BODY

1
CHAPTER 1
INTRODUCTION
1.1 INTRODUCTION
TMT (Thermo Mechanically Treated) Bar is manufactured in a process in
which the ribbed bar is heat-treated in three mills during the production process
namely roughing, intermediate and finishing mills. The complete milling process is
shown in Fig 1.1. The raw materials used in manufacturing of TMT Bars are
Ingots and Billets which are manufactured from scrap and sponge iron in the
heating furnace. The bar then goes to the roughing mill and the intermediate mills,
where rods are shaped. The finishing mill decides the thickness of rods produced.
At the end of the finishing mill, a scaling motor and a cutting motor is used. These
motors run unnecessarily when the rod is not present. In our project, we harness
power by running the motor at full speed only when necessary. There are various
methods available for controlling the speed of the induction motor. They are speed
control by variation of supply frequency, speed control by variation of supply
/stator voltage, speed control by changing number of poles, rotor resistance control
and other methods such as Kramer system of speed control and Scherbius system
of speed control.
Although a range of induction motor control techniques are available,
generating variable frequency supply is a popular control technique, having a
constant voltage to frequency ratio in order to attain constant (maximum) torque
throughout the operating period. This control technique is called as variable
frequency control. In Volts per Hertz control, the speed of an induction motor can
be easily controlled by varying the frequency of the 3-phase supply; however, to
maintain a constant flux density, the applied voltage must also be changed in the
same proportion as the frequency.

2
A combination of PLC and VFD is proposed in our project to minimize the
energy consumption in the existing system by operating the motors in full speed
only when it is required. The sensor arrangement consists of a proximity sensor
which senses the rod and gives the signal to the PLC. The PLC in turn operates the
VFD which runs the motor at full speed for a specified time and stops the motor,
thus minimizing energy consumption.
Fig 1.1 Process involved in Steel Rolling mills
Raw Material With Desired Shapes
Rough Scaling Process
Hot Rolling into TMT bars in Mill Stands
(Roughing, Intermediate & Finishing Mills)
Heating Furnace
Cutting Process
Quenching Process
Inspection and Storage of TMT Rods

3
1.2 LITERATURE SURVEY
In [1] and [2] we learnt the various features of Programmable Logic
Controllers and about implementing the Programmable Logic Controllers for
industrial automation.
In [3] we inferred the operation of Variable Frequency Drives and the
energy saving features while using the Variable Frequency Drives in electrical
machineries. The use of variable frequency drives to start and stop motors during
operational delays such as functioning period and non-functioning period
respectively.
In [4] the speed control of induction motors using Variable Frequency
Drives was studied. Variable Frequency Drive to a motor driven system can offer
potential energy saving in a system in which the load vary with time.
1.3 OBJECTIVE
To reduce electrical energy consumption and maintenance by upgrading
several fixed speed scaling and cutting motors with Variable Frequency Drives
(VFD) through Programmable Logic Controller (PLC).
1.4 EXISTING SYSTEM
In the steel rolling mill, the raw steel is passed through several mills where it
is processed into TMT bars. Finally, the TMT bars are processed through scaling
motor and cutting motor .Once the milling process is started, these motors run
continuously without stopping, irrespective of the presence of the rods. This leads
to wastage of tremendous amount of energy.
1.5 PROPOSED SYSTEM
The cutting motor and the scaling motor are automated with the help of PLC
and variable frequency drives. The VFDs are used to operate these motors at full

4
speed only when it is necessary (i.e. when the rod is present) thus minimizing the
energy consumption when the operation of motor is not required. A proximity
sensor is used to sense the presence of the rod and sends the input signal to the
PLC which drives the motor at full speed with the help of VFD.
1.6 BLOCK DIAGRAM OF THE PROPOSED SYSTEM
Fig 1.2 Block Diagram of Proposed System
1.7 ORGANIZATION OF THE REPORT
CHAPTER 1 deals with the introduction about the company, their process
and services, objective of the project and the case study.
CHAPTER 2 deals with the internal architecture, operation and features of
Programmable Logic Controller.
VFD 2
VFD 1 SCALING
MOTOR
CUTTING
MOTOR
PROGRAMMABLE
LOGIC
CONTROLLER
SENSOR
INPUT
SMPS
24V DC
SMPS
24V DC

5
CHAPTER 3 gives the programming of PLC in Ladder logic and STL coding for
various lengths of the rod.
CHAPTER 4 deals with the operations, features and the benefits of Variable
Frequency Drive.
CHAPTER 5 deals with the Hardware Description of PLC, VFD, Motors and
Sensors used in the project.
CHAPTER 6 gives the results of the project and their related discussions.

