1、Designation: D 5374 93 (Reapproved 2005)An American National StandardStandard Test Methods forForced-Convection Laboratory Ovens for Evaluation ofElectrical Insulation1This standard is issued under the fixed designation D 5374; the number immediately following the designation indicates the year ofor
2、iginal adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 These test methods cover procedures for evaluating thecharac
3、teristics of forced-convection ventilated electrically-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-
4、1, and are technically identical to it. This compilation of testmethods and an associated specification, D 5423, have re-placed Specification D 2436.1.3 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 s
5、tandard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D 2436 Specification for Forced-Convection LaboratoryOvens for Electrical InsulationD 5423 Specification for Forced-Convect
6、ion LaboratoryOvens for Evaluation 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 Ovens33. Terminology3.1 Refer to the terminology section of S
7、pecificationD 5423.4. Significance and Use4.1 It is essential that ovens used for thermal evaluation ofinsulating materials be capable of maintaining uniform condi-tions of temperature and air circulation over the extendedperiods of time that are required for conducting these tests.Specification D 5
8、423 specifies the permissible deviations fromabsolute uniformity that have been generally accepted interna-tionally for these ovens. These test methods include proceduresfor measuring these deviations and other specified character-istics of the ovens.5. Apparatus5.1 Multi-Point Recording Potentiomet
9、er, having provisionsfor at least nine iron-constantan or chromel-alumel thermo-couples, with scale readings to 0.1C or less. Use of a dataprocessor or a data logger may be helpful in reducing thenumber of calculations required.5.2 Calibrated Iron-Constantan or Chromel-Alumel Ther-mocouples, using 0
10、.5-mm diameter or smaller wire and havinga junction size not over 2.5 mm long. If calibrated thermo-couples are not available, thermocouples made from a singlespool of thermocouple wire may be used provided that, whenplaced within 10 mm of each other without touching in an ovenchamber at 200C, they
11、give values for temperature that do notdiffer from each other by more than 0.2C.5.3 A temperature measuring system other than thermo-couples and a potentiometer may be used, provided that thesensitivity, accuracy, and response time are at least equivalentto that of the equipment described above, and
12、 that the objec-tives of 6.2.3 relative to minimization of heat conductioneffects can be met.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
13、 junction of the thermo-couple must be capable of being moved at least 80 mm awayfrom the brass cylinder. An appropriate temperature indicator(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
14、Meter, of the appropriate voltage and phase,capable of reading to the nearest 1.0 Wh or less.1These 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.Curren
15、t edition approved Sept. 1, 2005. Published October 2005. Originallyapproved in 1993. Last previous edition approved in 1999 as D 5374 93 (1999).2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards
16、volume information, refer to the standards Document Summary page onthe ASTM website.3Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United S
17、tates.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 theoven at the same temperat
18、ure with its ports closed. The test isconducted at 100C and at the maximum temperature at whichthe oven may be 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 the blower motor ismo
19、unted 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 intake. Usethe oven tempe
20、rature 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 corresponding points of thecy
21、clic 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 its normaloperating con
22、dition. 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 ventilation in the oven usin
23、g thefollowing equation:N 5 3.59 P22 P1!/VrDT! (1)where:N = number of air changes per hour,P1= average power consumption, with no ventilation,obtained by dividing the energy consumption deter-mined from the watt-hour meter readings by theduration of the test in hours, W,P2= average power consumption
24、 during ventilation, cal-culated in the same manner, W,V = total volume of air circulated within the oven, m3(seeNote 1),r = density of the ambient room air during the test,kg/m3(see Note 2), andDT = difference in temperature between the oven and theambient room temperature, C.NOTE 1This volume incl
25、udes space outside the testing chamber. Theamount of this additional space depends on the physical design of theoven.NOTE 2The density of air at one atmosphere and 20C is 1.205 kg/m3.6.1.9 If the rate of ventilation is not within the specifiedlimits for the oven, adjust the vents and dampers and rep
26、eat6.1.7 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 may be used.6.1.11 Report the following information:6.1.11.1 Identification of the oven,6.1.11.2 Date and location of test,6.1.11.3 Test temperatures, and6.1.11.4 Rate of ventil
27、ation 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 space variationsof temperature. The time variation (temperature f
28、luctuation)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 range of rate of ventilation.6.2.3 Install nine thermocouples in th
29、e 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 for each thermo-couple within the oven chamber, in order to minim
30、ize 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 sufficient number of times during onecomplete temperature variation cyc
31、le 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 more than a total of 5 %during this measuring period.6.2.5.1 Calcul
32、ate 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 record as the temperature variation.6.2.5.3 Calculate the differenc
33、e 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 temperature and minimum tem-perature over the temperature cycle and r
34、ecord difference as thetemperature fluctuation.6.2.6 Maintain the oven at the same operating temperaturefor five days after the end of the stabilization period, and afterthe measurement of temperatures specified in 6.2.5. Maintainambient room temperature and supply voltage within the limitsin 6.2.5
35、during the entire period. Repeat the measurements andcalculations in 6.2.5 daily.6.2.7 For routine monitoring of oven characteristics, forexample, as recommended in Appendix X1 of SpecificationD 5423, the stabilization time specified in 6.2.4 may beD 5374 93 (2005)2reduced to 8 h, and the length of
36、the test period following theinitial temperature measurements specified in 6.2.6 may bereduced to 24 h (one day), with a single repetition of thetemperature measurements. In case of doubt or dispute, use thelonger time periods.6.2.8 Report the following information:6.2.8.1 Identification of the oven
37、,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 MethodA defined bras
38、s 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 difference.6.3.2 He
39、at 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-resistant nonmeta
40、llic 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 junctions of the
41、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 seconds since closi
42、ng 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 difference.6.3.6 Re
43、port 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 been determined, an
44、d 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; temperature gradient; t
45、hermal 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 determination of the validit
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48、 received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org).D 5374 93 (2005)3
