Any electrical equipment will experience losses over prolonged operation, and power transformers are no exception.
1. Definition and Principle
Copper plays a crucial role in transformers as the windings typically use copper wire. The term "copper loss" in transformers refers to the losses occurring in these copper windings. Copper loss, also known as load loss, is variable and changes with the operating conditions of the transformer. When a transformer operates under load, the current passing through the windings encounters resistance, leading to resistive losses. According to Joule's law, this resistance causes Joule heating, and the power loss increases with the square of the current. Therefore, resistive losses are proportional to the square of the current and are independent of the voltage. Because these losses vary with the magnitude of the current, copper losses (load losses) are variable and constitute the primary losses during transformer operation.
2. Influencing Factors
Current Magnitude: As mentioned, copper losses are proportional to the square of the current, making the current magnitude a crucial factor affecting copper losses.
Winding Resistance: The resistance of the windings directly impacts copper losses. Higher resistance results in greater copper losses.
Number of Coil Layers: More coil layers mean a longer path for the current through the windings, increasing resistance and thus copper losses.
Switching Frequency: The impact of switching frequency on copper losses is directly related to the transformer's distributed parameters and load characteristics. When the load characteristics and distributed parameters together exhibit inductive characteristics, copper losses decrease with increasing switching frequency. Conversely, when they exhibit capacitive characteristics, copper losses increase with higher switching frequency.
Temperature: Load losses are also influenced by the transformer's temperature. The leakage flux caused by the load current can induce eddy current losses within the windings and stray losses in the metal parts outside the windings.
3. Methods to Reduce Copper Losses
Increase the Cross-sectional Area of the Windings: Reducing the resistance of the conductors can effectively lower the transformer's copper losses.
Use High-quality Conductor Materials: Employing materials like copper foil or aluminum foil can reduce winding resistance.
Minimize Light-load Operation Time: Limiting the proportion of time a transformer operates under light load can help reduce copper losses.
By understanding and managing these factors, the efficiency and longevity of transformers can be significantly improved, reducing operational costs and enhancing performance.
