UNIVERSITY OF NAIROBI
FACULTY OF ENGINEERING
DEPARTMENT OF ELECTRICAL AND INFORMATION ENGINEERING
A CONTROL SYSTEM TO NUMERICALLY CHANGE THE POWER REQUIREMENTS OF
A COMPLEX BUILDING
PROJECT INDEX: PRJ 130
BY
ODUORY VICTOR WABWIRE
F17/2378/2009
SUPERVISOR: PROF. M.K. MANGOLI
EXAMINER: DR. C.WEKESA
Project report submitted in partial fulfillment of the
requirement for the award of the degree
of
Bachelor of Science in ELECTRICAL AND ELECTRONIC ENGINEERING of the
University of Nairobi 2014
i
Submitted on: 28TH April, 2014
DECLARATION OF ORIGINALITY
FACULTY/ SCHOOL/ INSTITUTE: Engineering
DEPARTMENT: Electrical and Information Engineering
COURSE NAME: Bachelor of Science in Electrical & Electronic Engineering
TITLE OF NAME OF STUDENT: ODUORY VICTOR WABWIRE
REGISTRATION NUMBER: F17/2378/2009
COLLEGE: Architecture and Engineering
WORK: A CONTROL SYSTEM TO NUMERICALLY CHANGE THE POWER
REQUIREMENTS OF A COMPLEX BUILDING
1) I understand what plagiarism is and I am aware of the university policy in this regard.
2) I declare that this final year project report is my original work and has not been submitted
elsewhere for examination, award of a degree or publication. Where other people’s work
or my own work has been used, this has properly been acknowledged and referenced in
accordance with the University of Nairobi’s requirements.
3) I have not sought or used the services of any professional agencies to produce this work.
4) I have not allowed, and shall not allow anyone to copy my work with the intention of
passing it off as his/her own work.
5) I understand that any false claim in respect of this work shall result in discplinary action,
in accordance with University anti-plagiarism policy.
Signature: ………………………………………………………………………………………
Date: ……………………………………………………………………………………………
ii
Acknowledgement
I wish to pass my sincere gratitude to the Department of Electrical and Information Engineering,
all my lecturers and laboratory technicians at the University of Nairobi, for giving me the chance
to pursue knowledge at this prestigious institution.
Special thanks to my supervisor Prof. M.K Mang’oli, for his unwavering guidance, support and
patience through the entire project period.
My gratitude and heart felt admiration goes to my examiner, Dr. Cyrus Wekesa, for his
participation in the success of this project, his constant support and guidance has contributed into
the person I am today.
Finally, I extend special thanks to my parents Mr. and Mrs. Nabwire for their support throughout
my education.
iii
ABSTRACT
A programmable logic controller is an electronic device that is used to automate any type
of processes. They are widely used in industrial and domestic applications.
In the project, the device will be used to control two generators that supply power to a
building. The two generators are rated 400KVA and 600KVA, the supply to the building will be
chronological and changes with time.
The PLC therefore is to be programmed to monitor the power consumed at the load
center and activate a suitable generator. As mentioned earlier, the generator have different rating
and one is to supply the load at a different time unless if the load demanded is more that what the
current generator can carry then a second generator has to be started and run in synchronism to
supply the load.
In this project, the PLC has been programmed to sense this situations and try to balance
the load at all times, such that no generator is overloaded.
Comparators have been used extensively as they determine the sequence of starting the
generators and also the load on the system. The analog input module is set to follow the primary
current and the scaling function (FC105) is programmed to follow the dynamic current though
the connection is from the secondary of the current transformer.
iv
DECLARATION OF ORIGINALITY ....................................................................................... ii
Acknowledgement ........................................................................................................................ iii
ABSTRACT .................................................................................................................................. iv
1
CHARPTER 1: INTRODUCTION ..................................................................................... 1
BACKGROUND INFORMATION ......................................................................................... 1
OBJECTIVE .............................................................................................................................. 1
METHODOLOGY .................................................................................................................... 1
ANALYSIS AND EXPECTED RESULTS ............................................................................. 1
CONCLUSION .......................................................................................................................... 2
2
CHAPTER 2: LITERATURE REVIEW ............................................................................ 3
INTRODUCTION ..................................................................................................................... 3
HISTORY .................................................................................................................................. 3
2.2.1) ........................................................................................................................................ 3
2.1.1 Parts of a PLC ............................................................................................................... 3
2.1.2 Why PLCs are popular ................................................................................................. 4
2.1.3 Functions of the central processing unit ....................................................................... 4
2.1.4 Advantages of the PLCs ............................................................................................... 5
2.1.5 PLC block diagram, ...................................................................................................... 6
2.1.6 I/O update ..................................................................................................................... 6
2.1.7 Sourcing and sinking signals ........................................................................................ 7
2.1.8 Logic functions ............................................................................................................. 7
2.2.2) Plc programming. ...................................................................................................... 7
2.1.9 PLC manufacturers ....................................................................................................... 8
2.1.10 Siemens PLCs ........................................................................................................... 9
2.1.11 Data acquisition, conversion and distribution system............................................. 13
Generator theory ..................................................................................................................... 16
2.1.12 Engine subsystem: .................................................................................................. 17
2.1.13 Cooling system........................................................................................................ 18
2.1.14 Starter: ..................................................................................................................... 18
2.1.15 Flywheel .................................................................................................................. 19
2.1.16 Synchronizers .......................................................................................................... 20
Generator operating modes and sizing: ................................................................................ 20
2.1.17 Introduction ............................................................................................................. 20
2.1.18 protection ................................................................................................................ 21
2.1.19 Critical Installation Considerations......................................................................... 22
2.1.20 Power System Operation......................................................................................... 23
v
3
CHAPTER 3: PROJECT IMPLEMENATION .............................................................. 24
Introduction ............................................................................................................................. 24
Operating sequences ............................................................................................................... 25
3.1.1 Sequence one .............................................................................................................. 25
3.1.2 Sequence two .............................................................................................................. 25
3.1.3 Sequence three ............................................................................................................ 25
3.1.4 Synchronization .......................................................................................................... 26
3.1.5 Sequence four ............................................................................................................. 26
Generator starting ................................................................................................................... 26
generator stopping................................................................................................................... 27
4
Chapter 4: METHODOLOGY........................................................................................... 28
INTRODUCTION ................................................................................................................... 28
4.1.1 Complete control system block diagram .................................................................... 31
5
Chapter 5: Design ................................................................................................................ 32
Blocks used in the programming ........................................................................................... 32
5.1.1 Timers ......................................................................................................................... 32
5.1.2 Comparators................................................................................................................ 32
5.1.3 OR gates. .................................................................................................................... 33
5.1.4 Contactors ................................................................................................................... 33
5.1.5 Output coils................................................................................................................. 33
5.1.6 Typical building power consumption and loading ..................................................... 34
5.1.7 Project program in ladder logic. ................................................................................. 36
fig 5. 1FC 105: ADC element ................................................................................................ 36
fig 5. 2Multiplier: to find the power at the bus ...................................................................... 36
fig 5. 4: comparator set_2 ...................................................................................................... 37
fig 5. 6Gen A starting ............................................................................................................ 38
fig 5. 7 alarm .......................................................................................................................... 38
5.1.8 interfacing with a real PLC ......................................................................................... 39
5.1.9 5.2 Control system algorithm: .................................................................................... 39
RESULTS AND SIMULATION: .......................................................................................... 41
CONCLUSION ........................................................................................................................... 41
RECOMMENDATION .............................................................................................................. 42
REFERENCES: .......................................................................................................................... 42
vi
LIST OF FIGURES
Fig 2. 1 the scan cycle of a PLC ...................................................................................................... 5
Fig 2. 2 typical PLC blocks ............................................................................................................ 6
Fig 2. 3programming flow chart ...................................................................................................... 7
Fig 2. 4 data acquisition block diagram ......................................................................................... 13
Fig 2. 5data distribution system ..................................................................................................... 14
Fig 2. 6 current sensor block diagram ........................................................................................... 14
Fig 2. 7 Automatic Voltage Regulator diagram ............................................................................. 17
Fig 2. 8fuel distribution system for a diesel engine ....................................................................... 18
Fig 2. 9 engine starter(crank) ......................................................................................................... 19
Fig 2. 10 flywheel .15 .................................................................................................................... 19
Fig 2. 11 ......................................................................................................................................... 30
Fig 2. 12 showing how the various components are connected .................................................... 31
Fig 2. 13 Control system flow diagram ...................................................................................... 41
vii
1 CHARPTER 1: INTRODUCTION
BACKGROUND INFORMATION
Many control systems exist today and in various forms. They include traffic light control
system, motor vehicle control systems , robotic control systems used in industries such as in car
assemblies also in the bottling industries, in the energy sector for instance oil and gas , they have
control systems to monitor different functions and at different stages.
