Some cores do not have a core, while others use some form of ferrite metal. Low frequency cores normally have an iron core. The type of material used to create the core determines the strength of the magnetic field and the inductance of the coil. Amorphous cores are made from layers of magnetic tape that reduces the flow of eddy currents and can operate at higher temperatures. They are normally used in high efficiency transformers.
Iron cores create magnetic flux and are able to retain high magnetic fields. One drawback to iron cores is the eddy currents they produce that produce heat at high frequencies. Vitreous metals are glassy and non-crystalline. They are used for high frequency transformers.
This type of metal has low conductivity that reduces eddy currents. Ferrite ceramics are composed of an iron oxide ceramic compound and metallic elements. This form of core is produced specifically to meet the needs of a variety of electrical applications.
The ceramic material acts as an insulator and helps decrease eddy currents. Laminated cores are thin iron sheets covered with a layer of insulation to prevent eddy currents that confine them to a loop inside the laminated layers.
It is the thinness of the laminate that dispels the eddy current effect. These unique cores are made from powdered carbonyl iron and have applications across a wide range of magnetic flux and temperature levels. They are made of small iron spheres coated with a layer of insulation and reduce the effects of eddy currents at high temperatures. Silicon steel has a high electrical resistivity and provides excellent performance over an extended period of time.
They have high flux density and are chosen for high performance applications. Molypermalloy is a powder core material that is produced by combining molybdenum, nickel, and iron. It has low core loss and signal distortion with temperature stability. It is used for audio frequency applications, resonant circuits, and loading coils.
Sendust is a metal powder that is a combination of iron, silicon, and aluminum, which is sintered into core material. These coils have excellent magnetic permeability, low coercivity, and temperature stability. They are used for abrasive applications like magnetic recording heads.
Nanocrystalline material is a polycrystalline that has a crystallite size in a few nanometers, which fills the gaps between amorphous materials. It is produced by casting molten metal into a thin ribbon that is rapidly cooled. The crystalline structure is created by careful annealing. The resistivity of NC is very high and effective at wide band frequencies. Components can be produced smaller and are ideal for complex EMI scenarios.
This shape of core is used to create a closed magnetic field with the circuit wrapped around the center leg that is twice the size of the other legs. A planar core comes in a variety of shapes but consists mainly of a flat piece of magnetic material that is above and below the coil. A toroidal core is a circle or donut shape with the circuit wrapped around the circumference of the circle.
Air coils do not have a core for its inductance, which is unaffected by the current it carries. They are free of iron losses that affect ferromagnetic coils, which is an advantage as frequencies increase. Air coils are capable of performing at one Ghz, unlike coils with a core. The choice of the type of electrical coil is determined by how it will be used, which includes whether the project requires a DC or AC electric motor.
Electric coils, regardless of what type, have electric current that interacts with a magnetic field. Different types of coils are used for motors, generators, transformers, magnetics, and sensors Electronics, electricity, and magnetism use different forms of coils for each application. The list below is a brief description of various types of coils. Electromagnetic wire which has been wound around a plastic core, or "bobbin".
Plastic cores come in many sizes, and bobbin wound coils may be impregnated, molded, or taped to meet various medical device, sensing, relay, and automotive applications. This form of coil is used when there is limited space and no room for a bobbin or core. Since they can be placed closer to the metal in the circuit, they have greater magnetic capabilities.
They are used for clutches, magnetic locks, and audio circuits. A choke coil has low resistance and high inductance. They are used with AC and DC currents. Choke coils block AC and allow DC to pass through. The resistance of a choke coil increases with the frequency of the current. Encapsulated coils, or molded coils, are protected from moisture, corrosive chemicals, vibration, explosions, and harsh working environments by being encapsulated in a tough temperature resistant thermoplastic. The design of encapsulated coils provides them with additional insulation and dielectric properties.
High voltage coils are used in applications where the voltage is higher than what is considered to be safe. The reference to high voltage indicates that the current is potentially dangerous due to sparks or electric shock.
The classification for high voltage is one thousand volts for AC circuits and fifteen hundred for DC circuits. The two types of high voltage coils are ignition and Tesla. A Tesla coil is a radio frequency oscillator that powers a resonant transformer to change high voltages to low voltages.
It is two open electric circuits connected to a spark gap. For the best results, Tesla coils are made from copper wire. Ignition coils are used to change lower voltage power to higher voltage to fire a spark plug. They are like an electric transformer and have primary and secondary coil windings. The most common and familiar use of ignition coils is in the auto industry.
With an impregnated coil, the void space in the winding has been impregnated with resin or other material to reduce the motion of the conductors. The material chosen for the process is designed to seal the openings in the structure of the coil. They have low viscosity, long usage life, good dielectric strength, and can operate at extremely high temperatures.
A solenoid coil has a conductive core with a hollow center and wire wrapped around the hollow center. As current passes through the solenoid coil, it activates a magnetic field that creates magnetic potential that converts to magnetic force for mechanical movement. In some instances, a metal core can trigger the movement of a hydraulic valve. Taped wrapped coils are designed for mild or less severe environments that do not contain chemicals or solvents.
