A VOCATIONAL TRAINING REPORT ON “MOTOR

CONTROL THROUGH VFD DRIVE IN VTL MACHINE”

Done At

Submitted

In partial fulfillment of the requirements for the degree of

Bachelor of technology in Electronics System Engineering

From

Bachelor of Technology

National Institute of Electronics and Information Technology

Department of Electronics and Information Technology

Government of India

SUBMITTED BY:

PRABHAT KUMAR

SECOND YEAR UNDERGRADUATE STUDENT

NIELIT AURANGABAD

DURATION: - 08.06.15 TO 07.07.2015

CERTIFICATE

I hereby certify that the work which is being presented on

the completion of the Vocational training as a Project Report entitled “MOTOR CONTROL

THROUGH VFD DRIVE IN VTL MACHINE”, in partial fulfilment of the requirements

for the award of the Bachelor of Technology in Electronics System Engineering and

submitted to the Department “MAINTENANCE & SERVICES (ELECTRICAL)” of

“TAYO ROLLS LTD”, Jamshedpur is an authentic record of my own work carried out

during a period from 08TH June 2015 to 07TH July 2015 under the supervision of MR.

DEBASIS DAS (Officer, Maintenance & Services, Forge Shop).

The matter presented in this work has not been submitted by me for the award of any other

degree elsewhere.

PRABHAT KUMAR

Date: NIELIT, AURANGABAD

This is to certify that the above statement made by the candidate is correct to the best of my

knowledge.

MR. A.G. SWAMY (TRAINING SUPERVISOR)

MR. DEBASIS DAS (PROJECT SUPERVISOR)

MR. PUSHKAR ANAND (HR)

Acknowledgement

It is a moment of great pleasure for me to acknowledge the people who contributed in

successful completion of my vocational training. The proposed study report on “MOTOR

CONTROL THROUGH VFD DRIVE IN VTL MACHINE” has made possible through

the direct and indirect help of the employee of TAYO ROLLS LTD. I would like to express

my appreciation and hearty gratitude to all of those employees.

I am extremely thankful to Mr. A.S. DATT, DGM (HRM & A) and Mr. PUSHKAR

ANAND (Asst. Manager, HRM & A) OF TAYO ROLLS LTD. for providing me the

opportunity to undergo my vocational training in their esteemed organisation.

I would like to express my thanks to my training guide Mr. DEBASIS DAS (SENIOR

OFFICER, MAINTENANCE & SERVICES) for guiding me and Mr. SARKAR, for his

kind support.

I express heartfelt gratitude towards all employees of the company, who in spites of their

busy and stressful schedule gave their valuable suggestions.

PRABHAT KUMAR

ELECTRONICS SYSTEM ENGINEERING

NIELIT, AURANGABAD

PREFACE

Vocational training is the best opportunity by which an engineering student upgrades his/her

skills and theoretical knowledge attained in the classroom. In the practical world, vocational

training is an occasion to learn and do experiment with the theoretical knowledge.

Training under “MAINTENANCE & SERVICES” under FORGE SHOP in TAYO

ROLLS LTD. is very important in this respect. Today is the time of modernization and there

is a very tough competition all around under which we have to prove ourselves worthy. This

training gives vital instruction to have edge over others. It shows a good sequence of work,

which takes place in various shops. This sequence would help duty in an authentic way.

I had an enriching experience while undertaking training in the FORGE SHOP of “TAYO

ROLLS LTD”, Jamshedpur. I got maximum exposure to the working environment of

FORGE SHOP on “MAINTENANCE & SERVICES” of VFD in different machines

installed in the shop. I can’t forget the working experience of “TAYO ROLLS LTD”.

