An Over View of Visakhapatnam Steel Plant

8/7/2019 An Over View of Visakhapatnam Steel Plant

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AN OVER VIEW OF VISAKHAPATNAM STEEL PLANT

Document By

SANTOSH BHARADWAJ REDDY

Email: [email protected]

More Papers and Presentations available on above site

INDEX

Contents :

1. Introduction of Visakhapatnam Steel Plant

2. An over view of Electrical Drive Technology

trends for Industry Cranes

3. Methods of speed torque control of a 3 phase

induction motor

4. Project Introduction

5. Project Details

5.1 Motor Details

5.2 Resistance Details

5.3 Feed back Control

5.4 Controller / Drive details
mailto:[email protected]:[email protected]


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6. Practical readings

7. Conclusion

AN OVER VIEW OF VISAKHAPATNAM STEEL PLANT

Visakhapatnam is popularly called as the Steel City of India and credit was

because of the Vizag Steel Plant a venture of Ispat Nigam. VSP is the first

coastal based steel plant of India and is located 16 km Southwest of city of

destiny. VSP has an installed capacity of 3 million Tones per annum of liquid

steel and 2.656 million tones of saleable steel. VSP products meet exalting

international quality standards such as JIS, DIN, BIS, BS etc.

VSP has the distinction to be the first integrated steel plant in India to become

a fully ISO-9002 certified company. The certificate covers quality systems,

training and marketing functions spreading over 4 regional marketing officer, 20

branch offices and 22 stockyards located all over the country.

VSP successfully installing and operating efficiently Rs. 460 crores worth of

pollution control and environment control equipment and converting the barren

land scape by planting more than 3 million plants has made the steel plant, steel

township a greener, cleaner place, which can boas of 3 to 40C lesser

temperature even in the peak summer compared to Visakhapatnam City.


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Exports quality pig iron and steel projects to Sri Lanka, Myanmar, Nepal,

Middle East, USA & South East Asia (Pig Iron). RINL VSP was awarded State

Trading House status during 1997-2000.

Besides these a captive power plant with a capacity of 247.5 MW, Oxygen

plant, Acetylene plant, compressed iron plant, extensive repair, maintenance

facilities, form part of facilities available at VSP. VSP has sufficient infrastructure

to expand the plant to 10 Million tones per annum of liquid steel capacity.

MAJOR PRODUCTION FACILITIES:

VSP has the following major production facilities :

3 Coke oven batteries of 67 ovens each having 41.6 m3 volume.

2 Sinter machines of 312m3 area.

2 Blast Furnace of 3200 m3 useful volume.

Steel Melt Shop with three L.D.> Converters of 150T capacities each and 6

nos of four stand continues bloom casters.

Light and medium merchant mills of 710, 000 tones per year capacity.

Wire Rod Mill of 850,000 tones per capacity.

Medium Merchant and Structural Mill of 850,000 tones per year capacity.


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MAJOR DEPARTMENT

RAW Materials Handling Plant (RMHP):

VSP annually requires quality raw materials viz. irion ore, fluxes,

coking and non-coking coals etc. to the tune of 12-13 Million tones for

producing 3 million tones of liquid steel to handle such large volume of

incoming raw materials received from different source and to ensure timely

support of consistent quality of feed materials to different VSP consumers,

raw material handling plant serves a vital function. The unit is provided with

elaborate unloading, blending, stacking & reclaiming facilities viz.,

Wagon Tripplers, ground & track Hoppers, Stock Yards crushing plants,

vibrating screens, single / twin boom stackers, weal in boom Blenser

recliners.

In VSP peripheral unloading has been adopted for the first time in the

country.

Coke Oven & Coal Chemical Division :


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Blast Furnace, the mother unit of any steel Plant requires huge qualities of

strong, hard and porous solid fuel in the form of hard metallurgical coke for

supplying necessary heat for carrying out the reduction and refining reactions

besides acting as a reducing agent.

Coke is manufactured by heating odd cursed coking coal, in absence of air at

temperature of 10000C and above for about 16 to 18 hours. A coke oven

comprise of two hollow chambers namely coal chamber and heating chamber

in which a gaseous fuel such as Blast Furnace Gas, coke oven gas etc., is

burnt. The heat so generate is conducted through the common wall to heat &

carbonize the coking placed in the adjacent coal chamber.