The coil is covered with a sealing tape to protect it from weather, dirt, and vibration. Tape wrapped coils are an economical choice since their cost is much lower than other types. Toroidal coils are used for inductors and transformers. The coil is formed by wrapping a wire around a circular core that is open in the center.
The shape of a toroidal coil allows for magnetic containment of the field limiting the amount of leakage of the field outside the coil. They are used in a variety of industries, which include transportation, audio, and power supply applications.
The purpose of a transformer coil is to transform voltage from one electrical circuit to another. Transformers can reduce or increase voltage. It is a passive device that uses electromagnetic induction to step voltage levels up or down between differing circuits. A voice coil is made up of a bobbin, wire, collar, adhesives, and lead out wire. The size of the bobbin is determined by voice coil gap diameter.
A voice coil converts electrical signals into linear magnetic energy. The initial use of a voice coil was to move the cone of a speaker. Its use has expanded into moving large masses at slow speeds.
The force between the voice coils magnetic field and electric current is referred to as the Lorentz force.
The purpose of an electric coil is to create a magnetic field, which becomes stronger with an increase in the number of turns. The strength of the magnetic field is proportional to the amount of current flowing through the field. By adding more current, the force of the magnetic field increases. Once the current is removed, the magnetic field stops, as was proven in its original discovery in the 19th Century.
All wires produce a magnetic field when current passes through them. By winding and looping the wires, the power of the produced field is increased and works to store energy.
The definition of a coil can be determined by the frequency of the current that flows through it, which are direct current DC , audio frequency AF , and radio frequency RF. Electric coils are further classified by their function such as an electromagnet, transformer, electric device, or some form of inductor.
The first electric coil was discovered by Nikola Tesla and has his name forever attached to it. The purpose of the coil is to achieve resonance, which occurs when the primary coil passes current into the secondary coil. When electricity passes through a circuit, it flows through a resistor and into an electric coil. An electric coil works to maintain stability and resists the flow of current, initially. As the current builds, the coil allows the current to pass through.
As with its previous state, when the current is removed, the electric coil works to maintain the flow and resists the change, allowing the electricity to continue to flow even though the current has been removed. The process of passing electricity through a circuit happens rather rapidly and can be barely noticed. So the AC output of the secondary coil needs to be converted into DC. This is done using something called a rectifier, which uses devices called diodes that allow only a one-way flow of current.
Transformers have many applications in electrical safety systems, which are discussed in Electrical Safety: Systems and Devices. A step-up transformer increases voltage and decreases current, whereas a step-down transformer decreases voltage and increases current. Conceptual Questions 1. Explain what causes physical vibrations in transformers at twice the frequency of the AC power involved. A plug-in transformer, like that in Figure 4, supplies 9.
A cassette recorder uses a plug-in transformer to convert V to What is the maximum input current if the input voltage is V? A multipurpose transformer has a secondary coil with several points at which a voltage can be extracted, giving outputs of 5. What are the numbers of turns in the parts of the secondary used to produce the output voltages? A large power plant generates electricity at Its old transformer once converted the voltage to kV. The secondary of this transformer is being replaced so that its output can be kV for more efficient cross-country transmission on upgraded transmission lines.
If the power output in the previous problem is MW and line resistance is 2. Unreasonable Results The kV AC electricity from a power transmission line is fed into the primary coil of a transformer. Construct Your Own Problem Consider a double transformer to be used to create very large voltages. The device consists of two stages. The first is a transformer that produces a much larger output voltage than its input. The output of the first transformer is used as input to a second transformer that further increases the voltage.
Construct a problem in which you calculate the output voltage of the final stage based on the input voltage of the first stage and the number of turns or loops in both parts of both transformers four coils in all. Also calculate the maximum output current of the final stage based on the input current. Discuss the possibility of power losses in the devices and the effect on the output current and power.
Skip to main content. Search for:. Transformers Learning Objectives By the end of this section, you will be able to: Explain how a transformer works. Example 1. Calculating Characteristics of a Step-Up Transformer A portable x-ray unit has a step-up transformer, the V input of which is transformed to the kV output needed by the x-ray tube. Discussion for a A large number of loops in the secondary compared with the primary is required to produce such a large voltage.
Discussion for b As expected, the current output is significantly less than the input. Multiple conductor continuous disc and helical windings are transposed throughout the winding to minimize circulating current losses. State-of-the-art design techniques are used to provide maximum impulse strength in the windings and to minimize voltage stresses. Special design consideration is also given to the line end discs to control voltage stress distribution. Ampere-Turn balancing techniques are used to minimize radial leakage flux and to minimize axial short-circuit forces.
In order to ensure short circuit performance, windings are manufactured to meet stringent design tolerances for coil winding electrical height, tap locations and spread section locations.
Cooling ducts are formed between discs in the continuous-disc and helical windings by keyed radial spacers made of special high-density pressboard insulation. These spacers are aligned in column to provide axial support for the windings and high short-circuit strength.
All windings are manufactured in a clean winding environment. Annealing all core steel after slitting provides optimal loss performance.
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