PRABHAT KUMAR

B.TECH, 4TH SEMESTER

ELECTRONICS SYSTEM ENGINEERING

CONTENTS

1) COMPANY PROFILE

2) INTRODUCTION

LATHE MACHINE

VERTICAL LATHE

LATHE SPEEDS, FEEDS, AND DEPTH OF CUTS

3) WHAT IS A VARIABLE FREQUENCY DRIVE

HOW DOES VFD WORKS

MERITS OF USING VFD

VFD DISADVANTAGES

APPLICATIONS OF VFD

VFD PANELMECHANISM

VFD TYPES AND RATINGS

4) NEXT GENERATION VFD

5) CONCLUSION

COMPANY PROFILE

TAYO Rolls Limited, a subsidiary of TATA Steel was promoted in 1968 in collaboration

with Yodogawa Steel Works of Japan. To update with the developing technology, in 1992,

TAYO forged an alliance with ESW of Austria for Technical up-gradation.

Since inception, TAYO has been a market leader and has met the Country's roll requirements

for a wide variety of industries. Through continuous improvements both in process as well as

products, TAYO has kept pace with the changing needs of the industry thus providing more

value to its customers in terms of more rolling per roll.

TAYO’s services to its customers are met through dedicated employees who have rich

experience and are well trained in the application of hot as well as cold rolling applications.

The Company has successfully diversified into production of Special Castings for use in

Power Plants and has made significant presence in the industry.

TAYO enjoys a wide customer base in India. It has also been exporting rolls to Australia,

Austria, Bangladesh, Belgium, Canada, Egypt, Germany, Indonesia, Kazakhstan, Nepal,

Norway, New Zealand, Oman, Quatar, Saudi Arabia, Sweden, Singapore, South Africa,

Triniland, Talwan, UAE, Romania, Chez Republic and USA. TAYO ensures that its products

not only meet customer expectation but also with after sales service which are comparable to

the best in the world.

TAYO as a part of its backward integration had set up a Mini Blast furnace of 40000 tpa for

the manufacture of Pig iron. Over the years its pig iron has captured a good share in the

eastern India market. TAYO embarks on setting up an integrated facility for the manufacture

of Forged Rolls and Engineering Forgings. This would enable the company to become a total

solution provider to the user industry for all categories of rolls both cast and forged rolls.

TAYO has entered into a License and Know-how agreement with Sheffield Forge masters

International Ltd. of United Kingdom for transfer of technology for the manufacture of

forging quality Ingots, including Round Ingots, Forged Bars, Engineering Forgings and

Forged Rolls

TAYO has a headquarter in Jamshedpur, Jharkhand with a 50% market share in domestic

market. It is listed in BSE (Bombay Stock Exchange).It’s a metal fabrication & processing

manufacturing company. Some of the products are being discussed below

CAST ROLL

It is an integrated facility with melting, foundry and machining capabilities. The facilities of

the company, due to their ability to do centrifugal casting (spun cast rolls) while they can also

produce static cast rolls are well designed to serve the requirements mainly of the FP (Flat

Product) mills due to their ability to do centrifugal casting (spun cast roll) while they can also

Produce static cast roll the current technology partner here is Yodogawa steel works, Japan

(who are also co-promoters of the company)

FORGED ROLL

This is a new facility and the only integrated one in India having melting capacities, Ingot

shop, forged shop and finishing facilities (tempering, grinding, milling etc).The technology

partner in this business is Sheffield forged masters international, UK.

PIG IRON

The company has mini blast furnace of 40000 TPA metric ton per annum capacity. The Hot

metal is consumed internally in the company as part of the integrated roll manufacturing

facility .The pig iron known for its quality is sold to customers, who process it further

FORGING QUALITY INGOT

As part of the new facility an ingot shop was commissioned in financial Year 2009-10.The

Plan was to use 60% for own consumption (in the forged shop)and 40% of ingot castings

were to be sold directly to several customers. The capacity of ingot shop is 24000 metric

tonne per annum.

ENGINEERING FORGING

The excess capacity of the forge shop is utilised in production of engineering forging (sugar

mill, wind mill shaft etc). The capacity works out to 5200 metric tonne per annum.

SNG(Super Nickel Grain)

HSS(High Speed Steel)

SEMI-HSS(Semi-high Speed Steel )

VISION

Five folds in 5 Years

MISSION

The purpose of TAYO’S existence is to create value for Tata Steel group and other customer

and shareholders. The means to achieve this are

People focus.

