After the special enameled wire was kept at 200℃ for 30 minutes, the Φ0.25 mm and Φ0.50 mm enameled wires showed good adhesion without cracking or falling off. The Φ1.00 mm wire showed slight cracks in the 250℃ test, indicating that the thick wire enameled layer is more susceptible to thermal stress at high temperatures.
The following are experiments conducted on thermal performance enameled round wires:
Thermal shock refers to the possibility that the wire will be subjected to temperature shock after being stretched and/or wound or bent on the mandrel.
3.2 Test specimens
3.2.1 Round wire
The test specimens shall be prepared in accordance with the following provisions:
• 5.1.1.1 of IEC 60851-3:2009 for enameled wire with a nominal conductor diameter ≤ 1,600 mm;
• 5.2 of IEC 60851-3:2009, applicable to enameled wire with a nominal conductor diameter exceeding
1,600 mm;
• 5.1.1.4 of IEC 60851-3:2009, applicable to wound wire with a nominal conductor diameter ≤ 1,600 mm;
• 5.5.4 of IEC 60851-3:2009, applicable to wound wire with a nominal conductor diameter exceeding 1,600 mm.
3.2.2 Rectangular wire
The specimens shall be prepared as specified in 5.1.2 of IEC 60851-3:2009, but shall be bent only in the thickness direction.
3.3 Procedure
The specimens shall be placed in a forced air circulation oven at a temperature specified in the relevant standard ±5 °C for 30 minutes. After removal from the oven, the specimens shall be allowed to cool to room temperature and then inspected for cracks under magnification according to Table 1.
Table 1 — Magnification
| Wire dimension |
Magnification |
| Round wire Of nominal conductor diameter up to and including 0,040 mm |
10 to 15 times |
| Round wire Of nominal conductor diameter over 0,040 mm up to and including 0,500 mm |
6 to 10 times |
| Round wire of nominal conductor diameter over 0,500 mm |
1 to 6 times |
| Rectangular wire |
6 to 10 times |
3.4 Results
Three specimens shall be tested for round wire and two specimens for square wire. Any cracks found shall be reported.
4 Test 10: Cutting breakdown (applicable to enameled round wire and wrapped round wire with nominal conductor diameter greater than 0.100 mm up to 1.600 mm)
4.1 GeneralThe cutting breakdown temperature indicates the temperature at which a short circuit occurs between two conductors crossing at right angles with a specified load applied at the crossing point.
NOTE: In many cases, the cutting breakdown temperature indicates that the insulation has decomposed.
4.2 Equipment
The following equipment shall be used:
• A brass or copper metal block, equipped with electrical heating, temperature measurement and temperature control, with two slots for inserting two conductors, the conductors cross vertically, the intersection point is located in the center of the metal block, and a ceramic piston is used to apply a load at the intersection point, as shown in Figure 1;
• A transformer of at least 100 VA, providing an AC test voltage of (100 ± 10) V, connected to an overcurrent protection device with an operating current of (5 ± 1) mA, and a resistor that limits the current to a maximum of 50 mA.
4.3 Procedure
Two straight conductors are inserted vertically and cross-connected into the metal block, which is preheated to the temperature specified in the relevant standards.
The temperature measurement shall be made as close to the intersection point as possible and shall not deviate from the specified value by more than ±3 °C. The intersection point shall be located directly below the piston. For conductors with a nominal conductor diameter of less than 0.200 mm, two straight conductors shall be placed parallel to each other and the third conductor shall be placed perpendicular to the first two conductors, with the intersection point symmetrical with respect to the piston axis.
The load shown in Table 2 shall be applied through the piston. Immediately thereafter, the test voltage shall be applied between the upper and lower conductors. If two lower conductors are used, they shall be connected. The load and test voltage shall be applied for 2 minutes. Three tests shall be carried out. Any failure shall be reported.
Table 2 – Loads applied to intersections
| Nominal conductor diameter |
Load |
| Over |
Up to and including |
|
| o, 100 |
o, 125 |
|
| O, 125 |
0,315 |
2,20 |
| 0,315 |
0,500 |
4,50 |
| 0.500 |
0.800 |
9, 00 |
| 0,800 |
1 ,250 |
18,00 |
| 1 ,250 |
1 ,600 |
36,00 |
5 Test 15: Temperature index
The temperature index shall be determined in accordance with IEC 601-72 (on unimpregnated specimens).
6 Test 21: Mass loss (applicable to enameled round wires)
6.1 General
The mass loss is the mass loss of the wire coating and indicates its degree of curing.
6.2 Specimen
A wire with a coating of not less than 0.5 g shall be cleaned by an appropriate method which shall not affect the coating. The specimen shall be heated in a forced air circulation oven at (130 ± 3) °C for 1 h. After removal from the oven, the specimen shall be placed in a desiccator and allowed to cool to room temperature for at least 30 min. The specimen shall then be weighed to the nearest 0.1 mg (M1).
6.3 Procedure
The crucible shall be preconditioned at (150 ± 3) °C for 2 h. The crucible containing the sample is then placed in a forced air circulation oven and dried for 2 hours. The oven temperature shall not deviate more than ± 3 °C from the value specified in the relevant standard. After removal from the oven, the sample shall be placed in a desiccator and cooled to room temperature for at least 30 minutes. The sample shall then be weighed to an accuracy of 0.1 mg (M2).
The coating shall be removed by an appropriate chemical method that does not affect the conductor, and the bare conductor shall be dried at (150 ± 3) °C for (15 ± 1) minutes, placed in a desiccator, and
cooled to room temperature for at least 30 minutes. The bare conductor shall then be weighed to an accuracy of 0.1 mg (M3).
The mass loss shall be calculated according to the following formula:
Mt-M2 x 100% Mt-M3
Two tests shall be carried out. The values of the two tests shall be reported.