Number of ovens built in series one after other from a coke oven battery. At

VSP there are 3 coke oven batteries, 7m tall and having 67 ovens each.

Each oven is having a volume of 41.6 cum and can hold upto 31.6 tones of

dry coal charge. The carbonization takes places at 1000-15000C in absence

of air for 16-18 hours.

Red hot coke is pushed out of the oven and sent to coke dry cooling plant

for cooling to avoid its combustion. There are 3 coke dry cooling plants each

having 4 cooling chambers. Heat capacity of each cooling chamber is 50-52

THP. Nitrogen gas is used as cooling medium. Generating steam and

expanding to pressure turbines to produce 75MW power each to the heat

recovery from nitrogen.

The Coal chemicals such as henzole, Tar, Ammonium sulphate etc., are

extracted in the coal chemical plant from Co Gas. After recovering the coal

chemical the gas is used as a by product fuel by mixing it with gases such

as BF, LD etc. A mechanical, biological & chemical plant takes care of the

effluents.

Sinter Plant :


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Sinter is a hard & porous ferrous material obtained by agglomeration of

iron ore fines, coke breeze, lime stone fines metallurgical wastes

Vizianagaram., mill scale D slag etc.

Sinter is a better fed material to blast furnace in comparison to iron ore

lumps and its usage in blast furnaces help in increasing productivity,

decrease the coke rate & improving the quality of hot metal produced.

Sinter is done 2 nos of 312 sq. m Sinter machines of Dwight Lloyd type

by heating the prepared feed on a continuous metallic belt made of pallets at

1200- 13000 C.

Hot Sinter discharged from sintering machine is crushed to +5mm

-50mm size and before dispatching to blast furnaces.

Blast Furnaces:

Hot metal is produced in blast furnace, which are tall vertical furnaces.

The furnace as 1 is run with blast at high pressure & temp. Raw materialssuch as sinter/ iron ore lumps, fluxes and coke are charged from the top and

blast at 11000C 13000C and 5.75 KSCH pressure is blown almost from the

bottom. The furnaces are designated for 80% sinter in the burden.

VSP has two 300 Cu.m blast furnaces equipped with Paul worth Bell

less top equipment with conveyor charging. Rightly named as Godavari &

Krishna, the furnaces will help VSP in bring the prosperity to the state the

two furnaces with their noval circular cast house and 4 tap holes each arecapable of producing 9720 tones of hot metal daily or 3.4 million tones of

sulphur not metal annually.

Steel Melting Shop:

Steel is an alloy of iron with carbon upto 1.8%. Hot metal produced inblast furnaces contains impurities such as carbon, silicon, manganese,


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sulphur and phosphorus is not suitable as a common engineering material to

improve the quality the impurities are to be eliminated or decreased by

oxidation process.

VSP produces steel employing 3 number of top blown oxygen

converters called LD converters or basics oxygen furnace / converter. Each

converter is having 133 cum volumes capable of producing 3 million tones of

liquid steel annually. Besides hot metal, steel scrap, fluxes such as calained

lime or dolomite from part of the charge to the converters.

99.5% pure oxygen at 15.16 KSCG pressure is blown in the converter

through oxygen lance having convergent divergent copper nozzles at the

blowing end. Oxygen oxidizes the impurities present in the hot metal, which

are fixed as slag with basic fluxes such as lime. During the process heat is

generated by exothermic rises to 17000C enabling refining & slag formation.

Converter / LD gas produced as by product is used as secondary fuel.

Liquid steel produced in LD converter is solidified in the form of blooms in

continuous bloom casters. However to homogenize the steel and to raise its

temp if needed, steel is first routed through, argon rising station IRUT ladle

furnace.

Continuous Casting Department :

Continuous Casting may be defined as teeming of liquid steel in a

mould with a false bottom through which partially solified ingot / bar iscontinuously with drawn at the same rate at which liquid is teamed in the

mould.

Facilities at a continuous casting include a lift and turn table for ladles

copper mould oscillating system tundish, primary & secondary cooling

arrangement to cool the steel bloom. Gas cutting machines for cutting the

blooms in required length.

