INDUSTRIAL PROJECT REPORT

Electromagnets Used in Bhilai Steel

SUBMITTED BY: - GUIDED BY: - Nikhil Yadav Mr. Remy Thomas Electrical and Electronics Engineering Assistant ManagerNIT, Delhi Electrical Repair Shop BSP, SAIL

ACKNOWLEDGEMENTI take this opportunity to express my profound gratitude and deep regards to Mr. Remy Thomas(Assistant manager, ERS) and Mr. R.K. Nayyar(Assistant Manager, MTRS) for their exemplary guidance, monitoring and constant encouragement throughout the course of this project.

 I am obliged to the officials and workers of ERS and MTRS, for the insight provided by them and for letting me work on the equipments. I am grateful for their cooperation during the period of our assignment.

Lastly, I would like to thank BHILAI STEEL PLANT for incessant help and also for providing me with all the resources I needed for this project, without which the completion of this project would not have been possible.

SUBMITTED BY: - GUIDED BY: - Nikhil Yadav Mr. Remy Thomas Electrical and Electronics Engineering Assistant ManagerNIT, Delhi Electrical Repair Shop BSP, SAIL

STEEL AUTHORITY OF INDIA LIMITED (SAIL)

BHILAI

This is to certify that “NIKHIL YADAV”; student of Electrical and Electronics Engineering at National Institute of Technology, Delhi has completed his Industrial Training Project on “Electromagnets used in Bhilai Steel Plant”. During the project he was highly responsive, dedicated and hard working. On the basis of his interest and devotion towards the assigned tasks and keenness to complete within stipulated period, I certify him to have completed the project successfully under my guidance. It was a great pleasure for me to guide him and share the knowledge.I wish him great success in life.

Date: Mr. Remy Thomas Assistant Manager

Electrical Repair Shop BSP, SAIL

BHILAI STEEL PLANT –AN OVERVIEW

Bhilai Steel Plant - a symbol of Indo-Soviet techno-economic collaboration, is one of the first three integrated steel plants set up by Government of India to build up a sound base for the industrial growth of the country, The agreement for setting up the plant with a capacity of 1 MT of Ingot steel was signed between the Government of erstwhile U.S.S.R. and India on 2nd February, 1955, and only after a short period of 4 years, India entered the main stream of the steel producers with the commissioning of its first Blast Furnace on 4th February, 1959 by the then President of India, Dr Rajendra Prasad. Commissioning of all the units of 1 MT stage was completed in 1961. A dream came true-the massive rocks from the virgin terrains of Rajhara were converted into valuable iron & steel.

In the initial phase the plant had to face many teething problems, mostly unknown to the workforce at the time, but by meticulous efforts and team spirit, these problems were surmounted and the rated capacity production was achieved only within a year of integrated operation of the plant.

Thereafter, the plant was expanded to 2.5 MT capacity per year, and then to 4 MT of crude steel per year, with Soviet assistance.

All the units of the plant have been laid out in sequential formation according to technological inter-relationship so as to ensure uninterrupted flow of in-process materials like Coke, Sinter, Molten Iron, Hot Ingots, as well as disposal of metallurgical wastages and slag etc., minimizing the length of various inter-plant communications, utilities and services.

BSP is the sole manufacturer of rails and producer of the widest and heaviest plates in India. Bhilai specializes in the high strength UTS 90 rails, high tensile and boiler quality plates, TMT bars, and electrode quality wire rods. It is a major exporter of steel products with over 70% of total exports from the Steel Authority of India Limited being from Bhilai. The distinction of being the first integrated steel plant with all major production units and marketable products covered under ISO 9002 Quality Certification belongs to BSP. This includes manufacture of blast furnace coke and coal chemicals, production of hot metal and pig iron, steel making through twin hearth and basic oxygen processes, manufacture of steel slabs and blooms by continuous casting, and production of hot rolled steel blooms, billets and rails, structural, plates, steel sections and wire rods. The

plant's Quality Assurance System has subsequently been awarded ISO 9001:2000.

Not content with the Quality Assurance system for production processes, Bhilai has one in for ISO 14001 certification for its Environment Management System and its Dalli Mines. Besides environment-friendly technology like Coal Dust Injection System in the Blast Furnaces, de-dusting units and electrostatic precipitators in other units, BSP has continued a vigorous afforestation drive, planting trees each year averaging an impressive 1000 trees per day in the steel township and mines.