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CHAPTER 2
INTRODUCTION TO PLC
2.1 INTRODUCTION
The Programmable Logic Controller has its applications in all automation
industries. Manufacturing processes were partially automated by the use of rigid
control circuits, electrical, hydraulic and pneumatic. It was found that whenever
changes have to be made, the system has to be rewired or reconfigured. With the
help of micro-computers it was realized that if the computer could switch things on
and off and respond to a pattern of inputs, then the changes should be made by
simply reprogramming the computer and so the PLC was born.
There are still more applications of automated systems with permanent
connection to perform a single control action. Often the system uses logic
components to produce the correct action. The PLC mimics the process by
performing the logical operations with the programme rather than real
components. In this way cost savings are produced in terms of fewer components
and flexibility is introduced as programs can be changed more easily than
reconfiguring a hardware system.
2.2 DEFINITION OF PLC
A Programmable Logic Controller has programmable memory to store
instructions and to implement functions such as logic sequencing, timing, counting
and arithmetic in order to control machines and processes. PLC‟s are optimized for
control tasks and industrial environment. It is an industrial computer that accepts
inputs from switches and sensors, evaluates these in accordance with a stored
program, and generates outputs to control machines and process. In operation, the
memory unit sequentially scans inputs in cyclic fashion to determine which
outputs should be turned on or off.

7
A Programmable Logic Controller is a mini computer specifically designed
for industrial and other applications, like
 Pneumatic machines
 Hydraulic machines
 Robots
 Production Processes
 Packaging Lines
 Signaling systems and traffic lights.
 Refining process.
2.3 INTERNAL ARCHITECTURE
A PLC consists of central processing unit (CPU) containing application
program, input and output interface module which are connected to the field I/O
devices. The program controls the PLC so that when an input signal from an input
device turns ON, the appropriate response is made by turning ON an output signal
to some sort of output devices. The components and operations of every block are
given in detail in the following section.
The basic architecture of PLC is shown in Fig. 2.1 resembles a digital
computer. The CPU controls all the processes and all the operation within the
PLC. It is supplied with the clock frequency in the range of 1 to 8MHz. This
frequency determines the operating speed of the PLC and provides timing and
synchronization for all the elements in the system.

8
Fig. 2.1 PLC Architecture
2.3.1 Central Processing Unit
CPU is the brain of the PLC. The processor is one receives, analyses,
processes and send the data. The processor section has signal flow connections to
other sub-sections of the CPU and to the external devices. The processor has ROM
with fixed operating system and program interfaces to the control section. The
unalterable programs manage to operate the PLC. For any program in RAM of the
PLC, the operating system determines the execution method.
The CPU size may vary depending on the complexity of the process to be
controlled. Some CPU‟s have got provisions of including additional memory for
future expansions. CPU contains varies receptacles for connecting the cables that
go the other PLC units. It is important to connect the proper receptacles with other
correct cables supplied by the manufacturers.
Many CPU‟s contain backup batteries that keep the programs in storage in
the event of power failure. Typical retentive backup is from one month to one year.
The basic operating program is not permanently stored.
I
N
P
U
T
O
U
T
P
U
T
POWER SUPPLY
SERIAL
PORT
CPU
DATA
MEMORY
USER
MEMORY
PROGRAMMING DEVICE

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2.3.2 Control Section
The heart of the processor consists of a control unit with a clock, ALU and a
few temporary storage registers. The control section determines the order of the
operating systems.
The input scan block scans the input and places the status of individual input
in RAM. After analysis, the user program updates the output scan block to the
appropriate status. Now the outputs depend on the output status signal of the CPU.
The keypad and the LCD display work based on the keypad operation.
Other peripherals such as tape drive, disk drive or printer may also be present.
There is a special section called optimal interface section. This section is required
when we need to interface with other PLC‟s or a PC for programming.
2.3.3 Memory module
Memory module consists of fixed and alterable memory. Fixed memory
(ROM) contains the program set by the manufacturer. This determines the way of
execution of the user program, management of input and output, divisions of
memory and data management. The alterable memory is mainly present in RAM.
It will lose any information, if the input power goes off. The CPU also has timers,
counters and flags present internally. The program can set, delete, start or stop the
timer or counter as required. The time and count values are stored in reserved areas
of RAM. Also EPROM, EEPROM and NOVPROM memory sub modules are
available. They may be used to store control program, externally.
2.3.4 Input module
The input module transfer information into the CPU. It accepts signals from
the machine or pilot devices like limit switches, proximity switches and push
buttons and convert them into signals that can be used by the controller.
The input module performs the following tasks:
 It senses the presence or absence of input signal at each of its input
terminals.

10
 Then it converts the input signal to a level (DC) usable by the modules
electronic circuits.
 To avoid damage of CPU due to erratic surges from the supply, the input
module is provided with an electronic isolator (optocoupler).
 Finally it produces an output that can be sensed by the CPU.
2.3.5 Output module
The output module transfer information from the CPU to the external or
peripheral devices. It converts the controller signal into one which is usable to
control the machines process. LED‟s are available to indicate ON/OFF status of
each output at the terminals of the module. All the terminals in a single module
have the same output system.
The signal from the CPU is converted to a usable output voltage level. The
goes through „isolation stage‟, which protects the CPU from damage caused by
erratic surges. The output is then transmitted to switching circuitry or converter
stage to produce required DC or AC voltage.
2.3.6 I/O interface
Input interfaces, which receives data from the field devices and transfers it
to the operand memory. Electrical isolation from external world is usually by
means of opto-isolators.
2.3.7 Power supply module
The power available is 230V, 50 Hz. PLC works on 24V DC or 230V AC.
The CPU has its own built in voltage converter unit.

