Glossary of Terms

Crane & Metallurgy ~ Glossary of Terms

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Crane Glossary

Metallurgical Glossary



A shaft which is fixed in the end truck and about which the wheel revolves.



A shaft which is fixed in the wheel and which rotates on bearings fixed in the end truck.


The B10 life of an anti-friction bearing is the minimum expected life in hours of 90% of a group of bearings which are operating at a given speed and loading.


An anti-friction bearing which is provided with seals and a high-stability oxidation-resistant grease to permit operation of the bearing without re-lubrication for not less than the specified B10 life.


The assembly of hook, swivel, bearings, sheaves, pins and frame suspended from the hoisting ropes. In a “short type” block, the hook and the sheaves are mounted on the same member, called the swivel. In a “long type” block, the hook and the sheaves are mounted on separate members. (The supporting member for the sheaves is called the sheave pin and the supporting member for the hook is called the trunnion.


A fixed assembly of sheaves, bearings, pins and frame, located on the trolley cross members, and which supports the load block and its load by means of the ropes.


A short end truck attached to the end of one girder (or to a connecting member if more than one bogie is used per girder). This type of end truck is used when more than four wheels are required on a crane due to the design of the runway.


A short end truck which is flexibly connected to one girder (or connecting member) by means of a pin upon which the truck can oscillate to equalize the loading on the two truck wheels. This construction uses a very rigid end tie between the girders.


A short end truck which is rigidly connected to one girder. A flexible end tie is used between the girders to permit equalization of the wheel loads by torsional deflection of the girders and flexing of the end tie.


A device, other than a motor, used for retarding or stopping motion by friction or power means.


A device for controlling load speed in the hoisting or lowering direction by placing a supplementary load on the motor. This load results from the interaction of magnetic fields produced by an adjustable direct current in the stator coils and induced currents in the rotor.


A friction device, usually using multiple discs, used for controlling load speed in the lowering direction only. The brake prevents the load from overhauling the motor.


A friction brake for a hoist, that is automatically applied and prevents motion when power is off.


A friction brake for bridge or trolley, automatically applied when power to the crane is interrupted.


A friction brake for bridge or trolley, automatically or manually applied, used during normal operation to apply a retarding force.


That part of a crane consisting of girder(s), trucks, end ties, walkway and drive mechanism, which carries the trolley(s) and travels along the runway rails.


An energy absorbing (bumper) or energy dissipating (buffer) device for reducing impact when a moving bridge or trolley reaches the end of its permitted travel, or when two moving bridges or trolleys come into contact. This device may be attached to the bridge, trolley or runway stop.



The operator’s compartment on a crane.


The slight, upward, vertical curve given to girders to partially compensate for deflection due to rated load and weight of the crane parts.


The minimum distance from any part of the crane to the point of nearest obstruction.


A contacting device for obtaining electrical current from the runway conductors. The runway collectors are mounted from the bridge.


A contacting device for obtaining electrical current from the bridge conductors. The trolley collectors are mounted from the trolley. (Sometimes incorrectly called bridge collectors)


The electrical conductors located along the bridge girder(s) to provide power and control circuits to the trolley. (Sometimes incorrectly called trolley conductors)


The electrical conductors located along the runway to provide power to the entire crane.


A method of controlling lowering speed of the load by removing energy from the moving load or by imparting energy in the opposite direction.

COUNTER TORQUE – A method of control by which the power to the motor is reversed to develop torque in the opposite direction to the rotation of the motor.
DYNAMIC – A method of controlling speed by using the motor as a generator, with the energy being dissipated in resistors.
EDDY CURRENT – A method of controlling or reducing speed by means of an electrical induction load brake.
MECHANICAL – A method of controlling or reducing speed by friction.
REGENERATIVE – A method of control in which the electrical energy generated by the motor is fed back into the power system.


A device or group of devices which serves to govern in some predetermined manner the power delivered to the motor to which it is connected.