A leader in terms of profitability, productivity and energy conservation, BSP has maintained growth despite recent difficult market conditions. Bhilai is the only steel plant to have been awarded the Prime Minister's Trophy for the best integrated steel plant in the country seven times.

Bhilai Steel Plant, today, is a panorama of sky-scraping chimneys and blazing furnaces as a modern integrated steel plant, working round the clock, to produce steel for the nation. Bhilai has its own captive mines spread over 10929.80 acres. We get our iron ore from Rajhara group of mines, 85 kms south-west of Bhilai. Limestone requirements are met by Nandini mines, 20 kms north of Bhilai and dolomite comes from Hirri in Bilaspur district, 135 kms east of the plant. To meet

the future requirement of iron ore, another mining site Rowghat, situated about 100 km south of Rajhara, is being developed; as the ore reserves at Rajhara are depleting.

Bhilai expanded its production capacity in two phases - first to 2.5 MT which was completed on Sept. 1, 1967 and then on to 4 MT which was completed in the year 1988. The plant now consists of ten coke oven batteries. Six of them are 4.4 metres tall. The 7 metre tall fully automated Batteries No 9 & 10 are among the most modern in India. Of Bhilai's seven blast furnaces, three are of 1033 cu. metre capacity each, three of 1719 cu. metre and one is 2000 cu. metre capacity. Most of them have been modernised incorporating state-of-the-art technology. Steel is made through twin hearth furnaces in Steel Melting Shop I as well as through LD Convertor -continuous Casting route in SMS II. Steel grades conforming to various national and international specifications are produced in both the melting shops. Production of cleaner steel is ensured by flame enrichment and oxygen blowing in SMS I while secondary refining in Vacuum Arc Degassing ensures homogenous steel chemistry in SMS II. Also in SMS II is a 130 T capacity RH (Ruhshati Heraus) Degassing Unit, installed mainly to remove hydrogen from rail steel and Ladle Furnace to meet present and future requirements of quality steel. Bhilai is capable of providing the cleanest and finest grades of steel.

The rolling mill complex consists of the Blooming & Billet Mill, Rail & Structural Mill, Merchant Mill, Wire Rod Mill and also a most modern Plate Mill. While input to the BBM and subsequently to Merchant Mill and Wire Rod Mill comes from the Twin Hearth Furnaces, the Rail & Structural Mill and Plate mill roll long and flat products respectively from continuously cast blooms and slabs only. The total length of rails rolled at Bhilai so far would circumvent the globe more than 4.5 times.

To back this up, we have the Ore Handling Plant, three Sintering Plants - of which one is most modern, two captive Power Plants with a generating capacity of 110 MW, two Oxygen Plants, Engineering Shops, Machine Shops and a host of other supporting agencies giving Bhilai a lot of self-sufficiency in fulfilling the rigorous demands of an integrated steel plant. Power Plant No.2 of 74 MW capacity has been divested to a 50:50 SAIL/NTPC joint venture company.

The plant has undertaken massive modernization and expansion plan to produce 7.5 MT of hot metal by the year 2010.

HUMAN PROFILEMore than the machinery and processes, it is the men i.e. the engineers, technicians, skilled and unskilled workers behind them that constitute the flesh and blood of this steel plant.

Bhilai at present has around 34000 persons to run this pulsating giant. The culture which has today become the hallmark of Bhilai is a result oriented approach to work. It is their effective and co-operative working relationship nurtured in a spirit of dedication and enthusiasm that has shaped Bhilai's image today.

Adjoining the plant, a modern township - Bhilai Nagar, having the spaciousness of a village and the cleanliness of a modern town is spread - over in 17 self sufficient sectors with schools, markets, parks and other facilities.

Free Medical aid is given to all the employees and their dependents through a network of health centres, dispensaries and hospitals. Medical facilities are extended to retired employees & their spouses also.

The Education Department runs a number of higher secondary, middle, primary, and pre-primary schools in Bhilai and also in the mines townships at Rajhara, Nandini and Hirri.