Temperature control systems used in monitoring temperature i.e. heaters, cars e.t.c. For
power application, a control system can be designed to measure and monitor power at various
load nodes, generating points and along the transmission lines.
Most control systems rely on some sort of controller to function as its “brain”, in this
project a PLC will be the main controller. It is a robust and versatile instrument that can be
adopted to service many engineering applications
In this project, a control system has to be designed that will monitor power at the busbars
and then execute a set of programmed instructions stored in the memory of the computer.
OBJECTIVE
To design and implement a control system that will monitor and control power
consumption of a complex building by using a Programmable Logic Controller
METHODOLOGY
To first analyze how a PLC functions, its limitations and strengths and finally adopting it
in the controlling of two sets of generators, monitor power consumed by the building under
consideration and finally programming it to carry out the said objective.
A current transformer and a transducer will be in the input stage of the PLC while alarm,
fuel and crank relays, control lamps will form the output devices.
ANALYSIS AND EXPECTED RESULTS
Each and every engineering application is designed for a specific purpose and as such it
has to give some results to enable analysis and scientific decision to be made. This project
heavily relies on programming and, therefore, in the implementation, the generators have to be
controlled through a program that carries the instruction executed by the PLC.
Results, therefore, are computed from continuously increasing loads at different times of
the day which are monitored by the PLC.
1
CONCLUSION
Since everything is familiar, we expect a computer program written in a language that the
PLC understands. The PLC accepts both analog and digital signals and they are the main
elements used in the program and the PLC bases its logic decision on them. Therefore, the
project has to use software to simulate this operation so as to achieve the objective.
The PLC hence has both inputs and outputs that facilitates interfacing between it and the
field devices.
2
2 CHAPTER 2: LITERATURE REVIEW
INTRODUCTION
At this point, emphasis will be laid in understanding what a PLC is and what it can do. It
will be analyzed and studied in detail to verify if it can be used in the project.
HISTORY
A PLC was designed in 1969 by Richard Dick E the founder of Modicon Corporation.
PLCs are versatile devices/ computers in the old times original hard wired relay panels were used
to be made for the factories, these huge panels were expensive and needed a lot of time to
configure or repair .PLCs were an advanced technological replacement.
2.2.1) Programmable Logic Controller
A PLC is a solid state system with programmable memory for storing instructions to
implement specific functions such as logic, sequencing, timing, counting, and arithmetic to
control machine and other types of processes
Two popular arrangements of PLCs are the modular and the rack types. PLCS are
available in the following ranges
a.
b.
c.
d.
e.
Micro PLC
Small PLC
Medium PLC
Large PLC
Very large PLC
2.1.1 Parts of a PLC
PLC is basically a computer and it has the following components:a. Central processing unit – interprets the input signals and carries out control
actions depending to program.
b. Memory- contains the control actions done by the microprocessor.
c. Power supply-converts AC mains to DC (5V) for the processor and the circuits
input and output interface module
d. I/O interface- where the processor receives information from external devices
and communicates the information to external devices
e. Communication interface-used to receive and transmit data on communication
networks from or to other places and does the following:
Device verification
3


Data acquisition
Synchronization between user applications and connection management
Programming device-used to enter required program into the memory unit of the PLC.[5]
The versatility of a PLC is seen as it can be adopted to a wide range of control system
since only the instructions need to be updated or reprogrammed to perform another operation e.g.
heater, lifts and escalators, packaging, robots etc .[4]
The PLC can be programmed to execute PID control mode for efficient control of the
generators. The generators are labeled 1 and 2 for the programming purposes, the addresses of
the input and outputs are internally assigned by PLC.[4]
2.1.2 Why PLCs are popular
I.
PLCs have incorporated object-oriented programming tools and multiple
languages based on the IEC 1131-3 standard.
II.
Small PLCs have been provided with powerful instructions, which extend the area
of application for these small controllers.
III.
High-level languages, such as BASIC and C, have been implemented in some
controllers’ modules to provide greater programming flexibility when
communicating with peripheral devices and manipulating data.
IV.
Advanced functional block instructions have been implemented for Ladder
diagram instruction sets to provide enhanced software capability using simple
programming commands.
V.
Diagnostics and fault detection have been expanded from simple system
diagnostics, which diagnose controller malfunctions, to include machine
diagnostics, which diagnose failures or malfunctions of the controlled machine or
process.
VI.
Floating-point math has made it possible to perform complex calculations in
control applications that require gauging, balancing, and statistical computation.
2.1.3 Functions of the central processing unit
The CPU is the brain of the PLC and controls all the operations done by the PLC, consider the
functions below
(1)Reads, or accepts, the input data from the field devices via the input interfaces,
(2)Executes, or performs, the control program stored in the memory system.
(3)Writes, or updates, the output devices via the output interfaces.
This process of sequentially reading the inputs, executing the program in memory,
and updating the outputs is known as scanning.