Environmental friendly & safe processes.

World class technology.

Ethical & responsible corporate citizenship.

Functional Departments

MBF (Mini Blast Furnace)

TAYO has a 215 meter cube capacity MBF, which produces foundry and SG grade pig iron

for commercial purpose and hot metal for in house consumption. It is initial step in iron

making .This department is responsible to make pig iron. They produce 85 to 90 tonnes per

day .As this department converts the raw material in liquid form so that it can be used as it is

for further processes. In short it can be said that raw material and air is taken to give out gas,

liquid metal and slag as a result.

Definition of Blast furnace

The purpose of a blast furnace is to chemically reduce and physically convert iron oxides into

liquid iron called "hot metal”. The blast furnace is a huge, steel stack lined with refractory

brick, where iron ore, coke and limestone are dumped into the top, and preheated air is blown

into the bottom. The raw materials require 6 to 8 hours to descend to the bottom of the

furnace where they become the final product of liquid slag and liquid iron. These liquid

products are drained from the furnace at regular intervals. The hot air that was blown into the

bottom of the furnace ascends to the top in 6 to 8 seconds after going through numerous

chemical reactions... Typical hot metal chemistry follows:

Iron (Fe) = 93.5 - 95.0%

Silicon (Si) = 0.30 - 0.90%

Sulphur (S) = 0.025 - 0.050%

Manganese (Mn) = 0.55 - 0.75%

Phosphorus (P) = 0.03 - 0.09%

Titanium (Ti) = 0.02 - 0.06%

Carbon (C) = 4.1 - 4.4%

Process

Iron oxides can come to the blast furnace plant in the form of raw ore, pellets or sinter. The

raw ore is removed from the earth and sized into pieces that range from 0.5 to 1.5 inches. This ore is either Hematite (Fe2O3) or Magnetite (Fe3O4) and the iron content ranges from

50% to 70%. This iron rich ore can be charged directly into a blast furnace without any further processing. Iron ore that contains a lower iron content must be processed or beneficiated to increase its iron content. Pellets are produced from this lower iron content ore.

This ore is crushed and ground into a powder so the waste material called gangue can be removed. The remaining iron-rich powder is rolled into balls and fired in a furnace to produce

strong, marble-sized pellets that contain 60% to 65% iron. Sinter is produced from fine raw ore, small coke, sand-sized limestone and numerous other steel plant waste materials that contain some iron. These fine materials are proportioned to obtain a desired product

chemistry then mixed together. This raw material mix is then placed on a sintering strand, which is similar to a steel conveyor belt, where it is ignited by gas fired furnace and fused by

the heat from the coke fines into larger size pieces that are from 0.5 to 2.0 inches. The iron ore, pellets and sinter then become the liquid iron produced in the blast furnace with any of their remaining impurities going to the liquid slag.

The coke is produced from a mixture of coals. The coal is crushed and ground into a powder and then charged into an oven. As the oven is heated the coal is cooked so most of the

volatile matter such as oil and tar are removed. The cooked coal, called coke, is removed

from the oven after 18 to 24 hours of reaction time. The coke is cooled and screened into pieces ranging from one inch to four inches. The coke contains 90 to 93% carbon, some ash and sulphur but compared to raw coal is very strong. The strong pieces of coke with a high

energy value provide permeability, heat and gases which are required to reduce and melt the iron ore, pellets and sinter.

The final raw material in the iron making process is limestone. The limestone is removed from the earth by blasting with explosives. It is then crushed and screened to a size that ranges from 0.5 inch to 1.5 inch to become blast furnace flux. This flux can be pure high

calcium limestone, dolomite limestone containing magnesia or a blend of the two types of limestone.

