Dry Type Test Transformer

Balanced Heat and DissipationStable temperature rise of the winding

Loss power on the winding is the heat source causing winding temperature rise.,This is quite manageable..The heat dissipation of the winding is a relatively complex issue..Heat within the winding is transferred to the winding's surface through conduction.,Heat is transferred to the external environment through convection and radiation on the surface..When the heating and cooling of the winding reach a balance.,It's the stable temperature rise of the winding.

Winding heat dissipation is a complex process. Key factors affecting winding heat dissipation include: winding temperature; insulation thickness; outer insulation thickness of the winding; thermal conductivity of the outer insulation material; width and length of the heat dissipation channels; air flow velocity; and the impact of the core and adjacent windings on heat dissipation. Therefore, the calculation of winding temperature rise varies depending on the type of insulation material and structure used.

Mathematical Model for Winding Temperature Rise Calculation

The stable temperature rise of the winding is generally calculated using a simplified formula.,The coefficients used for windings with different structures and insulation materials vary. The temperature range applicable to the formula is also limited.:

τ＝ K Q X

Q ＝ W／S

S ＝∑ αi Si

 In the formula:τ—Winding temperature rise

K—Coefficient;

 XCoefficient related to heat dissipation,Better heat dissipationX The value is smaller.

Q— Unit thermal load of the windingW/m2

 WWinding loss power at reference temperatureW

 S— Equivalent thermal dissipation surfacem2

 SiInsulated winding cooling surfacem2

 αiThermal Conductivity

2.1 Transformer calculation formulas vary depending on the structural type.

2.2 The cooling of dry-type transformers is primarily achieved through convection and radiation, with the temperature rise due to conduction in non-encapsulated transformers being minimal. Consequently, some calculation formulas omit the temperature rise caused by conduction from layer insulation and external insulation, while others require the addition of this temperature rise, such as the calculation formulas for European resin-insulated dry-type transformers.

2.3 Bold-faced thermal radiationNo Chinese content provided..Please provide the Chinese content to be translated.Temperature's 4 Proportionally squared, within a relatively small temperature range, the combined effect of convection and radiation on heat dissipation results in a temperature rise equation with a coefficient.XCoefficient related to heat dissipation,Enhanced heat dissipationX The value is smaller..As the temperature rise of oil-immersed transformer layer windingX Please provide the Chinese content to be translated.0.8While forcing oil circulationX No Chinese content provided.0.7Pie-shaped windingX Retrieve0.6Dry-type TransformerX Value gained0.8Please provide the Chinese content to be translated.80K At right angles, due to higher heat dissipation efficiency at high temperatures, in some calculation formulasX Please provide the Chinese content you would like to have translated into American English.0.75Therefore, when the temperature rises...100—125K At the moment,X The value should be smaller.

2.4 When the temperature range is wide, a single calculation formula may not be sufficient to address both ends, necessitating the use of two or more formulas.X The value varies, indicating different slopes. In fact, it is an approximate curve composed of several straight lines.

2.5 Unit thermal load of the windingQ Power refers to the power on an uncovered unit heat surface.W/m2The presence of a vented cooling surface requires determining the cooling coefficient of the vents.

2.6 If the calculated temperature rise is significantly different from the reference temperature, and the difference between the calculated winding loss power and the actual power is too great, resulting in a large error, then the reference temperature used to calculate the winding loss power should be adjusted.

Factory Method for Determining Mathematical Models

 A practical method for determining mathematical models is through the temperature rise test of typical transformers. The temperature rise of the airless winding is fundamental, such as the outer winding wrapped around a thick insulating tube. The size of the area outside the coil is the effective heat dissipation surface, and the heat load is first calculated. Q Value, as determined by the temperature rise obtained from the testQ Please place values on the log-log coordinate paper, at least.3 A set of experimental data can be plotted on a logarithmic graph paper to form a reasonable straight line, from which the two coefficients of the formula can be determined.K No Chinese content provided.X。

τ= K Q X

 τ1

 K = ————

Q1 X

 Lgτ2 - Lgτ1 Lgτ2/τ1

 X =———————— = ————

 Lg Q2 - Lg Q1 Lg Q2/Q1

 In the formula:

 τ1，τ2——Take the temperature rise of the two products along the straight line

 Q1，Q2—— Corresponding unit heat load

τ—the temperature rise of the product in question

 Q—— Unit heat load of the sought-after product

To determine the equivalent heat dissipation surface of the inner coil and the surface with the airway, it is first necessary to establish the heat dissipation coefficient of the airway. Calculate the heat load. Q Value, as determined by the temperature rise obtained from the testQ Plot values on a double logarithmic graph, at least3 A trial data, method as above.

It should be noted that this line has an acceptable error only within a certain temperature range. Outside of this range, the slope of the line is different, actually consisting of a curve composed of many broken lines.

Another point to note is that the calculated surface area for heat dissipation must match the actual manufactured product.