Rolling Mills :


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Blooms produced in sms-ccd do not find much applications as such

and are required to be shaped into products such as Billets, rounds, squares,

angles, channels, I-PE beams, HE-beams, wire rods and reinforcement bars

by rolling them in, there sophisticated high capacity, high speed, fully

automated rolling mills, namely light & medium merchants mills (LMMM), wire

rod mill (WRM) and medium merchant and structural mill (MMSM).

Light & Merchant Mill :

LMMM comprises of two units. In the Billet 250 x 320 mm size blooms

are rolled into billets of 125x125 mm size after heating them in two numbers

of walking beam furnaces of 200 tons/hr capacity each. This unit comprises of

7 stands and 5 alternating vertical & horizontal stands (730x1100 mm &

630x1000mm) billets are supplied from this mill to bar mill of LMMM & WRM.

The mill is facilitated with temp core heat treatment technology

evaporative cooling system in walking beam furnaces, automated pilling &

bunding facilities, high degree of automation and computerization.

Wire Rod Mill :

Wire Rod Mill is a 5 stands fully automated and sophisticated mill. The

mill has a four zone combination type reheating furnace of 2000 TPH capacity

for heating the billets received from billet mill of LMMM to rolling temp of12000C.

The heated billets are rolled in 4 strand no twist continuous mill having

a capacity of 850,000 tones of wire rod coils and having the following

configuration.

7 stand two high 4 strand horizontal roughing train.

6 stand two high 4 strand horizontal intermediate mills.


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2 stand 2 strand pre finishing mill.

10 stands 4 strand no twist finishing mill.

The mill produces rounds in 5.5-12mm range and rebars in 8-12mm range.

Medium Merchant and Structural Mill :

The medium merchant structural mill is a single stand filly continuous

rolling mill having an capacity of 850,000 tones of medium merchant and

structural products. The important feature of this mill is that it produces

universal beams both parallel and wide.

METHODS OF SPEED TORQUE CONTROL

There are in general five methods of modifying the speed torquecharacteristic of three phase induction motors:

Variation of Applied Voltage :

The torque at any value of slip varies as the square of the applied

voltage as indicated using this property a family of speed torque curves as

shown below can be computed for the machine when it operates at different

voltage.

The curves indicate that the slip at maximum torque is independent of

the terminal voltage the range of speeds within which steady state operation

may take place is the same for all voltages, namely between the speed


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Typical speed torque curves for four different frequencies are shown.

The slip at which maximum torque becomes larger as the operating frequency

decreases and the maximum torque gets reduced slightly the starting torque

increases for small reductions in frequency, but attains a maximum and then

decreases with further reduction in frequency.

Introduction of Stator Impedance :

Balanced resistors or inductors can be added to the stator circuit so as

to reduce the voltage at the machine terminals. Under these conditions, the

motor terminal voltage becomes a function of the typical speed torque curvesare shown in figure. For the cases of added resistance and inductance.

If the additional resistance or inductance were chosen such as to give

the same starting torque, the speed torque characteristic corresponding to

additional inductance would have larger torque than with additional

resistance. Besides, both these characteristic enable us to get larger torques

than with the characteristic obtained with reduced applied voltage, which

given the same starting torque.

Modify the characteristic by means of introducing external resistance in

the stator circuit will improve the power factor, but at the expense of slightly

greater losses at starting. These losses are minimized with reactor starting,

but the power factory becomes poor.

The reduction in developed torque at low frequencies is partly due to

the apparent increase in resistance of the machine and also due to the


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to a value (SE2-EJ), as a result of which the rotor current 12 and, hence the

torque developed decreases. But, since the load torque remains constant, the

speed of the motor starts decreasing. This process of reduction in speed

(increases in slip) continuous till the rotor induced EMF increases to circulate

enough current in the rotor to develop the desired torque. Current in the rotor

to develop the desired torque.

Let Sj be the new value of the slip and SjE2, the corresponding new of

the rotor DMF, once study state conditions have reached after the injection of

the additional EMF Ej. Then,

12=(S1*E2-EJ)/R2 since (SJx2) ^2S, the new slip Sj becomes negative, that is the machine runs at a

speed greater than the synchronous speed, maintaining its motor operation.

The modified speed torque characteristics are shown in figure.