The input/output system forms the interface by which field devices are connected to the
controller the main purpose of the interface is to condition the various signals received from or
sent to external field devices. Incoming signals from sensors (e.g., push buttons, limit switches,
4
Analog, sensors, selector switches, and thumbwheel switches) are wired to terminals on the input
interfaces.
Devices that will be controlled, like motor starters, solenoid valves, pilot lights, and
position valves, are connected to the terminals of the output interfaces.
The system power supply provides all the voltages required for the proper operation of
the various central processing unit sections.
Scan cycle
READ
EXECUTE
WRITE
Fig 2. 1 the scan cycle of a PLC
2.1.4 Advantages of the PLCs
The PLC has so many features that make it superior to other control methods available in the
market, such as
Inherent Features
Solid-state components
Programmable memory
Small size
Microprocessor-based
Benefits
• High reliability
• Simplifies changes and Flexible control
• Minimal space requirements
• Communication capability
• Higher level of performance
• Higher quality products
• Multifunctional capability
• Eliminate hardware
• Easily changed presets
• Reduce hardware/wiring cost
• Reduce space requirements
• Installation flexibility
• Easily installed
• Reduces hardware cost
• Expandability
• Controls a variety of devices
• Eliminates customized control
Software timers/counters
Software control relays
Modular architecture
Variety of I/O interfaces
5
• Eliminate long wire/conduit runs
• Reduce troubleshooting time
• Signal proper operation
• Neat appearance of control panel
Remote I/O stations
Diagnostic indicators
Modular I/O interface
2.1.5 PLC block diagram,
Input module
Input image table
Output module
CPU
User program
memory
Output image table
Variable data memory
Fig 2. 2 typical PLC blocks
A PLC has many inputs and outputs both digital and analogue that are wired to it field
devices for the purpose of control.
Within the PLC, there is a logic that tries to track the states of the field devices for
instance, a contactor can be closed or open, to further understand this process, consider the
updating sequences mentioned below:-.
2.1.6 I/O update
The data in the plc memory is updated using two formats :
1.
Continuous updating involves scanning the input channels as they occur
in the program instruction. Each point is examined individually and its effect on the
program determined within a 3ms delay.
2.
Mass I/O copying which simply means to scan all inputs and outputs copy
them into the RAM ,secondly, fetch and decode and execute all program instructions in
sequence , copying output instructions to RAM
6
2.1.7 Sourcing and sinking signals
Are terms used to describe the way in which d.c devices are connected to a PLC.
Sourcing: positive to negative input devices receives current from input module. And if current
flows from output module to an output load the output is said to be sourcing.
If current flows to output module from an output load then output module is referred to as
sinking.
Sinking: current flows to output module from an output load the output module is then
said to be sinking.
2.1.8 Logic functions
PLC programs can be well understood from the basic logic gates used to simulate digital
systems. Example of logic gates are:
1.
2.
3.
4.
5.
EXOR
OR
AND
NAND
NOR
The basic truth table of a digital gates, i.e., mentioned above, a ladder logic diagram can be
created for the control of the field devices.
2.2.2)
Plc programming. The following chart shows the various forms of programming
languages that can be used to program the PLC.
Fig 2. 3programming flow chart
7
a) Instruction list
This shows the various programming codes used by the listed PLC vendors; instruction list is a
form of programming usually called the structured text language. Consider:






LD=load
LDN=load a normally closed contact
AND= multiply contact using the logical AND gate
ANDN=multiply with a normally closed contact
OR= add using the logical OR gate
ORN=add using the logical NOR gate
ST= give an output to the output coil
The table below gives the types of programming language i.e. the structured text list
(STL)used by various PLC vendors and manufacturers
IEC 1131-3
MITSUBISHI
OMRON
SIEMENS
LD
LD
LD
A
LDN
LDI
LD NOT
AN
AND
AND
AND
A
ANDN
ANI
AND NOT
AN
OR
OR
OR
O
ORN
ORI
OR NOT
ON
ST
OUT
OUT
=
Fig 2.0.3) STL table
2.1.9 PLC manufacturers
There are several PLC manufacturers in the market today and just to mention a few
1.
2.
3.
4.
5.
6.
Siemens : step 7 PLCs from 100 to 1050
Allen Bradley
Fatek
Modicon
Telemecanique
Mitsubishi
8
From these categories one has to analyze carefully and decide which type of PLC is most suited
to the type of application they want to automate. Look at the list below for some of the reasons.
1. What is the number of inputs and output or capacity is required and considering
future expansion needs if the PLC will take care of that.
2. What are the different types of input/outputs are required ,that is , isolation , onboard processing and signal conditioning
3. What size of memory is required as it is linked to the number of input/output and
the complexity of the program.
4. The speed and power as it is linked to the number of instructions that can be
handled by the PLC
From the above list, I settled on Siemens PLC as they are locally available in the country so one
does not have to import a PLC.
2.1.10 Siemens PLCs
At this point, we will have a look at Siemens PLCs and the many features that make their
PLCs stand out from the rest.
We will go through the following:(1). Memory organization and I/O
Siemens PLCs are unique in that they have there own memory organization and
referencing methods unlike other PLC vendors or manufacturers.
Consider the table below of memory types
Memory type
Referencing letter
Process image input register
I
Process image output register
Q
Variable memory area
V
Bit memory area
M
Sequence control area
S
Special memory bits
SM
Local memory area
L
Timer memory area
T
Counter memory area
C
Analogue inputs
AI
Analogue outputs
AQ
The memory is further divided into bits, bytes, words and double words. The V-memory area is
used to store immediate results of the control logic operation and also store other data pertaining
to a specific process task.
9
The sequence control relay area (S) does the organizing of machine operations or steps
into an equivalent program segments. The local memory area parses the data.
The following references will be used with external/ peripheral inputs and outputs; PIB,
PIW, PID and PQB, PQW, PQD.
Data Blocks contain data that can be accessed from any block
In the programming, the programming blocks are:
1. Organization blocks(OB) – determines the structure of the user program
2. Functional Blocks (FB) have memory and data stored cannot be changed
3. System Functional Blocks and System Functions: allow access to important
system functions.
4. Functions : contain certain routine for frequently used functions
5. Instance Data Blocks : and also Data Blocks are used in the programming.
Registers: In normal programming of microprocessors, a register is a high speed storage are
onboard with the CPU and hence enable rapid execution of programs. In PLC we have the
accumulators, two of them that are 32bit. Look the table below:
Statu
s bits
215 214 213 212 211 210 29 28
B
R
27
26
25
24
23
22
21
20
CC
I
CC
O
O
S
O
S
O
R
ST
A
RL
O
F
C
Let us look at the PLC memory for an understanding of how data and information is arranged in
the memory that facilitates program execution and program control.
There are two, memory sections
1. Executive memory this type of memory is a collection of permanently stored
programs that are considered part of the PLC. Therefore these supervisory
programs direct all the activities i.e. execution of control program and
communication with peripheral devices.