MELTING

TAYO has the best combination of melting furnaces. The Electric Arc Furnace is used for

manufacture f high strength alloy iron, high quality SG and Steel Rolls. The mains frequency

induction furnaces are used for small and medium sized cast iron, steel and SG Rolls. These

furnaces also provide highly alloyed shell metal in indefinite chill quality rolls, which are cast

through static and centrifugal route. Shell metal for high chrome iron and steel rolls are also

processed in these furnaces. The wide variety of furnaces offers full flexibility in production

of rolls of different sizes and weights.

The melting is carried out using carefully segregated scarp, pig Iron and Ferro alloys to

achieve the desired composition. The melting unit is backed by a modern analytical

laboratory using a computerized vacuum spark emission spectrometer and other automatic

analysis for different elements.

In one day they Produce approx 45 to 50 tonne and their monthly target is 120 tonne.

Scrap Mix(Metallic charge+furnace)

Charge in arc furnace

Melting and Refining (Melting at 1550C)

Ready metal as per requirement for further processing tapped in laddle

Ladle brought to LF-VD station (laddle refining and vacuum degassing )

Laddle furnace (with flux burnt l ine)

FOUNDRY

Tayo has a well equipped with facilities for static casting, spin casting through a modern

centrifugal casting machine and heat treatment of rolls through state of the modern gas fired

heat treatment furnace. This ensures world class quality heat treatment of rolls.

STATIC CASTING

The foundry is equipped with modern facilities for preparing moulds to exacting

standards .All rolls are bottom poured with tangential ingrate to ensure maximum

cleanliness of the body surface All nodular iron rolls are poured with special ladle

inoculation followed by mould inoculation to ensure high strength requirements Hot

Topping equipment is used for all steel and steel base rolls to ensure internal

soundness , grain size and structure ,making the rolls absolutely free from cavities and

porosities.

SPIN CASTING

Horizontal spin casting is used to produce Work Rolls for flat rolling Spin cast rolls ranging

from 450mm. to 1200mm in diameter are Produces through this machine with strict control

of rotation speed, Cooling and casting time. The shell sleeve is titled to vertical policy and

core metal is poured from top with precise thermal synchronization

INGOT CASTING

This section is equipped with holding furnace, upgraded EAF, DRI, Feeder, Ingot caster,

ingot annealing furnace and inspection facility And ingot casting crane

HEAT TREATMENT

Subjected to heat treatment in special system controlled heat treatment furnaces. Uniformity of

temperature in all the heating zones of the furnace is ensured by special temperature controllers

and the rate of heating can be controlled to as low as2.8C/hour. The heat treatment programmers

comprises low temperature cycles for tempering and stress relieving as w

The final properties of a roll depend on the heat treatment .The Rolls are well as high temperature

cycles for soft annealing and spheroid sing.

MACHINING

The Machine shop is equipped with a versatile set of machine tools from Japan, Russia,

Czechoslovakia, Germany, Italy & India.

The heavy duty roll turning lathes can accommodate rolls up to a maximum of 1420 mm in

diameter and 30 tonnes in finished weight. Milling operation is carried out by special purpose

machine. Specially designed duplex milling machine are used for cutting a clove leaf

wobblers, flats and keyways .Fluting and special grooving are done through suitably designed

fixture.

Specified tolerances and desired surface finish are obtained through sophisticated grinding

machines. Stringent demands on accuracies and designs are met by CNC Lathes.

CDA/CDM Technology is available for translating the customer’s Drawings to internal

standard as well as direct programming of the CNC Lathes

The objective of this department is to finish the product conformance with drawing. Their

raw materials are from foundry and forge shop as they get as cast roll and by adding value

they finish product as per demand and finally despatch and forge roll.The whole cycle takes

20 days to get the final product.

INTRODUCTION

Lathe Machine

A lathe is a machine tool which turns cylindrical material, touches a cutting tool to it, and

cuts the material. The lathe is one of the machine tools most well used by machining. As shown in Figure, a material is firmly fixed to the chuck of a lathe. The lathe is switched

on and the chuck is rotated. And since the table which fixed the byte can be moved in the vertical direction and the right-and-left direction by operating some handles. It touches a

byte's tip into the material by the operation, and makes a mechanical part.