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An Overview of electrical drive technology for industrial cranes :

Slip ring motor control with variation of rotor resistance :

With the shifting of the technology from dc to ac in the 60s slip ring

motor became the traditional work horse for hoisting and traveling gears such

as been the mind set and comfort level of the user and maintenance people,

so that this technology is preferred in spite of knowing its various drawbacks

vice versa. The basic control slip ring motors uses contactors for the external

rotor resistance circuit. The early control circuits used timers for the switching

circuit of these contactors during the acceleration of the motor, irrespective of

the operating speeds. This resulted in a stressed motor with huge current and

torque surges when a low resistance value is witched in at a certain speed.

Siemens. The pioneer in crane technology introduced SIMOMAT control

during that time, which used speed dependant switching. The contractors in

the resistance circuit were switched on depending on the actual motor speed.


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The analog speed controllers were subsequently introduced in the early 80s

by Siemens. These drives combine the two traditional methods of variable

speed control of asynchronous machines.

Changing the motor voltage with the aid of stator phase angle control.

Changing the motor characteristics by means of variable rotor

resistance.

This combination gave excellent result and the controls became

extremely popular at that time. The advantage of Thyristor based speed

control of slip ring motors, apart from its ruggedness, is the fact that it can be

used for retrofit solutions on existing cranes which are still running with

conventional contractor control. The old steel plants mix of technology is

available with cranes running with dc motors, slip ring motors and cage

motors. The drives may have been retrofitted with digital versions in affect

substantial inventory to be planned by the maintenance team. In order to

minimize the inventory E-Vendors has standardized certain major accessory

cards, at drive I/O expansions boards, operator displays, technology boards

which can be used for either on any of the drives. With the advancement of

transistor technology in 90s cage motors controlled through VVVF drives

were found to be suitable for hoisting applications with better control and

dynamics. The limitations of the slip ring motors compare to the cage motor

came in the lime light, mainly:

Slip ring motors and rotor resistances are maintenance intensives.

Slip ring motor have higher weight and rotor inertia compared to cage

motors. The higher rotor inertia calls for higher acceleration torque and

selection of higher motor frame size. The weight of the motor and there by the

pulling weight of the trolley increases.


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Crane motions are more prone to jerks due to change over of rotor

contractors.

Smooth speed control as cage motor with VFDs not achievable.

Load dependent speeds corresponding to defined characteristics. The

max possible speed is defined by the number of poles and supplied

frequency, field weakening is not possible.

Usage of too many cables, leading to cumbersome festoon

arrangement.

The optimized commissioning of a slip ring motor with a drive

depends on the experience of the commissioning engineer, mainly due to the

fine tuning of the rotor resistances as per the load.

AC VARIABLE FREQUENCY DRIVE TECHNOLOGY WITH

CAGE MOTORS :

With the development and advancement in the arena of semi

conductor devices in the last 10 years. C VEDs has become the most reliable

crane drive control. A typical VFD consist of a Rectifier section, DC capacitor

bus and the Inverter section. The combination of the field vector control andthe latest IGBT devices, is the optimal control of the cage motor and it even

exceeds the performance of DC drives. The control of the flux and torque

generating vector components separately is similar to the DC machines. In

this section we will discuss the various effects of VFDs on cage motors, the

latest motor technology available and selection of the right drive configuration

for the application.


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One of the major obstacles faced during the early 90s was the use of

the standard cage motors with the VFDs, the transistor based VFDs uses

high impulse frequencies which gives rise to a very high dv/dt stress on the

motor winding. The typical IGBT devices switches at approximately 3-16kHZ.

The peak values of the voltage impulses are always considerably higher that

the normal voltage. It takes some time for impulse to propagate through the

windings of coil, and so the voltages between the turns of a coil or between

coils in the same phase can be abnormally high.

The life time and reliability of a motor mainly depends on the insulation

of the winding. The design and manufacturing of modern winding insulation

has to ensure reliable motor operation for many years. All components of the

insulation system, for example the turn insulation, the coil insulation, the

gradient tapes or the resin, and also the process parameters have to be

designed carefully in order to meet the electrical, mechanical and thermal

stresses on the winding for a long time.

In case of inverter feed, the motor terminal voltages and thus the

electrical stresses on the winding insulation differs significantly from those

when the motor is at lien operation.

Use of the vacuum pressure impregnation and special insulation, Ex-

Siemens, DURIGNIT 2000 is a common feature in these motors.

The effects of the PWM operation on the lifetime of the bearing of the

induction motor has been understood in recent times. Mr.Steve Barkers

paper on Avoiding premature bearing failure with inverter-fed induction

motors explain the degradation of the bearings, especially for larger motors

for hoists.