ELECTRICAL REPAIR SHOP

Fig. Electrical Repair ShopLooking towards any integrated steel plant scenario, the importance of an Electrical Repair Shop can be very well visualized. It is one of the major service shops which carry out repair of all electrical machines used inside the plant; there are around 42000 electrical machines installed and running continuously years together, in different processes of production, in Bhilai Steel Plant. General maintenance like cleaning, greasing and physical inspection / check-up is done by concerned shops where the machines are used. All major repairs like winding repairs, mechanical repairs, modification in existing winding and periodic overhauling etc. are being attended by Electrical Repair Shop either at site or at ERS.

SCOPE OF WORK: Electrical Repair Shop carries out repairs of motors, generators, welding and control transformers, load lifting magnets, brake & control coils of all types and capacities. It also manufactures a large number of spare parts like contact materials, switches, components, bus bar and various other electrical spare parts. Repair of load lifting magnets, welding transformers, control transformers and rectifiers are carried out in magnet and transformer repair shop (MTRS). MTRS also fabricates load lifting magnets of all varieties using all in-house technology and resources including the design concept. Traction motors and roll table motors from various Rolling Mills are overhauled in Motors Overhauling and Repair Section (MORS) adjacent to MTRS.

PRODUCTION TARGETS:

E.R.S. on an average repairs 380 motors and generators, manufactures/reclaims 535 nos. coils, repairs 17nos. load lifting magnets, 28nos. welding & control transformers per month. The monthly repair work in case of motors and generators is given below in tabular form:

Some repair work is off loaded to outside agencies strictly on need basis, such as core staggering, shaft change etc. for which repair facilities are not available in ERS. Such repairs are limited in number (5 - 10 machines per year) and applicable for big size and critical machines only.

MAN POWER: ERS has a present manning of 234 non-executives and 13 executives of various grades. The shop is headed by DGM (E - ERS).

METHODOLOGY AND PROCESS FLOW: Electrical machines are received from various shops within plant, township areas, mines etc. along with its work order. The work order contains the machine specification, its defect, previous job no. and any specific requirement by the concerned department. Receipt & Issue section (R&I) of ERS allots a job No. to each and every machine after proper verification of the machine and its accompanying work order. The number is painted on motor body and on all dismantleable parts. Thereafter the machine is traced in ERS by that job number only. R&I section intimates to the concerned sections through internal job register for repair of these machines or components on day to day basis. To facilitate a systematic repair process the shop is divided into different sections. These are:

1. R & I section

2. Computer section

3. Assembly and dismantling section

4. Winding section

5. Varnishing section

6. Testing section

7. Machine section

8. Spare parts manufacturing section

9. Commutator repair section

10. Stores

11. Shop maintenance

12. Magnet & Transformer Repair Shop (MTRS)

13. Motor Overhauling and Repair Section (MORS)

ASSEMBLY & DISMANTLING SECTION: Machines after dismantling are subjected to preliminary check-up (Meggering and visual inspection). Accordingly these components are sent to various sections on the basis of the repair work involved. The healthy components are cleaned thoroughly and varnished in varnishing section before being sent to testing section for preliminary test. These components after testing are sent to respective assembly sections. The defective components are sent to respective winding sections for repair / rewinding. The assembly section takes those components of a machine for assembly which are ready in all respects. Before assembly the components are thoroughly checked to ensure whether all the repairs as mentioned in work order or as noticed by assembly group are carried out or not. In case there is some omission, it is sent to concerned section for further repair. All the windings are meggered to ensure healthy IR value and continuity in winding. All the mechanical parts like end covers, grease cups, bearings and their seatings are thoroughly cleaned before final assembly. The assembly group also conducts certain post assembly checks like freeness of rotor / armature, proper brush seating, tightness of rocker arms and their corresponding assembly in case D.C.Machine, Meggering of components, tightness of body bolts etc. before sending the jobs to testing section for final testing.

WINDING SECTION: Winding sections take up jobs either for rewinding or partial repair. Before rewinding the soundness of core laminations is ensured by "Flux Test". In case there is some abnormal heating of at some patches as detected by "Flux Test" core repair is done to rectify it. Components are recommended for rewinding unless soundness of core is ensured. The components rewound / partially repaired are subjected to a set of tests as per norms like high voltage test, current balance test, magnetic field test, checking of all joints etc. for their soundness. These components, if passed through all these standard tests are preheated, varnished and cured in furnace for a period of 16 - 18 hours. Finally covering varnish is applied on these windings before sending to respective assembly sections.

