1、Designation: D5374 13Standard Test Methods forForced-Convection Laboratory Ovens for Evaluation ofElectrical Insulation1This standard is issued under the fixed designation D5374; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the
2、year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 These test methods cover procedures for evaluating thecharacteristics of forced-convection ventilated electric
3、ally-heated ovens, operating over all or part of the temperaturerange from 20C above the ambient temperature to 500C andused for thermal endurance evaluation of electrical insulatingmaterials.1.2 These test methods are based on IEC Publication 216-4-1, and are technically identical to it. This compi
4、lation of testmethods and an associated specification, D5423, have replacedSpecification D2436.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health pr
5、actices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D2436 Specification for Forced-Convection Laboratory Ov-ens for Electrical Insulation (Withdrawn 1994)3D5423 Specification for Forced-Convection Laboratory Ov-ens for Evaluation
6、 of Electrical Insulation2.2 Other Document:IEC Publication 216-4-1 Guide for the Determination ofThermal Endurance Properties of Electrical InsulatingMaterials, Part 4Aging Ovens, Section 1Single-Chamber Ovens43. Terminology3.1 Refer to the terminology section of SpecificationD5423.4. Significance
7、and Use4.1 Ovens used for thermal evaluation of insulating materi-als are to be capable of maintaining uniform conditions oftemperature and air circulation over the extended periods oftime that are required for conducting these tests. SpecificationD5423 specifies the permissible deviations from abso
8、luteuniformity that have been generally accepted internationallyfor these ovens. These test methods include procedures formeasuring these deviations and other specified characteristicsof the ovens.5. Apparatus5.1 Multi-Point Recording Potentiometer, having provisionsfor at least nine iron-constantan
9、 or chromel-alumelthermocouples, with scale readings to 0.1C or less. Use of adata processor or a data logger is helpful in reducing thenumber of calculations required.5.2 Calibrated Iron-Constantan or Chromel-AlumelThermocouples, using 0.5-mm diameter or smaller wire andhaving a junction size not o
10、ver 2.5 mm long.5.2.1 If calibrated thermocouples are not available, usethermocouples made from a single spool of thermocouple wirethat gives values for temperature that do not differ from eachother by more than 0.2C when placed within 10 mm of eachother without touching inside an oven chamber at 20
11、0C.5.3 It is acceptable to use a temperature measuring systemother than thermocouples and a potentiometer, provided thatthe sensitivity, accuracy, and response time are equivalent tothat of the equipment described above, and that the objectivesof 6.2.3 relative to minimization of heat conduction eff
12、ects aremet.5.4 Thermal Lag Time Specimen, consisting of a solid brasscylinder, 10 mm in diameter and 55 mm long, with onejunction of a differential thermocouple soldered to the surfacemidway between the ends. The other junction of the thermo-couple must be capable of being moved at least 80 mm away
13、from the brass cylinder. An appropriate temperature indicator1These test methods are under the jurisdiction of ASTM Committee D09 onElectrical and Electronic Insulating Materials and are the direct responsibility ofSubcommittee D09.17 on Thermal Characteristics.Current edition approved Sept. 1, 2013
14、. Published September 2013. Originallyapproved in 1993. Last previous edition approved in 2005 as D5374 93 (2005).DOI: 10.1520/D5374-13.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume in
15、formation, refer to the standards Document Summary page onthe ASTM website.3The last approved version of this historical standard is referenced onwww.astm.org.4Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036.Copyright ASTM International, 100
16、Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1(as in 5.1, or other) must be provided for indication oftemperature differences to the nearest 0.1C as measured by thedifferential thermocouple.5.5 Watt-Hour Meter, of the appropriate voltage and phase,capable of reading
17、 to the nearest 1.0 Wh or less.6. Procedures6.1 Rate of Ventilation:6.1.1 Summary of Test MethodThe rate of ventilation iscalculated using determinations of (1) the average powerrequired to maintain the oven at a given temperature with itsports open and (2) the average power required to maintain the
18、oven at the same temperature with its ports closed. The test isconducted at 100C and at the maximum temperature at whichthe oven is used.6.1.2 Seal all openings into the oven, including, but notnecessarily limited to, the vent ports, door, thermometer ports,and the space around the blower shaft (if