2. Application memory this type of memory provides a storage area for the user
programmed instructions that form the application program.
The Input and output subsections are the most important as without them there will be no
need for the PLC, therefore a careful analysis of these system is in order.
The executive and application memory can be divided into :I.
System10
II.
 Executive
 Scratch pad
Application Data table
 User program
The data table section has –
I.
II.
III.
Input table
Output table
Storage area
The storage area is where the changeable data is and consists of two part:
a. Internal bit storage
b. Register/ word
The internal bit storage area contains storage bit , that is , internal outputs , internal coils,
internal(control) relays.
The values placed into registers/ word registers storage areas represents input data from a
variety of devices such as thumbwheel switches, analog inputs and other variables.
Therefore to further comprehend how the memory is organized, consider the following
example: Total application memory of 4K words with 16 bits
 With a capability to connect 256 I/O devices (128 internal inputs and 128 internal
outputs)
 It has the capacity of up-to 256 storage registers, selectable in groups of 8-word
locations, that is 32 groups of 8 registers.
 Octal (base 8) numbering system with 2 bytes (16-bit) word length
The above information is organized as such inside the PLC environment:





First, the I/O table boundaries are set with the following input/output mapping
The input table will start at 𝟎𝟎𝟎𝟎𝟖 and end at 𝟎𝟎𝟎𝟕𝟖
The output table will start at 𝟎𝟎𝟏𝟎 𝟖 and end at 𝟎𝟎𝟏𝟕8
Since each memory word has 16bits, the 128 inputs will require 8 input table words also
for the outputs
The starting address for the internal output storage area will be at 𝟎𝟎𝟐𝟎𝟖 and continues
through 𝟎𝟎𝟐𝟕𝟖
11
(b). Programming
To program the PLC, we are going to use the resources of the PLC, to name them, they
are:
1. internal/auxiliary relays
2. timers
3. master control
4. data handling and manipulation
The following are programming types inside the PLC programmer
i.
Latching and internal relays
To latch is to hold a solenoid to a previous state even when an actuating signal is
removed.
ii.
Timers and counters
A timer is setup within the plc to either turn on or turn off an ongoing operations. Or tell
the plc that time has come to change over to another operation.
Counters are also available to count operations or steps of doing things and then stop to
do another; counters can either be an up-counter, down-counter or an up-down counter.
iii.
Shift registers
A register may be thought of as a bank of elements called auxiliary relays which are on or
off. Therefore, a shift register is continuously updated in that its contents are changing and there
corresponding outputs will follow that sequence of change. A shift register has three inputs:
1. one to hold data into the first element of register(OUT)
2. shift command(SFT)
3. register reset(RST)
iv.
Master and jump controls
12
A whole block of outputs can be simultaneously turned off or on by using the same
internal register.
E.g. MC M100 and MCR M100 to reset the master control.
Jumps, these are employed during program execution to enable the plc jump between
program code.
v.
Data handling
Various data types are used inside the plc e.g. int, word, dword, bit
1. Moving data using the MOV operand
2. Comparison of the magnitude of values i.e.(<,>,=>,<=,<>)
3. Arithmetic operations , these includes the normal mathematical functions i.e.(+,,/,*)
4. Conversion between BCD ,binary and octal also from real, int, word dword data
types
2.1.11 Data acquisition, conversion and distribution system
The following processes are an integral part of our input subsystem as in allows data to
be acquired by the PLC and processed. The signal conversion taking place in the digital control
system involves:I.
II.
III.
IV.
Multiplexing and demultiplexing
Sample and hold
ADC this is the quantizing and encoding part
DAC and is the decoding section for the analog outputs
2.1.11.1 Block diagram: data acquisition system
This is the typical steps an analog signal will pass through for it to be converted into a form
usable by digital computers
Transducer
Amplifier
Low pass
filter
Analog
multiplexer
Physical
variable
Fig 2. 4 data acquisition block diagram
13
Sample
and hold
circuit
Digital
computer
i)
Block diagram : data distribution system
From
digital
computer
Register
Demux
DAC
Hold circuit
To actuator
Fig 2. 5data distribution system
Apart from the PLC the following systems are also used
1)
2)
3)
4)
5)
Current transformers
ADC
Contactors
Generator alternator
Synchronizers
2.1.11.2 Building blocks for the current measurement system
This system forms the input stage of our control system, the signal is properly conditioned before
it is fed into the PLC
Current
3 phase busbars
Transducer
Transformer
C.T
Fig 2. 6 current sensor block diagram
14
PLC
2.1.11.2.1
current transformer
Let as look at the properties of the Current Transformers
I.
II.
III.
IV.
V.
VI.
VII.
VIII.
IX.
X.
XI.
XII.
𝐼𝑓 : maximum through current crossing a protected area
𝐼𝑠 :current threshold setting
𝐾𝑛 : nominal accuracy limit factor(ALF) of a CT
𝐾𝑟 real ALF of a CT associated with its real load
𝑃𝑖 : (= 𝑅𝑐𝑡 𝐼𝑛2 ) the internal loss of the CT at 𝐼𝑛
𝑃𝑛 : (=𝑅𝑛 𝐼𝑛2 ) accuracy power of the CT
𝑃𝑟 : (=𝑅𝑟 𝐼𝑛2 ) real load consumption of the CT at 𝐼𝑛
𝑅𝑙 : wiring resistance
𝑅𝑝 : protection relay resistance
Overrating of a CT : selection of a CT whose primary 𝐼𝑛 is greater than the 𝐼𝑛
immediately greater than the load 𝐼𝑛
Matching , auxiliary or interposing CT: low voltage CTs installed at the
secondary of the main cts for correcting the ratio and/ or current phase shift
SF: security factor
The above properties aid in the design and selection of a C.T for any type of application that
involves electrical power manipulation.
We can state that a current transformer is an electrical instrument used to detect current on a line
by using the principle of electromagnetic induction..
We know that the voltage and current relations between the secondary and primary of the
transformer is given by:
Power in primary = power in secondary
…………………..eqn.1
Therefore,
……………eqn.2
Or, using the turns ratio,
Voltage=current* number of turns
V=I*N, replacing the given formula in eqn 2, we find;
………………………………….eqn.3
15
2.1.11.2.2
Analog to digital converter
This is a system used to convert an analogue signal to a digital one that the plc can work
on. The following formulas can be applied to convert to a digital value if an analogue signal is
present at the input pins
Parameters
R=range of the ADC
N=number of bits
………………Number of A/D resolution
……….Error to be expected.
………..Relates voltage range and
resolution to voltage input to estimate the integer that the A/D converter will
record.
……….allows conversion from A/D
Generator theory
A generator can be said to be a union of mechanical and electrical components to produce
electricity. Normally the mechanical power is provided by engines either steam, diesel or nuclear
power.
This sections highlights some of the properties of a generator and features plus basic
introduction of generators, its vital in that it allows us to properly understand how the project
will be implemented.