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2.4 PLC OPERATION
A PLC continuously executes the program and updates the output as a result
of input signals. Each such loop is termed as an operating cycle. The typical PLC
operating cycle ranges from 1 to 25ms. The operation cycle is divided into three
scan cycles.
1) Input scan
2) Program scan
3) Output scan
2.4.1 Input scan
During the input scan PLC examines the external input devices ON/OFF.
The status of the input is temporarily stored in an input image memory file.
2.4.2 Program scan
The PLC scans the instruction in the ladder logic program, uses the input
status from the input image file and determines if an output will be energized. The
resulting status of the outputs is written into the output image memory file.
2.4.3 Output scan
Based on the data in the output image memory file the PLC energizes or de-
energizes its output circuits controlling external devices.
2.5 SCAN TIME AND THROUGH PUT TIME OF PLC
2.5.1 Scan time
The process of reading the inputs, executing the program and updating the
outputs is known as scan. The scan time is normally a continuous and sequentially
process of reading the status of inputs, evaluating the control logic and updating
the outputs. Scan time specification indicates how fast the controller can react to
field inputs and correctly solve the control logic.

12
2.5.2 Factors influencing the scan time
The time required to make a single scan (scan time) varies from 0.1ms to 10
ms depending on its CPU processing speed and the length of the user program.
The user of remote I/O subsystems increases the scan time as a result of having no
transmitted the I/O updates to remote system. Monitoring of the control program
also adds overhead time the scan because the controller‟s CPU has to send the
status of coils and the contacts to the CRT or other monitoring devices.
2.5.3 Through put time
The throughput time includes the time for actuation of the physical input;
time for PLC‟s input circuits to sense the signal time for scan program scan and
output scan; time for actuation of the output circuit and corresponding field device
and the time for the CPU‟s housekeeping or overhead functions.
2.6 SPECIAL FEATURES OF PLC
2.6.1 PLC timer
In many control tasks there is a need to control time. To incorporate such
control, PLC‟s are provided with built-in timers. Timer counts the value from 300
seconds using internal CPU clock. The mainly used timer configurations are ON
delay time and OFF delay time. PLC timer function can replace any of the
industrial timers like RC time constant or dashpot.
Advantage of PLC timer is that the time may be a programmable variable
time as well as a fixed time. It also has good accuracy and repeatability, since it is
based on solid state technology.

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2.6.2 PLC counter
A counter counts the number of occurrences of a signal. A counter is set to
some preset number value and when this value of signal has been recorded, the
contacts are operated. These PLC‟s include both types of counters, up counters and
down counters. The counter may be considered to consist of two relay coils, one to
count input pulses and the other to reset the counter. Up counters can be used to
count number of products produced and down counters can be used to count
number of raw materials used.
2.6.3 PLC registers
A register is a memory whose data can be stored. A register in PLC is
number of relays grouped together normally 8, 16 & 32. Each internal relay is
either strictly opened or closed and their status being as 0 or 1. Registers are used
from storing data that comes from sources with the shift registers. It is possible to
shift the stored bits. The data compression is also possible.
2.6.4 PLC internal relay
In PLC‟s elements that are used to hold data that is bits behave like relays
that can be switched ON or OFF and switch other device ON/OFF hence they are
called internal relays. They do not exist as real world switch devices but are nearly
bits in the storage memory that behave in the same way as relays for programming.
They can be tested in the same way as an external relay output and input. Thus
inputs of external switches can be used to give output from an internal relay.
2.7 ADVANTAGES OF PLC
1. Speed of operation:
Relays take an unacceptable time to activate. The operational speed of PLC
is very fast. The PLC speed is determined by the scan time.

14
2. Easier programming:
Programming is made simpler due to ladder diagram. The availability of
computer software has still reduced the programming difficulties.
3. Change of application is easier:
Any change in the application program can be made easily just by enabling
or disabling the required inputs and outputs.
4. Maintainability and Reliability:
Solid state devices are more reliable in general than mechanical devices (or)
relays. The control system maintenance cost is low and down time is minimized.