19、the blower motor ismounted externally).6.1.3 Install a watt-hour meter, as described in 5.5,intheoven electrical supply line.6.1.4 Install a temperature sensor, such as a thermometer, 2m to 3 m away from the oven, at least 1 m away from any solidobject, and approximately level with the oven air inta
20、ke. Usethe oven temperature indicator to measure the internal tem-perature of the oven.6.1.5 Raise the oven temperature to 100 6 2C. When thetemperature of the oven has stabilized, measure the consump-tion of power over a measured period of 30 to 40 min. Beginand end the measuring period at correspo
21、nding points of thecyclic temperature fluctuation; for example, the moment whenthe heaters are switched on by the thermostat in the case of an“on/off” control. Measure and record the room temperature,which must not vary by more than 2C during the test.6.1.6 Remove the seals to restore the oven to it
22、s normaloperating condition. If necessary, adjust the vents and dampersto positions estimated to provide the specified rate of ventila-tion.6.1.7 Repeat 6.1.5. The average ambient air temperaturemust be within 2C of the average ambient temperaturemeasured in 6.1.5.6.1.8 Calculate the rate of ventila
23、tion in the oven using thefollowing equation:N 5 3.59 P22 P1!/VT! (1)where:N = number of air changes per hour,P1= average power consumption, with no ventilation, ob-tained by dividing the energy consumption determinedfrom the watt-hour meter readings by the duration ofthe test in hours, W,P2= averag
24、e power consumption during ventilation, calcu-lated in the same manner, W,V = total volume of air circulated within the oven, m3(seeNote 1), = density of the ambient room air during the test, kg/m3(see Note 2), andT = difference in temperature between the oven and theambient room temperature, C.NOTE
25、 1This volume includes space outside the testing chamber. Theamount of this additional space depends on the physical design of theoven.NOTE 2The density of air is dependent on ambient temperature andpressure; at one atmosphere and 20C it is 1.205 kg/m3.6.1.9 If the rate of ventilation is not within
26、the specifiedlimits for the oven, adjust the vents and dampers and repeat6.1.7 through 6.1.8.6.1.10 Repeat 6.1.2 through 6.1.9, except heat the oven tothe maximum temperature at which the oven is used.6.1.11 Report the following information:6.1.11.1 Identification of the oven,6.1.11.2 Date and locat
27、ion of test,6.1.11.3 Test temperatures, and6.1.11.4 Rate of ventilation at each temperature.6.2 Temperature Variation, Gradient, and Fluctuation:6.2.1 Summary of Test MethodSimultaneous temperaturemeasurements are made at nine points in the oven chamberover a period of time to determine the time and
28、 space variationsof temperature. The time variation (temperature fluctuation)and the space variation (temperature gradient) can be reportedseparately from temperature variation, which is the combina-tion of the two.6.2.2 Set the vents and dampers in the oven to the settingsneeded for the specified r
29、ange of rate of ventilation.6.2.3 Install nine thermocouples in the oven chamber (see5.1 and 5.2). Place one thermocouple in each of the eightcorners of the chamber 50 to 60 mm from each wall, and theninth thermocouple within 25 mm of the geometric center ofthe chamber. Leave at least 300 mm of wire
30、 for each thermo-couple within the oven chamber, in order to minimize effects ofheat conduction along the wire.6.2.4 Bring the oven to the selected operating temperatureand allow it to stabilize for a minimum of 16 h.6.2.5 Measure the temperatures indicated by the nine ther-mocouples to 0.1C a suffi
31、cient number of times during onecomplete temperature variation cycle to permit the determina-tion of the maximum, minimum, and mean temperatures ofeach thermocouple during one cycle. Ambient room tempera-ture must not vary by more than a total of 10C, and supplyvoltage to the oven must not vary by m
32、ore than a total of 5 %during this measuring period.6.2.5.1 Calculate the average of the nine mean temperaturesto 0.1C and record as the set temperature of the oven.6.2.5.2 Calculate the difference between the highest maxi-mum temperature and the lowest minimum temperature deter-mined in 6.2.5 and r
33、ecord as the temperature variation.6.2.5.3 Calculate the difference between the highest tem-perature and the lowest temperature at any specific time duringthe temperature cycle, and record as the temperature gradient.6.2.5.4 Determine which thermocouple has the greatestdifference between maximum tem
34、perature and minimum tem-perature over the temperature cycle and record the difference asthe temperature fluctuation.6.2.6 Maintain the oven at the same operating temperaturefor five days after the end of the stabilization period, and afterD5374 132the measurement of temperatures specified in 6.2.5.