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AC MOTOR TECHNOLOGY TRENDS:

The motors available in the market for operation with VFT are provided

special insulation material and insulated bearings above frame 280.

The high power density induction are favorably priced and

standardized low-voltage motors. They are based on the technology of our

well-proven N-compact series that, for sophisticated applications, already set

standards for low-voltage motors. 4-pole N-compact Standard line motors

cover a power range from 250 to 500 KW.


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The Standard line motors have well-proven technology quality that is

already is use worldwide.

They offer flexibility in spite of standardization. In addition to the basic

version, we can provide a selection of options that allows you to use these

motors in a wide range of applications. These options include, among others,

sensing the winding and bearing temperatures, anti-condensation heating as

well as rotary pulse encoder.

The biggest advantage is short delivery times.

The motor design is extremely rugged for the toughest of ambient

conditions.

If offers the possibility of creating a favourably priced system

solution.

Brief overview

Self-ventilated Motors : 250 500 KW

Shaft heights : 317, 353, 355, 357mm

No. of poles : 4

Rated voltages : 400 V / 690 V Y

Drive converters : Possible

Degree of protection : IP55

Cooling type : IC 411


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Type of construction : IM B3

Bearings : Roller bearings

Regulations / Standards : IEC. EN

Explosion protection : Is not provided

Typical applications :

Pumps

Compressors

Fans

Blowers

Extruders

Conveyor systems

1PH7 Asynchronous Servo Motors

Compact induction motors with forced ventilation and

solid shaft

The 1PH7 motors are induction motors with compact dimensions. The motors

have a high power density at low construction volume. The 1PH7 motors

are available in a broad power, speed and option range. The motors have

excellent smooth-running and vibration properties and a high resistance to

transverse forces.


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1PH7 induction motors the compact motors with high

degree of protection

Require very little space.

High resistance to transverse forces.

Low maintenance costs.

1PH7 induction motors overview of the product range.

Rated

speed* :

400

2,900 rpm

Ratedpower* :

3.7 385kW

Rated

torque* :

22 2,480

Nm

1PH7 induction motors typical areas of application.

Main spindle drive for machine tools.

Production machines (e.g. hoist drives, high bay racking systems,

printing machines, wire-drawing machines, extruders, winding applications,

etc.)

ANTI SWAY CONTROL FOR INDUSTRIAL CRANE

Controlling the sway of the load is very important for certain cranes in steel

plant which requires positioning, Ex-Coil tracking cranes. Sway is induced in a

suspended load both by movement of the suspension point (trolley), and by

external forces such as wind and non-vertical lift. External forces are not so

predominant for indoor cranes. A skilled operated can remove sway using a

properly timed change in the suspension point to place it directly over the load

at a time when the is stopped, at the end of swing Catching the load in this

manner takes skill and practice.


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When the sway starts, it follows a SHM, where the oscillation time period is

governed by the basic formula

t = 2 l/g

Since the steel plant cranes are not affected by wind factor, the basic

algorithm developed in the sway controller works in a open loop. The Master

controller signal comes to the sway controller and the set point to the drive

comes from the controller.

Up to a certain extent, the sway control can be limited by adjusting the drive

ramp up curve.

PROJECT INTRODUCTION

2.1 Motor Details


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Motor Data for 15/dT. Crane :

1. No. of Poles : 10 Poles

2. Duty : 40% CDF

Data at Mechanical Computed Value:

1. Power : 26.42 KW

2. Stator Current : 78 A

3. Rotor Current : 61 A

4. Max Attainabe Speed At Rated

Torque in Hoisting Direction : 534 R.P.M.

5. Max Attainable Speed At Rated

Torque in Lowering Direction : 666 R.P.M.

2. Construction :


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The actual speed signal is obtained by reducing the tachogenerator voltage to

an approiat level. Since the polarities of the signals are always opposed, the

result at the summation point is a difference, the speed deviation, Undev.

The relations are as follows:

1. Uur > 0, Un < 0

Undev = Uur+ Un = Uur (Un)

2. Uur < 0, Un > 0

Undev = Uur+ Un = Uur (Un)

As this shows, the difference can be of either polarity, meaning that the speed

controller can control both positively and negatively.

