PROJECT REPORT ON

DIGITAL DRIVE CONTROL SYSTEM FOR DC DRIVES

IN WIRE ROD MILL

Details of Guide : Details of Individual :Name : S. Bhanu Murty Name : N. Eswara RaoEmp.No : 119479 Emp.No : 103299Designation : Manager(Electrical) Designation : J.O.(Electrical)Dept : Wire Rod Mill Dept : Wire Rod Mill

CERTIFICATE

This is to certify that Mr.N.Eswara rao, Emp.No : 103299,

J.O.(E)/WRM has done the project work titled “Digital drive control

system for DC drives in WRM” for the partial fulfillment of

Comprehensive managerial course Phase-III.

Signature of Guide :

Name : S. Bhanu Murty

Designation :

Manager(Electrical)

Dept : Wire Rod Mill

ACKNOWLEDGEMENT

I am grateful to my guide sri. S.Bhanu Murty, Manager (Elect) for his able guidance and encouragement.

I also take privilege to thank Sri. A.S.Machinchery, DGM(Elect) W.R.M. Sri.M.N.Murthy, AGM(Elect) and our Honorable DGM Sri. K.K.Ghosh for providing all the facilities required by me.

Beside this I am grateful to Sri.K.Maniraj, Asst. Manager(Elect) who has spent his valuable time and suggest all types of techniques and instructions in this project work.

(N.ESWARA RAO)J.O.(Elect)

Wire Rod MillVisakhapatnam Steel Plant

CONTENTS

Chapter-1 INTRODUCTION

Wire Rod Mill

Chapter – 2 ANALOG DC DRIVE CONTROL SYSTEM(BEFORE MODIFICATION)

2.1 Introduction2.2 Speed Control2.3 Armature Voltage control2.4 Field current control2.5 Combined Armature & Field control2.6 Control circuits2.7 Different types of triggering2.8 Synchronizing circuits

2.9 Major components of Main drive2.10 Physical Locations2.11 Purpose and Function2.12 Drive Faults2.13 Switching Sequence of Thyristor Converter2.14 Faults and Tripping2.15 Limitations of analog drive

Chapter – 3 DIGITAL DRIVE CONTROL SYSTEM(AFTER MODIFICATION)

3.1 Objectives of Upgradation3.2 Digital Drive with respect to WRM3.3 Digital Drive Series 6RA70 Simoreg DC Master3.4 Features of new System3.5 Operator Control Panel3.6 Faults and Alarms

Chapter – 4 CONCLUSION4.1 Conclusion

Chapter – 1

INTRODUCTON 1.1 WIRE ROD MILL:-

The wire rod mill of vsp is high speed 4- strand no-twist

continuous mill designed to produce 8,50,000 tonnes of wire rod coils.

The mill is designed to produce plain wire rods from 5.5 mm to 12.7 mm

dia and weight is approx. 1200kgs. The mill is constructed at an

elevated level of + 5350 mm. Rolled billets from LMMM of size125mm x

125 mm of length ranging from 9.8 meter to 10.4 meter and weighing

approx. 1235 kgs are used as input material. The mill is design to roll

steel stock of 0.9% max. carbon content. The rolled billets received

from billet mill are placed on charging grid 1& II at + 0.00 m level in

packets form with the help of EOT cranes. The charging grid–I is driven

by ac motor and charging grid –II is operated by dc motor. The cross

transport receives the billets individually from charging grid –II and

transfer them to billet elevator takes the individual billet to mill floor

level at +5.35 m. Using billet transfer device and billet positioning

device, the packet of 4 billets are further carried forward to furnace

entry using another 5 groups of roller table arranged in tandem .

After the billets are positioned in front of walking

beam furnace, the walking beam of furnace will collect the billets from

roller table & charge them into the furnace. The furnace is a combined

type walking hearth cum walking beam furnace of 200t/ hr capacity.

The homogenously heated billets are discharged by

hydraulically driven discharging device called peel bar into groove of

mill stand no.1.a billet withdrawing machine is arranged between

furnace exit and stand-1. The roughing mill comprises of seven

continuous 4-strand horizontal high stands. The mill stand housing is of

closed top design and roll neck is fitted with morgoil bearings for

rotation through spindle, gear & motor. Four rotating cropping &

chopping shears are provided after stand 7, one each for each line. The

cold &split front end of bar head is cropped automatically before feeding

to intermediate stand. The intermediate group comprises of 6 two high

horizontal stands. A water cooling stretch called A1 water box is

installed ahead of these prefinishers to facilitate partial cooling of stock

before final rolling in finishing blocks. The facility is used mainly during

rebar & high carbon wire rod rolling for grain refinement and increased

UTS in final wire rods.