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CHAPTER 3
PROGRAMMING THE PLC
3.1 LADDER LOGIC
Ladder logic is a programming language that represents a program by a
graphical diagram based on the circuit diagrams of relay logic hardware. It is
primarily used to develop the software for programmable logic controllers (PLC)
used in industrial control applications. The name is based on the observation that
programs in this language resembles ladder with two vertical rails and a series of
horizontal rungs between them. Ladder logic is widely used to program PLC‟s
where sequential control of a process or manufacturing operation is required.
Ladder logic is useful for simple but critical control systems for reworking old
hardwired relay circuits.
A PLC is used primarily to replace relays, timers and counters. It is hard to
beat the simplicity and usefulness of ladder diagram programming. Their ability to
accept programming in ladder logic format is one of the reasons for the success of
programmable logic controller in the industry.
The many similarities between the ladder diagrams used to program PLCs
and the relay ladder logic formerly used to control industrial systems eased the
transition from hardwired relay systems to PLC based systems for many people in
the electrical industry. The ability to monitor PLC logic in ladder diagram format
also made troubleshooting easier for those already familiar with relay based
control systems. Although there are many higher level languages now available for
PLC programming, the majority of the systems are still programmed in ladder
diagram format because of these advantages. The logic in the ladder diagram
typically flows from left to right.

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3.2 STEPS INVOLVED
STEP 1: START THE MILL PROCESS.
STEP 2: SENSOR SENSES THE INCOMING ROD.
STEP 3: SENSOR GIVES INPUT SIGNAL TO THE PLC.
STEP 4: PLC TIMER IS SWITCHED ON.
STEP 5: PLC TRIGGERS THE FORWARD OPERATION MODE OF THE
VFD.
STEP 6: THE VFDs RUNS THEIR MOTORS AT THEIR RATED SPEED.
STEP 7: AFTER THE SPECIFIED TIME OF THE PLC TIMER , THE PLC
GIVES THE STOP SIGNAL TO THE VFDs.
STEP 8: THE VFDs STOPS THEIR MOTORS.
STEP 9: REPEAT STEP 2 UNTIL THE MILL PROCESS ENDS.
STEP 10: STOP THE MILL PROCESS.

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3.3 FLOWCHART OF THE PROCESS
NO
Fig 3.1 Flowchart of the process
START
SENSOR INPUT
ASSIGN MEMORIES
M1, M2
VFD 1
(Max.
Freq)
VFD2
(Min.
Freq)
MOTOR1
MOTOR2
VFD1
(Min.
Freq)
VFD 2
(Max.
Freq)
TIMER 1 TIMER 2
YES
STOP

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3.4 FOR RODS OF LENGTH 20m
3.4.1 Ladder diagram
Fig 3.2 Ladder diagram for 20m rods

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3.4.2 Statement language coding
Fig 3.3 STL Coding for 20m rods

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3.5 FOR RODS OF LENGTH 10m
3.5.1 Ladder diagram
Fig 3.4 Ladder diagram for 10m rods

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3.5.2 Statement language coding
Fig 3.5 STL Coding for 10m rods

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CHAPTER 4
VARIABLE FREQUENCY DRIVES
4.1 INTRODUCTION
An induction motor can run only at its rated speed when it is connected
directly to the main supply. However, many applications need variable speed
operations. This is felt the most in applications where input power is directly
proportional to the cube of motor speed. In applications like the induction motor, a
speed reduction of 20% results in an energy savings of approximately 50%.Driving
and controlling the induction motor efficiently are prime concerns in today‟s
energy conscious world.
With the advancement in the semiconductor fabrication technology, both the
size and the price of semiconductors have gone down drastically. This means that
the motor user can replace an energy inefficient mechanical motor drive and
control system with a Variable Frequency Drive (VFD). The VFD not only
controls the motor speed, but can improve the motor‟s dynamic and steady state
characteristics as well. In addition, the VFD can reduce the system‟s average
energy consumption.
Although various induction motor control techniques are in practice today,
the most popular control technique is by generating variable frequency supply,
which has constant voltage to frequency ratio. This technique is popularly known
as VF control. Generally used for open-loop systems, VF control caters to a large
number of applications where the basic need is to vary the motor speed and control
the motor efficiently. It is also simple to implement and cost effective.
4.2 V/F CONTROL
The base speed of the induction motor is directly proportional to the supply
frequency and the number of poles of the motor. Since the number of poles is fixed

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by design, the best way to vary the speed of the induction motor is by varying the
supply frequency. The torque developed by the induction motor is directly
proportional to the ratio of the applied voltage and the frequency of supply. By
varying the voltage and the frequency, but keeping their ratio constant, the torque
developed can be kept constant throughout the speed range. This is exactly what
VF control tries to achieve.
Other than the variation in speed, the torque-speed characteristics of the VF
control reveal the following:
 The starting current requirement is lower.
 The stable operating region of the motor is increased. Instead of simply
running at its base rated speed (NB), the motor can be run typically from 5% of the
synchronous speed (NS) up to the base speed. The torque generated by the motor
can be kept constant throughout this region.
 At base speed, the voltage and frequency reach the rated values. We can
drive the motor beyond the base speed by increasing the frequency further.
However, the applied voltage cannot be increased beyond the rated voltage.
Therefore, only the frequency can be increased, which results in the reduction of
torque. Above the base speed, the factors governing torque become complex.
 The acceleration and deceleration of the motor can be controlled by
controlling the change of the supply frequency to the motor with respect to time.