Vertical Lathe

A metal

cutting lathe designed for large articles with relatively small length in comparison to diameter D (l/D < 1 for light and medium lathes, l/D < 0.5 for heavy lathes).

The vertical lathe makes it convenient to mount, align, and fasten the items to be worked. For

this reason it has replaced the facing lathe,

which was used previously. The distinguishing feature of the vertical turning lathe is the verti

cal position of the spindle. A chuck is located onthe top of the spindle; the piece to be worked

is fastened to the chuck, using radially displaced cams. It is the item itself that goes throught

he principal rotary motion on the vertical lathe; the cutting tool, fixed on a support, has a tran

slatory feed motion. The strain on the spindle ispartially relieved because the weight of the ite

m and the cutting forces are absorbed by the circularly directing chucks.

There are open-sided and double-sided (portal) vertical lathes. Open

sided vertical lathes usually have both vertical and lateral supports; two-

sided lathes have two vertical and either one or two lateral supports. A rotating turret is often

placed on one of the vertical supports. Thevertical lathe is usually driven by several electric

motors (many, in the case of the heavy lathe), which, during operation, transmit the motionto

the chuck spindle and supports (working and idling or accelerated) and serve to attach the cro

sshead and brake engagement.

The vertical lathe is used to machine and bore cylindrical, conical, and contoured surfaces an

d to trim face ends. Lathes with a turret canalso drill, counterbore, and ream. Engraving, slotti

ng, milling, and polishing are possible with special attachments. It is possible on a verticallat

he to work with a number of cutting tools simultaneously, with each tool fastened to a separat

e support. This increases efficiencysignificantly.

The rigidity of construction of the vertical lathe makes it possible to work on particularly larg

e items with a high degree of precision. Forexample, pieces weighing as much as 500 tons an

d more, with diameters to 30 m (parts of powerful hydraulic turbines, turbogenerators,atomic

reactors, and proton synchrotrons), may be worked on heavy two-sided models.

LATHE SPEEDS, FEEDS, AND DEPTH OF CUTS

General operations on the lathe include straight and shoulder turning, facing, grooving, parting, turning tapers, and cutting various screw threads. Before these operations can be

done, a thorough knowledge of the variable factors of lathe speeds, feeds, and depth of cut must be understood. These factors differ for each lathe operation, and failure to use these

factors properly will result in machine failure or work damage. The kind of material being worked, the type of tool bit, the diameter and length of the work piece, the type of cut desired (roughing or finishing), and the working condition of the lathe will determine which speed,

feed, or depth of cut is best for any particular operation. The guidelines which follow for selecting speed, feed, and depth of cut are general in nature and may need to be changed as

conditions dictate. What is a VFD?

A Variable Frequency Drive (VFD) is a type of motor controller that drives an electric motor

by varying the frequency and voltage supplied to the electric motor. Other names for a VFD are variable speed drive, adjustable speed drive, adjustable frequency drive, AC

drive, micro drive, and inverter.

Frequency (or hertz) is directly related to the motor’s speed (RPMs). In other words, the faster the frequency, the faster the RPMs go. If an application does not require an electric

motor to run at full speed, the VFD can be used to ramp down the frequency and voltage to meet the requirements of the electric motor’s load. As the application’s motor speed requirements change, the VFD can simply turn up or down the motor speed to meet the speed

requirement.

A variable-frequency drive (VFD) (also termed as adjustable-frequency drive, variable-speed drive, AC drive, micro drive or inverter drive) is a type of adjustable-speed drive used in electro-mechanical drive systems to control AC motor speed and torque by varying motor

input frequency and voltage.

VFDs are used in applications ranging from small appliances to the largest of mine mill drives and compressors. However, around 25% of the world's electrical energy is consumed

by electric motors in industrial applications, which are especially conducive for energy savings using VFDs in centrifugal load service and VFDs' global market penetration for all

applications is still relatively small. That lack of penetration highlights significant energy efficiency improvement opportunities for retrofitted and new VFD installations.

