Active power One of the three types of power found in every electrical circuit. In electric arc furnace practice, it’s the active power that actually melts the scrap. It is usually expressed as kilowatts (kW) or megawatts (MW). Active power is also known as real power. The other two powers are the Apparent Power (MVA) and the reactive power (MVAR).
Additions Agents introduced into the molten metal in the furnace or ladle to enhance corrosion resistance and other chemical and physical properties of the end product. Typical additives include alloys of chromium, manganese, nickel, and silcon.
Alternating current (A.C.) An electrical current which continually reverses at regularly recurring time intervals and which has alternatively positive and negative values.
Ammeter An instrument for measuring the magnitude of an electrical current.
Amperage (ampere) A numerical value for an electrical current as measured by an ammeter. Amperage is designated by the capital letter I.
Arc flare The movement of the arc, propelled by electromagnetic forces, toward the sidewalls of the electric arc furnace.
Arc furnace electrode A consumable electrical conductor made of manufactured graphite in cylinders of various lengths and diameters. Electrodes are joined in columns extending from the holders above the furnace, downward to the furnace charge.
Arc furnace regulation A preset, automatic means of controlling furnace current and voltage by phase. Regulation simultaneously permits the control of the arc length through current voltage feedbacks and , thus, the overall power intput to the furnace.
Arc furnace secondary power circuit The part of the furnace power circuit starting at the secondary windings of the furnace transformer and extending through the arc to the furnace charge.
Arc length The distance between the electrode tip and the furnace charge. Under the influence of electromagnetic forces, however, the arc inevitably lengthens and flares outward.
Auxiliary equipment In the melt shop, the support devices required by the arc furnace in its production of hot metal.
Balance furnace An electrical condition within the arc furnace where the power in all three phases is equal. The phase currents, however, do not need to be equal for the furnace to be in balanced condition.
Batch Enough material to make one complete melt including unfused material (if furnace melting non-metallics).
Breakdowns Unscheduled interruptions as a result of electrical or mechanical malfunctions which interfere with the production process.
Bridging The tendency of feed to form a crust-like structure in the upper portion of an arc furnace, thereby impeding the normal downward movement of the feed into the arc zone. This condition sometimes causes damaging cave-ins.
Briquettes Compacted feed material.
Bus bars Hollow copper cylindrical structures which conduct electrical power from the secondary power cables to the electrode holders. Water flows through the bus tubes to cool these holders.
Bushings The porcelain insulators mounted atop the power transformer.
Butts The stub or lower portion of the bottom electrode in the column.
Butt loss The dropping off of the remaining portion of the lowest electrode into the molten bath during the process of melting.
Cables In arc furnace practice, the electrical conductors extending from the furnace vault to the arc furnace.
Capacitive reactance An opposition to the flow of alternating current. Capacitive reactance, designated by XC, arises from capacitors in the power circuit and is measured in ohms. Normally, an arc furnace power circuit does not exhibit a capacitive reactance unless capacitors are introduced.
Carbon steel The most widely used industrial construction material. Carbon steel is defined by the AISI in terms of its percentage of carbon content which may range for 0.06 percent to slightly over 1.00 percent. Carbon steel contains only minimal amounts of alloying elements.
Castings Metal molded into predetermined shapes, normally produced by pouring hot metal into mold cavities where it subsequently solidifies.
Cave-in The collapse of a scrap charge which has been undermined by the hot metal bath or which has been hung up along the sidewalls of the arc furnace.
Center-winding, hot-spot temperature indicator A heat sensing device at the transformer center winding which simulates the center winding temperature by interpreting current and top oil temperature feedback.
Charge Raw material in the form of scrap and additives placed within the furnace for melting.
Circuit breakers Electrical disconnection devices normally employed in power supply systems to protect electrical circuits and equipment.
Continuous charging The uninterrupted feeding of the arc furnace automatically without recourse to conventional bath feeding.
Control panel A centralized assemblage of instruments, switches, and other electrical devices required in the operation and monitoring of the arc furnace.
Current refers to the rate of flow of electricity through an electrical conductor. It is measured in amperes and designated by the capital letter I.
Current adjustment rheostat A variable type of resistor in an arc furnace control circuit mounted on an arc furnace operating panel. A rheostat is used to vary the current feedback for changing the arc length and, consequently, the furnace power input.
Current transformer (C/T) An instrument transformer usually connected to the primary and secondary power circuits of an arc furnace to measure current for furnace regulation and instrumentation.
Delta closure An electrical connection universally used in arc furnace operation. A delta closure is arranged so that the individual secondary windings of the three-phase power transformer are joined to form a closed circuit.