The electrical part is provided by an alternator that is coupled to the engine mechanical
and the engine is hence said to be the prime mover. As it rotates it also rotates the alternator
through a magnetic field and as it cuts this field, a voltage is induced in the stator windings using
the following principles
Faraday’s Law :
Any change in the magnetic field of a coil of wire will cause a voltage (emf) to be
"induced" in the coil. No matter how the change is produced, the voltage will be generated. The
change could be produced by changing the magnetic field strength, moving a magnet toward or
away from the coil, moving the coil into or out of the magnetic field, rotating the coil relative to
the magnet, etc.
Alternator operating principle When the magnetic field around a conductor changes, a current
is induced in the conductor. In a alternator, a rotating magnet called the rotor turns within a
16
stationary set of conductors wound in coils on an iron core, called the stator. The field cuts
across the conductors, generating an electrical current, as the mechanical input causes the rotor to
turn.
Voltage Regulator (AVR):- This is the most important element of the alternator. At
asymmetrical loads, the voltage regulator senses three phases as a reference therefore the
maximum voltage asymmetry is 5%. Electrical and thermical tests are applied before mounting
on the alternator. The output voltage could be adjusted manually by a potentiometer
Consider the following block diagram of the Automatic Voltage Regulator (A.V.R)
Alternator
Load
Voltage
regulator
Setting
values
Fig 2. 7 Automatic Voltage Regulator diagram
2.1.12 Engine subsystem:
At this juncture,we have a look at parts of generator and in a more specific detail, the engine or
the prime mover of the alternator.


Fuel system
The cooling system
Fuel system
It contains fuel that is required for running engine and cleans fuel.It increases fuel. pressure and
sends fuel to cylinders by depending on burning time and burning turn.
Parts of the fuel system





Low pressure pipes
Feeding pump
Fuel tank
Filters
Fuel pumps
17


Regulators
Injectors
Fig 2. 8fuel distribution system for a diesel engine
2.1.13 Cooling system
Parts of cooling system:








Circulation water pump
Radiator
Water canal
Thermostat
Temperature sensor
Fan engine
Ventilator
Heater
2.1.14 Starter:
It gives first movement to the engine. It takes supply from battery (DC supply). It
produces mechanical energy and forwards it to the flywheel. Thus engine will crank.
The generators are started by applying a voltage to the crank relay which then activates
the crank and that rotates the flywheel. As the flywheel rotates it transmits power to the crank
shaft.
18
Fig 2. 9 engine starter(crank)
2.1.15 Flywheel
Flywheel is a significant mass at the end of the crankshaft that stores energy during a
power stroke and release energy during the rest of the cycle. It helps to stabilize the shaft
rotation. Consider the formulas below;
POWER (KW)=𝑻𝑶𝑹𝑸𝑼𝑬 ∗ 𝑨𝑵𝑮𝑼𝑳𝑨𝑹 𝑽𝑬𝑳𝑶𝑪𝑰𝑻𝒀
P=T*
𝑻∗𝟐∗∗𝑵
P= 𝟏𝟎𝟎𝟎
N=engine speed in rpm
Torque angular for produced by the engine (Nm)
Fig 2. 10 flywheel .15
19
2.1.16 Synchronizers
These devices ensure correct operation of many power synchronous machines to operate in
parallel.
The following steps are used for correct matching:•
The steps are:
–
Verify that the phase sequence of the two systems is the same.
–
Adjust the machine speed with the turbine that drive the generator until the
induced voltage and network frequency are nearly the same. within ±0.067%
–
Adjust the terminal voltage of the generator by changing the field current until the
terminal voltage is almost equal to the network voltage. Acceptable limit is 5%
–
Adjust the phase angle of the generator to be nearly equal with the phase angle of
the network voltage. Within ±10%
•
The voltages between the terminals of the circuit breaker are measured, when this
voltages are small, about 5% and the two frequencies are nearly equal the circuit breaker
is closed.
•
In the past lamps, connected across the open breaker, were used to detect the voltage
differences.
•
Today electronic circuits compare the voltages and control the generator. However some
operators still prefers to synchronize the generator manually with an out of range
synchronizer overriding.
Generator operating modes and sizing:
2.1.17 Introduction
Proper sizing of a generator is an important task. The following guidelines represent the
general and specific considerations that must be taken into account in properly sizing a generator
for a specific application.
These guidelines are based on Caterpillar Generator Sets as an industry leader.
A common practice in the industry is to base a given design around a specific manufacturer of a
major piece of equipment, such as a generator, and to make allowances for idiosyncratic
differences that allow competitive bids and supply to the purchaser. Most generator
manufacturers now use computer software programs for proper sizing of generators in specific
applications.
The following is provided to give a basic understanding of the methodology and can be
used for preliminary calculations. It is in this context that the Caterpillar guidelines are offered.
20
APPLICATION DATA RATINGS
Diesel-Electric Power Generation
All ratings shown and thermal ratings are subject to manufacturing tolerances
of 3 percent.
When using a generator set, use the following guidelines to determine whether standby,
prime, prime plus 10 percent, or continuous rating applies.
STANDBY RATING:
Typical load factor = 60 percent or less
Typical hours/year = 100 h
Typical peak demand = 80 percent of standby-rated kilowatts with 100
percent of rating available for the duration of an emergency outage
Enclosure/sheltered environment
PRIME + 10 PERCENT RATING:
Typical load factor = 60 percent or less
Typical hours/year = 500 h
Typical demand = 80 percent of standby-rated kilowatts with 100 percent
of rating available for the duration of an emergency outage
Typical application = Standby, rental, power module, unreliable utility,or interruptible
rates
PRIME RATING:
Typical load factor = 60 to 70 percent
Typical hours/year = No limit
Typical peak demand = 100 percent of prime-rated kilowatts used occasionally, but for
less than 10 percent of operating hours
Typical application = Industrial, pumping, construction, peak shaving,or cogeneration
CONTINUOUS RATING:
Typical load factor = 70 to 100 percent
Typical hours/year = No limit
Typical peak demand = 100 percent of continuous-rated kilowatts for
100 percent of operating hours
Typical application = Base load, utility, cogeneration, or peak shaving
For conditions outside the above limits, refer to the manufacturer.
Operating units above these rating definitions will result in a shorter life until overhaul.
2.1.18 protection
Protection of the engine and generator against motorization is provided.
A reverse-power monitor, upon sensing a motorizing condition on any plant, will initiate load
shedding, disconnect the failing plant, and shut it down.
21
Sometimes a higher level of reliability is economically justifiable in a parallel generation
arrangement for critical loads such as hospitals and data centers. This is known as providing an
(N + 1) level of reliability (redundancy) (i.e., providing one more generator than is needed to
serve the emergency load). Thus, if one of the emergency generators fails to start or is out of
service for any reason, the remaining plants can serve the entire emergency load. This precludes
the need for automatic load shedding, which can be expensive in itself. Thus, this provides for
two levels of contingency operation,
 the first being loss of the normal source of power, and
 the second being loss of one of the emergency/ standby generators. Providing an
even higher level of reliability is rarely justifiable.
