Test 13:How to do breakdown voltage of enameled wire?
1. This test is applicable to enamelled round wire with a nominal conductor diameter over 0,250 mm and to enamelled rectangular wire.
The test is not suitable for round wires with a nominal conductor diameter up to and including 0,250 mm, grade 1 to grade 3.
2.This test is applicable to enamelled round wire.
Resistance to refrigerant is expressed by the quantity of matter extracted from the coating of the wire and by the breakdown voltage after exposure to a refrigerant.
refrigerant
NOTE 1 The data in this test method apply to monochlorodifluoromethane (refrigerant R 22). Other refrigerants that have been determined by investigation to be appropriate for this test are provided in Annex A. When these other refrigerants are used, it is important for safety reasons to observe the critical data for these refrigerants and to comply with the revised test conditions during operation of the pressure vessel.
3. Procedure
The specimen shall be conditioned in the oven (1 50 ± 3) °C for 4 h and then placed in the pressure vessel, which shall be assembled and charged with (1 400 ± 50) g of refrigerant. The pressure vessel shall be heated according to 4.2.4 but for a period of (72 ± 1 ) h.
At the end of the exposure period, the pressure vessel shall be cooled and discharged as described under 4. When the pressure inside the tube is less than 2 bar (0,2 MPa) absolute, the pressure vessel shall be opened and the specimen, within a period of 25 s to 30 s, transferred to the oven at a temperature of (1 50 ± 3) °C. The specimen shall remain in the oven for (1 0 ± 1 ) min. After the specimen is removed from the oven and allowed to cool to room temperature, the breakdown voltage shall be determined as follow:
Test at room temperature
A straight piece of wire, approximately 400 mm in length, with the insulation removed at both ends, shall be twisted back on itself for a distance of (1 25 ± 5) mm on the twisting device. The ends of the wire shall be joined, and the load applied with the number of twists. The loop at the end of the twisted section shall be cut at two places to provide a maximum spacing between the cut ends. Any bending to ensure adequate separation between the two wire ends shall avoid sharp bends or damage to the coating.
The test voltage shall be applied according to between the conductors of the wires.
Five specimens shall be tested. The five single values shall be reported.
The breakdown voltage is determined after exposure of the specimen to the refrigerant under pressure and at elevated temperature.
4. The eight specimens shall be placed in the siphon cup, which is suspended (25 ± 5) mm below the condenser coil on the pressure vessel cover. The pressure vessel shall be assembled and charged with (700 ± 25) g of distilled refrigerant free from lubricant. The condenser water supply and drain line shall be connected and the pressure vessel shall be heated by means of a controlled heating system with the temperature set to (75 ± 5) °C or a lower temperature if required to comply with the conditions of the following paragraph relating to critical pressure. The water flowing through the condenser shall be adjusted to maintain a reflux rate of 20 to 25 discharges per hour from the siphon cup. The extraction period shall be 6 h.
5. Result
Five specimens shall be tested. The five individual values shall be reported.