Electricals for a Steel Melt Shop, Itemised: Furnace to Caster

A steel melt shop (SMS, also called a steel melting shop) needs a complete electrical chain in process order: a high voltage intake substation, a furnace-duty medium voltage breaker, a furnace transformer, furnace auxiliary drives, crane duty motors for charging and ladle handling, cooling water pumping, a ladle refining furnace supply, and the drives of the continuous casting machine, all fed from LT power and motor control centres. Every item in that chain carries a duty that a general industrial specification does not describe. The job is to itemise each one against that duty, from the first charge of scrap or sponge iron to the billet leaving the caster.

TL;DR

• The melt route sets the electrical design. Induction furnaces produced 35.4% of India’s crude steel in 2023-24, up from 29.5% in 2019-20, and they need converter-duty furnace transformers rather than arc furnace transformers.

• The furnace breaker is not a normal feeder breaker. On arc furnace duty it switches hundreds of times a day, and every opening is an overvoltage event for the furnace transformer.

• The furnace changes the supply for everything else on the bus. Plan for harmonics, reactive demand and voltage dips of 10 to 15%, and make sure critical motors can develop torque at 80% voltage.

• Cooling water is the load you cannot lose. Furnace panels, induction coils, caster moulds and transformer windings all depend on it.

• Melt shop cranes are intermittent-duty machines, rated by duty type, cyclic duration factor and starts per hour, not by kW alone.

• The caster is a precision drive system: mould oscillation, strand withdrawal, stirring, cutting and runout, each with its own electrical requirement.

What does a steel melt shop electrical package contain, in process order?

A steel melt shop electrical package contains eleven itemised systems, from the grid intake to the caster runout. The table below lists them in the order the metal moves, with the duty that should drive each specification and the New India Electricals Ltd (NIEL) product line that addresses it.

Everything in that table is the balance of plants around the core process equipment; our guide to balance of plant electricals covers why the interfaces between the items matter as much as the items.

Why does the melt route decide the electrical design?

The melt route decides the electrical design because an induction furnace and an electric arc furnace load the supply in completely different ways. The Ministry of Steel Annual Report 2024-25 puts the induction furnace share of Indian crude steel production at 35.4% in 2023-24, against 21.9% for the electric arc furnace and 42.7% for the basic oxygen furnace. The induction share rose from 29.5% in 2019-20, so a growing number of Indian melt shops are built around converter-duty electricals.

An induction furnace does not take power at 50 Hz. NIEL’s furnace transformer page describes the arrangement: the inverter applies a medium frequency voltage, generally 500 Hz or 1000 Hz, to the induction coil, and it needs a DC voltage obtained by rectifying the three-phase supply. The transformer feeding that rectifier is a converter duty transformer designed for the converter it feeds.

An arc furnace and a ladle refining furnace take their power directly through the transformer secondary into the electrodes. Furnace transformers step 11 kV to 33 kV down to a few hundred volts, which produces massive secondary currents. NIEL’s furnace transformer range covers:

The Dd0y11 vector group matters on induction furnace service. It gives two secondaries 30 degrees apart, which is the arrangement ABB’s Technical Guide No. 6 describes for a 12-pulse rectifier. ABB states that a 6-pulse rectifier generates high low-order harmonics at the 5th, 7th and 11th, and that with 12-pulse connection “some of the harmonics are in opposite phase and thus eliminated.” That decision is made in the vector group, long before anyone measures the bus.

What does the furnace breaker have to survive?

The furnace breaker has to survive a switching duty measured in hundreds of operations a day, not a handful a year. A 2019 CIRED paper by ABB engineers, High Performance Smart MV Apparatus for Arc Furnace Applications, states that the medium voltage circuit breaker on arc furnace duty “is required to cope up with hundreds of close/open operations per day,” and reports one steel plant installation running at 1,000 operations per week.

Every opening is also an insulation event for the transformer. The same paper notes that severe degradation of arc furnace transformer insulation results from overvoltages arising at circuit breaker opening, and that the standard protection is an RC surge suppressor installed near the furnace transformer together with surge arresters on the transformer terminals. That protection belongs in the feeder specification, not after the first transformer failure.

Furnace-duty breakers are specified by mechanical endurance: ABB’s VD4-AF, rated up to 38 kV, is designed for up to 150,000 mechanical operations.