To illustrate the operation of a typical multiengine automatic paralleling
system and its sequence of operation, The loads are connected to the emergency bus in ascending
order of priority beginning with priority one. For load shedding, the loads are disconnected in
descending order of priority beginning with the last priority of load to be connected.
Upon a loss of normal-source voltage as determined by the PLC a signal initiates starting
of all engine-generator sets.(assuming that mains utility is provided) The first set to come up to
90 percent of nominal voltage and frequency is connected to the source bus.
Control circuitry should prevent the automatic transfer or connection of loads to the bus
until there is sufficient capacity to carry these loads. Provision is made for manual override of
the load addition circuits for supervised operation.
During shut down, the sets are run up to 15 min for cooling down and then for shutdown.
2.1.19 Critical Installation Considerations
The following summary contains important points to remember for a successful generator
installation:
a) The generator set must be sized properly for the installation. Determine the duty cycle:
continuous, prime, standby, or peak shaving or sharing (paralleled or not paralleled with
the utility).
 Continuous: Output available without varying load for an unlimited time.
 Prime: Output available with varying load for an unlimited time.
 Standby: Output available with varying load for the duration of the interruption of the
normal source of power. The standby duty cycle is usually sized initially for 60 percent of
actual load, because loads tend to increase during the 30-year life of the unit. Normal
hours of operation are less than 100 h per year.
 Peak shaving/sharing: Prime if paralleled with the utility, standby if not paralleled with
the utility and if the load meets the definition of prime or standby. Normally peak
shaving/sharing is less than 200 h per year of operation.
Loads that are too light cause engine slobber. Overloading causes excessive piston
loading and high exhaust temperatures. Standby engines that must be exercised regularly but
cannot be loaded should only be run long enough to achieve normal oil pressure and then shut
off—less than 5 min of running time. Good practice dictates that this be done weekly and that
once a month the generators be run under load for a half hour or so, then unloaded briefly for
cooldown.
22
The load should be at least two-thirds of capacity, either using a dummy resistive load
bank, or preferably under actual building load.
b) The generator set must be properly installed in an atmosphere that allows it to achieve the
required life.
Air flow: Provide adequate clean, cool air for cooling and combustion. High engine room
temperatures may require ducting cooler outside air to the engine intake to avoid power derating.
Restriction of radiator air reduces its cooling capability.
Exhaust: Isolate exhaust piping from the engine with flexible connections. Wrap the
piping with a thermal blanket to keep exhaust heat out of the engine room. The exhaust stack and
muffler need to be sized so that the exhaust back pressure at the turbocharger outlet does not
exceed 6.7 kPa (27 in) of water. Excessive back pressure raises exhaust temperatures and reduces
engine life.
Fuel: Use clean fuel. Fuel day tanks should be below the level of the injectors.
Mounting: The generator sets must have a flat and secure mounting surface. The
generator set mounting must allow adequate space around the generator set for maintenance and
repairs.
Starting: Batteries should be close to the starter and protected from very cold
temperatures. Do not disconnect batteries from a running engine or a plugged-in battery charger.
c) SCR loads can affect generator output waveform. Make sure the SCR supplier is aware of
the possible problems. Every generator set installation is unique and requires careful
consideration of the particular application and site-specific conditions. It is therefore best
to determine the foundation, ventilation, exhaust, fuel, vibration isolation, and other
requirements in conjunction with the generator set manufacturer for the specific
application and site conditions.
2.1.20 Power System Operation
•
When the induced voltage is:
–
larger than the terminal voltage the generator produces reactive power
(capacitance).
–
smaller than the terminal voltage the generator absorbs reactive power
(inductance).
•
The synchronous generator starting torque is zero, the machine has to be driven by a
mechanical device (turbine, recipricating engine, etc).
•
The proper interconnection of a rotating machine with the network is called
synchronization.
23
3
CHAPTER 3: PROJECT IMPLEMENATION
Introduction
A control system is designed to achieve the design requirements and in this project a
system is required to control the power supply to a building.
From theory section power, that is the three phase power is fed into the load center which
in-turn is connected to the building power distribution system.
Since the PLC is an instrumentation device and can only accept small signal in the range
(4mA-20mA, 0mA-20mA or 0V- 10V DC), we will need a Current transformer and a potential
transformer in the input stage of the PLC.
An analog to digital converter will then convert these analog signals into a digital format
so that the PLC can use the signals for its own logic processing. The logic program will then
control the two generator sets.
The sets ratings is given as 400KVA and 600KVA, a load profile of the building is
required as it display in a graphical form how the building consumes electrical power at different
times of the day.
Various methods are available apart from using PLC but in these case PLCs, as
mentioned , will automate the process so human intervention will be minimized.
But first we have to understand the base load appliances to formulate a proper operating
sequence of the generators. These appliances are the ones that contribute to the baseload demand
for the system. They include:1. Television
2. Fridge
3. Dishwasher
4. Cloth washer
5. Cloth dryer
6. Computer, printer and other office appliances
7. Lighting both internal and external
8. Water heaters
9. Electric cooker
10. Microwave oven and other kitchen appliances
The peak load appliances include
1. Air conditioners
2. Electric resistance heaters.
24
Therefore , its appropriate to state that the generator operating sequence will closely
follow the approximation below:- Most generators come with their own control module that has
both measuring and controlling abilities. Such as auto starting and stopping, voltage, current and
power measurement. These devices are directly mounted on a panel.
Most industry based generator modules are deepsea electronics, aksa, cartepillar, Volvo,
Mitsubishi, etc
Therefore the control program of the PLC has to monitor load and make a logic decision
to either start or stop a given generator.
Operating sequences
1. Manual starting of the generators then transfer control to PLC
2. Initiate timing in the PLC to allow the voltage to stabilize
3. Release the breaker to connect the load
3.1.1 Sequence one
1. Monitor power on the load bus
2. Establish the condition to start the next generator
3. Close contactor
Initially power will be zero therefore generator one will require a manual/ automatic start by the
PLC.
3.1.2 Sequence two
1. Compare the current or by using an internal threshold relay to monitor if the
power is above or below a certain threshold.
2. Start generator two and switch of one after a specified time
3. Close contactor
3.1.3 Sequence three
1. Compare the power at the bus
2. Make a decision to start generator one for them to operate in parallel
3. After a specified time period (2 min),close contactor for generator one
25
3.1.4 Synchronization
As engine-generator_1 set achieve 90 percent of the nominal voltage and frequency, their
respective synchronizing monitors will control the voltage and frequency of these oncoming
units to produce synchronism with the bus. Once the oncoming unit is matched in voltage,
frequency, and the phase angle with the bus, its synchronizer will initiate paralleling. Upon
connection to the bus, the governor will cause the engine-generator set to share the connected
load with the other on-line sets.
