Table 1 – Maximum normal temperature rises Continued
Parts
Temperature rise K
3)
This limit applies to cables, cords and wires complying with the relevant IEC standards; for
others, it may be different.
4)
The values in parentheses apply, if the material is used for handles, knobs, grips and the like,
and is in contact with hot metal.
5)
There is no specific limit for thermoplastic material, which has to withstand the tests of 29.1, for
which purpose the temperature rise must be determined.
6)
The limit specified concerns the deterioration of wood, and it does not take into account
deterioration of surface finishes.
7)
There is no limit for the temperature rise of capacitors which are short-circuited in 18.10
If these or other materials are used, they shall not be subjected to temperatures in excess of the
thermal capabilities as determined by ageing tests made on the materials themselves.
The value of the temperature rise of a winding is calculated from the formula:
∆
t = (R
2
- R
1
/R
1
)(k + t
1
) - (t
2
- t
1
)
where:
∆
t is the temperature rise;
R
1
is the resistance at the beginning of the test;
R
2
is the resistance at the end of the test;
k is the equal to 234,5 for copper windings, and 225 for aluminum windings;
t
1
is the ambient temperature at the beginning of the test;
t
2
is the ambient temperature at the end of the test.
At the beginning of the test, the windings are to be at ambient temperature. It is recommended
that the resistance of windings at the end of the test be determined by taking resistance
measurements as soon as possible after switching off, and then at short intervals so that a curve
of resistance against time can be plotted for ascertaining the resistance at the instant of switching
off.
12.6 If the windings are classified according to IEC 60085 and the temperature rise does not exceed the
value in Table 1, the following test is not necessary.
Three additional samples are subjected to the following tests.
a) The temperature rise of the windings is determined by the test of 12.2.
b) The samples are then dismantled as far as is possible without damaging any part. Windings
are kept for 10 days (240 h) in a heating cabinet, the temperature of which is (80
±
1) °C in
excess of the temperature rise determined according to item 1.
c) After this treatment, the samples are reassembled and no interturn short circuit shall occur.
Interturn short circuits may be detected by means of a winding tester.
d) Immediately afterwards, the samples shall withstand the tests of clause 13 and 15.
e) The samples are then subjected to a humidity treatment as specified in 14.3.
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