A crop & dividing shear is provided ahead water cooling stretch to crop

cold front end of bar before feeding to finishing blocks. Also, this gives a

dividing cut to bar in the event of trouble in forward stream equipment.

Horizontal looper is provided before prefinishing blocks and 10-stand no

twist finishing blocks. All the 10 stands of finishing block are used for 5.5

to 6.5 mm size wire rod rolling. After final rolling at finishing block,

controlled cooling of wire rod starts using retarded stelmor cooling

system. Three water cooling boxes & in between two equalizing zones

are provided ahead of finishing block.

The vertically formed coil, inside the chamber on mandrel, is

received by downender and loaded onto C-hook horizontally at

downender station the C-hooks are carried by a power &free hook

conveyer circuit. The coils are finally taken out from turnstiles by EOT

magnet cranes.

Chapter -2

ANALOG DC DRIVE CONTROL SYSTEM(BEFORE MODIFICATION)

2.1 INTRODUCTION:

D.C. machine is a highly versatile energy conversion device. It can

meet the demand of load requiring high starting torques, high

accelerating and decelerating torques. At the same time DC machine is

easily adaptable for drives requiring wide range speed control and quick

reversals. These inherent characteristics can further be modified by

feed back circuits. DC machine possesses a high degree of flexibility.

These are therefore widely used in industry, particularly for tough jobs

as are encountered in steel mill drives- in spite of their higher initial

cost.

2.2 SPEED CONTROL:

As most of the industrial loads require constant motor torque and

hence separately excited DC motors are used. In a separately excited

DC motor effect of change of armature voltage is not reflected on the

field. In a separately excited DC motor there is no direct interlocking

between armature and field circuits.

In a drive for Rolling mills armature voltage is much higher than

the field voltage. Separately excited motors are widely used for

precision control of position, speed and torque output.

Speed control of separately excited D.C. motor is possible in two

ways.

i) Field current is maintained constant and armature voltage is

varied. This is armature control.

ii) Field current is controlled to obtain various speeds. When

motor field is weakened by maintaining armature voltage

constant the maximum speed is decided by the commutation

current limit of the motor.

The speed range is divided into two parts.

i) Variation in speed at constant torque(ΦIa)

ii) Variation in speed at constant (Ia) armature current by varying

field flux.

The armature voltage range is called constant torque range

and the range obtained by field weakening is called constant horse

power range.

Base speed is the speed that motor develops at nominal rated

voltage at full excitation.

By armature voltage control we can control the speed of the

D.C. motor below the base speed.

By field control we can control the speed above the base

speed.

Speed control characteristics of separately excited D.C. Motor.

2.3 Armature voltage control:

Fig. gives the circuit for controlling motor speed from zero up to rated speed, with the use of dual converter speed can be controlled in either direction with the facility of regenerative breaking.

Armature voltage control

Desired speed is set by the operator on the reference potentiometer. Rate of acceleration can be adjusted by varying the slope of the ramp circuit. Speed reference and feed back signal is applied to the speed controller whose output is applied to the current controller. A limiting circuit is incorporated between speed controller and current controller to limit the armature current to maximum allowable value.

Output at current controller is fed to the firing circuit which adjust the firing angle to give the required armature voltage for the desired motor speed.

In this scheme the output of speed controller- a voltage proportional error is used as command for current and compared with the armature current.

The output of the current controller is the control voltage to the trigger circuit and controls the out of thyristor circuit.

When the motor is accelerating it is likely to draw an excessive current. The maximum output voltage of the speed controller will be limited to suit the maximum current in the motor.

2.4 Field current control: Fig. shows the schematic diagram for controlling the motor speed beyond rated speed by weakening the field flux.

Field current controlAs the motor speed is to be increased field reference is reduced.

This vary the firing angle of the thyristor converter in such a way that the field current is reduced. Study state condition is reached when the field reference is equal to the feed back value.