TESTING SECTION:

Fig. To show high voltage tester

Testing section conducts the following tests on all repaired machines on no load at ERS besides conducting a set of tests on all machine components in intermediate stages. These include:

AC SQUIRREL CAGE INDUCTION MOTOR:

Fig. To show squirrel cage rotors

Meggering, physical inspection, HV test, no load running test (for 30 minutes), inter turn insulation test (for 2 minutes)

AC SLIP RING MOTOR:

Meggering, physical inspection, HV test, ratio test no load running test (for 30 minutes), inter turn insulation test (for 2 minutes), supply to rotor.

D.C. MOTOR: Meggering, physical inspection, no load running test (for 30 minutes), over speed running test (120% of rated speed for 3 minutes), load test (for 5 minutes). All these machines during “No Load Test " should draw current as per prescribed norms and there should not be any abnormal heating, vibration, sound etc. so as to be declared fit for despatch. D.C. machines in addition to these should run sparkless and speed fall should be within reasonable limits on load condition. Testing group after ascertaining all quality checks despatches these machines to R & I.

MAGNET & TRANSFORMER REPAIR SECTION (MTRS): MTRS repairs all load lifting magnets, control transformers, welding transformers, rectifiers. It also fabricates load lifting magnets of all varieties. The design of these magnets is developed by planning & technical department (P.T.D.) with the development of drawing for shell, centre pole, coil and non magnetic plates. The magnet shell is cast from high permeability steel. Centre pole is an integral part of the shell and the pole shoe is bolted to the shell. Shell and centre pole shoe have been cast in Foundry shop and machined to dimension in machine shop - I as per the drawing developed by P.T.D. These machine shells are tested by various ultrasound testing techniques and found acceptable. After insulating and curing the shell, coils are assembled into the shell with suitable inter coil insulation. Heat resistant compound is poured into the shell to make all the internals monolithic. These magnets after fixing nonmagnetic plate and providing terminal boxes are delivered to shops after testing on no-load and load test at M.T.R.S. These magnets are working satisfactorily at various shops.

MOTOR OVERHAULING & REPAIR SECTION (MORS): MORS does overhauling of traction motors and roll table motors received from various rolling mills.

MAIN EQUIPMENTS INSTALLED AT ERS

1. Three E.O.T. Cranes 5 Ton, 15/3 Ton and 10 Ton (Reclamation)

2. Four Cantilever cranes (1 ton each)

3. Two induction regulators

4. One H.T. & L.T. D.O.L. starter

5. One load testing equipment (Dynamometer - up to 50 kW.)

6. One load testing equipment (Load generating system - 150 kW, 1000 r.p.m.)

7. Nine numbers coil winding machines

8. Six numbers lathes of various sizes

9. Five numbers furnaces

10. One bandaging machine

11. One balancing machine

12. One shaping machine

13. One stator coil forming machine

14. One coil cutting and pulling machine

15. Five telphers, 1 Ton each

16. Four drilling machines

17. Three grinding machines

18. One punching machine

MAIN EQUIPMENTS INSTALLED AT MTRS 1. One 20 Ton E.O.T. crane

2. One coil making machine

3. One furnace

4. One grinding machine

MAIN EQUIPMENTS INSTALLED AT MORS

1. One 20 Ton E.O.T. crane

2. One Hydraulic press

3. One bandaging machine

4. One lathe

5. One furnace

PROCESS FLOW OF ERS

ELECTROMAGNETSAn electromagnet is a type of magnet in which the magnetic field is produced by an electric current. The magnetic field disappears when the current is turned off. Electromagnets usually consist of a large number of closely spaced turns of wire that create the magnetic field. The wire turns are often wound around a magnetic core made from a ferromagnetic or ferrimagnetic material such as iron; the magnetic core concentrates the magnetic flux and makes a more powerful magnet.

The main advantage of an electromagnet over a permanent magnet is that the magnetic field can be quickly changed by controlling the amount of electric current in the winding. However, unlike a permanent magnet that needs no power, an electromagnet requires a continuous supply of current to maintain the magnetic field.

