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The Capacitor function in Induction furnace power supply
2024-10-30 11:06:20
Induction furnace power supply was developed to support and assure optimum performance. The power supply of the induction furnace takes a 3-phase frequency into a single-phase power at the desired frequency.
The capacitor is the most important componnents which regulate the power supply. The capacitor banks store energy to release it in controlled bursts later while ensuring a stable output. When the energy is controlled carefully, it helps the power supply to deliver the required power according to the demand of the induction furnace.
Choice of induction heating frequency
✧Low temperature heating of metal, annealing – 50 – 500 HZ.
✧Melting, deep heat penetration – 500 HZ – 10 KHz
✧Surface heating of metals – 10 KHz – 200 KHZ
✧Surface hardening – 100 KHZ – 500 KHZ
✧Heating metal pieces, wire and metal strips – 400 – 1000 KHZ
✧Dielectric heating – 1MHZ – 50 MHZ.
Advantages of induction heating/melting
✧It is quick, clean and convenient method.
✧Heat produced in the body to be heated up directly, hence wastage is less.
✧Eddy current heating can easily take in vacuum or special atmosphere.
✧Temperature control is easy achieved.
✧Heat can be made to penetrate into the metal surface to any desired depth.
Principle of eddy current heating
1.It works on the principle of electromagnetic induction.
2.A finite value of diametre and thickness of a metal disc surrounded by a copper coil in which an alternating current is flowing.
3.We find that a secondary current I is caused to circulate around the outer surface of the disc.
4.In transformer the electrical energy is available in secondary while in induction heating it is used to heat the charge itself which acts as a short circuited secondary.
5.The high frequency current carrying coil is known as heater coil or work coil. The material which is to be heated is known as the charge or load.
6.The current flows on the outer surface of the metal disc and in so doing, heats this surface. The heat energy is transferred to the metal at an extremely rapid rate, much faster than conventional methods of heating metal.
7.The heat is generated within the metal without any physical contact between the source of electrical energy and the metal being heated.
8.The medium of energy transmission, the magnetic field, can penetrate any non-metallic substance placed between the heating coil and the material being heated.
9.The process employed is referred to as high frequency eddy current heating.
10.The heat in the disc can be increased by increasing the coil current, increasing the number of turns, frequency of supply, close spacing between the coil and work, using higher permeability magnetic material and higher electrical resistivity of the disc.
Eddy current loss
ddy current loss is responsible for the production of heat although hysteresis loss also contributes to some extent in the case of magnetic material. As the eddy current loss is proportional to Bm^2 F^2, this loss can be controlled by controlling Bm and the supply frequency f.
The depth of penetration ‘d’ of eddy currents into the charge is given by:
D = [1/2∏] √ρx 10^9/μf cm, ρ – specific resistance of molten charge in ohm-cm
f – frequency in Hz , μ – permeability of the charge
This shows higher the frequency of supply the lower the depth of penetration.
The depth is directly proportional to 1/√f. The supply frequency is usually employed between 10kHZ to 40kHZ
Induction heating takes place due to hysteresis and eddy current losses in the object such as Iron. Both these are results of alternating magnetic flux inside the object, induced by the applied AC Magento motive force in another coil or excitor. Mutual inductance is the key, and this is possible with AC power. Flux change given by. ..d(phi)/dt causes induction . Phi is the number of flux lines. The capacitor banks usually being applied in the AC power circuit here. It is used for surface hardening, annealing, soldering, welding, melting of metals, forging of bolts and rivet heads, pipe heating and welding.
Application of induction heating
It is used for surface hardening, annealing, soldering, welding, melting of metals, forging of bolts and rivet heads, pipe heating and welding.