2.5 COMBINED ARMATURE AND FIELD CONTROL

Fig. Shows the combined armature and field control scheme :

Combined Armature and Field control schemeWith this the speed can be controlled from zero to maximum value

with automatic change over from armature control to field control and vice-versa. Speed from zero to rated value is obtained from armature voltage control. If now attempts are made to increase the speed beyond rated value, motor back E.M.F. will tend to increase beyond its rated value because field circuit is sluggish in response due to its large time constant.

In the field circuit two signals are applied to a field controller, one is the normalized full field reference and the other is maximum of the normalized value of actual value of field current and back E.M.F.

Up to rated speed normalized value of back E.M.F. is less than one and hence feed back to the field controller is maintained corresponding to full field current. But as soon as attempts are made to increase the speed beyond rated speed, normalized value of the back E.M.F. tends to increase beyond one and the feed back value applied to the field regulator is more than one. This forces the field regulator to vary the firing angle to reduce the field current to such a value as to limit back E.M.F. to its normalized value of one. Hence for obtaining speed beyond rated value, field is automatically weakened.

2.6 CONTROL CIRCUIT

A thyristor controlled circuit can be roughly divided into (i) Power circuit (ii) Trigger circuit (iii) Controller.

Power circuit consists of thyristor and diodes mounted on heat sinks together with protective circuits and transformer.

Controller consists of amplifiers, logic circuits, transducers and has a direct relation to the controlled machine and process. A trigger circuit is the link between controller and the power circuits.

To turn on the thyristor three conditions are required.

i) SCR should be forward biasedii) The load impedance should not be too high so that if SCR turns

on the current in the SCR would reach more than the latching current value.

iii) The gate must be made positive with respect to the cathode.

2.7 DIFFERENT TYPES OF TRIGGERING

1) DC Triggering : In this method a D.C. voltage is applied to the gate in the entire interval of conduction. Such voltage cause large gate dissipation. Used to latch very highly inductive loads.

2) Pulse Triggering : It uses a pulse train for triggering. Each pulse is sufficient to trigger the SCR and the pulse duration is chosen to give a sufficient duration for SCR to latch. Pulse triggering has following advantages

a) Low gate dissipation at higher gate currentb) Small gate isolating pulse transformerc) When first pulse fail to trigger the following pulses can

succeed in latching the SCR. This is particularly a boon while triggering inductive circuits and circuits having back E.M.F.

In Wire Rod Mill we are using dual pulse firing. Pulse voltage is 24 volts. Pulse width is 11 deg. To 18 deg. At 7 KHz.

The principle of control is simple. A saw tooth voltage is generated in the firing circuit and a DC control voltage is supplied from out side. Firing pulse is released of the point of intersection of these two waves.

Trigger circuit is built with following sub-circuitsi) Synchronising circuitii) Pulse generatoriii) Power amplifier and AND gate to combine various

signalsiv) Pulse transformer to isolate the trigger circuit from

power circuit.

Fig. shows the schematic circuit diagram of a trigger circuit to trigger a thyristor

The pulse train is synchronized with the corresponding A.C. voltage from the mains. The synchronizing voltage is selected from A.C. mains. In fact the transformer used for feeding power to the electronic circuit is used for synchronization also.

2.8 SYNCHRONISING CIRCUITThe A.C. Voltage chosen for synchronization is that voltage

whose zero occurs at the instant of triggering corresponding to no delay

i.e. d=0. In multi SCR converters the duration is not 180 deg. For

example in three phase bridge circuit the conduction duration of each

SCR is 120 deg. In this case two synchronizing voltages are required to

fix the conduction interval. One fixes the beginning of conduction and

other decides the end of the conduction. This depends on the mains

voltage some times result into interaction of spurious spikes in the A.C.

main voltage interacting with synchronizing circuit and thus resulting

spurious triggering. This is avoid by taking synchronizing voltage via a

filter circuit. Second precaution is taken by not connecting the

synchronizing voltage transformer across the secondary of the power

supply transformer which feeds the converter. Instead of the same is

connected in parallel with the primary input supply and observing the

correct relationship.

When the input to the converter circuit is a by delta/Star

transformer there is a phase sift of 30 deg. in the input to the

transformer and output to the converter. The synchronizing transformer

correction should correct this 30 deg. phase shift by proper correction of

the primary winding of the synchronizing transformer,

Power Amplifier and AND gate : The main function of the power amplifier

is to make the trigger pulse capable of triggering the largest SCR. It

maintains the rise time at sufficiently low value by fast turn on. Usually

this is done by AND gating the pulse with the synchronizing signal and

end stop pulse generator output.

