Wireless Energy Transfer

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Section 7: Energy Efficiency
www.leonardo-energy.org February 2007

Power Quality & Utilisation Guide

Induction Heating
Jean Callebaut, Laborelec
1 2 Introduction.................................................................................................... 2 Physical principles ....................................................................................... 2 2.1 2.2 2.3 Electromagnetic induction ................................................................................. 2 The Joule-effect .................................................................................................... 3 Penetration depth ................................................................................................. 3 General aspects .................................................................................................... 5 Power supply and generators ........................................................................... 5 Inductors................................................................................................................. 5 Power Transfer: simplified calculation ........................................................... 6 Electrical efficiency.............................................................................................. 7 Power factor........................................................................................................... 7 Characteristics of induction heating ............................................................... 7 Melting of metals by means of induction crucible furnaces ..................... 8 Brazing .................................................................................................................... 8 Inductive hardening of steel .............................................................................. 8

3

Induction Installations ................................................................................. 5 3.1 3.2 3.3

4

Properties of induction heating ................................................................. 6 4.1 4.2 4.3 4.4

5

Industrial Applications................................................................................. 8 5.1 5.2 5.3

6 7

Conclusions ................................................................................................... 9 References...................................................................................................... 9

www.l eonar do- ener gy. or g

1

Introduction

Electromagnetic induction, simply induction, is a heating technique for electrical conductive materials (metals). Induction heating is frequently applied in several thermal processes such as the melting and the heating of metals. Induction heating has the important characteristic that the heat is generated in the material to be heated itself. Because of this, induction has a number of intrinsic trumps, such as a very quick response and a good efficiency. Induction heating also allows heating very locally. The heating speeds are extremely high because of the high power density.

2
1. 2.

Physical principles
Electromagnetic induction The Joule effect

The principle of induction heating is mainly based on two well-known physical phenomena:

2. 1

El e ct ro mag n et ic i nd u ct i on

The energy transfer to the object to be heated occurs by means of electromagnetic induction. It is known that in a loop of conductive material an alternating current is induced, when this loop is placed in an alternating magnetic field (see Figure 1a). The formula is the following:

E=
E Φ t

dΦ dt
: : : Voltage [V] magnetical flux [Wb] time [s]

When the loop is short-circuited, the induced voltage E will cause a current to flow that opposes its cause – the alternating magnetic field. This is Faraday - Lenz’s law (see Figure 1b).

Figure 1: Induction law of Faraday If a ‘massive’ conductor (e.g. a cylinder) is placed in the alternating...
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