Leakage inductance occurs when transformer windings are not perfectly aligned, causing a voltage drop between primary and secondary currents. It can be advantageous in power distribution transformers and gas discharge lamps, but can also cause issues with regulating power and affecting the performance of MOSFETs and relays. It can be calculated mathematically and measured graphically.
Leakage inductance occurs inside a transformer because the internal wire windings are not perfectly aligned. The phenomenon occurs as a leak in magnetic flux deposits and releases energy, causing the flux to act as an inductor. This causes a certain voltage to drop between the primary and secondary currents. The leakage is usually too small to have much effect, but in high power transformers and a metal oxide field effect transistor (MOSFET) it is possible. Power distribution transformers can take advantage of leakage inductance as an advantage, as can gas discharge lamps, such as those used in neon signs.
When leakage inductance is present, one winding of the transformer shows signs of self-inductance. Voltage is raised based on how fast current changes, so any additional inductance has an effect on a transformer’s output power. It becomes difficult to regulate power when the transformer core and windings are not designed properly. This becomes more apparent when more electrical load is applied.
The performance of a MOSFET can be severely degraded because it turns on and off very quickly. Leakage inductance creates a current that cannot dissipate between cycles. Current also flows when the circuit is in an off state, which can affect applications that require the MOSFET to be on or off at certain times, or the state it actually is in can be misunderstood. A relay, on the other hand, can increase voltage if it is not turned off. If the voltages get high enough, damage to a resistor or switch contact can occur.
Many times, leakage inductance is used as a design advantage. Some transformers are built to limit current flows in this way, without integrating a sophisticated and expensive power dissipation system. It is also crucial for gas discharge lamps. In neon signs, the current must be limited so that the transformer is still usable in the event of a short circuit and the lamp is not damaged by high currents. It is also possible to control the current in transformers for arc welding systems, for which variable leakage inductance is a desirable characteristic.
Leakage inductance is calculated mathematically using the capacitance, coupling coefficient, and other properties of the wire. Graphical measurements allow you to visualize it by showing the difference in timing between the input and output signals. Instantaneous voltage changes on a conductor are not possible. The result is that increasing the leakage inductance will cause longer delays in the timing of the electrical signal.
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