A controller having all of its basic functions performed by devices which are operated by hand.


An assembly of electrical components (magnetic or static) which governs the flow of power to or from a motor in response to signals from a master switch, pushbutton station, or remote control.


The top or bottom plate of a box girder.


A machine for lifting and lowering a load and moving it horizontally, with the hoisting mechanism an integral part of the machine.


A crane controlled by an operator in a cab attached to the bridge or trolley.


A crane which is controlled by a means suspended from the crane, with the operator on the floor or on an independent platform.


A crane similar to an overhead crane except that the bridge is rigidly supported on two or more legs.


An overhead crane used for transporting or pouring molten material.


A crane whose hoist mechanism is driven by pulling an endless chain, and/or whose travel mechanism is driven in the same manner or by manually moving the load or hook in a horizontal direction.


A special type of gantry crane of long span and with long legs, usually used for the storage of bulk material such as ore, coal, limestone, or sane. This type of crane normally will have one or two cantilevered girder ends with through legs.


A crane with a single or multiple girder movable bridge, carrying a movable trolley or fixed hoisting mechanism, and traveling on an overhead fixed runway structure.


An overhead or gantry type crane which travels on a circular runway.


A crane controlled by an operator located other than on the crane and by any method other than a means suspended from the crane. Radio control is the most common means of remote operation.


A gantry crane with one end of the bridge supported on one or more legs and the other end of the bridge supported by an end truck connected to the girders and running on an elevated runway.


A very slow, constant, continuous, fixed rate of motion of the hoist, trolley, or bridge: usually established at 1% to 10% of the normal full load speed.


As defined by the Nuclear Regulatory Commission, “A critical load is a load of magnitude or kind that under certain conditions, if dropped, could result in damage leading to unacceptable release of radioactivity or impair the capability to safely shut down the plant.”



The vertical displacement of a bridge girder due to its own weight plus the weight of parts permanently attached thereto, such as footwalk, drive mechanism, motor and control panels. The dead load deflection is fully compensated for in the girder camber.


The vertical displacement of a bridge girder due to the weight of the trolley plus the rated load.


A vertical plate (or channel) between the girder webs, which serves to support the top cover plate and bridge rail and to transfer the forces of the trolley wheel loads to the webs.


A control point on a travel motion which releases the electric brake without energizing the motor.


The assembly of the motor and gear unit used to propel the bridge or trolley.


The cylindrical member around which the hoisting ropes are wound for lifting or lowering the load.



A structural member, other than the end truck, which connects the ends of the girders to maintain the squareness of the bridge.


An assembly consisting of structural members, wheels, bearings, axles, etc., which supports the bridge girder(s) or the trolley cross member(s).


A sheave or bar which compensates for unequal length or stretch of the hoisting rope(s) or swinging of the load block.


Capable of being contacted inadvertently (applies to hazardous objects not adequately guarded or isolated).



The angle formed by the wire rope and the drum groove or sheave groove in the plane which contains the wire rope and is parallel to the drum or sheave axis.


A walkway with handrail and toeboards, attached to the bridge or trolley for access purposes.



The horizontal distance center-to-center of the bridge rails.


The principal horizontal beam(s) of the crane, which supports the trolley, is supported by the end trucks, and is perpendicular to the runway.


the bridge girder to which the bridge motor and gearcase(s) are attached. For cranes having a drive on each girder, it is the girder to which the control panels and/or the cab are attached.


The bridge girder which does not have the bridge drive attached, but which usually carries the bridge conductors.


A horizontal beam attached to the building columns or wall, and supporting a runway rail on which the crane travels.


An additional girder, either solid or latticed, arranged parallel to the bridge girder(s) for supporting the footwalk, control panels, operator’s cab, etc., to reduce the torsional forces such loads might otherwise impose.



A machinery unit that is used for lifting and lowering a load.


