The magnetic lines of force generated by the coil cannot pass through the secondary coil, so the inductance that causes magnetic leakage is called leakage inductance. Refers to the part of the flux that the primary and secondary of the transformer are missing during the coupling process.
Cause of leakage inductance
The leakage inductance is generated because some primary (secondary) magnetic flux is not coupled to the secondary (primary) through the magnetic core, but is returned to the primary (secondary) by air closure.
The conductivity of the wire is about 109 times that of the air conductivity, and the ferrite core material for the transformer has a magnetic permeability of about 104 times that of the air. Therefore, when the magnetic flux passes through the magnetic circuit formed by the ferrite core, a part of the air leaks into the air, and a closed magnetic circuit is formed in the air, thereby generating magnetic leakage. Moreover, as the operating frequency increases, the magnetic permeability of the ferrite core material used decreases. Therefore, at high frequencies, this phenomenon is more pronounced.
Leakage inductance must exist in the main circuit of the switching power supply, especially in transformers, inductors, etc. In the past, it was generally ignored in the discussion, and the design was even more unconsidered. Now with the increasing capacity of the switching power supply and the increasing capacity of the whole machine, this parameter affects the main parameters of the switching power supply. For example, the switching power supply of 40A/5V output has a voltage loss of 20%, which also affects the weight of the switching power supply. And efficiency. Therefore, the discussion and research on leakage inductance has been put on the agenda. The pulse voltage VS(t) is applied to the transformer coil to generate a current, which produces a closed main magnetic flux Φ(t) along the core magnetic path and a closed leakage magnetic flux Φσ(t) in a portion of the path near the core. Φ(t) and Φσ(t) will respectively generate induced electromotive forces e(t) and eσ(t) in the coil, and the sum of the two plus the resistance voltage drop is balanced with the applied voltage, obeying the KVL equation. In the past, the general book omitted oσ(t), and the KVL equation was simplified to Vs(t)=Δt.
Impact of leakage
Leakage inductance is an important indicator of switching transformers. It has a great influence on the performance of switching power supply. The existence of leakage inductance, when the switching device is turned off, will generate back electromotive force, which is easy to over-voltage breakdown of the switching device; leakage inductance can also be The distributed capacitance in the circuit and the distributed capacitance of the transformer coil form an oscillating circuit, causing the circuit to oscillate and radiate electromagnetic energy outward, causing electromagnetic interference.
The conclusion that the leakage inductance of the transformer affects the rectifier circuit is as follows:
1. The commutation overlap angle y occurs, the average value Ud of the rectified output voltage decreases, and the power factor of the rectifier circuit decreases;
2. A gap occurs in the phase voltage during the commutation, causing distortion of the power grid waveform and becoming a source of interference. Producing a positive du/dt may cause the thyristor to be mis-conducted, for which an absorbing circuit must be added;
3. The leakage inductance of the transformer can limit its short-circuit current and reduce the di/dt of the thyristor, which is beneficial to the safe opening of the thyristor;
4. The working state of the rectifier circuit increases.
Vertical Dip Centronic Connector
Vertical Dip Centronic Connector.
Current Rating:5A
Dielectric Withstanding Voltage:1000V for one minute
Insulation Resistance:1000MΩ Min.(at 500V DC)
Contact Resistance:35mΩ Max.
Temperature:-55°C to +105°C
Vertical Dip Centronic Connector
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