Electromagnets are widely used as components of other electrical devices, such as motors, generators, relays, loudspeakers, hard disks, MRI machines, scientific instruments, and magnetic separation equipment. Electromagnets are also employed in industry for picking up and moving heavy iron objects such as scrap iron and steel.

A simple electromagnet consisting of a coil of insulated wire wrapped around an iron core. A core of ferromagnetic material like iron serves to increase the magnetic field created. The strength of magnetic field generated is proportional to the amount of current through the winding.

History

Sturgeon's electromagnet, 1824

One of Henry's electromagnets that could lift hundreds of pounds, 1830s

Danish scientist Hans Christian Ørsted discovered in 1820 that electric currents create magnetic fields. British scientist William Sturgeon invented the electromagnet in 1824. His first electromagnet was a horseshoe-shaped piece of iron that was wrapped with about 18 turns of bare copper wire (insulated wire didn't exist yet). The iron was varnished to insulate it from the windings. When a current was passed through the coil, the iron became magnetized and attracted other pieces of iron; when the current was stopped, it lost magnetization. Sturgeon displayed its power by showing that although it only weighed seven ounces (roughly 200 grams), it could lift nine pounds (roughly 4 kilos) when the current of a single-cell battery was applied. However, Sturgeon's magnets were weak because the uninsulated wire he used could only be wrapped in a single spaced out layer around the core, limiting the number of turns.

Beginning in 1830, US scientist Joseph Henry systematically improved and popularized the electromagnet. By using wire insulated by silk thread inspired by Schweigger's use of insulated wire to make a galvanometer, he was able to wind multiple layers of wire on cores, creating powerful magnets with thousands of turns of wire, including one that could support 2,063 lb (936 kg). The first major use for electromagnets was in telegraph sounders.

The magnetic domain theory of how ferromagnetic cores work was first proposed in 1906 by French physicist Pierre-Ernest Weiss, and the detailed modern quantum mechanical theory of ferromagnetism was worked out in the 1920s by Werner Heisenberg, Lev Landau, Felix Bloch and others.

Uses of electromagnets

Industrial electromagnet lifting scrap iron, 1914

A portative electromagnet is one designed to just hold material in place; an example is a lifting magnet. A tractive electromagnet applies a force and moves something.

Electromagnets are very widely used in electric and electromechanical devices, including:

Motors and generators Transformers Relays, including reed relays originally used in telephone exchanges Electric bells and buzzers Loudspeakers and earphones Actuators Magnetic recording and data storage equipment: tape recorders, VCRs,

hard disks MRI machines Scientific equipment such as mass spectrometers Particle accelerators Magnetic locks Magnetic separation equipment, used for separating magnetic from

nonmagnetic material, for example separating ferrous metal from other material in scrap.

Industrial lifting magnets magnetic levitation Induction heating for cooking, manufacturing, and hyperthermia therapy

Laboratory electromagnet Magnet in a mass spectrometer

Physics

The magnetic field lines of a current-carrying loop of wire pass through the centre of the loop, concentrating the field there

Current (I) through a wire produces a magnetic field (B). The field is oriented according to the right-hand rule.

An electric current flowing in a wire creates a magnetic field around the wire, due to Ampere's law. To concentrate the magnetic field, in an electromagnet the wire is wound into a coil with many turns of wire lying side by side. The magnetic field of all the turns of wire passes through the centre of the coil, creating a strong magnetic field there. A coil forming the shape of a straight tube (a helix) is called a solenoid.

The direction of the magnetic field through a coil of wire can be found from a form of the right-hand rule. If the fingers of the right hand are curled around the coil in the direction of current flow (conventional current, flow of positive charge) through the windings, the thumb points in the direction of the field inside the coil. The side of the magnet that the field lines emerge from is defined to be the North Pole.

Much stronger magnetic fields can be produced if a "magnetic core" of a soft ferromagnetic (or ferrimagnetic) material, such as iron, is placed inside the coil. A core can increase the magnetic field to thousands of times the strength of the field of the coil alone, due to the high magnetic permeability μ of the material. This is called a ferromagnetic-core or iron-core electromagnet. However, not all electromagnets use cores, and the very strongest electromagnets, such as superconducting and the very high current electromagnets, cannot use them due to saturation.

Side effects

There are several side effects which occur in electromagnets which must be provided for in their design. These generally become more significant in larger electromagnets.

