[CENTER]Electric arc Furnace (EAF) The main function of EAF, is to melt the scrap & raw material and convert it to high quality liquid steel as fast as possible by using high-power electric arcs. EAF operation The EAF operates within one cycle called tap-to-tap cycle. One complete cycle produce one “Heat” The cycle is made up of the following operations: * Furnace charging * Melting * Refining * De-slagging * Tapping * Furnace turn-around Modern operations aim for a tap-to-tap time of less than 60 mins. Some twin shell furnace operations are achieving tap-to-tap times of 35 to 40 minutes. Melting Melting is accomplished by supplying energy to the furnace interior. This energy can be electrical or chemical. * Electrical energy is supplied via the graphite electrodes and is usually the largest contributor in melting operations. * Chemical energy is being supplied via several sources including oxy-fuel burners and oxygen lances. Oxy-fuel burners burn natural gas using oxygen or a blend of oxygen and air. Heat is transferred to the scrap by flame radiation and convection by the hot products of combustion. Heat is transferred within the scrap by conduction. Electrical energy Electric Arc Furnace power is the food for a hungry furnace
Electrical arc Furnace power starts at the utility company’s generator which puts out 3 phase , 60 cycle A.C power & the power is stepped down by transformers till the furnace transformer
Electrical principles
Electrical power is Voltage ( E or V) multiplied by current ( I )
P = V x I
Voltage expresses the difference in electrical pressure between the conductor in which current flowing and the ground, or, between two or more conductors.
This pressure differential is known as the electrical potential.
Voltage is a push from the pump
Voltage ( E ) in electrical system like a water in a piping system.
A pump creates pressure to force water through a pipe.
An electrical generator creates voltage to force electricity through conductors.
the electricity passes to the arc furnace through power lines, breakers, transformers, cables, bus bars and electrodes.
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[CENTER]Current Current ( I ) refers to the rate of flow of electricity along throughway to your furnace. Correspond to volume of water flowing in a pipe and just as you turn a valve to start water flowing, you close a switch to start current flowing
Resistance
In electrical conductor , resistance ( R ) slows down the flow of electricity. Just as pipe size affects flow in water pipe, so the resistance of electrical conductors affect the flow of electricity. It expressed in ohm (Ω), measure how much electrical friction from the generating station to your furnace.
Resistance is the amount of resistance ( R) through which one ampere ( I) flows when pressured by one volt (E)
That’s Ohm’s Low, Cornerstone of all electrical calculations. It comes in three forms:
The Relation between Current flow and resistance changing with fixing voltage value
Power – That’s Watt Power – That’s Watt[SIZE=3][COLOR=#000000] - Power is expressed in watt ( W). In D.C (direct current) W = V X I. In Arc furnace 1000 W = KW or 1000000 W = MW
Electrical Energy – Watts at work Electrical energy is [ power (KW) X Time (Hr) ] = KWH . In Elect. Arc Furnace, the objective is to utilize electrical energy to produce useful heat as well as the home appliances like stoves and toasters. How much electrical energy does your stove consume? You find out with this simple equation: KWH = w x Hr/1000
Arc Furnaces use A.C ( Alternating Current ) Arc furnaces use three PHASE A.C Alternative current has complicated formula .
Alternating Current ( A.C ) - Arc furnace operates on A.C current - A. C. continually changes in direction and magnitude and it’s form called sine waves. - In each wave, current and voltage start at zero and reach the max value together, then reach zero again, then repeat in the negative direction to complete one cycle. - The cycles / second is called (Hertz) - The frequency of these cycles are 60 cycle/second so it called 60 Hz/second [FONT=Times New Roman]
Phase or phases ? Phase - Electrical phase refer to a single conductor in multi-conductor circuit. In the small load supplied by 110v or 220v, the power require only a single phase. This is like home system having two conductors – one is positive , the other is negative. Some circuits have a third wire which is usually grounded but the circuit is still single phase.
Phases - Heavy electrical loads from 380 v and up use three phase with three wires, there is no return wire. This is the system in the power circuit of electric arc furnace. - Phases are normally A,B,C or 1,2,3 - Each of the three electrodes is connected to one of These phases. - Each phase has its individual phase voltage and current with frequency 60 cycle/ second. - In arc furnace & most other AC circuits, the voltage & current don’t pass through zero at the same time because the load has inductance lead to phase difference [/font][/color][/size]
