IEC standard ambient temperatures are as follows:
Maximum temperature +40℃
Minimum temperature -30℃
Altitude 1000m
The temperature rise decreases by the following values
The self-cooled transformer is 2.5%, and the air-cooled transformer is 5%.
The hot spot temperature rise and average temperature rise of winding can be calculated by the following formula:
∆θwhn=Z∆θwr KQn
Average winding temperature of dry type transformer after short circuit
| Heat resistance rating of windings |
Θ2/℃ |
|
| Copper | Alumium | |
| A | 180 | 180 |
| B | 250 | 200 |
| C | 350 | 200 |
| F , H | 350 | - |
Dry type transformer can be divided into resin type and non - resin type two categories. The winding of the numerical dry type transformer is wrapped with resin, and the winding wires cannot be contacted from the outside surface. The turn insulation and main insulation of the non-resin dry type transformer are all insulating materials that can work in the air, and the winding wires can be directly contacted from the outside surface without using resin to wrap the winding.
For ventilation and cooling of windings and iron cores, the necessary cooling airways will be provided in the windings and iron cores as required. The heat dissipation surface of dry type transformer can be divided into internal heat dissipation surface and external heat dissipation surface. The internal heat dissipation surface only relies on convection heat dissipation, and the external heat dissipation surface can be dissipated by convection and radiation. When calculating the temperature rise, the difference between the heat dissipation capacity of the internal heat dissipation surface and the external heat dissipation surface is converted by the equivalent coefficient, so that the two kinds of heat dissipation surface is converted into the equivalent one. Therefore, the heat dissipation equivalent coefficient α is introduced, and the heat dissipation capacity of the internal heat dissipation surface is multiplied by the heat dissipation equivalent coefficient α, so that the heat dissipation capacity of the internal heat dissipation surface can be converted into the heat dissipation capacity of the external heat dissipation surface.
