16. General
16.1 The following sections outline certain modifications to the Procedure for Making Referee Tests, permissible(1) when it is desirable to get an approximation of the dissipation factor or power factor of a sample, or (2) when testing a group of samples of the same type of insulating liquid to determine if the dissipation factor or power factor is greater or less than some specified value.
17. Test Cell
17.1 Any test cell conforming to the requirements given in the Annex may be used. For routine tests, however, the requirement for a guard electrode may be waived, provided that the two-electrode cell used is of adequate capacitance and with sufficient ratio of surface area to sample thickness, in order to provide proper operation of the measuring equipment.
18. Test Chamber
18.1 An oil bath having uniform temperature distribution and provided with adequate temperature regulation may be used for routine tests, provided that when the test cell is immersed in the bath, the temperature difference in the test cell between any part of the inner electrode and the outer electrode does not exceed 2°C. A less satisfactory method is use of a hot plate, but variations in temperature throughout the cell may lead to questionable results. In general, the use of a forced-draft air test chamber or automatic thermo-regulator cell is preferable.
19. Test Temperature
19.1 The loss characteristic measurement may be made when the test specimen is within 62.0°C of the desired temperature.
20. Test Voltage
20.1 In order that low-voltage instrumentation may be used for making the routine tests, no minimum voltage stress is specified. However, the precaution on high electrical stresses given in Section 9 shall be observed.
20.2 Frequencies from 25 to 1000 Hz may be used for routine tests.
21. Cleaning Test Cell
21.1 Since some two-electrode cells can not be dismantled, the cleaning procedure given in 10 can not always be followed. Where this applies, it is imperative that each laboratory evolves a good cleaning procedure for the cell used so that repeatable results can be obtained. Solvents mentioned in 10.2 as being satisfactory may be used as cleaning agents.
21.2 When a number of samples of the same type of fluid are to be tested consecutively, the same test cell may be used without cleaning it, provided the measured value of power factor or dissipation fact or of the sample previously tested was less than the specified value. If the measured value of the last sample tested was greater than the specified value, the test cell shall be cleaned before being used for further tests.
22. Preparation of Specimen and Filling Test Cell
22.1 Because of the difference in construction of the various types of test cells that may be used for routine tests, no detailed procedure for preparation of the specimen and filling of the test cell is given. Due regard should be given to the precautions outlined in Section 11.
22.2 Always rinse the test cell with a portion of the sample to be tested before the cell is filled.
23. Electrical Connection
23.1 When making electrical connection to a two-electrode cell, securely clip the shield on the lead usually connected to the guard electrode (see Fig.1) to the TFE-fluorocarbon insulation in order to prevent contact with any surface.
23.2 Always connect the high-voltage lead to the outer electrode as shown in Fig.1.
24. Number of Tests
24.1 Only a single test specimen need be tested in measuring dissipation factor or power factor.
25. Report
25.1 Report the following information:
25.1.1 Sample identification,
25.1.2 Type of test cell used,
25.1.3 Measurement procedure: routine,
25.1.4 Average voltage gradient in the test specimen sample, while under test, in volts per millimetre(voltspermil)(rms),
25.1.5 Frequency of applied voltage,
25.1.6 Temperature of the sample while under the test,
25.1.7 Temperature and humidity of the room during test, and
25.1.8 Dissipation factor or power factor of the sample, usually expressed as a percentage(%).
26. Precision and Bias
26.1 Precision:
26.1.1 The precision of this test method for making routine tests has not been determined through an inter-laboratory test program. Refer to 15.2 for precision regarding refere etesting.
26.1.2 A single operator statement was developed from ten results on one material from a single laboratory.
26.1.2.1 The single operator coefficient of variation for power factor by the routine method at 25°C has been found to be 3.8%; therefore, results of two properly conducted tests by the same operator on the same sample using the same equipment should not differ from each other by more than 11% of their average.
26.1.2.2 The single operator coefficient of variation for power factor by the routine method at 100°C has been found to be 3.1%; therefore, results of two properly conducted tests by the same operator on the same sample using the same equipment should not differ from each other by more than 9% of their average.
26.2 Bias - As there is no accepted reference material available for dissipation factor (or power factor), no bias statement can be made.
27. Keywords
27.1 dielectric constant; dissipation factor; power factor; relative humidity
