Classifications

• • 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

Definitions

• the invention relates to method and apparatus for no destructive testing electric insulation by measuring t total voltage response signal.
• the invention should be us advantageously for testing high voltage insulations well.
• the testing and measuring system has been based on measuring the total voltage respon signal, i.e. on measuring the decay voltage diagram and t recovery voltage diagram as the function of the time and measuring the initial slope of said diagrams referring the unit charge voltage . These ' data measured are used f characterizing and testing the condition of the insulations
• the portable apparatus operating on the basis of the metho according to the invention can be used for diagnosti testing insulation system in the low voltage and high vol tage equipments on the site and without destroying sai system.
• the task of an electric insulation is alwyas to separat electrically the metal elements of an equipment bein connected to different voltages.
• the insulation ca fulfil reliably the task set only if the electric strengt of said insulation has been made safety higher than th electric stress occuring in operation.
• the electric strength of the insulating materials used i the insulations can not be regarded to be constant. Th value of the electric strength is being continous decreasing from its initial value referring to the n insulation on the effect of the chemical and physic deteriorating processes, ageing etc., occuring during t operation. The decrease of the electric strength effects decrease of the electric safety of the operation of sa insulation system.
• the puncture and breakdown during the operation of an ap paratus or machine causes unexpected operating troubles fo example longer or shorter failure or absence of the main supply voltage, which causes troubles and inconvenience no only to the civilien population, but the working machine will stop too, decreasing the production or casusing troubl for example in the traffic on the streets.
• the real value of the electric strength of the insulation in operation could have been determined by measurements onl which destroy the insulation at the time of the measuring As such this way of measuring the electric strength can no be used in insulations being in operation.
• the change of the insulating resistance measured in th period for example in one minute following switching on th measuring voltage can characterize in some cases, fo example in case of impregnated paper insulation, the dete rioration process.
• the disadvantage of this measuring metho lies in that the value of the insulation resistance measure e. g. after one minute will be influenced not only by th condition of the insulation that on one hand by th polarization processes in the material on the other hand b the geometrical form of the insulation as well, it mean that the insulation resistance measured can be ver different in dependence on the form and dimension of th insulation to be tested.
• the value of the measuring voltage is limited on one hand by the safety operation on the other hand by the electric strength of the apparatus investigated or by the dielectric strength of the air in the measuri circuit (i.e. starting partial discharges on the met conductors and electrodes) , and the requirement that t test voltage never should risk or endanger the insulation be measured.
• the measuring volta in general never should be higher that 5 kV or the proof operating voltage of the insulation to be measured.
• the aim of the invention lies in developing the method and apparatus, using also the measuring the voltage response, i.e. the measuring of the decay voltage and the recovery voltage, however, the object of the invention is to eliminate the mentioned disadvantages, i.e. to shorten significantly the measuring time period, and to enable its using in industrial circumstances as well.
• the whole voltage response of the insulations can be determined in a single measuring method if the requested conditions is ensured,i.e. during measuring the slope of the decay voltage U j , the voltage on the electrodes of the insulation does not decrease under the 90% of the measuring direct voltage U 0 , as charging voltage.
• T mentioned decrease slightly influences the just aft executed measuring value by means of the recovery voltag The extent of the influence depends on the charging ti period t-t, the discharge time period t rz , the slope of t decay voltage, and the time constant of the polarizati range. Generally the influence is slight in operati measurements, in particular cases the extent of t influence can be determined and the effect can be improved
• the period of the measurement can considerably shortened by for example 80-85 %, therefor the method can be applied for checking operating insulatio as well.
• the previously used measuring method comprises t following steps: the charge had been taken place for t charging time period t*t, Uj- was the measuring slope of t decay voltage, then followed the discharge of the sample f a period of 5 x t , then a further charge took place f measuring the recovery voltage U v .
• Uj- was the measuring slope of t decay voltage
• the invention relates to a method for non-destructiv testing electric insulations by measuring the direct voltag response by connecting to the insulation direct voltage an measuring the decay voltage and the recovery voltage.
• the essence of the method according to the invention is i that in the first step the measuring direct voltage will b connected on the terminals of the insulation to be teste for a charging time period depending on the time constant o the polarization processes in the said insulation, afte expiration of the charging time period in the second ste the measuring direct voltage will be switched off and th initial slope of the decay voltage will be determined, i the third step said insulation will be short-circuited for discharge time period depending on the time constant of th polarization range to be investigated, following th discharge time period the short ciruit will be interrupte and the initial slope of the recovery voltage will b determined.
• the measuring direct voltage i lower than the operational voltage of the insulation, optinonally the measuring voltage range is 1 kV...5 kV.
• the method according to the invention ensures the measuring conduction and polarization in the insulation, i.e the character of the condition of the insulation will be characterized by the initial slopes measured.
• the method according to the invention can be applied so that the whole measuring process will be repeated regularly or irregularly, the measured values will be registrated, and the condition and state of the insulation will be watched a controlled on the basis of the data measured.
• the invention relates to furthermore an apparatus for no destructive testing electric insulations by charging t insulation to be tested to direct voltage and subseque discharging said insulation, wherein to the insulation to tested the voltage source producing the measuring direc voltage is connected through the serious connected switc element.
• the essence of the apparatus according to the inventio is in that between the insulation to be tested, i.e. th sample tested and the direct voltage source a firs controlled switch element is serious connected, to it outlet connected to the sample tested one outlet of th second controlled switch element coupled parallel with th sample tested is connected, while parallel with the sampl tested a non-consumption voltmeter and/or recorder i connected.