The output circuit : The output of trigger circuit is made available to the

SCR’s via the secondary windings of the pulse transformer. Invariably

there are two secondary windings so that these can be used to trigger

two SCR’s simultaneously. A pulse transformer insulates the electronic

circuit from the power circuit.

2.9 MAJOR COMPONENTS OF MAIN DRIVE

The following are main components of main drive.i) High tension circuit breakerii) Converter transformeriii) Thyristor converter iv) Field transformerv) Field converter vi) Protection & Interlocking cubiclevii) Regulation cubicleviii) D.C. Reactorix) D.C. High speed circuit breakerx) D.C. No load contactor

xi) Tacho Generatorxii) Digital Tacho generatorxiii) Over Speed monitoring unit

2.10 PHYSICAL LOCATIONS

i) High Tension Circuit Breaker : For each main drive motor, one H.T. breaker is provided in the load block distribution Substation No : 4 LBDS-4 in ECR-1 at +/-0.00 level. Voltage is at 11 KV

ii) Converter Transformer : Each main drive motor had its own converter transformer located on other side of ECR-1 of WRM parallel to mill bay. The transformer step down the voltage to about 700 volts.Thyristor converter, field transformer, Field converter, Protection & interlocking cubicle and regulation cubicle is situated in ECR-1 at +9.00 Mtr.level.D.C. Reactor, D.C. High speed circuit breaker, and D.C. No load contactor is installed at +/-0.00 levelin ECR-1.Main drive D.C. motors fed from 4 LBDS-4 11 KV bus designed to with stand fluctuating loads.Aux. Loads as Shear, Pinch Rolls, Laying Heads etc., driven by D.C. motors & Thyristor converter.A.C. loads are the balance drives as slip ring & squirrel cage motor is employed. Hence load on motor will remain almost constant. These are called non fluctuating load fed from 4 LBDS-5

2.11 PURPOSE AND FUNCTION

i) H.T.C.B. : This is used to feed power to the converter transformer and

Isolate the power under fault conditions. The minimum oil circuit breaker are of “ASEA” make. They have over load and earth fault tripping.

ii) Converter Transformer : These converter transformers are used to step down the 11 KV supply to the requisite voltage required by

device. The specifications for stand No-1 converter transformer is Rating : 1020KVA, Primary : 11 K.V. +/-5%+/-2½%, secondary :

745 V, DY11, 5% Imp.

iii) Thyristor Converter Cubicle : The converter cubicle converts the A.C.Supply given by the secondary of the converter transformer into D.C. Supply. The magnitude of D.C. voltage depends on the Thyristor conduction angle.

The cubicle consists of a) Non reversible converter bridge b) Gate pulse transformers c) Semi conductor Fuses d) Fuse monitoring unit

e) Pulse distribution Board f) Air flow monitoring unit g) Parallel sharing reactor h) Cooling fan

i) Control unit equipped with Simadyn cards,

in single tier track arrangement for giving stabilized power supply to the converter auxiliaries such as Gate Pulse transformer, fuse monitoring unit, Pulse distribution board etc., Thyristor used one of type R-66, 166 and arrangement of thyristor in the armature is of Bastain type. Non draw out and mounted in cubicle on the front side of the panel door a lamp indication is provided for thyristor fuse failure.

iv) Field Transformer Cubicle : This cubicle mainly consists of 1 No. transformer for supplying voltageto fieldconverter panel. It also have 1 No. Current transformer for regulation in field circuit and a surge suppressor. This surge suppressor is a combination selenium stack selected in such a way that they breakdown under transient voltage condition. v) Field Converter Cubicle : The field converter cubicle consists

of dual converter with SITOR thyristor assemblies of 60611 with pulse transformer and semiconductor fuses.2 Converters in anti parallel its main function is to give D.C. power to field in normal operation mode with 1 converter and 2nd converter is used for quick braking. The change over from the converter I to converter II is done with the help of digital command module. In the main drive braking is with field reversal as in field circuit less voltage and current is to be controlled. Field circuit time constant is more. Main drive reversal is only for jogging operation. Reversal is not important, so cheaper arrangement is used.

The sub assemblies are a) cooling fanb) Thyristor fuse monitoring unitc) Current transformer

vi) Protection and Interlocking cubicle : This gives the protection for the equipments installed and for the personnel operating and maintaining the system. Interlocking of all protection measures for proper start up, stopping, tripping during faults and restartingafter fault tripping and annunciation system displaying the status of faults.