NIEL’s Power+ V indoor VCB panels cover 3.3 kV, 6.6 kV and 11 kV at 630 A to 3,150 A and short time ratings up to 40 kA, with the breaker designed to IEC 62271-100. For a furnace feeder, the enquiry should state the expected operations per day and the transformer being switched, so the breaker, the surge protection and the protection relay settings are chosen for that duty. On NIEL melt shop scopes, the MCCs and VCB panels are built to handle the extra electrical stress the furnace puts on them.

What does the furnace do to the rest of the melt shop supply?

The furnace distorts, loads and depresses the supply that every other machine in the shop depends on. The Central Electricity Authority’s Electricity Distribution Network Planning Criteria (January 2024) names rectifiers and arc furnaces among the non-linear loads that principally cause harmonic distortion. It lists the effects: overloading of equipment, resonance causing excessive voltage and current, metering errors, overheating of rotating machines through increased iron losses, and overheating of transformer windings.

The CEA criteria also state that where a substation feeds loads with high harmonic levels, suitable harmonic filters shall be installed, and that harmonic voltage distortion at the point of common coupling shall follow the CEA Regulations, which refer to IEEE 519-2014.

Voltage is the second casualty. Our motor selection notes for steel plant duty record that steel plants often see voltage drops of 10 to 15% during arc furnace operation, and that critical motors should be selected to develop their required torque at 80% voltage. A motor that stalls when the furnace strikes is a production stop.

Reactive demand is the third. On a hot strip mill project in Nepal, NIEL supplied a 2,600 kVAR HT capacitor bank with reactors alongside the 66/11 kV power transformers. Capacitors on a furnace bus need reactors because harmonic current concentrates in them; the sizing method is set out in our guide to power factor correction and APFC panels. Measure the harmonic spectrum before fixing the kVAR.

Which motors run around the furnace?

The motors around a melt shop furnace drive four jobs: positioning the electrodes, tilting the furnace to pour, pulling fume out of the shop, and feeding material in. On NIEL’s melt shop scopes these are three-phase induction motors in TEFC, IP55 construction, wound rotor motors where a heavy load has to be started gently, and crane duty motors for the overhead cranes that charge the furnace.

Fume extraction fans are high volume blowers on large TEFC squirrel cage motors running close to continuously, which makes them strong candidates for variable speed control. Where fan power moves into medium voltage, NIEL’s high voltage motor range runs from 355 kW to 18,000 kW at 3.3, 6.6 and 11 kV, in cage or wound rotor. Before adding drives, read our guide to VFD panels, because they add to the harmonic load already on the furnace bus.

Heat is the constant. Our steel plant selection notes put ambient temperatures near furnaces at 60 to 70 degrees Celsius, far above the 40 degree reference that nameplate ratings assume. That is why furnace-area motors should carry Class F insulation with Class B temperature rise and a derating check against the real ambient.

What do melt shop cranes need from their motors?

Melt shop cranes need motors rated for intermittent duty with frequent starts, heat and dust, because a crane charging a furnace or carrying a ladle starts and stops constantly. NIEL’s crane duty and slipring motors run from 0.37 kW to 350 kW, in cage or wound rotor, at 220 V to 690 V, IP55, to IS 325. The range is designed to take variable and shock loads with high inertia.

Crane motors are specified by duty type, not just kW. NIEL’s ready stock of crane duty motors is catalogued in the form S4-40%-150 S/Hr: duty type S4, a 40% cyclic duration factor, and 150 starts per hour. A continuous duty S1 motor substituted into crane service burns out for lack of starting-heat headroom.

Our view is that squirrel cage with VFD control is the default for most crane duty, with slip ring kept for heavy lifts that need very high starting torque at limited starting current. The common mis-specification is buying slip ring because the old crane had one. Hoists also need a holding brake, which is where crane duty brake motors come in.

Why is cooling water the melt shop load you cannot lose?

Cooling water is the load a melt shop cannot lose because arc furnace panels, induction coils, caster moulds and transformer windings all rely on it. A melt shop that loses its cooling supply does not slow down. It shuts down, immediately and dangerously.

