IEC 60172:2015 pdf free download – Test procedure for the determination of the temperature index of enamelled andtape wrapped winding wires
5.2Varnish impregnation
Experience has shown that insulated wire according to lEC 60317 and impregnating agentsaccording to IEC 60455-3-5 or IEC 60464-3-2 can affect one another during the thermalageing process.
NOTE 1 Testing varnished specimens will allow for evaluation of the compatibility of the wire insulation with animpregnating agent.Thus the temperature indices of different combinations can be compared.
Interaction between wire insulation and such agent may increase or decrease the relativethermal life of this combination compared with the life of the wire tested without impregnation.Therefore，with impregnated specimens,this test procedure may give an indication of thethermal endurance of a combination of wire insulation and impregnating agent.
lf such impregnation is required, the following procedure shall be applied:
With the specimen in the vertical position, it shall be immersed in the impregnating agent for(60 ±10) s (see note). It shall be removed slowly and uniformly at a rate of about 1 mm/s. ltshall be drained horizontally for 10 min to 15 min and cured horizontally according to themanufacturer’s recommendation or to an agreed schedule. If more than one treatment is to begiven，immerse，drain and cure the specimen vertically reversing the specimen for eachsubsequent treatment.
NOTE 2 Some impregnating agents, such as high viscosity or thixotropic products require alternative processingmethods.
5.3 Notes on number of test specimens
The accuracy of the test results depends largely upon the number of test specimens aged ateach temperature. A greater number of test specimens is required to achieve an acceptabledegree of accuracy if there is a wide spread in results among the specimens exposed at eachtemperature.
Experience has shown that twenty specimens without impregnation and ten specimens withimpregnation give results with an acceptable tolerance.A minimum of ten specimens shall beused.
5.4 Specimen holder
5.4.1 For specimens according to 5.1.1
Since individual handling of the twisted specimens may result in premature failures，it isrecommended that the specimens be placed in a suitable holder, as shown in Figure 8. Theholder should be designed in a manner that will protect the twisted specimens from externalmechanical damage and warping. The holder will be so constructed as to allow the ends ofthe twist to protrude from the holder to make electrical connection for the proof testing asshown in Figure 9. The holder shall be designed for at least ten specimens to decreasehandling time.
NOTE The recommendations in Table 3 differ from those in lEC 60216-3 but have been found to be moresuitable for enamelled wires.
Thermal endurance values obtained from test specimens subjected to an average of less thaneight or more than twenty cycles at the exposed temperature may not be reliable and shouldnot be used to predict the temperature rating of the enamelled wire. Therefore, a shorter orlonger cycle time than those given in Table 3 may be chosen for certain exposuretemperatures, to ensure that the average number of cycles to failure falls within this range.
After the specimens have been subjected to a particular cycle, the time may be appropriatelyincreased or decreased to control the number of cycles required to reach the time to failure.
Test specimens should be exposed to a minimum of three and preferably four exposuretemperatures. The lowest temperature，recommended at 20 °C above the desired thermalclass，should be one which results in a time frame to failure of more than 5 000 h. Thehighest exposure temperature shall have a value of at least 100 h to be considered a validdata point. Exposure temperatures should not be more than 20 °C apart.The accuracy of thetemperature index predicted from the results will improve as the exposure temperatureapproaches the temperature to which the insulation is exposed in service.