It consists of 2 numbers Protection & Interlocking cubicles.

Cubicle 1 mainly consists of 3 Nos distribution transformers and power to other sections is distributed by miniature circuit breakers. The ratings of transformers and the loads are as follows :

i) 4 KVA Transformer, 415/380/220 V, (YYO) feeding power to logic control unit.

- Regulation Power- Pulse power armature- Pulse power field- D.C. Current Transformer- Converter ventilation Supervision.

ii) 2.5 KVA Transformer 415/240 V, feeding power to - AC Control HSCB- No load contactor.

iii) 0.25 KVA Transformer 220/20V, feeding power to - indication (18 volts) in Central Supervisory panel

- Local control posts- Control Pulpits

Cubicle-II consists of logic control unit for indication of faults of thyristor converter with an indication lamp and viewing glass group fault lamp will glow where there is a fault in the thyristor. The fault indications for each converter transformer can also be seen in this P & I cubicle.

vii) Regulation cubicle : This cubicle mainly consists of regulation cards in ES-902 frame with 4-5 tiers. Many of the cards used for analog regulation are of Symadyne and few are of Simatic cards for logic operation.

viii) D.C.Reactor : It is an Air core D.C. Reactor an the function of it is to limit the rate of raise of current during fault condition on D.C. side. The abnormal fault condition may be short circuit in the commutator of main drive motor, and to smoothen the D.C. output i.e. it reduces the ripple content in the D.C. supply feeding the main drive. It also reduces the system I t i.e. the square current under short condition with respect to time is reduced by which the ratings for the Semi-Conductor fuses, thyristors are chosen in such a way that

I t of HSCB < I t of Semi conductor fuses

< I t of thyristorunder short circuit condition, the full load current flows in

HSCB,

Semi conductor fuses and thyristors. Before the semiconductor fuses

and thyristors are damaged. Due to short circuit current the D.C. HSCB should trip and in the case of failure of the HSCB

semiconductor fuses should blow before thyristors are damaged. This care is

takenbecause semiconductor fuses and thyristors are very costly.

Air core reactor is used because iron core reactor in the case of short circuit yield saturation.

ix) D.C. High Speed Circuit Breaker : This is a single pole high speed D.C. circuit breaker used for switching and over current protection in D.C. systems. The principle feature of HSCB is exceptionally short opening time, the contacts open before the over current reaches its maximum value. As a result of their very short arc development time they interrupt the short circuit current during the rise and therefore limit its magnitude and duration. These breakers are supplied as over current protection circuit breakers fitted with magnetic over current releases independent of current direction. Two types of HSCB are used. They are 3 WVI and 3WV5. For main dives of 700 KW & 1000KW motors type : 3WVI is used. For main drives of 2000 KW motors type : 3WV5 is used.

Technical data :

Parameter 3WVI 3 WV5

Rated voltage 1500 V 1500 V

Rated current 2500 A 4000 A

Raise of current 10 KA/ms 10 KA/ms Di/dt (t=0)Total closing time 750 ms 750 ms

Total opening time opening delay + Arc duration

Opening delay : Over current release 3 ms (approx)Shunt release 15 to 20 ms (approx)

Arc duration : It depends up on arc voltage, operating voltage, circuit time constant and breaking current.

Rated mechanical life 20,000(switching operations)

Permissible Switching frequency i/n = 30x) D.C. No load contactor : Since the D.C. contactor is of no load

type, interlocking is made to ensure that the D.C. contactor can be energized or de-energized only when armature current and rotational speed of the motor is zero. It can be energized only when HSCB closed.The purpose of it to feed D.C. power to the main drive and operation of the D.C. no load contactor is under control of C.P.H.

xi) Permanent Magnet Analog Tacho : Permanent Magnet Analog Tacho is used for speed feed back. In case of D.C. motors the back E.M.F. is proportional to speed and this can be used feed back. For an electrical isolation and long time stability tachgenerator is used. A D.C. tacho generator is widely used and is basically a permanent magnet generator with low internal resistance. The polarity of the out put direction is indication of direction of rotation. Tacho generator must be mounted stiffly to the motor shaft.

xii) Digital Tacho : Digital Tacho is used for correction of speed only. The signal from it is going to the computer.

xiii) Surge Supressor : Selenium back to back diodes are used as D.C. surge suppressor sudden switching of transformer causes so surge suppressor is used.