Dielectric test A procedure for analyzing transformer oil to determine its insulating value.
Downtime Non-productive time resulting from electrical or mechanical breakdowns or other delays during the melting cycle.
Electric arc An electrical discharge which, in electric arc furnace practice, refers to the luminous transfer of electrical energy between the electrode tip and the furnace charge. The arc creates the heat to melt the charge.
Electric arc furnace The term refers to the direct arc furnace, a flexible melting tool in increasingly widespread use for the production of iron, steel, and various alloys. In this furnace, which uses electrical energy to create the heat-producing arc, the charge is a path of the electrical circuit. Other types of arc furnaces are the indirect arc and the submerged arc.
Electrical balance Refers to an electrical condition within the electric arc furnace where the power in all three phases is equal, a balance condition, however, does not necessarily imply that all three phase currents are equal.
Electrical energy The capacity to perform electrical work. Electrical energy is usually expressed in kilowatt hours (KWHr) – that is, in power multiplied by time.
Electrical imbalance The uneven distribution of power to the three arcs during melting.
Electrical optimum The condition that exists within an arc furnace when the power and energy inputs are maintained to produce the most efficient melting climate.
Electrical phase Refers to an electrically conductive pathway extending all the way from the power station to the furnace charge. To service the requirements of arc furnaces, three such pathways, or phases, are required.
Electrical potential The difference in voltage between two points of a circuit or between a conductor and ground.
Electrode additions The procedure whereby an electrode is added to an existing column on an electric arc furnace.
Electrode bevel The angle formed at the tip of the electrode by the action of the arc.
Electrode column An assemblage of electrode consisting of two or occasionally three electrodes securely joined together and extending downward into an electric arc furnace.
Electrode consumption The usage of electrodes as measured in terms of pounds of graphite per ton of material produced in the electric arc furnace.
Electrode end covers Steel lids placed on the tops of the electrode columns and used to protect electrode faces and sockets from damage, dirt, and excessive oxidation while the electrodes are in position on the furnace.
Electrode holders Clamping devices to secure and position the electrodes during melting operations, electrical energy passes from the holders to the electrode columns.
Electrode joint The interface between two electrodes secured by a threaded graphite connecting pin.
Electrode master control switch A switching device on the operator’s furnace panel used to move all three electrodes in unison upward or downward in either the automatic or manual mode.
Electrode slippage a planned procedure in which electrodes are permitted to move downward through the holders to adjust the length below the holder of the individual electrode columns, usually after an electrode addition.
Electrode tip The area of the electrode closest to the charge and the area from which the electric arc originates.
End caps Protective covers of hardboard of similar material used to protect the end faces and sockets of electrodes during shipment and in storage.
Feed Raw material mixed as required and fed into the furnace.
Forced oil water (FOW) cooling A method of cooling transformer oil by forcing that oil through a water-cooled external heat exchanger.
Furnace auxiliary circuits Circuits used exclusively for operating electric arc furnace instruments and controls. These circuits are not part of the main or secondary power circuits.
Graphite One of the forms of the element carbon characterized by a lustrous black appearance, relative softness, a natural lubricity, and good electrical and thermal conductivity.
Graphite electrode An electrically conductive cylinder of manufactured graphite engineered for conducting electrical current into the arc furnace.
Ground A conducting connection by which an electrical circuit or equipment is connected to the earth to establish ground potential and/or a common return.
Ground relay A safety device for detecting electrical leakage to ground in an energized circuit.
Guide rollers A part of the superstructure of the arc furnace which bears against the mast girder to assure the maintenance of proper electrode alignment.
Heat In arc furnace practice, the term refers to the quantity of hot material produced during the time between when the furnace is started and the completion of the melt
Heat cycle The period that elapses from the time the furnace started until the next time the furnace is started.
Heat log An alternate expression for the heat sheet.
Heat sheet A complete record of all the significant events occurring during one heat cycle.
Hertz A unit of frequency of one cycle per second. Sixty cycles, or 60 Hertz, is commonly used in the North America.
Hot spot A localized deterioration of sidewall lining resulting from the arc flare attack in an unbalance electric arc furnace.
Impedance The total opposition offered by an electrical circuit to the flow of alternating current. It is designated as (Z). The real part of impedance is resistance (R); the imaginary part of reactance (X).
Induction An electrical phenomenon that occurs when one current-carrying conductor induces a voltage in an adjoining conductor.
Inductive reactance An opposition to the flow of alternating current. Inductive reactance, designated by LX, arises from a coil or other inductive devices in the power circuit. Normally the only reactance in the power circuit of an electric arc furnace is inductive reactance, measured in ohms.