Ohmic heating

Large aluminium bus bars carrying current into the electromagnets at the LNCMI (Laboratoire National des Champs Magnétiques Intenses) high field laboratory.

The only power consumed in a DC electromagnet is due to the resistance of the windings, and is dissipated as heat. Some large electromagnets require cooling water circulating through pipes in the windings to carry off the waste heat.

Since the magnetic field is proportional to the product NI, the number of turns in the windings N and the current I can be chosen to minimize heat losses, as long as their product is constant. Since the power dissipation, P = I2R, increases with the square of the current but only increases approximately linearly with the number of windings, the power lost in the windings can be minimized by reducing I and increasing the number of turns N proportionally, or using thicker

wire to reduce the resistance. For example, halving I and doubling N halves the power loss, as does doubling the area of the wire. In either case, increasing the amount of wire reduces the ohmic losses. For this reason, electromagnets often have a significant thickness of windings.

However, the limit to increasing N or lowering the resistance is that the windings take up more room between the magnet's core pieces. If the area available for the windings is filled up, more turns require going to a smaller diameter of wire, which has higher resistance, which cancels the advantage of using more turns. So in large magnets there is a minimum amount of heat loss that can't be reduced. This increases with the square of the magnetic flux B2.

Inductive voltage spikes

An electromagnet has significant inductance, and resists changes in the current through its windings. Any sudden changes in the winding current cause large voltage spikes across the windings. This is because when the current through the magnet is increased, such as when it is turned on, energy from the circuit must be stored in the magnetic field. When it is turned off the energy in the field is returned to the circuit.

If an ordinary switch is used to control the winding current, this can cause sparks at the terminals of the switch. This doesn't occur when the magnet is switched on, because the voltage is limited to the power supply voltage. But when it is switched off, the energy in the magnetic field is suddenly returned to the circuit, causing a large voltage spike and an arc across the switch contacts, which can damage them. With small electromagnets a capacitor is often used across the contacts, which reduces arcing by temporarily storing the current. More often a diode is used to prevent voltage spikes by providing a path for the current to recirculate through the winding until the energy is dissipated as heat. The diode is connected across the winding, oriented so it is reverse-biased during steady state operation and doesn't conduct. When the supply voltage is removed, the voltage spike forward-biases the diode and the reactive current continue to flow through the winding, through the diode and back into the winding. A diode used in this way is called a fly back diode.

Large electromagnets are usually powered by variable current electronic power supplies, controlled by a microprocessor, which prevent voltage spikes by accomplishing current changes slowly, in gentle ramps. It may take several minutes to energize or deenergize a large magnet.

Lorentz forces

In powerful electromagnets, the magnetic field exerts a force on each turn of the windings, due to the Lorentz force acting on the moving charges within the wire. The Lorentz force is perpendicular to both the axis of the wire and the magnetic field. It can be visualized as a pressure between the magnetic field lines, pushing them apart. It has two effects on an electromagnet's windings:

The field lines within the axis of the coil exert a radial force on each turn of the windings, tending to push them outward in all directions. This causes a tensile stress in the wire.

The leakage field lines between each turn of the coil exert a repulsive force between adjacent turns, tending to push them apart.

The Lorentz forces increase with B2. In large electromagnets the windings must be firmly clamped in place, to prevent motion on power-up and power-down from causing metal fatigue in the windings. In the Bitter design, above, used in very high field research magnets, the windings are constructed as flat disks to resist the radial forces, and clamped in an axial direction to resist the axial ones.

Core losses

In alternating current (AC) electromagnets, used in transformers, inductors, and AC motors and generators, the magnetic field is constantly changing. This causes energy losses in their magnetic cores that are dissipated as heat in the core. The losses stem from two processes:

Eddy currents: From Faraday's law of induction, the changing magnetic field induces circulating electric currents inside nearby conductors, called eddy currents. The energy in these currents is dissipated as heat in the electrical resistance of the conductor, so they are a cause of energy loss. Since the magnet's iron core is conductive, and most of the magnetic field is concentrated there, eddy currents in the core are the major problem. Eddy currents are closed loops of current that flow in planes perpendicular to the magnetic field. The energy dissipated is proportional to the area enclosed by the loop. To prevent them, the cores of AC electromagnets are made of stacks of thin steel sheets, or laminations, oriented parallel to the magnetic field, with an insulating coating on the surface. The insulation layers prevent eddy current from flowing between the sheets. Any remaining eddy currents must flow within the cross section of each individual lamination, which reduces losses greatly. Another alternative is to use a ferrite core, which is a non-conductor.