24
Fig 4.1 Torque-Speed characteristics of Induction motor without using VFD
Fig 4.2 Torque-Speed characteristics of Induction motor with using VFD

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4.3 VFD OPERATION
Understanding the basic principles behind VFD operation requires
understanding the three basic sections of the VFD: the rectifier, dc bus, and
inverter. The voltage on an alternating current (ac) power supply rises and falls in
the pattern of a sine wave. When the voltage is positive, current flows in one
direction; when the voltage is negative, the current flows in the opposite direction.
This type of power system enables large amounts of energy to be efficiently
transmitted over great distances.
The rectifier in a VFD is used to convert incoming ac power into direct
current (dc) power. One rectifier will allow power to pass through only when the
voltage is positive. A second rectifier will allow power to pass through only when
the voltage is negative. Two rectifiers are required for each phase of power. Since
most large power supplies are three phase, there will be a minimum of 6 rectifiers
used. Appropriately, the term “6 pulse” is used to describe a drive with 6 rectifiers.
A VFD may have multiple rectifier sections, with 6 rectifiers per section, enabling
a VFD to be “12 pulse,” “18 pulse,” or “24 pulse.” Rectifiers may utilize diodes,
silicon controlled rectifiers (SCR), or transistors to rectify power. Diodes are the
simplest device and allow power to flow any time voltage is of the proper polarity.
Silicon controlled rectifiers include a gate circuit that enables a microprocessor to
control when the power may begin to flow, making this type of rectifier useful for
solid-state starters as well. Transistors include a gate circuit that enables a
microprocessor to open or close at any time, making the transistor the most useful
device of the three. A VFD using transistors in the rectifier section is said to have
an “active front end.”
After the power flows through the rectifiers it is stored on a dc bus. The dc
bus contains capacitors to accept power from the rectifier, store it, and later deliver
that power through the inverter section. The dc bus may also contain inductors, dc
links, chokes, or similar items that add inductance, thereby smoothing the

26
incoming power supply to the dc bus. The final section of the VFD is referred to as
an “inverter.” The inverter contains transistors that deliver power to the motor. The
“Insulated Gate Bipolar Transistor” (IGBT) is a common choice in modern VFDs.
The IGBT can switch on and off several thousand times per second and precisely
control the power delivered to the motor. The IGBT uses a method named “pulse
width modulation” (PWM) to simulate a current sine wave at the desired frequency
to the motor.
Motor speed (rpm) is dependent upon frequency. Varying the frequency
output of the VFD controls motor speed.
Speed (rpm) = frequency (hertz) x 120 / no. of poles.
4.4 LOW INRUSH MOTOR STARTING
Motor manufacturers face difficult design choices. Designs optimized for
low starting current often sacrifice efficiency, power factor, size, and cost. With
these considerations in mind, it is common for AC induction motors to draw 6 to 8
times their full load amps when they are started across the line. When large
amounts of current are drawn on the transformers, a voltage drop can occur,
adversely affecting other equipment on the same electrical system. Some voltage
sensitive applications may even trip off line. For this reason, many engineers
specify a means of reducing the starting current of large AC induction motors.
4.4.1 Soft starters
Wye-delta, part winding, autotransformer, and solid state starters are often
used to reduce inrush during motor starting. All of these starters deliver power to
the motor at a constant frequency and therefore must limit the current by
controlling the voltage supplied to the motor. Wye delta, part winding, and
autotransformer starters use special electrical connections to reduce the voltage.
Solid-state starters use SCRs to reduce the voltage. The amount of voltage
reduction possible is limited because the motor needs enough voltage to generate

27
torque to accelerate. With maximum allowable voltage reduction, the motor will
still draw two to four times the full load amps (FLA) during starting. Additionally,
rapid acceleration associated with wye-delta starters can wear belts and other
power transmission components
4.4.2 VFD as starters
A VFD is the ideal soft starter since it provides the lowest inrush of any
starter type. Unlike all other types of starters, the VFD can use frequency to limit
the power and current delivered to the motor. The VFD will start the motor by
delivering power at a low frequency. At this low frequency, the motor does not
require a high level of current. The VFD incrementally increases the frequency and
motor speed until the desired speed is met. The current level of the motor never
exceeds the full load amp rating of the motor at any time during its start or
operation. In addition to the benefit of low starting current, motor designs can now
be optimized for high efficiency.
STARTER TYPE
STARTING CURRENT
(% OF FULL LOAD)
VFD 100%
Wye-Delta Starter 200-275%
Solid State Soft Starter 200%
Autotransformer Starter 400-500%
Part Winding Starter 400-500%
Table 4.1 Comparison of Starters
4.5 IMPROVEMENT OF POWER FACTOR
Power converted to motion, heat, sound, etc. is called real power and is
measured in kilowatts (kW). Power that charges capacitors or builds magnetic
fields is called reactive power and is measured in Kilovolts Amps Reactive