The output of the speed control system tries to make Undev as small as

possible, i.e.,, to make Uur to make Uur ~ Un .this is done by allowing Undev to

control the magnitude and direction of the motor torque, i.e., Umr= K1. Undev

where K1 is a positive constant.

The sign of Undev controls the direction of the output torque of the motor via the

automatic reversing equipment.

Howerver, in an induction motor the torque M is not directly proportional to

motor current (as in dc motor); instead it is proportional to the square of the

motor current, i.e.,

/ M / + K 2l2

From which / Umr / = K2. U2 ir where K2 is positive constant.

The equations are valid for any speed. Consequently, to obtain a linear

system, the reference value Ulr for the following current control must be

proportion to the square of Umr, i.e.,


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Umr = -K3 / UMr/

Or

Ulr = -K4 / Undev /

Umr is determined and the root obtained in the reversing modules (4d) by

inverting circuit and diode networks. The single Ulr thus obtained, which is

always negative, is summated with the current signal, U l from the current

measuring module at the summation point of the current controller. Since U l is

a always positive, the difference Undev = U l U lr is produced at this point, andcontrols the current controller. The control system make this difference as

small as possible, i.e., it makes Ul ~ Ulr this is done by using the output signal

of the current controller as the control voltage (Us) of the trigger pulse

module.

This control voltage alters the phase position of trigger pulses relative to thephase of the main voltage, thus varying the firing time of the thyristors within

the period, i.e., varying their control angle. This principle is known as phase

control : the output voltage (=motor stator voltage) is given as rms value.

Determined by the control voltage, and a chopped wave from When the

regulator is operating at less tan full output. At full output the waveforms is

completely sinusoidal.

Torque limiting, and consequently a current limit, which is adjustable, is

obtained by limiting the Output of the n- controller.


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3. Description Of SIMTRAS HD Controller :

3.1 Applications:

SIMOTRAS HD converters in the 6SG70 series are fully digitalcompact converters and have been developed for regulating three-

phase lifting gear motors with slip ring rotors in the output range upto

580 KW and for higher-level control of the drive.

3.2 Design :

Series 6SG70 SIMOTRAS HD Converters are characterized by their

compact, space-saving construction. Their compact design makesthem particularly easy to service and maintain since individual

components are readily accessible. The electronics box contains the

basic electronic circuitry as well as any supplementary boards.

All SIMOTRAS HD converters are equipped with a PMU simple

operator panel mounted in the converter door. The panel consists of a

five-digit, seven segment display, three LEDs as status indicators and

three parameterization keys. The PMU also features connector X 300

with a USS interface in accordance with the RS 232 or RS485

standard. The panel provides all the facilities for making adjustments

or settings and displaying measured values required to startup the

converter.

The OP1S optional converter operator panel can be mounted either in

the converter door or externally, eg in the cubicle door. For thispurpose, it can be connected up by means of a 5m long cable. Cables

of upto 200m in length can be used if a separate 5V supply is

available. The OP1S is connected to the SIMOTRAS HD via connector

X300.

The OP1S can be installed as an economic alternative to control

cubical measuring instruments which display physical measured

quantities.


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converter functions in plug braking mode (braking) or it drives the

machine in the other direction of rotation (driving). A driving cycle that

is both highly dynamic and gentle is possible because the conventional

stator contractor is no longer required.

The voltage on the motor is adjusted using the stator phase-angle

control from three inverse-parallel thyristor pairs. In this process, the

supply frequency of the motor is not changed; it is always identical to

the relevant mains frequency.

The thyristors are controlled by the gating unit. This generates line-

synchronous firing pulses. The control electronics are separated from

the line potentional by ignition transducers. The operating states are

displayed on the unit via the 7-setment display and LEDs or via the

optional OP1S operator control panel.

All converter settings (e.g. controller parameters, limit values, etc) are

saved in non-volatile memory in the converter. The adjustment is made

digitally via the converter control panel or via the optional OP1S control

panel. The values can therefore be easily reproduced at any time.

SIMOTRAS HD combines two traditional procedures for adjusting the

speed of asynchronous machines:

Changing the motor voltage using the stator phase-angle control

Gradient of motor characteristic curve using variable rotor

resistances.

This combination permits excellent control response where the

advantages of both procedures are exploited and the disadvantages

are largely avoided. Both procedures are described below.


