What is transformer leakage inductance and how harmful it is

We know that transformers are mainly composed of primary coils, secondary coils, and iron cores (also known as magnetic cores). It is a device that uses the principle of electromagnetic induction to change the AC voltage. An ideal transformer has no losses, but that is only under ideal conditions.

In practice, not all of the magnetic flux generated by the primary and secondary coils of a transformer passes through the main magnetic circuit core. A portion of it passes through the air to form a circuit, which is called leakage flux. The corresponding inductance value is called leakage inductance, because leakage inductance is not necessary for us.

The leakage inductance increases with the increase of working frequency. Due to the low working frequency of power frequency transformers (the working frequency of power frequency transformers generally refers to 50Hz or 60Hz; the working frequency of high-frequency transformers is generally above 1KHZ, or even hundreds of KHZ), the impact of leakage inductance can generally be ignored. However, for high-frequency transformers, reducing leakage inductance is particularly important. Nowadays, the frequency requirements of switching power supplies are becoming higher and higher, Transformers have become an important indicator for measuring the quality of switching power supplies, as they have a significant impact on the performance of switching power supplies. Leakage inductance can cause radiation interference in the circuit, causing interference noise to the entire switching power supply. Some transformers are shielded, but there may still be some interference present.

How to measure leakage inductance?

The size of the leakage inductance of a transformer is an important factor in measuring whether a transformer is in good condition, because a transformer has both primary and secondary coils. Therefore, when measuring leakage inductance, the secondary winding is usually short circuited and the inductance of the primary winding is measured. This inductance value is the leakage inductance from the primary to the secondary. Similarly, short circuiting the primary winding can be tested using an LCR meter.

How to reduce leakage?

1. Change the winding method of the transformer and use a sandwich like structure to winding the transformer, which will reduce leakage inductance;

2. For low-power transformers, shell type iron cores can be used with ferrite as the material, which can increase the shielding effect;

3. Determine the configuration between windings in the coil based on different situations, and cross winding can enhance mutual coupling and ultimately reduce leakage inductance;

4. The place where the lead out line is located should be average, and try to form a right angle as much as possible