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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
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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.