Over the last four decades, power electronics technology has reduced VFD cost and size and

has improved performance through advances in semiconductor switching devices, drive topologies, simulation and control techniques, and control hardware and software.

VFDs are available in a number of different low- and medium-voltage AC-AC and DC-AC topologies.

How does a Variable Frequency Drive work?

The first stage of a Variable Frequency AC Drive, or VFD, is the Converter. The converter is comprised of six diodes, which are similar to check valves used in plumbing systems. They

allow current to flow in only one direction; the direction shown by the arrow in the diode symbol. For example, whenever A-phase voltage (voltage is similar to pressure in plumbing

systems) is more positive than B or C phase voltages, then that diode will open and allow current to flow. When B-phase becomes more positive than A-phase, then the B-phase diode will open and the A-phase diode will close. The same is true for the 3 diodes on the negative

side of the bus. Thus, we get six current “pulses” as each diode opens and closes. This is called a “six-pulse VFD”, which is the standard configuration for current Variable Frequency

Drives.

Let us assume that the drive is operating on a 480V power system. The 480V rating is “rms” or root-mean-squared. The peaks on a 480V system are 679V. As you can see, the VFD dc

bus has a dc voltage with an AC ripple. The voltage runs between approximately 580V and 680V.

We can get rid of the AC ripple on the DC bus by adding a capacitor. A capacitor operates in a similar fashion to a reservoir or accumulator in a plumbing system. This capacitor absorbs

the ac ripple and delivers a smooth dc voltage. The AC ripple on the DC bus is typically less than 3 Volts. Thus, the voltage on the DC bus becomes “approximately” 650VDC. The actual

voltage will depend on the voltage level of the AC line feeding the drive, the level of voltage unbalance on the power system, the motor load, the impedance of the power system, and any reactors or harmonic filters on the drive.

The diode bridge converter that converts AC-to-DC is sometimes just referred to as a converter. The converter that converts the dc back to ac is also a converter, but to distinguish

it from the diode converter, it is usually referred to as an “inverter”. It has become common in the industry to refer to any DC-to-AC converter as an inverter.

When we close one of the top switches in the inverter, that phase of the motor is connected to

the positive dc bus and the voltage on that phase becomes positive. When we close one of the

bottom switches in the converter, that phase is connected to the negative dc bus and becomes

negative. Thus, we can make any phase on the motor become positive or negative at will and

can thus generate any frequency that we want. So, we can make any phase be positive,

negative, or zero.

Notice that the output from the VFD is a “rectangular” wave form. VFD’s do not produce a sinusoidal output. This rectangular waveform would not be a good choice for a general purpose distribution system, but is perfectly adequate for a motor.

If we want to reduce the motor frequency to 30 Hz, then we simply switch the inverter output transistors more slowly. But, if we reduce the frequency to 30Hz, then we must also reduce

the voltage to 240V in order to maintain the V/Hz ratio (see the VFD Motor Theory presentation for more on this). How are we going to reduce the voltage if the only voltage we have is 650VDC?

This is called Pulse Width Modulation or PWM. Imagine that we could control the pressure in a water line by turning the valve on and off at a high rate of speed. While this would not be

practical for plumbing systems, it works very well for VFD’s. Notice that during the first half cycle, the voltage is ON half the time and OFF half the time. Thus, the average voltage is half of 480V or 240V. By pulsing the output, we can achieve any average voltage on the output of

the VFD.

Merits of using Variable Frequency Drives

As VFD usage in HVAC applications has increased, fans, pumps, air handlers, and chillers

can benefit from speed control. Variable frequency drives provide the following advantages:

energy savings

low motor starting current

reduction of thermal and mechanical stresses on motors and belts during starts

simple installation

high power factor

lower KVA

Reduce Energy Consumption and Energy Costs

If we have an application that does not need to be run at full speed, then we can cut down

energy costs by controlling the motor with a variable frequency drive, which is one of the benefits of Variable Frequency Drives. VFDs allow us to match the speed of the motor-

driven equipment to the load requirement. There is no other method of AC electric motor control that allows us to accomplish this. Electric motor systems are responsible for more than 65% of the power consumption in

industry today. Optimizing motor control systems by installing or upgrading to VFDs can reduce energy consumption in your facility by as much as 70%. Additionally, the utilization

of VFDs improves product quality, and reduces production costs. Combining energy efficiency tax incentives, and utility rebates, returns on investment for VFD installations can be as little as 6 months.