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3.3.2 Speed Control using Stator phase-angle control:

The amplitude of the fundamental wave of the supply voltage is

changed using the stator phase-angle control. With a constantly

ascending ramp for the setpoint voltage from zero to maximum

activation, the control angle and therefore the voltage time-area are

continually increased. This increases the motor voltage (UM)

continually and the drive is thereby slowly accelerated. The motor

torque increases proportionally to UM2.


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3.3.3 Speed control by changing the rotor resistance levels:

The torque can be influenced by switching on an additional ohmic

resistance in the rotor circuit in the asynchronous motor. To do this,

however, an asynchronous machine with a slipring rotor is required.

Starting with the characteristic curve for a squirrel-cage motor, the

gradients or the speed torque curves increase as the resistance in the

rotor circuit increases. The level of the pull-out torque Mk remains

constant.

This means that at a specific load torque ML, the various constant

speeds n2, n3 or n4 can be set. If the load changes, the speed

increases as well.


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3.3.4 Method of operation of electronic phase reversal with plug braking.

The drive starts up with the positive speed and stabilizes at point a. A

constant load profile is assumed during this process. If a lower setpointor a setpoint with the opposite polarity is connected when in this state,


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the SIMOTRAS HD will be switched to counter-torque operation. The

rhyristors that are currently conducting for the clockwise rotating field

are fist blocked. The thyristors for the anti-clockwise rotating field are

then fired. This changes the phase sequence on the output terminals

to produce a new direction of rotation, point b.

The motor then starts plug braking and reduces its speed.

A slip value S=2 exists on the machine immediately following the

switchover from motor operation at point a with the speed n=NN to

braking operation at point b. With a direct switchover at full supply

voltage, the motor current would now be greater than the start-up

current (slip S=1, maximum current). SIMOTRAS HD therefore

automatically reduces the motor voltage at this point, thereby limiting

the maximum current.

3.3.5 SIMOTRAS HD- Control Characteristics for lifting gear :


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3.3.6 SIMOTRAS HD- Control Characteristics for travel gear :


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Technical Data Design Details :

Order No 65SG70 - OEB60 - 0


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50 52 55 60 62 65Rated supply voltage power

section

V 3AC 110V- 10% to 3AC 500V+10% 50/60 Hz

Rated frequency Hz Converter self adapt to the frequency of available

suply voltage in the range from 45 to 65 HzRated current of A 60 78 98 112 142 180

Rated Electronics supplyvoltage

V 2AC 380 (-25%) to 460 (+15%) Ln= 1A1AC 190 (-25%) to 230 (+15%); in=2A (-35%) for 1min

Fan rated supply voltage V - - DC 24V internalOver load capacity 20S duration : l = 2 ln

Then 70S duration : 1= lnThen 60S duration : 1= OACycle time 150S

Power loss at rates current(approx) W 272 306 386 439 500 639Maximum head A 3 6 6 6 7 7Operational ambienttemperature at rated current

0C 0 to 45 self cooled 0 to 40 forced cooled

Upper limit temperature with

current rating

0C 55 50

Cooling air requirement M3/h - 100Sound pressure level dBA - 40

Storage and transporttemperature

0

C -25 to +70

Installation altitude above sea level < 1000m at rated current max 3500m with

voltage 4 current reductionEnvironmental class DIN IEC 721-3-3 3K3Degree of protection DIN40050 IEC

144

IP00

Dimensions Sec dimensional changingsWeights (approx) kg 16 16 16 16 17 17

6.1 Block Diagram with suggested connection


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PRACTICAL READINGS :


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CONCLUSION

The drive system plays a key role in determining the reliability and efficiency

of the crane, the effects on the power system.

Conservative attitude in the industry still leads to a preference for slip motors

and thyristor controllers. It has been shown that slip ring motors do have their

inherent limitations, which can not be overcome by future technology

developments.

Maintenance issues with AC squirrel cage motors are negligible compared to

the slip ring motors. At the same time, the correct configuration of AC drive

has to be selected based on the requirements of the cranes and the user.

With all the relevant aspects taken care of AC drive systems will offer a

performance and reliability superior to slip ring motor and DC motor.

It can be concluded that the AC drive technology is the future of steel plantcranes and lot of more breakthrough development can be expected in this

arena.

An Over View of Visakhapatnam Steel Plant

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