6. Apparatus
6.1 Measuring equipment used in these procedures shall be in accordance with Test Methods D150.
6.2 Use only a three-terminal cell for these tests.
6.3 The design of test cells that conform to the general requirements given in the Annex are considered suitable for use in making these tests.
6.4 Forced-Draft Oven:
6.4.1 When the tests are to be made above room temperature, a suitable forced-draft, thermostatically controlled oven shall be used as the test chamber. The oven must be capable of meeting the temperature requirements set out in Section 11. For tests at room temperature the unheated oven can be conveniently used as the test chamber.
6.4.2 Provide the test chamber with an opening in the wall through which two lengths of TFE-fluorocarbon-insulated(or similar) shielded cable pass to make electrical connection from the measuring equipment and high-voltage transformer, respectively, to the test cell. Use a perforated ceramic plate or disk to insulate the test cell from the metal flooring of the oven if the flooring is not insulated from the oven. Provide a safety interlock on the door of the oven so that the electrical circuit supplying voltage to the test cell will be broken when the oven door is opened.
6.4.3 A cross-sectional view of the test chamber with a three-electrode test cell in place and with test cables connected is shown in Fig.1.
6.5 Automatic Thermo-Regulator Cell:
6.5.1 When tests are to be made above room temperature but below the flash point, an automatic thermo-regulator cell can be used as long as it provides uniform heating of the test cell.
6.5.2 The automatic thermo-regulator cell must be able to provide rapid, controlled rate of temperature rise, and be able to maintain a liquid temperature constant to within more or less 1°C.
7. Calibration
7.1 Calibration of test instruments shall be traceable to national standards.
7.2 Verify the calibration at least annually using reference devices that are traceable to national standards.
7.3 Refer to Practice D2865 and IEEE Standard 4 for guidelines on calibrating test equipment.
8. Test Temperature
8.1 The temperature at which a referee test is made shall be mutually agreed upon between the purchaser and the seller. Measurements are made at many different temperatures. For acceptance tests, it is generally made at a temperature of 100°C, while for routine testing it is usually made at 25, 85 or 100°C. In some research investigations, tests may be made at considerably higher temperatures while in other cases, particularly for tests on cable oils in service, tests may be made over a range of temperatures.
9. Test Voltage
9.1 The average stress to which the specimen is subjected shall not be less than 200V/mm (5V/mil)(rms). Tests at higher stresses are desirable but shall not reach such values that electrical discharges across the cell insulating surfaces occur or that internal ionization of the specimen may be expected. Stress ranges in normal usage for referee tests are 200 to 1200V/mm (5 to 30V/mil)(rms).
9.2 Because the ac loss characteristics can vary with voltage stress, for reference purposes it is desirable to make the measurements at a specific value of voltage stress within the limits in 9.1.
9.3 Referee tests should be carried out in the frequency range 45 - 65Hz.
