P C S , about 50ns in the example case.
  • the capacitance C s changes, the current in the test gap decreases.
  • a small steady gap current is then sustained by the high value series resistance R s with an equilibrium value of about V P /R S , about 0.1 amp .
  • the pulser is off, and there is no breakdown.
  • the circuit is decaying to rest so that all currents and voltages in this circuit tend toward zero. This process typically takes on the order of seconds or minutes, so the above time constants are more than fast enough to ensure that the circuit is at rest before the next pulse test.
  • the net effect on the discharge was measured and shown to reduce the energy delivered to the oil gap by more than ten times compared to without the series impedance.
  • a further experimental indicator of improvement achieved by the added series impedance was a major reduction of micro-bubbles in the oil observed after a microbreakdown discharge with series impedance versus those after a discharge without the series impedance.
  • a second series resistance R ss (22) of the pulser is set to be a moderate value, such as 500 ohms. This value is much greater than the raw 50 ohm impedance used at first and is tolerated because the resultant time-constant remains suitable for a typical test pulse of 300ns duration. Greater than 50 ohms is desirable because it is a simple way to limit the current during the initial time just after breakdown. This higher resistance may be obtained in practice for example, by creating a high impedance transmission line pulser or using a typical 50 ohm pulser and adding a series output resistance to attain an approximately 500 ohm value.
  • the pulser effective series impedance may need to be adjusted to allow for the charge and discharge features discussed above associated with the pulse duration and gap capacitance.
  • the series impedance 22 is coupled between a pulse input port 14 and a gap device port 16.
  • the series impedance 22 includes a series capacitor C s and a series resistor R s as discussed above with reference to Figures 1 and 2, and further includes a second series resistor, R ss , on either side of the R S C S pair.
  • the value of R P is the inherent pulser source impedance, perhaps associated with the surge impedance of a transmission-line type pulser; here typical values might be 50 or 75 ohms due to the surge impedance of many practical coaxial cables.
  • the added series resistor R ss is introduced to further limit the current to the test gap.
  • R ss might be about 500 ohms for a test pulse width of 300ns and a gap capacitance of about 10 pF, and R P of 50 ohms.
  • the capacitance C s also serves the purpose of creating a short pulse of current.
  • This current has been found to be linked to a pulsive oil flow circulation at the gap when the pulse is applied and thereby helps keep the test gap clear of debris.
  • the exact cause as to how the action by the electrical pulse is linked to the oil flow is not fully understood, but example mechanisms may be the magnetic repulsive force associated with the pulsed current or charge carrier motion. While the use of a capacitor produces a pulse of current, beneficial for oil flow clearing, the selection of a suitably short time constant allows this pulse current to subside rapidly so as to limit possible subsequent damage to the oil.
  • the values of the series impedance and the pulser effective source impedance are chosen together to create an overall control of the NDBD pulse supplied to the test gap, including rise and fall times, peak currents and steady currents as well as voltages.
  • the series impedance of this invention may be comprised of single lumped elements, or may include distributed elements that cause equivalent current control.
  • An illustration of the overall resultant voltages and currents associated with the test gap for the disclosed invention is depicted in Figures 4A and 4B. As shown in Figure 4A, an applied pulse width (of for example 300 ns) is shown at 30, and the voltage with breakdown is shown at 32 while the voltage without breakdown is shown at 34.
  • the selection of the series impedance may also be influenced by the circuit equivalent of the apparatus to which it is connected. For example, a smaller capacitance test gap, C g may allow the series capacitance, C s , to be smaller and yet keep the same voltage ratio between pulser output and the voltage on the test gap.
  • C g may allow the series capacitance, C s , to be smaller and yet keep the same voltage ratio between pulser output and the voltage on the test gap.
  • the use of standard classical circuit and transmission line analysis techniques may be used to establish the series impedance needed to achieve the desired current control. These calculations include factors such as capacitances and surge impedances.
  • the application of the disclosed invention is for any high-voltage diagnostic measurement where an essentially capacitive test gap is driven by a pulse voltage source.
  • Examples provided which are illustrative but not limiting in scope, reveal that the basic circuit topology comprised of a pulser with effective output impedance may be connected to an essentially capacitive test gap via a series impedance selected to control currents in order to reduce damaging effects from the discharge by limiting the steady current while at the same time provide a short pulse of current and adequately fast voltage transitions.
  • the methods and systems of the invention may be used to evaluate fluid degradation is other fluid containing apparatus, including gas turbines or internal combustion engines, or other machinery in which the degradation of a fluid may develop.
  • the system and method of this invention provide numerous benefits compared to systems and methods that involve a classical current limit approach that is imposed by a fixed surge impedance of the output characteristics from a typical transmission line pulser or other standard high-voltage pulser.