Ingot mold A cast iron container, customarily rectangular in cross-sections, into which molten material is poured to cool and form a solid ingot.
Instrument transformer A transformer that produces in its secondary circuit a current or voltage used by the instruments and devices that monitor and control the electric arc furnace. Such transformers are designated as C/T for current transformer and P/T for potential (or voltage) transformer.
Jointing The process of joining two electrodes together with a connecting pin to form a continuous electrode column.
Kilowatts (kW) A unit of electrical power. One kilowatt equals 1,000 watts. In an arc furnace, kilowatts refer to the real, or active power, which creates the heat to melt the charge.
Kilowatt hours A unit of electrical energy obtained by multiplying power by time. One kilowatt hour equals 1000 watts times one hour.
kVA The abbreviation for kilovolt amperes. It is also called the apparent power. Power transformer ratings are normally expressed in KVA.
kVAR The abbreviation for kilovolt ampere reactive. It is also called reactive power and is one of the three types of power found in alternating current circuits.
Lift plug A threaded steel device dimensioned like the lower half of a connecting pin. When screwed into an electrode socket, a lift plug provides a means to raise, transport, and position an electrode.
Load In an arc furnace, the term refers to the total power flowing into the furnace during the melting cycle.
Magnetic field The region surrounding an energized electrical conductor or a permanent magnet. In an arc furnace secondary power circuit, strong magnetic fields are created by the flow of high currents.
Make-up The term used to describe the assembling of an electrode column.
Megawatts Designates units of real power measured in millions of watts (MW). In arc furnace practice, it is the real power which performs the melting.
Melt-down That period of melting cycle during which the furnace charge is converted to molten metal.
Melting power The total power employed in an arc furnace during the melting period.
Melting rate A unit of production normally expressed in tons per hour of hot metal.
MVA A unit of apparent power in an alternating current circuit that contains reactance. The expression one MVA designates on million volt amperes.
MVAR A unit of reactive power in an alternating current circuit. MVAR expresses one million volt ampere reactive.
MW A unit of active, or real, power in any electrical circuit. The expression MW designates one million watts.
Nipple Popular term for the threaded connecting pin used in joining electrodes.
No-load tap changer A device for switching from one tap to another on a transformer. With this type of changer, as opposed to an on-load changer, it is essential that the arc be extinguished before changing taps.
Ohms A term to express electrical resistance in a circuit. It is designated by the symbol Ω.
Open circuit An electrical circuit which has been interrupted so that no current flows through it.
Open joint An improperly made connection between two electrodes in which their end faces are not intimately interfaced. In an open joint, the connecting pin is forced to carry a disproportionate part of the electrical load.
Optimum current The current that provides maximum melting in tons per hour in arc furnace operations.
Optimum power The power that provides for maximum productivity in arc furnace melting. It is not necessarily maximum power.
Over-current Current which exceeds that specified for a particular piece of equipment. The term also refers to current that exceeds a set limitation.
Oxidation The process of burning. With graphite, it occurs when the temperature exceeds 750°F (400°C) and oxygen is present. Sockets, end faces, and columns should be guarded against excess burning.
Pellets A form of prereduced material used as feed material in the electric arc furnace.
Phases Separate voltage wave forms coordinated into an alternating current supply system. The arc furnace is supplied by a three-phase system.
Phase rotation The order in which the successive elements of a three-phase system reach their maximum positive values.
Phase-to-neutral The voltage potential that exists between a conductor and ground or between a conductor and the neutral point of an electrical system.
Potential transformer An instrument transformer whose primary winding is connected in parallel with a circuit in which the voltage is to be measured and controlled. It is also known as a voltage or P/T transformer.
Power cables The flexible conductors carrying the power from the transformer to the arc furnace.
Power circuit breaker An automatic disconnecting device in a power supply system to protect the system from abnormal electrical conditions.
Power curves display the power-current relationship in arc furnace circuits. These curves are helpful in optimizing the arc furnace.
Power factor The ratio of active power to apparent power in an alternating current circuit. It is symbolized by P.F., and P.F. equals MW divided by MVA.
Power-off time In arc furnace operation, that time interval, during a heat, in which no electrical power flows.
Power-on time In arc furnace operation, the total time the power flows during the course of a heat.
Preventive maintenance A preplanned maintenance program to prolong equipment life and reduce downtime. Its goal is increased productivity and reduced total costs.
Primary The high voltage side of a transformer.
Primary coil The high voltage winding in a transformer.
Primary power circuit The high voltage part of a power circuit. In the arc furnace melt shop, it refers to the circuit on the power-company side of the furnace transformer.
Production capability The rated output of an arc furnace melt shop.
