Iron loss and copper loss of transformer

Any electrical equipment will suffer losses during long-term operation, and power transformers are no exception. The losses of power transformers are mainly divided into copper loss and iron loss.

Definition and Principle

Copper plays an important role in transformers. Copper wires are usually used in transformer windings. The "copper loss" in the transformer is the loss caused by the copper wires. The "copper loss" of the transformer is also called load loss. The so-called load loss is a variable loss, which is variable. When the transformer is running under load, there will be resistance when the current passes through the wire, resulting in resistance loss. According to Joule's law, this resistance will generate Joule heat when the current flows through it, and the greater the current, the greater the power loss. Therefore, the resistance loss is proportional to the square of the current and has nothing to do with the voltage. It is precisely because it changes with the current that the copper loss (load loss) is a variable loss, and it is also the main loss in the operation of the transformer.

Influencing factors

Current size: As mentioned above, copper loss is proportional to the square of the current, so the current size is the key factor affecting copper loss.
Winding resistance: The resistance of the winding directly affects the copper loss. The larger the resistance, the higher the copper loss. Number of coil layers: The more coil layers there are, the longer the path for the current to flow in the winding, and the resistance will increase accordingly, resulting in increased copper loss. Switching frequency: The effect of switching frequency on transformer copper loss is directly related to the distributed parameters and load characteristics of the transformer. When the load characteristics and distributed parameters are inductive, the copper loss decreases with the increase of switching frequency; when they are capacitive, the copper loss increases with the increase of switching frequency. Temperature influence: Load loss is also affected by the temperature of the transformer. At the same time, the leakage flux caused by the load current will generate eddy current loss in the winding and stray loss in the metal part outside the winding.

Calculation method

There are two calculation formulas
1. Formula based on rated current and resistance:
Copper loss (unit: kW) = I² × Rc × Δt
Where I is the rated current of the transformer, Rc is the resistance of the copper conductor, and Δt is the operating time of the transformer.
2. Formula based on rated current and total copper resistance: Copper loss = I² × R
Where I represents the rated current of the transformer, and R represents the total copper resistance of the transformer. The total copper resistance R of the transformer can be calculated by the following formula:

R = (R1 + R2) / 2
Where R1 represents the primary copper resistance of the transformer, and R2 represents the secondary copper resistance of the transformer.

Methods to reduce copper loss

Increase the winding cross-sectional area of the transformer: reduce the conductor resistance, thereby effectively reducing the copper loss of the transformer. Use high-quality conductor materials: such as copper foil or aluminum foil to reduce winding resistance. Reduce the light-load operation time of the transformer: limit the proportion of the time when the transformer is light-loaded, which is conducive to reducing the copper loss of the transformer.