• th control input of the first switching element is connected t the element producing the charging time period, while th control input of the second switching element is joined t the element producing the discharge time period, which ar arranged in the control unit realizing the requested, i itself known, timed operation of the first and secon switching elements.
• Fig.l. shows the measuring principle of the measurement according to the invention representing the schematic circuit diagram.
• Fig.2. represents the time function of the voltage to be realized on the course of the measuring method according to the invention
• Fig.3 shows the detailed embodiment of the apparatus according to the invention.
• Fig. 1 can be seen the direct voltage source G, one of its outlets is connected to one of the outlets of the first switching element Kl of high voltage, the other outlet of the first switching element Kl of high voltage connects to one of the outlets of the second switching element K2 of also high-voltage, while the other outlet of the second switching element K2 joins to the other outlet of the direct voltage source G.
• Parallel with the second switching element K2 the sample tested Pr symbolizing the insulation to be examined and a voltmeter - non-consumption voltmeter - are coupled.
• Fig. 2. can be seen the the time function to be realized by the method according to the schematic circuit diagram according to the Fig. l.
• the measuring direct voltage U 0 by closing the switch Kl should be connected to the sample tested Pr for charging time period -fc then the measuring direct voltage U 0 by opening the switch Kl is disconnected and the voltage will be discharge on the sample tested Pr.
• This slope of the decay voltage U ⁇ is the initial slope of the decay voltage, as the discharg is performed up to the 90% of the measuring direct voltag U 0 , i.e. on the sample tested Pr only a voltage decrease o
• Fig. 3. shows in details the circuit diagram of th apparatus realizing the method " according to the invention, wherein a supply source T can be seen producing the measuring direct voltage U 0 and which produces the stable direct voltage of a previous given value from the mains voltage by the way known in itself, and the signal comprises the transformer Tr separated by bipolarly, and a rectifier El series connected to the output of the transformer.
• the output measuring direct voltage U 0 of the supply source T is connected to the first switching element Kl and the second switching element K2 in the way shown in Fig.
• the first switching element Kl and the second switching element K2 are controlled switches of high-voltage with high resistance, the control coins of which is connected to the output of the control unit V producing the charging time period t--- as well as the discharge time period t rz .
• the control unit V is not described in detail, while it can be realized in every case from the elements known in itself, as the charging time period t-t and the discharge time period t r2; can be adjusted in the range given in advance necessary for the operation of the first switching element Kl and the second switching element K2 have to be ensured.
• the first switching element Kl and the second switching element K2 form together a switching unit K, the output of which is connected to the voltmeter F; this voltmeter contains the non-consumption voltmeter element Fl, and the A/D converte Al joining thereto, which connects to the control unit V.
• the output of the voltmeter F is connected to the insulatio to be tested.
• the measuring direct voltage U Q has to be determined suitable for the insulation to be tested.
• the measuring direct voltage U 0 has to be determined so that it should not be harm to the insulation, but its value should be enough for developing the dielectic processes. According to our experiences the value of the measuring direct voltage U 0 depending on the operation voltage of the insulation to be tested is optinonally between 1 kV...5 kV. Should the value of the measuring direct voltage U 0 is available, in the first step, the first switching element Kl is closed up to a previously given charging time period t- ⁇ , then the charging time period t ⁇ can be determined in the way known in itself, in the knowledge of the time constant of the polarization processes having in the insulation to be tested.
• the first switching element Kl is opened, so disconnecting it from the direct voltage source G producing the measuring direct voltage U 0 , and by the aid of the voltmeter - which is non-consumption, for example electrostatical voltmeter - the slope Mj ⁇ of the decay voltage U ⁇ on the electrodes of the sample tested Pr is measured resp. recorded. The measurement is taking place up to the time, when the initial slope M ⁇ of the decay voltag Uj ⁇ can be determined.
• the electrodes of the sample teste Pr resp. the insulation to be tested will be short circuite with the second switching element K2 for a discharge tim period t r2 determined in advance, i.e. the charge accumulated on the electrodes of the insulation will b discharged.
• the period of the discharge time t rz depends o the time constant of the polarization range to be tested however the data can be known from the respectiv bibliography.
• the secon switching element K2 After the discharge time period tt elapsed the secon switching element K2 is opened, so the short circuit of th sample tested Pr (resp. the insulation to be tested) i interrupted, and the slope of the recovery voltage U v bein on the electrodes of the insulation is measured resp recorded. In this case the measurement is taking place als up to the time, when the initial slope M v of the recover voltage U v can be determined.
• the intensity of the conduction resp. polarization processe having on the insulation - the condition of the insulatio due to the deterioration processes - can be characterized b the slopes ⁇ H _ resp. M v (relating to the unit chargin voltage) of the decay voltage U ⁇ resp. of the recover voltage U v . After the measurement the insulation has to b short circuited for safety reasons.
• the measuring direct voltage U 0 used for testing insulation is lower than the previously used one, i.e. its value range is 1...5 kV which on one hand fulfills the safety requirements, on the other hand-, no discharge is taken place by the applied measuring voltage, so, does not disturb the measurement not deteriorating the insulation.
• the method according to the invention can be applied fo testing electric insulation of high-voltage, such a insulations for rotors, transformers as well as cables.
• controlle can be of the control unit V with both computer an microprocessor as well, however, it cannot be described now as it is known in itself.
• first switchin element Kl and the second one K2 are concerned, they ar switching means of high resis-tance resp. they have to b controlled suitably.
• They can be of various switches wit semi-conductor or for example vacuum- or Reed switsches.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Testing Relating To Insulation (AREA)

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• 1992
  • 1992-01-21 HU HU9200183A patent/HU207897B/hu not_active IP Right Cessation
• 1993
  • 1993-01-21 WO PCT/HU1993/000002 patent/WO1993014411A1/en not_active Ceased
  • 1993-01-21 EP EP93902489A patent/EP0623218A1/de not_active Withdrawn

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