Increase Production through Tighter Process Control

By operating our motors at the most efficient speed for our application, fewer mistakes will

occur, and thus, production levels will increase, which earns our company higher revenues. On conveyors and belts we eliminate jerks on start-up allowing high through put.

Extend Equipment Life and Reduce Maintenance

Our equipment will last longer and will have less downtime due to maintenance when it’s controlled by VFDs ensuring optimal motor application speed. Because of the VFDs optimal

control of the motor’s frequency and voltage, the VFD will offer better protection for our motor from issues such as electro thermal overloads, phase protection, under voltage, overvoltage, etc... When we start a load with a VFD you will not subject the motor or driven

load to the “instant shock” of across the line starting, but can start smoothly, thereby eliminating belt, gear and bearing wear. It also is an excellent way to reduce and/or eliminate

water hammer since we can have smooth acceleration and deceleration cycles.

Speed Variations

Beyond energy saving, applications such as crushers, conveyors and grinding mills can use

the motor and VFD’s packages to provide optimal speed variations. In some crucial

applications, the operating speed range can be wide, which a motor supplied with a constant

Frequency power source cannot provide. In the case of conveyors and mills, a VFD and

motor system can even provide a “crawl” speed foe maintenance purposes eliminating the

need for additional drives.

Soft Starting

When Variable Frequency Drives start large motors, the drawbacks associated with large

inrush current i.e. starting current (winding stress, winding overheating and voltage dip on

connected bus) is eliminated. This reduces chances of insulation or winding damage and

provides extended motor life.

High Power Factor

Power converted to rotation, heat, sound, etc. is called active power and is measured in kilowatts (kW). Power that charges builds magnetic fields or charges capacitor is called

reactive power and is measured in kVAR. The vector sum of the kW and the kVAR is the Apparent Power and is measured in KVA. Power factor is the ratio of kW/KVA. Typical AC motors may have a full load power factor ranging from 0.7 to 0.8. As the motor load is

reduced, the power factor becomes low. The advantage of using VFD’s is that it includes capacitors in the DC Bus itself which maintains high power factor on the line side of the

Variable Frequency Drive. This eliminates the need of additional expensive capacitor banks.

VFD Disadvantages

Variable Frequency Drives require specific fuse types and can cause Harmonic

Distortion. Harmonic Distortion affects other equipment in a building by basically

transmitting noise back through the power wires supplying the equipment. This is

easily cured with Line Reactors or Isolation Transformers. The Line Reactor is the

most common and economical component used to isolate Harmonic Distortion.

Additionally, no one size fits all! We must acquire a VFD to specifically match the

size and voltage of the motor (by Horse Power), as well as the incoming voltage to the

VFD. We can undersize the motor to a VFD (match a 5 HP VFD to a 3 HP motor),

but never oversize. For the sake of economics, always properly size the VFD to the

Horse Power of the motor. Additionally, it is recommended we match only one motor

to one VFD. We can operate two motors from a single VFD if properly sized

(Example; One 5HP VFD to Operate Two 2HP Motors). However, if one of the

Motors thermally shuts down for any reason, once it resets and restarts, it will error

out the VFD, and may damage it.

Applications of Variable Frequency Drive

1. They are mostly used in industries for large induction motor (dealing with variable load)

whose power rating ranges from few kW to few MW.

2. Variable Frequency Drive is used in traction system. In India it is being used by Delhi

Metro Rail Corporation.

3. They are also used in modern lifts, escalators and pumping systems.

4. Nowadays they are being also used in energy efficient refrigerators, AC’s and Outside-air

Economizers.