3.1.5 Sequence four
1. Determine if the power is decreasing or increasing or decreasing to sound an
alarm.
2. If decreasing then open contactor two and stop generator two
We have established the necessary conditions to formulate a working program.
The input is an analogue signal that will be converted to a digital signal of the PLC.
The outputs are the following:
1. Start and stop relays of the generators. Which are basically DC with either 12 or
24 volts requirement.
Generator starting
Two options are available:
1. Manual and auto start
Manual if human intervention is required and auto for complete automation of generator starting
For the project we will assume that it is a commercial or industrial facility and the generators
will operate at different hours and closely follow the load changes so as to properly meet the load
requirements.
Auto starting of the generators will be done by the PLC by sending a DC voltage to the starter
solenoid for a specified time. To stop the generators, a DC voltage is sent to the fuel solenoid
hence effectively cutting the fuel supply to the engine and, stopping the generator.
since, the project involves several steps, planning and design, the following process was adopted
as it is a standard in many automation design project.
26
generator stopping
A given generator is stopped if it is not required or if there is an emergency condition.
The PLC can do this by activating a relay through one of its output to the fuel relay of the
generator and efficiently stop the generator by cutting of the fuel supply.
27
4 Chapter 4: METHODOLOGY
INTRODUCTION
The PLC is programmed by following a specific procedure as outlined below:
Divide the process into tasks
Describe individual areas
Define safety requirements
Describe required operator display and control
Create configuration diagrams of the program control
It is obvious by know that in order to successfully do the project, the above steps have to
be carefully followed as :
a) Tasks
I. Analogue data acquisition and conversion
II. Manipulation of the data by the user program
III. Close monitoring of the operation of the two generators by carefully keeping track
of the load.
b) Individual areas
I. The analogue data is changed from real to integer
II. A multiplication function then calculates the apparent power
III. The power is then used in a comparator block with a reference value to detect the
load changes
IV. Then OR gates are used to switch on or off a given coil requiring two operating
conditions
V. An alarm section to sound continuously if the generators are overloaded.
c) Safety requirements
Safety standard should be observed in order to protect the electrical equipment as well as
the personal operating on the equipment.
28
There the first line of defense is to monitor the load current so that it does not exceed a
certain threshold value and it it does that generator of a much bigger rating should be
automatically switched on so that the latter one is not overloaded.
d) Generator protection
The generator just like any other electrical equipment should be protected. ANSI
stipulates the following;1. Differential protection (87G)
2. Overvoltage(59G)
3. Under voltage(27G)
4. Over current(51G)
5. Ground current(51N)
6. Loss of excitation(40G)
7. Reverse power(67G)
8. Winding temperature
e) Operator display
Proper current and power values are displayed through the Human Machine Interface, a
separate module provided by the PLC.
Visual aids for the operator can possibly be a lamp to show which generator is on and
which is off connected to an output pin of the PLC. We can have four lamps that are colored
differently, i.e.
I.
II.
Two red lamps for off load condition
Two green lamps for the on condition.
The lamps are labeled accordingly, that is GEN-1 ON ,GEN-2 ON, GEN-1 OFF,GEN-2 OFF.
f) Configuration diagrams
This diagrams show the sequence followed in the user program execution and control
methods employed. We will rely more on the comparator blocks as they function to switch on a
generator if the threshold value is exceeded.
29
4.1) Design flow chart
The chart indicates the interconnection of various units that make up the PLC, the PLC needs to
be supplied by DC power, the circuit breakers provide protection . the sensor panel provides
input signals to the PLC while the load panel indicates the power being consumed.
Fig 2. 11
PERSONAL COMPUTER
INERFACE UNIT
INPUT
MODULE
CPU
OUTPUT
MODULE
SENSOR
PANEL
Power circuit breaker
24V dc power supply
for the PLC
LOAD
PANEL
24V dc power supply for
the lamp
Main power supply
30
4.1.1
Complete control system block diagram
PLC
Setpoint
ADC
DAC
ACTUATOR
PROCESS
MEASUREMENT
Fig 2. 12 showing how the various components are connected
From above block diagram, it is clear that to be able to control the operation of the two
generators; we need to have a feedback signal from the bus that is fed into the plc for processing
31
5 Chapter 5: Design
As mentioned two generator will be controlled using a Siemens PLC. The programming
language is Ladder logic .
Blocks used in the programming
1.
2.
3.
4.
5.
6.
Timers
Comparators
OR gates
Contactors
Output coils
Tags
5.1.1 Timers
A timer is basically a device that will do a certain operation after a specified time has
elapsed.
At this point, they will be used an output after a time of 2 seconds and 120 seconds This
times are appropriate as it will allow systems/equipments connected to the power system to
continue having power.
Four timers are involved and they are as follows; three of 2 seconds and one of 120
seconds and they will be as follows.
1. Timer (T1) is a 2 second timer and allows the generator_1 starter 2 seconds to
crank the generator and after 2 seconds, it cuts battery voltage to the starter.
2. Timer (T2), a 2 second timer and allows generator_2 starter to crank generator_2
and stop generator_1
3. Timer (T3) a 2 minute timer and has three functions, it starts generator_1,activates
the synchronizer and at the same time allow some time for voltage stabilization.
4. Timer (T4) a 2 second timer that stops generator_2 and allows generator_1 to
continue running.
5.1.2 Comparators
Four comparators are used for the four sequences that will govern the operations of the
generators.
1. Less than(<) 400KVA, at this point, the power consumed is entirely provided by
generator_1 as it is the smaller set.and at this point generator_2 is off. This
comparator ,therefore, checks when the threshold rating of generator_1 is not
exceeded and if it does, it activates the starter of generator_2 and hence cranks the
generator.
32
2. Comparator two(>400KVA) this comparator ensures that generator_2 is started
and running since generator_1 will be offline. Generator two has the rating of
600KVA and hence can handle the load.
3. Comparator three(>600KVA) this comparator ensures that generator_1 is started
and connected to the system bus as if the load is greater than what generator_2
can provide, then generator_1 has to be started and synchronized to the system
bus to supply the extra load.
4. Comparator four(>1MVA) this comparator has the function of starting an alarm
and stopping the two generators to avoid damage to them.
5.1.3 OR gates.
These gates are used to activate an output coil given either of the conditions is fulfilled.
For instance when starting and already stopped generator, we have two conditions as stated.
Timer (T1and T3) are connected in an OR gate to start generator_1 in the first and the
third sequence.
Timer (T2 and T4) are connected in an OR gate to stop generator_1 in the second and
fourth sequences.
5.1.4 Contactors
This are electromechanical switches that are used to control how the generator supply is
connected to the load bus bars.
They are four pole and two in number for the two generators.