2.12 Drive faults: Drive faults is in two categories.

i) Internal Faultii) External fault

Internal faults are the fault within the thyristor converter.

External faults are external to converter as earth fault, short circuit overload fault reflecting from the load to the converter. HSCB clears all these faults. Semiconductor fuses blow only for internal faults. In the case of voltage dip Armature voltage back E.M.F. will be reflected to system bus so high current is developed.

2.13 SWITCHING SEQUENCE OF THYRISTOR CONVERTER

A) Switching “ON” sequence :i) Controller auxiliaries ON (HIB)ii) H,T.C.B. ON iii) Armature auxiliaries ON (AHIB)iv) D.C. HSCB ONv) D.C. No load contactor(AS)vi) Run reference ON (SW)

2.12 SWITCHING OFF SEQUENCE OF THYRISTOR CONVERTER

i) Run reference OFFii) D.C. Load contactor OFFiii) D.C.HSCB OFFiv) Armature auxiliaries OFFv) H.T.C.B. OFFvi) Controller auxiliaries OFF

The above switching “ON” and “ OFF” sequence are followed whenever a main drive motor is to be started/stopped.

The following switching operation is to be completed.Sl.No. Device Location 1 HIB P & I cubicle (can be made ON or OFF) or C.S.P. 2 H.T.C.B. P & I cubicle (can be made ON or OFF) or C.S.P. or 4LBDS-4 3 A.H.I.B. P & I cubicle (can be made ON or OFF) or C.S.P. 4 H.S.C.B. C.S.P. (can be made ON or OFF)

5 DC contactor C.P.H. (can be made On or OFF)

6 Run Reference C.P.H. (can be made On or OFF)

The Run reference for the main drives are coming from the computer when the control from Pulpits are selected for the drives. The command for releasing reference goes to PLC where all interlockings are checked before passing the command to process computer.

2.14 FAULTS AND TRIPPING

Faults are segregated into three categories

a) Category “A” fault : These are the faults which are require immediate tripping of the drive. The faults are :

- A.C. incomer fuse blown- Thyristor fuse blown. If many thyristors are in

parallel in one phase then for the first fuse failure only indication will come and for 2nd fuse failure it trips the drive.

- Motor over voltage- Motor over speed- Field circuit breaker tripped- Field thyristor fuse blown- A.C. or D.C. control supply circuit breaker

tripped.

For the above faults, the H.S.C.B. trips immediately followed by H.T.C.B. with adjustable delay.

b) Category “B” Fault : These faults are not severe and hence can be tolerated for a short time so that the material under rolling can be chopped OFF. The faults are :

- Thermal (Bimetal) release in the A.C. circuit - Transformer Over temperature (trip)- Earth fault- Motor ventilation failure- Motor over temperature trip- Converter ventilation failure

For above faults, the H.T.C.B. and H.S.C.B. are tripped after a preset time delay.

c) Category “C” faults: These faults are not harmful and the mill can be operated for a long time with out rectifying the faults.

- Armature side A.C. surge suppressor fuse un healthy

- Field side A.C. surge suppressor fuse unhealthy.Since these faults are of motor minor nature no tripping is required but annunciation is providing on Supervisory panel and on the converter as a group fault.

Annunciations are given in the control Pulpit for concerned drives. Group fault in C.S.P. and in the individual drive converter panels.

2.15 LIMITATIONS OF ANALOG DRIVE

As the present system is obsolete and sufficient spare support from OEM was not available.

The analog drive control system technology out dated.

Maintenance cost was high.

Fault diagnosis and trouble shooting was difficult due the presence of no. of cards and complex relay logics.

All the control system functions are realized with the help of cards, so the number of cards is more.

These cards contain a no. of active and passive components, which are prone to aging and are temperature sensitive.

Due to presence of more number of cards there are frequent break downs and lead to loss of production.

System is sensitive to voltage fluctuations and result in loss of production.

Chapter-3DIGITAL DRIVE CONTROL SYSTEM

(AFTER MODIFICATION)

3.1 OBJECTIVES OF UPGRADATION

Analog regulation system to be replaced with digital controllers.

Start/Stop, Tripping interlocks to be envisaged in PLCs.

All drives and PLCs to be networked by profibus.

Annunciations and diagnostics features for analyzing faults and trends.

Enhancing production by minimizing the mill down time.

Continuous data acquisition of various drive parameters.