Variable frequency drives, inverters, drives, and variable speed drives are all terms that in

common industrial usage today imply an electronic control unit that can be used to vary the

speed or torque delivered by a motor. While most new variable speed applications today use

either induction, permanent magnet AC (PM), or Switched Reluctance (SR) motors, we will

ignore these technology differences for the purpose of this article; each technology has its

benefits and strengths.

VFD types and Ratings

AC drives can be classified according to the following generic topologies

Voltage-source inverter (VSI) drive topologies : In a VSI drive, the DC output of

the diode-bridge converter stores energy in the capacitor bus to supply stiff voltage

input to the inverter. The vast majority of drives are VSI type with PWM voltage

output.

Current-source inverter (CSI) drive topologies : In a CSI drive, the DC output of

the SCR-bridge converter stores energy in series-reactor connection to supply stiff

current input to the inverter. CSI drives can be operated with either PWM or six-step

waveform output.

Six-step inverter drive topologies : Now largely obsolete, six-step drives can be either

VSI or CSI type and are also referred to as variable-voltage inverter drives, pulse-

amplitude modulation (PAM) drives, square-wave drives or D.C. chopper inverter

drives. In a six-step drive, the DC output of the SCR-bridge converter is smoothed via

capacitor bus and series-reactor connection to supply via Darlington

Pair or IGBT inverter quasi-sinusoidal, six-step voltage or current input to an induction

motor.

Load commutated inverter (LCI) drive topologies: In an LCI drive (a special CSI case),

the DC output of the SCR-bridge converter stores energy via DC link inductor circuit to

supply stiff quasi-sinusoidal six-step current output of a second SCR-bridge's inverter and

an over-excited synchronous machine.

Cycloconverter or matrix converter (MC) topologies: Cycloconverters and MCs are AC-

AC converters that have no intermediate DC link for energy storage. A cycloconverter

operates as a three-phase current source via three anti-parallel-connected SCR-bridges in

six-pulse configuration, each cycloconverter phase acting selectively to convert fixed line

frequency AC voltage to an alternating voltage at a variable load frequency. MC drives

are IGBT-based.

Doubly fed slip recovery system topologies: A doubly fed slip recovery system feeds

rectified slip power to a smoothing reactor to supply power to the AC supply network via

an inverter, the speed of the motor being controlled by adjusting the DC current

Next Generation Variable Frequency Drives

Variable frequency drives have emerged as a sure-fire way to reduce energy

costs in induction motor systems. From pumps and fans to material handling and industrial

processes, VFDs help save many millions of kilowatt-hours around the world each and every

year.

And energy savings are only part of the VFD value proposition. VFDs can help extend the

working life of induction motors–by allowing them to operate at lower speeds for significant

portions of their lifecycle. VFDs can also improve process control capabilities. In fact, the

most advanced vector controlled drives, when paired with appropriate feedback devices in a

closed-loop control system, can offer positioning performance close to that of servo systems.

One thing speeding the adoption of VFD technology is

the fact that it continues to grow more efficient and reliable due to continuous improvements

in the underlying power electronics, such as the insulated gate bipolar transistor (IGBT)

technologies developed and employed by Fuji Electric. IGBTs have also seen dramatic

improvements in power densities, allowing VFDs to become more compact.

CONCLUSION

It was a wonderful learning experience at TAYO ROLLS LTD. JAMSHEDPUR completed

project on VFD after one month in TAYO. I gained a lot of insight regarding almost every

aspect of FORGE SHOP. I was given exposure in almost all the departments at the site. The

friendly welcome from all the employees is appreciating, sharing their experience and giving

their peace of wisdom which they have gained in long journey of work. I am very much

thankful for the wonderful CANTEEN facility from TAYO. Learn about need of industrial

automation through VFD and scope orientation in industry.

In review this training has been an excellent and rewarding experience. I have been able to

meet and network with so many people that I am sure will be able to help me with

opportunities in the future.

I hope this experience will surely help me in my future and also in shaping my career.

PRABHAT KUMAR

NIELIT, AURANGABAD