28
(kVAR). The vector sum of the kW and the kVAR is the Total Power (energy) and
is measured in Kilovolt Amperes (KVA). Power factor is the ratio of kW/KVA.
Motors draw reactive current to support their magnetic fields in order to
cause rotation. Excessive reactive current is undesirable because it creates
additional resistance losses and can require the use of larger transformers and
wires. In addition, utilities often penalize owners for low power factor. Decreasing
reactive current will increase power factor.
Typical AC motors may have a full load power factor ranging from 0.84 to
0.88. As the motor load is reduced, the power factor becomes lower. Utilities may
require site power factor values ranging from 0.85 to 0.95 and impose penalties to
enforce this requirement. Power factor correction capacitors can be added to
reduce the reactive current measured upstream of the capacitors and increase the
measured power factor. To prevent damage to the motor, power factor correction
capacitors should not exceed the motor manufacturer‟s recommendations. In most
cases, this results in maximum corrected values of 0.90 to 0.95.
The VFDs include capacitors in the DC Bus that perform the same function
and maintain high power factor on the line side of the VFD. This eliminates the
need to add power factor correction equipment to the motor or use expensive
capacitor banks. In addition, VFDs often result in higher line side power factor
values than constant speed motors equipped with correction capacitors.
4.6 HARMONIC DISTORTION
A discussion of the benefits of VFDs often leads to a question regarding
harmonics. When evaluating VFDs, it is important to understand how harmonics
are provided and the circumstances under which harmonics are harmful.

29
4.6.1 HARMONIC DEFINITION
A three-phase AC power typically operates at 50 hertz (50 cycles in one
second). This is called the fundamental frequency. A harmonic is any current form
at an integral multiple of the fundamental frequency. For example, for 50-hertz
power supplies, harmonics would be at 100 hertz (2 x fundamental), 150 hertz, 200
hertz, 250 hertz, etc.
4.6.2 CAUSES OF HARMONICS
VFDs draw current from the line only when the line voltage is greater than
the DC Bus voltage inside the drive. This occurs only near the peaks of the sine
wave. As a result, all of the current is drawn in short intervals (i.e., at higher
frequencies). Variation in VFD design affects the harmonics produced. For
example, VFDs equipped with DC link inductors produce different levels of
harmonics than similar VFDs without DC link inductors. The VFDs with active
front ends utilizing transistors in the rectifier section have much lower harmonic
levels than VFDs using diodes or silicon controlled rectifiers (SCRs).
Electronic lighting ballasts, uninterruptible power supplies, computers,
office equipment, ozone generators, and other high intensity lighting are also
sources of harmonics.
4.6.3 HARMFUL HARMONICS
Harmonics that are multiples of 2 are not harmful because they cancel out.
The same is true for 3rd
order harmonics (3rd, 6th, 9th etc.). Because the power
supply is 3 phase, the third order harmonics cancel each other out in each phase 3.
This leaves only the 5th, 7th, 11th, 13th etc. to discuss. The magnitude of the
harmonics produced by a VFD is greatest for the lower order harmonics (5th, 7th
and 11th) and drops quickly as you move into the higher order harmonics (13th
and greater).

30
Harmonics can cause some disturbances in electrical systems. Higher order
harmonics can interfere with sensitive electronics and communications systems,
while lower order harmonics can cause overheating of motors, transformers, and
conductors. The opportunity for harmonics to be harmful, however, is dependent
upon the electrical system in which they are present and whether or not any
harmonic sensitive equipment is located on that same electrical system.
4.7 BENEFITS OF VFD
As VFD usage in HVAC applications has increased, fans, pumps, air
handlers, motors 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

31
Fig 4.3 Wiring Diagram
SMPS
R
Y
B
0V
24V
N
Ph N + -
PLC
+ - I1 I2 l3 l4 l5
SENSOR
q + -
VFD 1
R
Y
B
0V
24V
N
E
R/L1 S/L2 T/L3 E
VFD 2
R/L1 S/L2 T/L3 E
U/T1 V/T2 W/T3 U/T1 V/T2 W/T3
M1
SCALING
MOTOR
CUTTING
MOTOR
DCM
M1
DCM

32
4.8 WIRING THE PLC AND VFD
The PLC and the Proximity Sensor requires a 24 V DC supply. The 24 DC
Supply is provided by an SMPS. The SMPS is powered by a single phase supply.
The output of the sensor is fed to the input terminal I1 of the PLC.
The DCM of the VFD 1 is connected to common terminal of the Qo of the
PLC. The Normally open terminal of PLC is connected to the M1 of the VFD 1.
The 3 phase supply is given to the input terminals (R/L1,S/L2,T/L3) of the VFD 1.
The output terminals (U/T1,V/T2,W/T3) of the VFD 1 is connected to the Scaling
Motor as an input supply to it.
The DCM of the VFD 2 is connected to common terminal of the Q1 of the
PLC. The Normally open terminal of PLC is connected to the M1 of the VFD 2.
The 3 phase supply is given to the input terminals (R/L1,S/L2,T/L3) of the VFD 2.
The output terminals (U/T1,V/T2,W/T3) of the VFD 2 is connected to the Cutting
Motor as an input supply to it.