Hysteresis losses: Reversing the direction of magnetization of the magnetic domains in the core material each cycle causes energy loss, because of the coercivity of the material. These losses are called hysteresis. The energy lost per cycle is proportional to the area of the hysteresis loop in the BH graph. To minimize this loss, magnetic cores used in transformers and other AC electromagnets are made of "soft" low coercivity materials, such as silicon steel or soft ferrite

ROUND ELECTROMAGNETS

Round electro magnets are known for their applicability in various fields. The electro magnets are designed in such a manner to develop deep penetrating electromagnetic field to lift scrap and other diversified forms of ferrous materials. Circular lifting electro magnets are used in transporting steel blocks, pigs and scrap in scrap yards, ports and foundries. They also crush clinker in skull cracker ball operations.

Electromagnets in Bhilai steel Plant are operated on 220V DC supply. The cover of round magnets is made up of stainless steel (non magnetic) plate. So it cannot be cut by normal welding. To open the cover either we have to use a lathe machine or Gouging arc. Gouging arc is generated by using a carbon rod at a current of 2000A and at high pressure (80-100psi). The maximum strength of the magnetic field is at the centre pole (made up of cast iron and attached to the outer frame).

Stainless Steel plate used as a covering for the electromagnet.

How to Distinguish between Underwater and surface magnets?

Underwater Magnets: Single wire comes out from the terminal box (highly sealed to keep it away from water). Another distinguishing feature i the provision of a hut adjacent to the terminal box to protect the wire from wear and tear.

Surface Magnets: Two wires come out from the terminal box.

Bulldog is used to keep the wire from terminal box in fixed position.

The magnets designed for underwater use but absorb moisture and will have more life if used as a surface magnet is marked as Striker.

Terminal Box:The coils inside the magnet are connected in series. The starting point of the first coil and the ending point of the last coil are put through to the terminal to give them supply voltage. Testing of electromagnet is done through the terminal box. Megger is used to measure the voltage drop while resistance is measured by using a multimeter. The terminal box can be seen in the image below. It will be divided in to two compartments using a Texolite sheet. The hut for protecting the supplying wire can also be seen adjacent to the terminal box.

Fig. To show Terminal Box along with Hut. Coils An electromagnet can be constructed by using 4, 6 or 8 coils. 4 coil electromagnets are common but one with 8 coils is rare. The thickness of the coil varies according to the number of coils to be placed in the magnetic cell. The coils are made up of insulated copper strips.

Fig. To show cross-sectional view of a coil.

Insulation

(1) Paramite sheet: The thickness of paramite sheet varies from 1.6 to 3.2mm. It can absorb moisture.

Fig. To show rolled up paramite sheet

(2) Mica Sheet: It comes in the form of square shaped sheets. 4 mica sheets are used to cover the coil periphery once.

Paramite and mica sheets along with varnish are used to provide insulation between the coils.

Fig. To show a part of mica sheet

(3) Glass Sheets:

Fig: To show a glass sheet Glass sheets are heat and fire proof and do not absorb moisture. These are used to provide the in insulation between the centre pole and the coils. 2 layers of glass sheet are fitted between pole and coils. Space between the glass sheets is filled with paramite and mica. If space is left then it is again filled with glass sheets by applying force so that the coils get fixed.

Compounds(1) SR (Silicone rubber) Compound:

Structure is just like normal rubber. It is formed by mixing liquid and hardener along with continuous stirring. The mixture becomes solid after leaving it undisturbed for 3 to 4 hours. It is used to provide the insulation between the coil and the magnetic cell.

(2) HRC (High Rupturing Capacity) Compound: The liquid and hardener are mixed in the ratio of 4:1 (5l hardener for 20l HRC). It is very hard and possesses high strength.

SR Compound is more commonly used because when the magnet comes for repairing, SR Compound is easy to dismantle whereas if HRC compound is used, the magnet is first heated in the furnace and then only the compound can be removed.