Push block A spring loaded device to press the electrode against the contact surface in an electrode.
Reactance The opposition offered to the flow of alternating current by a coil (inductive reactance) or bay a capacitor (capacitive reactance). Reactance is measured in ohms.
Reactive power One of the type of power found in an alternating current circuit. It is part of the apparent power, yet does no work. It is designated as million volt ampere reactive or MVAR.
Read-outs A numerical display on the furnace operator’s panel showing, for example, the number of kilowatt hours consumed.
Real power The power that does the actual melting in an arc furnace. It is also termed active power and is measured in megawatts (MW).
Refining cycle The period following the meltdown in an arc furnace. During this cycle, the bath is brought up to temperature and chemistry specification.
Regulator An electrical or electronic device for automatically controlling the movement of the electrodes of an arc furnace.
Relay An electrical device for the control or protection of circuitry and equipment.
Resistance A force which opposes the flow of current in an electrical conductor. It depends on the material, dimensions, and temperature of the conductor. Resistance is symbolized by R and is measured in ohms.
Rheostats Variable resistors, one per phase, in the electrode regulator circuit. They are mounted on the operator’s panel and used for changing the arc length and, thus, the input of power into the furnace.
Secondary coil The secondary winding of a transformer. In most cases, the secondary is the low voltage output side.
Secondary power cable The flexible electrical conductor between the furnace transformer and the electric arc furnace.
Secondary power circuit The electrical conductors extending from the transformer secondary to the three arc tips in an electric arc furnace.
Secondary voltage The output voltage of a transformer. Usually, it is lower than the primary voltage.
Single phase In arc furnace operation, denotes a condition whereby only two of the three electrodes complete the circuit with the charge. In such case, the furnace is said to operate in the single phase mode.
Skull A shell of material that solidifies on the sides and bottom of the interior of a ladle. Skulls are recycled as charge material for the arc furnace.
Slipping practice The procedure by which electrodes are released from their holders, moved downward into the furnace, and subsequently, reclamped in their new position.
Socket The machined cavity on both ends of an electrode. This cavity is threaded to receive the connecting pin which joins two electrodes.
Spalling One of several factors in the consumption of electrodes in the arc furnace. It is evidenced by small pieces chipping off from the electrode.
Stubbage Losses of graphite from the arc end of the column such as butt losses, chunking, or low-column breakage.
Superheating A procedure for bringing the molten material to a slightly greater temperature than normal in order to compensate for anticipated temperature losses following tapping.
Supplementary reactance Additional inductive reactance built into a furnace transformer to improve its electrical efficiency. Supplementary reactances are normally used in transformers rated 7.500 KVA or less.
Tap-to-tap interval The elapsed time between two successive furnace ingots. This time interval is used as a standard in measuring productivity of the electric arc furnace.
Tap voltage Arc furnace operating voltage selected by the operator to provide the desired heat transfer during various stages of the melting.
Tapering A progressive decrease in the diameter of an electrode column from its top to the arc tip area. It arises from the effects of heat and oxygen over a period of time during the melting process.
Three-phase system A three-conductor electrical distribution system in an alternating current circuit.
Total heat time The time that elapses from the completion of one melt until the completion of the next melt.
Transformer nameplate A metal shield mounted on the transformer to show its rated capacity and all other electrical parameters.
Transformer oil Oil used as a cooling and insulating medium in a transformer.
Transformer rating A measure of the transformer’s electrical capability. The rating defines the transformer’s capacity in terms of continuous kVA output.
Transformer ratio The relationship derived by dividing the primary voltage by the secondary voltage.
Triangular configuration The physical spacing of three conductors in a three-phase alternating current circuit.
Tune-up A procedure for optimizing the electrical characteristics and the regulator performance in an electric arc furnace.
Turns Windings on the primary or secondary sides of a transformer. In arc melting, the term is also used to define work shifts.
Unbalanced (imbalanced) furnace An electrical or mechanical condition which must be corrected for the electric arc furnace to operate efficiently. Electrical unbalance results from an uneven distribution of power; mechanical unbalance arises from misalignment of the electrodes.
Vacuum switch A power disconnecting device in which the making and breaking of an electrical contact is done in a vacuum.
Vector diagram A graphic display showing the magnitude and direction of various electrical parameters.
Voltage Electrical pressure or potential which causes current to flow through an electrical conductor. Voltage is designated as E.
Water-cooled cable A type of secondary power cable between the arc furnace transformer and the furnace, usually found on medium and large arc furnaces.
Wattless power An expression for reactive power.
Winding-hot-spot A centrally located spot within the transformer windings which, because of its position, is particularly susceptible to thermal overloading.