33
CHAPTER 5
HARDWARE DESCRIPTION
5.1 PROGRAMMABLE LOGIC CONTROLLER-
ZEN PROGRAMMABLE RELAY (OMRON)
5.1.1 Features
 Easy direct Programming
 Future expandability
 EEPROM backup of Programs
 Monitorable from PC
 Direct Analog input
 Programming Security
Fig 5.1 PLC Hardware

34
5.2 VARIABLE FREQUENCY DRIVE-DELTA DRIVE (VFD-E)
5.2.1 For cutting motor (5 hp)
Item Number : VDF075E23A
Manufacturer : Delta Products
Series : VFD-E
Nominal Input VAC : 480 Volts AC
Input Range VAC : 380 to 480 Volts AC
HP : 5 Horsepower
Current : 8.5 Amps
Input Phase : 3
Max. Frequency : 600 Hertz
Braking Type : DC Injection; Dynamic
Motor Control : Open Loop Vector (Sensor less Vector)
5.2.2 For scaling motor (1 HP)
Item Number : VFD007E43A
Manufacturer : Delta Products
Nominal Input VAC : 480 Volts AC
Input Range VAC : 380 to 480 Volts AC
HP : 1 Horsepower
Current : 2.5 Amps
Input Phase : 3
Max. Frequency : 600 Hertz
Braking Type : DC Injection; Dynamic
Motor Control : Open Loop Vector (Sensorless Vector)

35
Fig 5.2 VFD Wiring
5.2.3 STEPS FOR SETTING THE VFD
STEP 1: SWITCH ON THE VFD.
STEP 2: SELECT THE MODE OF INPUT CONTROL.
STEP 3: SELECT THE FREQUENCY MODE.
STEP 4: SET THE BASE FREQUENCY.
STEP 5: SET THE MAXIMUM FREQUENCY.
STEP 6: SET THE ACCELERATION TIME.
STEP 7: SET THE DECELERATION TIME.

36
STEP 8: SAVE THE CHANGES.
5.3 INDUCTION MOTORS
5.3.1 Scaling Motor
OUTPUT POWER : 5 HP
TYPE OF INSULATION : Class „F‟
RATED SPEED : 1430rpm
RATED VOLTAGE : 415±10% V
RATED CURRENT : 7.6 A
FULL LOAD TORQUE : 2.6 Nm
5.3.2 Cutting Motor
OUTPUT POWER : 1 HP
TYPE OF INSULATION : Class „F‟
RATED SPEED : 1380rpm
RATED VOLTAGE : 415±10% V
RATED CURRENT : 1.93 A
FULL LOAD TORQUE : 0.5 Nm
5.4 PROXIMITY SENSOR
An proximity (inductive) sensor is an electronic proximity sensor, which
detects metallic objects without touching them.
The sensor consists of an induction loop. Electric current generates a
magnetic field, which collapses generating a current that falls toward zero
from its initial state when the input electricity ceases. The inductance of the
loop changes according to the material inside it and since metals are much
more effective inductors than other materials the presence of metal increases
the current flowing through the loop. This change can be detected by sensing
circuitry, which can signal to some other device whenever metal is detected.

37
CHAPTER 6
SURVEY AND RESULTS
6.1 PROCESS SURVEY
6.1.1 For 20m rods
SCALING MOTOR- 5 HP
• For 1 length,
Final scaling time=15 sec, Non-operating time of Scaling motor=165 sec
• Therefore for 20 lengths(1 hr) ,
Non-operating time of Scaling motor=165*20= 3300 sec=0.916 hrs
• For 1 day(8 hrs working),
Non-operating time of Scaling motor=0.916*8=7.33hrs
• Power Wasted,
5HP (3.7 KW)*7.33HRS=27.121 KWhr (Around 270 Rs/day)
S.No Time
Energy consumed
without VFD (KWhr)
Energy consumed with
VFD(KWhr)
Energy
difference
(KWhr)Theoretical Practical Theoretical Practical
1 9am-10am 3.7 3.12 0.154 0.135 2.98
2 10am-11am 3.7 3.57 0.154 0.15 3.42
3 11am-12pm 3.7 3.9 0.154 0.160 3.74
4 12pm-1pm 3.7 3.29 0.154 0.138 3.15
5 2pm-3pm 3.7 3.54 0.154 0.124 3.41
6 3pm-4pm 3.7 4.32 0.154 0.175 4.14
7 4pm-5pm 3.7 3.41 0.154 0.147 3.26
8 5pm-6pm 3.7 3.87 0.154 0.162 3.70
Table 6.1 Experimental results of Scaling Motor for 20m rods

