Inductor coil: device, principle of operation, purpose

Inductors are widely used in electrical engineering as energy storage, oscillatory circuits, current limiting. Therefore, they can be found everywhere, from portable electronics to substations in the form of giant reactors. In this article we will tell you what an inductor is, as well as how it works and much more.

Definition and principle of action

An inductor is a coil of insulated conductor coiled or otherwise coiled. Main features and properties: high inductance with low capacitance and active resistance.

It stores energy in a magnetic field. In the figure below you see its conventional graphic designation on the diagram (UGO) in different types and functional purposes.

It can be with or without a core. At the same time, with a core, the inductance will be many times greater than if it is not there. The amount of inductance also depends on the material from which the core is made. The core can be solid or open (with a gap).

Let us recall one of the laws of commutation:

The current in an inductor cannot change instantly.

This means that an inductor is a kind of inertial element in an electrical circuit (reactance).

Let's talk, how does this device work? The larger the inductance, the more the current change will lag behind the voltage change, and in alternating current circuits, the current phase will lag behind the voltage phase.

This is the principle of operation of inductors - the accumulation of energy and the delay of the front of the current rise in the circuit.

This also implies the following fact: in case of an open circuit in a circuit with high inductance, the voltage on the key rises and forms arcif the key is semiconductor, it breaks down. To combat this, snubber chains are used, most often from resistor and capacitorinstalled parallel to the key.

Types and types of coils

The coil design may vary depending on the application and circuit frequency.

By frequency, it can be conditionally divided into:

• Low frequency. An example is a fluorescent lamp choke, a transformer (each winding is an inductor), a reactor, EMI filters. The cores are most often made of electrical steel, for AC circuits from sheets (laminated core).
• High frequency. For example, looped coils of radio receivers, communication coils of signal amplifiers, storage and smoothing chokes of switching power supplies. Their core is usually made of ferrite.

The design differs depending on the characteristics of the coil, for example, the winding can be single-layer and multi-layer, wound by turn or with a pitch. The pitch between turns can be constant or progressive (varying along the length of the coil). The way of winding and construction affects the final dimensions of the product.

Separately, it is worth talking about how a coil with variable inductance is arranged, they are also called variometers. In practice, you can find different solutions:

• The core can move relative to the winding.
• Two windings are located on one core and are connected in series; when they move, the mutual induction and inductive coupling change.
• The turns themselves for tuning the loop can move apart or narrow when approaching each other (the denser the winding, the greater the inductance).

Etc. In this case, the moving part is called the rotor, and the stationary part is called the stator.

The winding method is also different, for example, filters with a counter-winding suppress network interference, and wound to one side (matched winding) suppress differential noise.

What are they for and what are they

Depending on where the inductor is used and its functional features, it can be called differently: chokes, solenoids, etc. Let's take a look at what inductors are and their scope.

Chokes. Usually the so-called devices for current limiting, scope:

• In ballasts for ignition and power supply of gas-discharge lamps.
• For noise filtering. In power supplies - an electromagnetic interference filter with a double choke at the input of a computer power supply, shown in the photo below. Also used in acoustic equipment and more.
• For filtering specific frequencies or frequency bands, for example in loudspeakers (to split frequencies across the appropriate speakers).
• The basis in pulse converters is an energy storage device.

Current-limiting reactors - used to limit short-circuit currents on power lines.

Note: chokes and reactors must have low resistance to reduce heating and losses.

Loop inductors. They are used in tandem with a capacitor in an oscillating circuit. The resonant frequency is matched to the frequency of reception or transmission in radio communications. They must have a high Q factor.

Variometers. As mentioned, these are tunable or variable inductors. Most often they are used in the same oscillatory circuits to fine tune the resonance frequency.

Solenoid - this is the name of the coil, the length of which is much larger than the diameter. This creates a uniform magnetic field inside the solenoid. Most often, solenoids are used to perform mechanical work - translational motion. Such products are also called electromagnets.

Consider where solenoids are used.

This can be a lock activator in a car, the rod of which is retracted after the voltage is applied to the solenoid, and a bell, and various actuating electromechanical devices such as valves, lifting magnets on metallurgical productions.

In the relay, contactors and starters the solenoid also acts as an electromagnet to drive the power contacts. But in this case, it is more often called simply a coil or a relay coil (starter, contactor, respectively), as it looks like, using the example of a small-sized relay, you see below.

Loop and ring antennas. Their purpose is to transmit radio signals. Used in car immobilizers, metal detectors and wireless communication.

Induction heaters, then it is called an inductor, instead of a core, a heated body (usually a metal) is placed.

main parameters

The main characteristics of an inductor include:

1. Inductance.
2. Current strength (for the selection of a suitable element during repair and design, this must be taken into account).
3. Loss resistance (in wires, in core, in dielectric).
4. Quality factor is the ratio of reactance to active resistance.
5. Parasitic capacitance (capacitance between turns, in simple terms).
6. Temperature coefficient of inductance - the change in inductance when an element is heated or cooled.
7. Temperature coefficient of quality factor.

Marking

To designate the rating of the inductor, use letter or color coding. There are two types of lettering.

1. Microgenry designation.
2. Designation by a set of letters and numbers. The letter r is used instead of a decimal point, the letter at the end of the designation denotes a tolerance: D = ± 0.3 nH; J = ± 5%; K = ± 10%; M = ± 20%.

The color coding can be recognized in the same way as on the resistors. Use the table to decipher the colored stripes or rings on the element. The first ring is sometimes made wider than the rest.

This is where we finish considering what an inductor is, what it consists of and why it is needed. Finally, we recommend watching a useful video on the topic of the article:

Related materials:

• How to make an induction boiler with your own hands
• What is self-induction
• Inductor coil calculator

Author: Alexey Bartosh