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18 common terms for induction heating

The following terms are intended for those with little or no experience in inductive heating and are intended for practical applications rather than to give a scientific definition. At the same time, the electromagnetic energy radiation of the power supply unit is ignored and the International System of Units (SI) is adopted.

1.Induction heating

When an alternating current flows through the inductor coil, an alternating magnetic field will be generated around it. The metal conductor in the alternating magnetic field will draw electromagnetic energy from the magnetic field and generate heat, so induction heating is also electromagnetic heating.

2. Current

The current is short for current intensity. It measures the amount of charge passing through the cross-section of A conductor in unit time, similar to the rate at which tap water flows down A pipe, in amperes. In inductive heating applications, the current in the inductor coil ranges from tens to tens of amperes.

3.Voltage

Voltage (electric potential) is the driving force of the current, which is generated by batteries, AC power, and hf generators. The voltage and voltage drop resembles the pressure difference between a pump and a line. Voltage is always applied at both ends of the circuit element, in volts (V). The voltage at both ends of the single-turn inductor is several volts, and for the multi-turn coil in the melting furnace, it reaches several kilovolts.

4. Impedance

Impedance is the ratio of voltage and current, is one of the basic parameters of the circuit, the unit is Ω,1Ω=1V/A。

5. Magnetic field

A magnetic field is a kind of physical field, which is distributed in the surrounding space and changes in time with the change of field source. Both electric current and permanent magnet are magnetic field sources.

6. Magnetic line of force

Magnetic field lines are helpful to observe the distribution of the magnetic field. Where the density of magnetic field lines is high, the magnetic field is stronger.Magnetic lines of force are always closed around the source of the field, just as water flows in a closed-loop pipe.

7. Magnetic flow(φ)

Magnetic flux is a measure of a magnetic field. It is like the flow of a liquid. A magnetic potential produces a flux in the same way that an electric potential produces a current.The current in the coil, or exactly the number of ampere-turns in the coil is the magnetic potential. The path of the flux must be closed in Weber (Wb).

8. Magnetic induction intensity(B)

It’s a measure of the flux density, it’s a vector, and it’s comparable to the velocity vector of the fluid at some point, in teslas (T).

9. Magnetic field intensity(H)

It’s a measure of the strength of the magnetic potential, like a pressure gradient somewhere in the water flow. The units are the amperes per unit length A/m.

10. Magnetic conductivity

For linear magnetic media, the ratio B/H has a definite value called the absolute permeability of the substance. We can define the relative permeability of a substance by calibrating the “permeability” of air to 1.For all non-magnetic materials, the relative permeability is 1. The relative permeability of ferromagnetic material can reach tens of thousands, and its value is also affected by the magnetic field strength, which indicates that the magnetic potential is reduced under the same magnetic flux.

11. Reluctance

Magnetoresistance is like the resistance in a circuit. The current generated by the voltage (potential) in the circuit flows through the resistance. In a magnetic circuit, the magnetic flux produced by the number of ampere-turns (magnetic potential) of a coil “flows” through the magnetic circuit’s reluctance. In the case of the same magnetic flux, the current required for the ferromagnetic material to be put into the magnetic circuit is small, and the current required for the non-ferromagnetic material is large; in other words, the magnetic flux produced by the former is large when the same current is put into the coil, while the latter is small.

12. Magnetic (field) energy

Magnetic energy is a kind of energy associated with the magnetic field. It exists in the space around the current-carrying conductor, which is the source of the magnetic field. In the case of alternating current, magnetic energy is continually converted to electrical energy in the coil circuit, which in turn is converted to magnetic energy. A conductor absorbs some of the energy during each period of energy conversion. The unit of magnetic energy is the Joule (J), more commonly used in industrial applications is the kilowatt-hour (kw•h),1 kw•h = 3600000 J。

13. Apparent power

It is the product of the voltage and current in a circuit in kilovolt ampere (kva). For example, if the original voltage of a transformer is 800V and the current is 500a, the power appears to be equal to 400kva.In a direct current circuit (DC), where the apparent power is equal to the active power, “apparent” is meaningless. In an ALTERNATING current (AC) circuit, especially in the slot circuit of an induction heating device, only a portion of the energy is absorbed by the workpiece as the electrical and magnetic energy are continuously exchanged, just as only a portion of the energy is absorbed in the circuit of a 50Hz AC motor.

14. Active power

It is the amount of absorbed power in a unit of time (1 second), usually in kilowatts (kW). Active power is always less than (at most equal to) apparent power.For example, if the voltage at both ends of the inductor is 50V and the current flowing through is 4000A, the perceived power is 200kva, and the active power absorbed by the workpiece and the inductor is 30kw (power factor is 0.15) or 80kw (power factor is 0.4).

15. Reactive power

It is the size of electromagnetic power in an inductive heating device, in an oscillating channel consisting of an inductor and a capacitor bank when electrical energy and magnetic energy are exchanged. This indicates that some of the power supplied by the power supply is returned to the power supply by the oscillating channel. The unit used is kvar, whose value is equal to the square root of the square root of the apparent power and active power.

16. Power factor(cosφ)

It is the ratio of the active power to the apparent power (kW/kva), and its value indicates the proportion of the active power absorbed in the apparent power in one period of an electromagnetic oscillation.

17. Magnetic hysteresis loss(HL)

Magnetic molecules inside ferromagnetic materials change direction back and forth constantly under the action of the alternating magnetic field, and the loss caused by internal friction is called hysteresis loss. In the induction heating process, the hysteresis loss at low frequency does not exceed 10%, and the loss increases with the increase of frequency due to the aggravation of friction. For non-magnetic materials (paramagnetic and antimagnetic materials) HL value is zero.

18. Eddy-current loss

Due to the coupling effect of the magnetic field, eddy currents are generated in the conductor when alternating magnetic field lines cross the cross-section of the conductor. A conductor must have a closed circuit to produce eddy currents and heat. Imagine placing a thin metal ring in an alternating magnetic field, so that there is a voltage at both ends of the opening and it does not generate heat. It is emphasized that for an induction heating device with fixed external dimensions and frequency, the relationship between hysteresis loss and eddy current loss is certain, but hysteresis heating and eddy current heating cannot be separated, the former only accounts for a small part of the total loss, while the latter accounts for the main part.

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