3.2 DIGITAL DRIVE WITH RESPECT TO WRM

In WRM The Analog system control for DC drives was up graded by digital control system. Retrofitting job was done in WRM where the earlier power stack was used. Only the control electronics was upgraded.Simoreg 6RA70 is the trade name for DC drives as used by Siemens. Siemens had first launched 6RA22 which was a combination of both analog and digital features. With increasing time additional features were incorporated and the latest version came as 6RA70.

By drive we mean :

1. Control electronics 2. Power electronics (Converter) 3. Motor

The power and control electronics is generally termed as drive. In WRM the specification of the box is 6RA7013-6DV62 6RA is the trade name (Product Code) 70 is the converter model. Here it is Simoreg DC master. 13 is the code for rated DC current and cooling. 6 Corresponds to "Thyristor modules" D corresponds to rated supply voltageV is 4 Quadrant operation 6 is closed loop control (4Q Digital) 2 is closed loop control (Controlled field)

IN 6RA70 Box we have : 1. An electronics box with control card called CUD1 2. Interface card 3. Snubber card 4. Power module

In addition to above we use pulse interface card (PIC) for triggering the thyristors.

3.3 DIGITAL DRIVE Series 6RA70 SIMOREG DC MASTER

Series 6RA70 SIMOREG DC MASTER converters are fully digital,

compact units for three-phase supply which supply the armature and

field of variable-speed DC drives. Series 6RA70 SIMOREG DC MASTER

converters are characterized by their compact, space-saving

construction. Their compact design makes them 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 SIMOREG DC MASTER units 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 X300 with

a USS interface in accordance with the RS232 or RS485 standard.

The panel provides all the facilities for making adjustments or settings

and displaying measured values required to start up the converter.

3.4 FEATURES OF NEW SYSTEM

Digital drive control system Simoreg- DC master 6RA70 for speed

regulation of drives.

Technology card T-400 for Position control of Shear Drives.

PLC siemens S-7 400 for sequential interlocking, logic control and

Looper control of drives using remote I/Os.

WinCC HMI for historical trending, alarms and events logging.

Lab view Software for continuous trending of speed and currents.

Drive monitor for diagnosing of drive faults.

All drives and PLCs are networked.

3.5 OPERATOR CONTROL PANELS

The basic converter is equipped with a simple operator panel (PMU) as standard.

Simple operator control panel (PMU “Parameterization Unit“)

The simple operator control panel is mounted in the converter door and consists of a 5-digit, 7-segment display with three status display LEDs and three parameterization keys below.

All adjustments and settings that need to be undertaken for the purpose of start-up can be made on the simple control panel.

X300

Run Ready Fault

P key

Switches over between parameter number (parameter mode), parameter value (value mode) and index number (index mode) on indexed parameters.

Acknowledges active fault messages.

P and RAISE keys to switch a fault message and alarm to the background (see Section 10, Fault Messages and Alarms)

P and LOWER key to switch a fault message and alarm from the background back to the foreground display on the PMU (see Section 10, Fault Messages and Alarms)

UP key (▲)

Selects a higher parameter number in parameter mode. When the highest number is displayed, the key can be pressed again to return to the other end of the number

range (i.e. the highest number is thus adjacent to the lowest number).

Increases the selected and displayed parameter value in value mode.

Increases the index in index mode (for indexed parameters)

Accelerates an adjustment process activated with the DOWN key (if both keys are pressed at the same time).

DOWN key (▼)

Selects a lower parameter number in parameter mode. When the lowest number is displayed, the key can be pressed again to return to the other end of the number range (i.e. the lowest number is thus adjacent to the highest number).

Decreases the selected and displayed parameter value in value mode.

Decreases the index in index mode (for indexed parameters)

Accelerates an adjustment process activated with the UP key (if both keys are pressed at the same time).

LED displaysRun green LED

LED illuminated Þ in “Torque direction active” state (MI, MII, M0).

(see r000 in Section 11)Ready yellow LED

LED illuminated Þ in “Ready” state (o1 .. o7).(see r000 in Section 11)

Fault red LEDLED illuminated Þ in “Fault signal present” state (o11)

(see r000 in Section 11 and Faults and Alarms (Section 10))

LED flashing Þ An alarm is active (see Faults and Alarms in Section 10).