Anabond 901B: Part A: Resin Part B: CatalystPart A and Part B are thoroughly mixed in the ratio of 100:1.25 and stirred well.

Safe Handling Method: Provide ventilation to control vapour exposure within inhalation guidelines when handling at elevated temperature.

Anabond Two Part SystemStorage: Catalyst is highly moisture sensitive. Store in a cool, dry place away from moisture.

Texolite Sheet: It is also called chemical wood. From outside surface looks smooth like tiles and its texture is wooden from the sides. It is used to separate the two columns in the terminal box.

Texolite Sheet

Metrosil: It is a device connected in parallel to the supply wires in the terminal box. It is used to tackle the sudden surges in power supply when all other equipments are turned off at once. It is generally a Metal Oxide Varistor (MOV). The resistance of a varistor varies according to the voltage across its terminals. When the voltage across its terminals is high, its resistance decreases to provide an alternative path for the excess current to flow thus saving the coils of the electromagnet from burning out.

Metrosil (Surge Suppressor)

RECTANGULAR MAGNETS

To show a Rectangular ElectromagnetMost of the description for round and rectangular electromagnets is same. The key differences are:

(1) The shape is different from that of round magnets. The coils used are rectangular in shape instead of round.

(2) Basically divided in to three types depending upon the manufacturer and the shape.

(3) Out of the three types only the box type electromagnet uses Metrosil to protect its thin copper strips from burning out.

(4) The total resistance of coils in case of round electromagnets is around 2.8-3.2 mega ohms. In case of rectangular magnets the total resistance of coils is high (between 7-8 mega ohms).

(5) Rectangular electromagnets are used to lift the finished products in billet mill, merchant mill etc.

Rectangular Magnet to be repaired

Complete Repairing Process for Load Lifting Electromagnet

The complete procedure basically consists of External supervision, dismantling and assembly. Procedures are same for most of the lifting magnets the only difference is that the terminal box is waterproof in case of underwater magnets.

Procedure for magnet repairing:

Supervision1. Identify the job number of the magnet which is to be repaired.2. Using cranes put the magnet in the repair section carefully & open it using

proper tools.3. External inspection is done by looking at outer terminal, magnetic &

nonmagnetic body of the magnet.4. Record the fault present in the magnet & highlight it by using a chalk.5. Test the insulation resistance using multimeter. If resistance is not

appropriate then the magnet will be opened for further repairing processDismantle1. First the base of the electromagnet is detached by using gas welding.2. Silicon compound is removed from the terminal box without damaging the

metrosil.3. Check the metrosil and the wires in the terminal box for any damage.

The remaining electromagnet is inverted using overhead crane.4. To remove the stainless steel plate, Gouging arc is used.5. Insulation sheets are removed and coils are taken out one by one from the

cell.6. Resistance and voltage drop across each coil is measured using multimeter

and megger respectively.Assembly1. After dismantling, the inner part of the cell is cleaned using a wire brush and

checked for any damage to the body.2. Bottom of the cell is insulated by double layers of mica sheet & double

layers of 1.6mm paramite sheet or 3.2 mm single Permanente sheet3. One more layer of mica sheet is provided & thermosetting varnish is done

over the layer.4. Centre pole is insulated & rolled with mica and glass sheet up to appropriate

height & then it is varnished.5. After the insulation, varnishing is done to remove the moisture & allowed to

settle by putting weight on it.

Weights that are used after varnishing.

6. Heating is done in heating furnace for 24 hours at 120oC.7. Once it is done then it is allowed to cool & weights are removed.8. Good quality coils are used. It is cleaned & insulation is removed for brazing. 9. Coils are in series, number of coils represents the ampere turn & magnetic

field capability of the magnet.10. Red varnish is used on both sides of coil winding for insulation purpose.

11.Brazing is done to take out lead from copper coil. T.C.I cleaning agent is used & then rolled with glass tape.

12.To tighten the coils, mica sheets and glass sheets are filled into the gaps between the coil & centre pole. SR or HRC compound is used to fill the gap between the cell & the coils.

13.Jumper is taken out from the coil for series coil connection.For putting another coil in series same layers of insulation are provided with same procedure.

Conclusion This project is made on the basis of study & observation of different types of magnets and their properties. All the parameters are based on SAIL IPSS standards. The project is only for study purpose in colleges.