About creating a cabinet for a transformer
Transformer design in a cabinet
First what you need to know is the ambient t temperature Ta ( normally 40°C) outside of the cabinet. On the next step you have to set the average air temperature rise dTc.av around the transformer. Tthis temperature rise can be calculated as follows:
dTc.av = (dTc.max + dTc.min)/2
Now you know the range of the value dTc.av = 10 - 18 °C. This value has to be set in the Large Transformers Program:
The cabinet design supports 5 different cabinet types:
In order to select a cabinet type for your application you can use the following diagram:
Assume you would like to have dTc.max = 25°C at the loss dansity q = 50W/m2 on the cabinet surface then you can use the cabinet type 0. For q = 300W/n2 you need to use the cabinet type 4.
The loss density q is calculated:
q = P/A
t is recommended to design the transformer by using the design criterion Active Short Circuit Voltage Ucca. With this criterion you can presribe the value of the transformer losses. Also, to keep the total transformer losses low it is recommended to use a good steel quality.
Here is the input form for the design of a cabinet
In the yellow output fields are the resulta of the transformer design:
Wt =>Ttransformer width
Note that the min. dimensions of the cabinet must be
Also, note that the cabinet design supports the max. loss density q.max as follows:
After you have selected the cabinet type and set the
cabinet dimensions Wc,Hc and Dc the program will calculate the
current loss dancity q with the transformer total losses P. If the
calculated current loss dancity q is smaller than q.max then you can
increase the loss density if needed If q>q.max then the
program will stopp running and return to the start position..
|0 Wc||0.15 Wc and 0.85 Wc||0.5 Wc|
|=.9 Hc||12 °C||29 °C||35 °C|
|0.1 Hc||5 °C||7 °C||10 °C|
This cabinet type has the oprming on the top and botton of the cabinet surface. The heat transfer runs over the cabinet surface and over the heated air flow through the openings (holes, gaps,shots, gill clefts) . Its thermal properties depends on the size of the cabinet survace and the opening factot Ka = Ao/Ac , where:
Ac = Wc Dc + 2 Hc (Wc+Dc)
Ao => survace of the opening on the top of the cabinet surface .
Note that the cabinet design supports Ka.max 0.5%.
Here is the typical field of the temperature rise at q=120W/m2 and Ka = 0.5%:
|0 Wc||0.15 Wc and 0.85 Wc||0.5 Wc|
|=.9 Hc||10 °C||20 °C||30 °C|
|0.1 Hc||3 °C||5 °C||10 °C|
If the bottom side is open, the transformer distance to the vertical cabinet walls bigger than 50mm and the distance of the cabinet roof to the vertical cabinet walls bigger than 30mm thenthe cooling condition of the transformer are very similat to the case without the cabinet.
This cabinet type is completly closed. The heat transfer runs only over the cabinet surface. Its thermal properties depend on the size of the survace and the air flow m = number of cabinet volumens per hour. In this cabinet type the transformer cooling and the heat transfer to the inside surface of the cabinet are better than in the cabinet type 0. Note that you have to set the air speed in the transformer design,
If the ambient temperature Ta is 40°C, do not use the max. air temperatur rise higher than 35°C because the temperature of the cabinet survace can be higher than 55°C.
The heat transfer runs over the air flow. Its thermal properties depend on the air flow m => number of cabinet volumens per hour. In this cabinet type the transformer cooling and the heat transfer to the inside surface of the cabinet are better than in the cabinet type 3. Note that you have to set the air speed in the transformer design,
Air speed in m/s = m Hc Wc Dc /(Wc Dc - Wt Dt)/3600
Note that the cabinet design calculates the max. air temperature rise in the cabinet dTc.max. In order to compare the calculated dTc.av use the formula:
dTc.av = (dTc.max+dTc.min)/2