38
 After Practical observation from Table 6.1,
For a Scaling Motor, Energy Saved per day = 25.4 KWhr.
CUTTING MOTOR- 1 HP
• For 1 length,
Final cutting time= 17 sec, Non-operating time of Scaling motor=163 sec
• For 20 lengths(1 hr) ,
Non-operating time of Scaling motor=163*20=3260 sec=0.90 hrs.
• Power Wasted
1 HP (0.75 KW)*7.2HRS=5.43 KWhr (Rs 50/day)
S.No Time
Energy consumed without
VFD (KWhr)
VFD(KWhr)
Energy
difference
1 9am-10am 0.747 0.6832 0.003527 0.0025 0.6807
2 10am-11am 0.747 0.7336 0.003527 0.0032 0.8280
3 11am-12pm 0.747 0.6978 0.003527 0.0035 0.6908
4 12pm-1pm 0.747 0.8312 0.003527 0.0041 0.7295
5 2pm-3pm 0.747 0.8136 0.003527 0.0039 0.8097
6 3pm-4pm 0.747 0.5213 0.003527 0.0033 0.5157
7 4pm-5pm 0.747 0.7754 0.003527 0.0038 0.8721
8 5pm-6pm 0.747 0.7584 0.003527 0.0038 0.7546
Table 6.2 Experimental results of Cutting Motor for 20m rods

39
For a Cutting Motor, Energy Saved per day = 5.9 KWhr.
6.1.2 For 10m rods
SCALING MOTOR- 5 HP
• For 1 length,
Final scaling time=7.5 seconds,
Non-operating time of Scaling motor=112.5 sec
Non-operating time of Scaling motor=112.5*30= 3375 sec=0.93 hrs
• Power Wasted
5HP (3.7 KW)*7.5HRS=27.75 KWhr (Around 270 Rs/day)
S.No Time
Energy consumed
without VFD (KWhr)
Energy consumed
with VFD (KWhr)
Energy
difference
1 9am-10am 3.7 3.12 0.0077 0.0042 3.115
2 10am-11am 3.7 3.04 0.0077 0.0067 3.03
3 11am-12pm 3.7 3.9 0.0077 0.0092 3.89
4 12pm-1pm 3.7 3.29 0.0077 0.0062 3.28
5 2pm-3pm 3.7 3.24 0.0077 0.0072 3.23
6 3pm-4pm 3.7 3.51 0.0077 0.0094 3.5
7 4pm-5pm 3.7 3.21 0.0077 0.0061 3.20
8 5pm-6pm 3.7 3.27 0.0077 0.0083 3.26
Table 6.3 Experimental results of Scaling Motor for 10m rods

40
For a Scaling Motor Energy Saved per day = 28.4 KWhr.
CUTTING MOTOR- 1 HP
• For 1 length,
Final cutting time= 8.5 seconds
Non-operating time of Scaling motor=111.5sec
Non-operating time of Scaling motor=111*30=3345 sec=0.93 hrs.
• For 1 day(8 hrs. working),
• Power Wasted,
1 HP (0.75 KW)*7.43HRS=5.57 KWhr (Rs 50/day)
S.No Time
Energy consumed without
VFD (KWhr)
VFD(KWhr)
Energy
difference
1 9am-10am 0.747 0.6832 0.00176 0.0008 0.6824
2 10am-11am 0.747 0.7336 0.00176 0.0007 0.7329
3 11am-12pm 0.747 0.6978 0.00176 0.0004 0.6974
4 12pm-1pm 0.747 0.8312 0.00176 0.0024 0.8288
5 2pm-3pm 0.747 0.8136 0.00176 0.0019 0.8127
6 3pm-4pm 0.747 0.5213 0.00176 0.0005 0.5208
7 4pm-5pm 0.747 0.7754 0.00176 0.0018 0.7736
8 5pm-6pm 0.747 0.7584 0.00176 0.0019 0.7565
Table 6.4 Experimental results of Cutting Motor for 10m rods

41
For a Cutting Motor, Energy Saved per day = 6.4 KWhr.

42
CHAPTER 7
CONCLUSION AND FUTURE SCOPE
7.1 CONCLUSION
The Scaling motor and Cutting motors of the Steel Rolling Mills were
upgraded using VFD and PLC. With the help of VFD & PLC, the motors are made
to operate only when it is required. This eliminates the electrical energy
consumption when the operations of the motors are not required. Therefore this
system results in efficient utilization of the electrical energy consumption in Steel
Rolling Mills.
7.2 FUTURE SCOPE
Electrical Energy Conservation can further be increased by implementing
the Variable Frequency Drives to all the Motors and pumps in the mills. All these
drives can be controlled using a Master PLC, thus automating the whole Milling
process.

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