A supplemental hoisting unit, usually designed to handle lighter loads at a higher speed than the main hoist.


The primary hoist mechanism provided for lifting and lowering the rated load of the crane.


The minimum horizontal distance, parallel to the runway, between the centerline of the hook(s) and the face of the wall (or columns) at the end of the building.


The minimum horizontal distance, perpendicular to the runway, between the centerline of a hook (main or auxiliary) and the centerline of the runway rail.



See “jog”. Often used incorrectly to refer to “creep speed” (which see).



To move the hook, trolley, or bridge in a series of short, discontinuous, increments by momentary operation of a controller.



A device used to bridge the throat opening of a hook.


A reference to parts or dimensions on the viewer’s left of the centerline of span, established when facing the drive girder side of the crane.


The maximum vertical distance through which the hook(s) can move, as determined by the length of rope and/or the number of grooves on the drum.


Devices which are not reeved on to the hoist ropes, such as hook-on buckets, magnets, grabs, and other supplemental units used for ease of handling certain types of loads. The weight of these devices is to be considered part of the rated load.


An electrical device which is operated by the bridge, trolley, or hoist motion to disconnect the circuit, to establish a new circuit, or to provide a warning.


The load(s) on a portion of the crane, which remain(s) in a fixed position relative to the member being considered.


A load which moves or varies relative to the member being considered. For the trolley, the live load consists of the rated load plus the weight of the block. For the bridge, the live load consists of the rated load plus the weight of the trolley.


The maximum static vertical load for which a crane or an individual hoist is designed.


A control system which enables stepless operation of a hoist in either the lifting or lowering direction for a range of about 0-5% of full rated speed, as well as permitting the load to be suspended stationary for a very short time with the holding brake(s) released.



A manually operated device which governs the operation of contactors and/or auxiliary devices of an electric control.


A horizontal member, mounted along a handrail or girder, supporting movable carriers from which festooned wires are hung. The festooned wires may be used to transmit current from the bridge to the trolley or from the bridge to a pendant control unit.



Those conditions during which a crane is being operated and is performing functions within the scope of the original design. For a cab operated crane, the operator is at the operating control devices in the cab and no other person is on the crane. For a floor operated crane, the operator is at the operating control devices, which are suspended from the crane but operated with the operator off the crane, and no person is on the crane. For a remote operated crane, the operator is at the operating control devices, which are not attached to any part of the crane, and no person is on the crane.



Any hook load greater than the rated load.



The distance, measured through the center of a drum or sheave, from center-to-center of a rope passed about the periphery of the drum or sheave.


To operate a controller in such a manner that the motor line voltage polarity or phase sequence is reversed before the motor rotation has stopped, thereby developing a counter torque which acts as a retarding force.


A current relay used on a bridge or trolley control panel which senses current in the motor secondary circuit of an alternating current motor and limits reverse torque of the motor to the first control point until the motor rotation has stopped. In a direct current control panel, the relay performs the same function by establishing a patented sensing circuit at the motor armature. (Sometimes called an anti-plugging relay.)



The track supported by the bridge girder(s), on which the trolley travels.


The track supported by the runway beams, on which the crane travels.


A mechanical device attached to the end truck of a bridge or trolley, located in front of the leading wheels, to remove foreign objects from the rail.


A reference to parts or dimensions on the viewer’s right of the centerline of span, established when facing the drive girder side of the crane.


The assembly of rails, girders, brackets and framework on which the crane operates.



The induced open-circuit voltage in the rotor of a wound-rotor (slip-ring) motor at standstill, as measured across the slip rings with rated voltage applied to the primary (stator) winding.


The shaft(s) extending the length of the bridge, used to transmit torque from the motor to a wheel(s) at each end of the bridge.


When used in a Code or Standard, this word indicates that the rule is mandatory and must be followed. (See “should”)


When used in a Code or Standard, this word indicates that the rule is a recommendation, the advisability of which depends on the facts in each situation. (See “shall”)


The portion of the hoist rope pull acting horizontally when the hoist ropes are not operated vertically.