35、 Maintainambient room temperature and supply voltage within the limitsin 6.2.5 during the entire period. Repeat the measurements andcalculations in 6.2.5 daily.6.2.7 For routine monitoring of oven characteristics, asrecommended in Appendix X1 of Specification D5423, reducethe stabilization time spec
36、ified in 6.2.4 to 8 h, and the length ofthe test period following the initial temperature measurementsspecified in 6.2.6 to 24 h (one day). Conduct the temperaturemeasurements two times. In case of doubt or dispute, use thelonger time periods.6.2.8 Report the following information:6.2.8.1 Identifica
37、tion of the oven,6.2.8.2 Date and location of test,6.2.8.3 Calculated set temperature for each measurement,6.2.8.4 Temperature variation for each measurement, and6.2.8.5 If specified, temperature gradient and temperaturefluctuation for each measurement.6.3 Thermal Lag Time:6.3.1 Summary of Test Meth
38、odA defined brass bar speci-men is placed in the heated oven, and the difference between itstemperature and the oven air temperature is plotted againsttime. The thermal lag time is the time in seconds required forthe temperature difference to be reduced to 10 % of themaximum observed temperature dif
39、ference.6.3.2 Heat the oven to 200 6 5C and allow it to stabilizefor at least 1 h. Stabilize a brass bar specimen (5.4) at roomtemperature for at least 1 h.6.3.3 Without turning off the oven, open the door(s) of theoven 90. Quickly hang the specimen in the geometric centerof the oven, using a heat-r
40、esistant nonmetallic cord. Theorientation of the axis of the specimen is not significant.Suspend the other junction of the thermocouple 80 to 100 mmfrom the brass bar. Leave the oven door(s) open for a total of60 6 1 s, then close the oven. Record the temperaturedifference, as indicated by the two j
41、unctions of the differentialthermocouple, at least once every 10 s until the maximumtemperature difference has been obtained. Continue recordingat least once every 30 s until the temperature difference hasdropped below 10 % of maximum.6.3.4 Plot the recorded temperature values against the timein sec
42、onds since closing the oven.6.3.5 Divide the maximum temperature difference by tenand record as T10. Then record as the thermal lag time the timein seconds, taken from the plot of temperature differenceversus time, for the temperature difference to reach T10, afterthe time of maximum temperature dif
43、ference.6.3.6 Report the following information:6.3.6.1 Identification of the oven,6.3.6.2 Date and location of the test,6.3.6.3 Set temperature of the oven, and6.3.6.4 The determined thermal lag time, in seconds.7. Precision and Bias7.1 The precision of the individual methods given hereinhas not bee
44、n determined, and no activity is planned todetermine the precision.7.2 The bias of the individual methods is largely dependentupon the accuracy of temperature measurement attainableusing the available apparatus.8. Keywords8.1 forced-convection; ovens; set temperature; temperaturefluctuation; tempera
45、ture gradient; thermal endurance evalua-tion; thermal lag time; ventilated; ventilation rateASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determinatio
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