5.1.5 Output coils
These are the output points that are connected to the field equipments. On the PLC we
have eleven output coils, they are
Cranking_gen_A
Cranking_gen_B
Alarm
Stop_gen1
Stop_gen2
contactorA
conatctorB
Red lamp_A
Red lamp_B
Green lamp_A
Green lamp_B
Q 0.0
Q 0.1
Q 0.2
Q 0.3
Q 0.4
Q 0.5
Q 0.6
Q 0.7
Q 0.8
Q 0.9
Q 1.0
33
5.1.6 Typical building power consumption and loading
Individual facility
Demand factor
Load factor
Communication building
Telephone exchange center
Academic institution
Cold storage, warehouse
Hospital
Single family housing
Apartments
60-65
55-70
40-60
70-75
38-42
60-70
35-40
70-75
20-25
22-26
20-25
45-50
10-15
38-42
As per now the total generating capacity is 1 MA , with the power factor of 0.9, the toal power
generated is 900KW.
Now assuming that the building is a two storey with the following businesses:1.
2.
3.
4.
An ex-ray facility
Welding services
Consulting firm
An academic institution
general
Watts/SF
Connected
load
Specific load
factor factor
Maximum
demand
load (line 2 x
line 3)
Annual
operating
(1-shift)
usage
Annual usage
(megawatt
hrs)(line 4
x line 5)
Demand
factor –
lighting
Air condition
Total
1.0
250KW
Miscellaneou
s fractional
and small
appliances
1.0
200KW
2.7
150KW
4.5
250KW
9.2
850KW
40%
30%
75%
80%
80KW
100KW
200KW
300KW
1200hrs
1500hrs
2200hrs
1600hrs
36
15
440
504
680KW
965
60%
34
Formula =
line4/line 2
Load factor =
line
6/(line 4 x
8760 hrs)
20%
The reserve capacity as per the above analysis is 900KW – 850KW=50KW, in terms of KVA,
we have 50KW/0.9=55.56KVA.
The generator supply the above loads, and we there for have a maximum overload capacity of
5% of 900KW, if the load is above this , load shedding is initiated by disconnecting the loads
depending on the level of priority.
35
5.1.7 Project program in ladder logic.
fig 5. 1FC 105: ADC element
fig 5. 2Multiplier: to find the power at the bus
fig 5. 3comparator set 1
36
fig 5. 4: comparator set_2
fig 5. 5 gen B starting
37
fig 5. 6Gen A starting
fig 5. 7 alarm
38
5.1.8 interfacing with a real PLC
At this point, the programming is confirmed and verified to be working , therefore, it has
to be loaded to the PLC and the PLC will then be used to control the field devices. We require an
interfacing module to enable the Program to be loaded.
There are several modules used as mentioned below:
First we must define the correct interface in the target settings:
a) Target: RS232 The PC is connected to the PLC via a serial MPI adapter or a USB MPI
adapter (with a virtual COM-port)
b) Target: MHJ-Netlink The PC is connected to the PLC via the MHJ Netlink adapter,
Netlink-Lite or IBH-link.
c) Target TCP/IP Direct The PC is connected to the PLC are connected via a standard
Ethernet patch cable.
d) Target: MHJ-Netlink TS The PC is connected to the PLC via the MHJ-Netlink adapter,
Netlink-Lite or IBH-Link.
(Use this setting to establish the connection via the Internet.)
e) Target: NETLink-PRO TCP/IP The PC is connected to the PLC via the
Netlink-PRO or the NETLink-Pro Compact adapter.
f) Target: SIMATIC-NET The PC is connected to the PLC via the Simatic ®
Net-driver. With this setting you select the interface by means of the PG/PC interface
dialog of the Simatic ® manager or the Teleservice software V6.
5.1.9 5.2 Control system algorithm:
1) Scan all inputs and update memory
2) Start generator one
3) Compare new values with the old ones
4) Check to see if new ones are greater than stored
5) Start gen2 and switch of gen1
6) Repeat step 1, 3 and 4
7) If greater, start gen1
8) Repeat step 1 and 3
9) Check to see if new values are falling
10) Stop gen2
11) Return to 1
39
START
SCAN ALL INPUTS AND UPDATE
MEMORY
START
GEN-1
IS
INPUT>
GEN-1?
KEEP GEN-1
ON
START
GEN-2
IS
INPUT>
GEN-2?
KEEP GEN-2
ON
START GEN-1
IS INPUT
<GEN1 &
GEN-2
STOP GEN-2
GEN-1 ON
40
Fig 2. 13 Control system flow diagram
RESULTS AND SIMULATION:
Data to be collected will be in the following format:
DAY
GENERATOR-1
OFF
SWITCHING ON
MONDAY
TUESDAY
WEDNESDAY
THURSDAY
FRIDAY
GENERATOR-2
ON
OFF
BOTH
ON
OFF
The table shows the number of times each generator will be on or off and from that we
can be able to determine the baseload supply and the baseload demand. For instances if
Generator-1 is on for 5 hours, we can calculate the power consumed within that time similarly
for generator-2.
The switching row indicates the transition times for a whole week.
THE FOLLOWING TABLE INDICATES THE POWER DEMANDED AT
DIFFERENT TIMES OF THE LOAD WITHIN 24HRS AND SHOULD BE USED IN THE
INITIAL STAGES OF THE DESIGN
Time
Power demanded
Generator on
6AM to 8 AM
8AM to 10AM
10AM to 12 NOON
12 NOON to 1400HRS
1400HRS to 1600HRS
1600HRS to 1800HRS
2000HRS to 2200HRS
0000HRS to 2AM
2AM to 4AM
4AM to 6AM
CONCLUSION
The project is interesting in that I am able to learn and actually monitor machines that are
operating at different times. The control system design itself is simple to understand how it
works as its functionality is dependent on an industrial based Programmable controller.
The instrumentation signal used is 0 to 20mA range.
41
RECOMMENDATION
Proper selection of generators and PLC type should be of priority to the designer.
Understanding of the demand should be carefully conducted to enable classification of
the loads i.e. essential and non-essential loads.
Due to global warming and environmental factors, green energy should be utilized in the
design of the building i.e. solar and biogas as alternative sources of energy.
REFERENCES:
[1]; CONTROL SYSTEMS ENGINEERING, 6TH EDITION BY NORMAN S.
NISE,JOHN WILEY & SONS
[2]; SCHAUMS, FEEDBACK AND CONTROL SYSTEMS BY JOSEPH
J.DISTEFANO
[3];ELECTRICAL POWER ENGINEER’S HANDBOOK,SECOND EDITION,BY D.F
WARNE
[4]; PROGLERAMMAGLE CONTROLLERS,THEORY AND
IMPLEMENTATION,SECOND EDITION BY L.A BRYAN AND E.A BRYAN
[5]; NEWNESS PROGRAMMABLE LOGIC CONTROLLERS FIFTH EDITION BY
W.BOLTON
42