A bifilar coil is an electromagnetic coil that has two parallel, closely spaced windings. Three wires insulated from each other can also be used - such a device will be called a “trifilar coil”.
In electrical engineering, the word "bifilar" describes a conductor or a wire that is made of several (in particular, two - from the word "bi") cores isolated from each other. This term is often used to refer to special types of wires for transformer windings. The bifilar wire is basically two colored enameled and insulated wires connected together.
A bifilar coil is a device that needs and can be classified by the method of application. There are four main types of such devices:
- Coil with serial connection and parallel winding.
- Parallel connection and winding.
- The coil is wound counterclockwise, and the connection is serial.
- The coil winding is made as in the previous paragraph (counter), but the connection is already parallel.
The bifilar coil is usually wound so that in both its components the current will flow in the same direction. The magnetic field created by the first winding will be added to the field created by another coil. This effect leads to the imposition of fields and the creation of a common large magnetic flux.
There are cases when the bifilar coil is assembled a little differently. For example, when the turns of the windings are arranged so that the electric current flows in opposite directions. These are the so-called coils with a zero coefficient of self-induction (because the magnetic field created by one winding will be in the direction opposite to the field created by the second winding, but it will be equal in value to it, which in the case of superposition of fields gives a total of zero).
Such devices are often used in modern electronic technology as one of the ways to create a wire resistor with a small inductance.
Another type of device, such as bifilar coils, can be seen in the windings of relays or transformers. They are also used in pulsed electrical power sources due to their ability to suppress reverse electromotive force (EMF). The winding of the inductors in this case is as follows. Two windings are located very close to each other and are wound parallel to each other, but effectively insulated. The main winding will control the relay, but the auxiliary winding is short-circuited inside the case. The current through the first winding is interrupted (when the relay is turned off), absorption of part of the magnetic energy by the auxiliary winding takes place. Such bifilar coils also generate heat to increase internal resistance.
When using such a coil in pulse transformers, one winding is used as an energy diffuser. Due to the proximity of the windings, both conductors pick up one magnetic flux and compensate for it.