The pumping is sized in three tiers. Main recirculating cooling water uses horizontal split casing pumps such as the UP series, with capacity up to 20,000 m3/hr and head up to 160 m. Secondary cooling and cooling tower feed use the DSM series, up to 470 m3/hr and 180 m. Auxiliary and booster duties around the caster use CE end suction pumps, up to 600 m3/hr, 100 m head and 140 degree liquid temperature.

On the Nepal hot strip mill project, NIEL supplied 32 end suction and 17 horizontal split casing pump sets for the steel melt shop alone. The pumps that protect the furnace and the caster mould need a supply that survives a plant trip. Soft starters on the large pumps also prevent water hammer at start-up.

What electricals does the continuous casting machine need?

The continuous casting machine (CCM) needs a set of precise, speed-controlled drives rather than one large load. According to SMS Concast’s account of its CONDRIVE development with Kollmorgen, To Get the Casting Die Oscillating, liquid steel flows from the ladle into a tundish, which distributes it into one to eight strands and buffers the supply during ladle changes.

The caster’s electrical items, in the order the strand moves:

1. Mould oscillation drive. The water-cooled copper mould oscillates so the fresh strand shell does not stick. The negative strip time typically lies between 0.08 and 0.18 seconds, and oscillation can be driven by a mechanical eccentric, hydraulics or electromechanical direct drives. A torn shell releases molten steel into the machine, so the drive must hold its profile precisely.

2. Mould electromagnetic stirring. Mould electromagnetic stirrers are excited by three-phase AC at low frequency to create swirling flow in the liquid steel, according to a 2019 study in the journal Metals.

3. Withdrawal and straightening drives. The strand is pulled continuously out of the mould, so these drives need accurate, coordinated speed control across every strand. They are the natural application for mill duty DC motors with DC drives, or AC motors on variable speed drives.

4. Secondary cooling pumps. Water sprays below the mould continue solidification. Uneven cooling causes cracks, so flow and pressure must be stable.

5. Cutting and runout. The strand is cut to billet length and moved to the cooling bed on roller tables. Roller table motors in this zone see frequent start-stop duty and radiant heat from the hot billet.

Where does NIEL’s melt shop experience come from?

NIEL supplies the electrical layer around furnaces, not the furnaces themselves. On an integrated steel plant in Karnataka that runs an induction furnace melt shop, NIEL designed, supplied and commissioned the 66 kV substation and switchyard, followed by outdoor 11 kV, 630 A switchgear and outdoor main LT panels. The changeover from the old substation to the new one was completed in a single day without disturbing the existing installation.

On the Nepal hot strip and cold rolling mill project, the scope ran from the 66 kV breaker and relay panels through 25/31.5 MVA 66/11 kV transformers, an 11 kV VCB lineup and the HT capacitor bank to the melt shop pump sets and 690 V AC motors, each item bought against the others.

What should a melt shop electrical specification include?

Each line of this checklist closes a gap that otherwise surfaces at commissioning.

1. State the melt route and furnace rating. Induction, arc or both, with furnace MW, and whether a ladle refining furnace is included.

2. Specify the furnace transformer by duty, not kVA alone. State converter or arc duty, secondary voltage, tap range, vector group and cooling.

3. State the furnace breaker switching duty. Give expected operations per day and require surge protection at the furnace transformer terminals.

4. Commission a harmonic and reactive power study before sizing compensation. Include furnace, drives and the existing bus, and check the result against the CEA limits at the point of common coupling.

5. Set a voltage dip requirement for critical motors. Require starting and running torque at 80% voltage for pumps, fans and hoists that must ride through furnace operation.

6. Rate crane motors by duty type, CDF and starts per hour. Write S4, the CDF and the starts per hour into the specification, and state the load inertia.

7. Identify the cooling water loads that must never stop. Decide which pumps sit on a secure supply and how they restart after a trip.

8. Itemise the caster drives separately. List oscillation, stirring, withdrawal, cutting and runout, with speed accuracy and the number of strands.

9. State the real ambient for every motor and panel. Measure the air at the machine, not the site weather, and derate accordingly.

10. Define the interfaces. Name who owns each boundary between furnace supplier, caster supplier and the electrical package.

Send us your furnace rating, melt route and caster configuration, and New India Electricals Ltd will itemise the electrical package against them. Contact our team to start with the single-line diagram.

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