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Abstract

L'invention concerne un système servant à contrôler la qualité d'un fluide interne contenu dans un dispositif. Ce système comprend une entrée d'impulsion, une unité d'essai présentant un écartement et une unité à impédance réactive. L'entrée d'impulsion reçoit un signal d'entrée d'impulsion d'essai provenant d'une source d'impulsion. L'unité à écartement d'essai produit une tension d'essai à travers un écartement d'essai, tandis que cette unité est immergée dans le fluide interne contenu dans le dispositif. Ces électrodes à écartement d'essai possèdent une capacité inhérente. L'unité à impédance réactive produit une impédance en série avec la capacité inhérente de l'unité à écartement d'essai restreignant le transfert du courant vers cet écartement et est couplée à l'entrée d'impulsion, ainsi qu'à l'unité présentant un écartement d'essai.
PCT/US2001/046977 2000-12-06 2001-12-06 Systeme et procede servant a mesurer la resistance dielectrique d'un fluide WO2002046730A2 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU2002225977A AU2002225977A1 (en) 2000-12-06 2001-12-06 System and method for measuring the dielectric strength of a fluid

Applications Claiming Priority (2)

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US25169700P 2000-12-06 2000-12-06
US60/251,697 2000-12-06

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WO2002046730A8 WO2002046730A8 (fr) 2002-08-01
WO2002046730A3 WO2002046730A3 (fr) 2003-03-20

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2013052892A1 (fr) * 2011-10-05 2013-04-11 Wicor Americas Inc. Système de surveillance diélectrique et procédé pour celui-ci

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US3879657A (en) * 1972-08-23 1975-04-22 Economics Lab Electrical apparatus for minimizing polarization of conductivity cell electrodes
US3996512A (en) * 1974-04-19 1976-12-07 Josef Baur Container for receiving an insulating or cooling medium for electrical apparatus to be tested for resistance to electrical breakdown
US4663585A (en) * 1984-01-31 1987-05-05 Baur Pruf-und Messtechnik K.G. Apparatus for testing dielectric strength of materials
US4686857A (en) * 1983-03-04 1987-08-18 Kabushiki Kaisha Toyota Chuo Kenkyusho Method and apparatus for evaluating the performance of dielectric substances
GB2187290A (en) * 1986-01-31 1987-09-03 Perchem Ltd Determining breakdown of liquid samples

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SU1050098A1 (ru) * 1981-06-08 1983-10-23 Научно-Исследовательский,Проектно-Конструкторский И Технологический Институт Производственного Объединения "Уралэлектротяжмаш" Им.В.И.Ленина Генератор импульсов напр жени

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US3879657A (en) * 1972-08-23 1975-04-22 Economics Lab Electrical apparatus for minimizing polarization of conductivity cell electrodes
US3996512A (en) * 1974-04-19 1976-12-07 Josef Baur Container for receiving an insulating or cooling medium for electrical apparatus to be tested for resistance to electrical breakdown
US4686857A (en) * 1983-03-04 1987-08-18 Kabushiki Kaisha Toyota Chuo Kenkyusho Method and apparatus for evaluating the performance of dielectric substances
US4663585A (en) * 1984-01-31 1987-05-05 Baur Pruf-und Messtechnik K.G. Apparatus for testing dielectric strength of materials
GB2187290A (en) * 1986-01-31 1987-09-03 Perchem Ltd Determining breakdown of liquid samples

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Title
DATABASE WPI Section EI, Week 198427 Derwent Publications Ltd., London, GB; Class U22, AN 1984-170048 XP002220056 & SU 1 050 098 A (URALELEKTROTYAZHMAS), 23 October 1983 (1983-10-23) *
SHARBAUGH ET AL.: "Progress in the field of electric breakdown in dielectric liquids" IEEE TRANS. ELECTR. INSUL., vol. EI-13, no. 4, 1978, pages 249-276, XP001119777 *
VENKATASESHAIAH ET AL.: "studies on the dielectric strength of transformer oil under oscillatory impulse voltages" 1996 IEEE SYMPOSIUM ON ELECTRICAL INSULATION, 19 July 1996 (1996-07-19), XP002220055 *

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2013052892A1 (fr) * 2011-10-05 2013-04-11 Wicor Americas Inc. Système de surveillance diélectrique et procédé pour celui-ci

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WO2002046730A3 (fr) 2003-03-20
AU2002225977A1 (en) 2002-06-18

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