Parameterization is the process of changing setting values

(parameters) via the operator panel, activating converter functions or

displaying measured values. Parameters for the basic converter are

called P, r, U or n parameters. Parameters for an optional supplementary

board are called H, d, L or c parameters. The basic unit parameters are

displayed first on the PMU, followed by the technology board parameters

(if such a board is installed). It is important not to confuse the

parameters of the S00 technology software of the basic unit with the

parameters of an optional supplementary board (e.g. T300). Depending

on how parameter P052 is set, only some parameter numbers are

displayed.

Display parameters are used to display current quantities such as the

main set point,

Set point/actual value difference of speed controller, etc. The values of

display parameters are read only values and cannot be changed.

Setting parameters are used to both display and change quantities

such as the rated motor

current, thermal motor time constant, speed controller P gain, etc.

Indexed parameters are used to both display and change several

parameter values which are all assigned to the same parameter

number.

3.6 FAULTS AND ALARMS

When a fault or alarm message is activated, it is displayed both on the simple operator control panel (PMU) and on the OP1S user-friendly operator control panel (see also Section 7.2, Operator control panels).An alarm stops being displayed immediately the cause of the alarm signal has been eliminated.

A fault message must be cancelled by pressing the P key on the PMU or Reset key on the OP1S (panel must be in "Operational display" status) as soon as the cause has been eliminated.

Fault DescriptionF001 Failure of electronics power supply

(Active in all operating states)

Failure of the electronics supply voltage (terminals 5U1, 5W1, 5N1) in

“RUN” state for longer than the “restart” time set in parameter P086 or

the electronics are operating on under voltage.

Possible fault causes:

· Line contactor has opened in “RUN” state

· Brief supply failure

· Supply voltage too low

Fault value: r047 Index 002 to 016:

1 Electronics supply voltage in “RUN” has been interrupted for longer

than setting in P086

2 Supply failure prewarning responds periodically

3 Supply failure prewarning is active for longer than 1.28 s

F004 Phase failure on power connections (1U1, 1V1, 1W1)

(active in operating states of <= o4)

The supply voltage RMS value, calculated from the area of each supply

half-wave (rectified average value * peak factor), must be greater than

the response value for phase failure monitoring

P078.001 * P353/100%

The distance between two identical supply zero passages of a

phase must not exceed 450 degrees. If one of these two conditions

remains unfulfilled for longer than the “restart time” set in P086, a fault

message is activated. After switch-on, the converter waits in operating

states o4 and o5 together for a period not exceeding the setting in P089

for voltage to appear at the power terminals before activating the fault

message.

Possible fault causes:

· Parameter P353 is incorrectly set

· Line contactor has opened in operation

· Fuse has blown in incoming power section supply

· Interruption in a thyristor firing pulse cable (auxiliary cathodes at

connectors X12, X14, X16 are voltage carriers).

F006 Under voltage

(active in operating states of = o4)

The voltage at terminals 1U1, 1V1 or 1W1 is lower than the response

threshold for longer than the “restart time” set in P086.

Response threshold for supply voltage:

(P078.001 *(1+ P351/100%)

Possible causes of fault

· Line under voltage

· Monitoring values set too sensitively or incorrectly (P351, P078)

Fault value: r047 Index 002 to 016:

1 Under voltage has occurred

i002 Number of phase that has activated fault message

0 ... Phase UV

1 ... Phase VW

2 ... Phase WU

i003 Incorrect voltage value (normalized to 16384)

4 Under voltage persists for longer than time set in parameter P086

(if this is set to >0)

F007 Overvoltage

(active in operating states of = o4)

The voltage at terminals 1U1, 1V1 or 1W1 is higher than the response

threshold (for longer than the “restart time” set in P086).

Response threshold for supply voltage:

P078.001 *( 1+ P352/100%)

Possible causes of fault

· Line overvoltage

· Monitoring values set too sensitively or incorrectly (P352, P078)

Chapter – 4CONCLUSION

4.1 CONCLUSION

Drives are not tripping during power dip on over current as

the drive control action is very fast. Large voltage and frequency

variation range resulting in reduced fuse failure. Ease of maintenance

due to fewer cards and lesser amount of wiring. No drift in

components (op. amps.) which is present in Analog system resulting

in consistent performance. Being a digital system, security of

parameter settings is ensured. In the existing analog system, the pot

settings can be easily changed. Diagnostics with the help of PC based

drive monitoring software package. Less power consumption

compared to analog control electronics. Increase system availability

improves productivity.