|
Temperature characteristics and insulating material
|
|
Dimensions of transformers
|
|
Our transformers are dimensioned in a way that doesn’t allow impermissible temperatures. The insulating materials have at least class E conform to IEC 85, mostly class B and on request even higher temperature classes. For the technical calculation, the temperature is computed at 1,06 times the primary voltage in rated operation and in short-circuit case.
|
|
Valid heat rise in standard operation conform to EN61558-1
|
|
The transformers may not reach improper temperatures when used as intended. The conformance is checked according to DIN EN 61558-1 § 14.2. The transformers and chokes are connected to the rated input voltage and then they are stressed with an impedance, which would give the rated power at rated output voltage and at alternating currents with the rated power factor. Subsequently the input voltage is increased for 6%. After this voltage increasement, the current circuit won’t be changed. The test is repeated in no-load condition, if this would be an infavourable situation.
Temperatures of windings are calculated with the resistance method. The value of temperature increasement of a winding can be calculated with the following equation:
Here: x = 234,5 for copper and:
D temperature increasement over t2, the highest temperature is D+t2
R1 resistance at test begin with temperature 1
R2 resistance at test end, in a presevered state
t1 ambient temperature at test begin
t2 ambient temperature at test end
At test begin the windings need the be at the same temperature as the ambient temperature.
For transformers with more than one input- or output winding or transformers that have a tapped input or output winding, the values with the highest temperature are considered. During the test, the temperature may not exceed the values given in table 1, if the transformer is operated with rated ambient temperature (25°C or ta).
|
|
Table 1: Highest temperature values at intended use
|
|
Components
|
Temperature
|
|
Windings (coils and metal sheets in connection to them), if the insulation system is made of:
- Material with thermal class A
- Material with thermal class E
- Material with thermal class B
- Material with thermal class F
- Material with thermal class H
|
100
115
120
140
165
|
|
The classification of materials is conform to IEC 60058 and IEC 60216. The values are adapted given the fact, that during these tests, the temperatures are average values, not hotspots.
|
|
|
|
Immediately after the test, the test item has to pass sthe voltage solidity, which is set in § 18.3 EN61558, though the test voltage is just connected between input and output current circuit. After the test, the electrical terminals may not be detached, the air and creepage distance may not be smaller than the values set in § 26 EN 61558-1; potting compound may not have phased out and overload protection may not have reacted. With extensive technical calculation (done with a computer software) of each transformer, we make sure, that the values in table 1 are not exceeded. A higher ambient temperature lowers the possible power of a transformer at given size.
|
|
Max. warming at short-circuit and overload conform to DIN EN61558-1
|
|
Table 2: Peak values of temperature in short-circuit and overload conditions
|
|
Classification of the insulation
|
A
|
E
|
B
|
F
|
H
|
|
|
max. temperature °C
|
|
absolutely short-circuit proof windings
|
150
|
165
|
175
|
190
|
210
|
|
Windings with protection device:
- during the length of T, see table 33)
- after the first hour, peak value
- after the first hour, arithmetic average
|
200
175
150
|
215
190
165
|
225
200
175
|
240
215
190
|
260
235
210
|
|
Outer housings (which can be touched with norm probe)
Rubber insulation of the conductors
PVC-insulation of the conductors
Surface (e.g. every area of the surface of a plywood board, which is covered by the transformer)
|
105
85
85
105
|
|
|
|
Table 3: Values of T and k for fuses
|
|
given rated current In of the protective fuses for gG in A
|
T
h
|
k
|
|
In < 4
4 < In < 16
16 < In< 63
63 < In < 160
160 < In< 200
|
1
1
1
2
3
|
2,1
1,9
1,6
1,6
1,6
|
|
|
|
Insulation declaration conform to IEC 85
|
|
On request, you obtain an insulation declaration for each transformer. This includes information about the used insulation materials and their temeprature class.
|
