Technology Literature

What are transformer losses and what is the best economical operating point?

Transformer loss is a concept in the field of modern physics, which refers to the sum of no-load loss Po, short-circuit loss Pk and stray loss Ps. When the rated voltage is applied to one winding of the transformer and the rest of the windings are open, the active power absorbed by the transformer is called no-load loss.

Several transformer losses and their causes:

1. Copper loss: The heat loss caused by the winding resistance, this is because the resistance is an energy dissipating element. The copper loss of the transformer is a variable loss, which is related to the load rate of the transformer. As the load increases, the copper quality also increases.

2. Ferrous (magnetic) core hysteresis loss: that is, in the process of alternating magnetization of ferromagnetic materials, because the magnetic domain flip is an irreversible process, the change of magnetic induction always lags behind the change of magnetic induction. field strength. The loss caused by this hysteresis phenomenon in the iron (magnetic) core is called iron (magnetic) core hysteresis loss.

3. Iron (magnetic) core eddy current loss: When alternating current passes through the winding coil, an alternating magnetic field will be generated around the coil, causing induced electromotive force and induced current core to be generated in the iron (magnetic) core. This induced current is called eddy current, and the resistive energy dissipation generated by the eddy current flowing in the iron (magnetic) core is called the eddy current loss of the iron (magnetic) core.

4. Frequency characteristics. The frequency characteristic means that the transformer has a certain working frequency range, and transformers with different working frequency ranges generally cannot be used interchangeably. Since the transformer operates outside its frequency range, the temperature will rise or it will not work properly during operation.

5. Insulation resistance. Insulation resistance refers to the resistance between each coil of the transformer and between each coil and the iron core (case). Its size is related to the size and time of the voltage applied by the transformer, its own humidity and the humidity of the insulating material. The insulation resistance of an ideal transformer should be infinite, but the insulation of the actual transformer material itself cannot be ideal, so its insulation resistance cannot be infinite. Insulation resistance is the ratio of the applied test voltage to the resulting leakage current.

Insulation resistance is a parameter to measure the insulation performance of a transformer. If the insulation resistance of the power transformer is too low, there may be a short circuit of the primary and secondary sides or a short circuit of the iron core shell, which may cause damage to the electrical equipment or the danger of the chassis being electrified. In general, between the primary and secondary coils of a power transformer, as well as between them and the iron core, there should be insulation properties that can withstand 1000V AC voltage for 1 minute without being broken down. When testing with a 1000V insulation resistance meter, the insulation resistance should be above 10M.

6. Leakage inductance. The magnetic flux generated by the current in the primary coil of the transformer does not all pass through the secondary coil, and this part of the magnetic flux that does not pass through the secondary coil is called leakage flux. The inductance caused by the leakage flux is called leakage inductance. The existence of leakage inductance not only affects the efficiency and other performance of the transformer, but also affects the circuit operation around the transformer, so the smaller the leakage inductance of the transformer, the better.

7. Temperature rise. The temperature rise of the transformer is mainly for the power transformer. It means that when the temperature of the transformer rises to a stable value after the transformer is energized, the temperature of the transformer is higher than the ambient temperature. The smaller the temperature rise of the transformer, the better. It should be noted, however, that sometimes the maximum operating temperature is used instead of temperature rise in the parameters.

The economic operating point with the least loss of transformer is when the load rate is 0.5-0.6, that is, when the iron loss of the transformer is equal to the copper loss. Whether to operate the transformers in parallel can be decided according to the economic operating point of the transformers. The power loss of a general transformer can be calculated as follows


In the formula, △P0=no-load loss of the transformer;

△Psc = short-circuit loss of the transformer;

△P = total loss of transformer;

Scp = the average capacity of the transformer;

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