The horizontal distance center-to-center of the runway rails.


A device used on a manual controller, master switch, or pushbutton to cause the unit to return automatically to the neutral position, when


A member to physically limit the travel of a trolley or bridge. This member is rigidly attached to a fixed structure and normally does not have energy absorbing ability.



The minimum torque which a squirrel-cage motor will develop at rest, for all angular positions of the rotor, with rated voltage applied at rated frequency. Not applicable to wound-rotor (slip-ring) motors.


The maximum torque which a squirrel-cage or wound-rotor (slip-ring) motor will develop with rated voltage applied at rated frequency, without an abrupt drop in speed.


The torque developed by an electric motor (A.C. or D.C.) to produce its rated horsepower at rated full-load speed.


The minimum torque developed by a squirrel-cage or wound-rotor (slip-ring) motor during the period of acceleration from rest to the speed at which breakdown torque occurs. For squirrel-cage motors with 8% or greater slip, the pull-up torque, the breakdown torque and the starting torque are all equal and occur at zero speed.


The unit consisting of frame, end trucks, drive, hoisting mechanism, rope and load block, which travels on the bridge rails and supports the load.


Inadvertent physical contact between the load block and the upper block or other part of the trolley.



The vertical plate(s) connecting the upper and lower flanges or cover plates of a girder.


The distance from center-to-center of the outermost wheels of the bridge or trolley, measured parallel to the rail.


The vertical force (without impact) produced on any bridge wheel by the sum of the rated load, trolley weight and bridge weight, with the trolley so positioned on the bridge as to give maximum loading.


The vertical force (without impact) produced on any trolley wheel by the sum of the rated load and the trolley weight.


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).


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.


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.


Enough material to make one complete melt including unfused material (if furnace melting non-metallics).


Unscheduled interruptions as a result of electrical or mechanical malfunctions which interfere with the production process.


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.


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.


The porcelain insulators mounted atop the power transformer.


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.



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.


Metal molded into predetermined shapes, normally produced by pouring hot metal into mold cavities where it subsequently solidifies.


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.


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.


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.


Non-productive time resulting from electrical or mechanical breakdowns or other delays during the melting cycle.


Electric arc furnace

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.



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.



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.


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.



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.


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.



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).


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.


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.


The abbreviation for kilovolt amperes. It is also called the apparent power. Power transformer ratings are normally expressed in KVA.


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.


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.


The term used to describe the assembling of an electrode column.


Designates units of real power measured in millions of watts (MW). In arc furnace practice, it is the real power which performs the melting.


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.


A unit of apparent power in an alternating current circuit that contains reactance. The expression one MVA designates on million volt amperes.


A unit of reactive power in an alternating current circuit. MVAR expresses one million volt ampere reactive.


A unit of active, or real, power in any electrical circuit. The expression MW designates one million watts.


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.



A term to express electrical resistance in a circuit. It is designated by the symbol.

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.


Current which exceeds that specified for a particular piece of equipment. The term also refers to current that exceeds a set limitation.


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.



A form of prereduced material used as feed material in the electric arc furnace.


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.


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.


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.



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.


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.


An electrical or electronic device for automatically controlling the movement of the electrodes of an arc furnace.


An electrical device for the control or protection of circuitry and equipment.


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.


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.


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.


The machined cavity on both ends of an electrode. This cavity is threaded to receive the connecting pin which joins two electrodes.


One of several factors in the consumption of electrodes in the arc furnace. It is evidenced by small pieces chipping off from the electrode.


Losses of graphite from the arc end of the column such as butt losses, chunking, or low-column breakage.


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.


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.


A procedure for optimizing the electrical characteristics and the regulator performance in an electric arc furnace.


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.


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.


A centrally located spot within the transformer windings which, because of its position, is particularly susceptible to thermal overloading.

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