Roofings Report

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MAKERERE UNIVERSITY

FACULTY OF TECHNOLOGY

DEPARTMENT OF ELECTRICAL ENGINEERING

INDUSTRIAL TRAINING REPORT

BY

NSUBUGA MANSEN

REG. NO.: 08/U/3080/PSA

COURSE: Bsc. ELECTRICAL ENGINEERING

TRAINING FIRM: ROOFINGS LIMITED

02/06/2010 - 10/07/2010

SUPERVISORS:

MR.PATRICK MUGISHA

DEPARTMENT OF ELECTRICAL ENGINEERING

MAKERERE UNIVERSITY

Sign«««««««««««««.. Date«««««««««««««..

MR. MATOVU AFZARI

SENOIR MAINTENANCE MANAGER

ROOFINGS LIMITED

Sign«««««««««««««.. Date«««««««««««««...



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Acknowledgement First and foremost, I would like to thank the University for the Provision of the program of internship, this is an important program in the development of an effective engineer. My

gratitude also extends to Mr. Patrick Mugisha my supervisor for his continued guidance andwisdom that he has generously offered to me.

Secondly, my gratitude goes to Roofings limited for enrolling me for training in their company,it has been through this opportunity that I have discovered my self as an engineer in power. I alsoacknowledge the guidance offered to me during my training officer Engineer Matovu Afzal.

Lastly, I would like to thank my parents for continued support both financially and emotional. Ican¶t express how much grateful I am to them.



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DedicationThis work is dedicated to all the people I have worked with, those who have helped develop my practical skills in one way or the other and to my caring parents.



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PrefaceChapter one discusses two items. The first one being the program of industrial training asarranged by the university, and the objectives of industrial training.

Secondly, chapter one discusses the profile of Roofings Company in which the reader isintroduced to the management structure of Roofings. It also discusses the various raw materialsused in the production of their products. And finally, the machinery used the production of various products.

Chapter two Talks about various installation activities we executed plus the relevant theory behind the work done. The work discussed ranges from the installation work in the substation tothe wiring of the new production bay. Among the theory discussed are the substationcomponents such transformers etc. Chapter two goes ahead to discuss the programmable logiccontrollers in details.

Chapter three goes into the maintenance field by first discussing the theory about motors, discussthe various tools in troubleshooting and maintenance of motors. It goes ahead to discuss all the possible faults in motors and the recommended procedures for troubleshooting the motors.

Chapter four discusses the acknowledgements to the training to the various respects. It further discusses the challenges I experienced during my training, the potential risks and hazards Iencountered and the possible measures taken by the company to cub and reduce on thesehazards. The chapter finally ends with a conclusion and my personal opinion about the training.



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Table of Contents

Contents

Acknowledgement .............................. .......................... .............................. ............................. ................. i

Dedication ............................................................................................................................................... ii

Preface ................................................................................................................................................... iii

Table of Contents ................................................................................................................................... iv

List of Figures ........................................................................................................................................ vii

List of Tables ......................................................................................................................................... viii

CHAPTER ONE: ................................ ......................... ................................ ............................ .................... 1

INTRODUCTION ....................................................................................................................................... 1

1.1 INDUSTRIAL TRAINING..................................... ................................ ...................... ....................... 1

1.2 COMPANY PROFILE........................... .......................... ............................ ................................ ...... 2

1.2.1 Company Background ......................... ................................ ...................... ............................. 2

1.2.2 Production Sections and Machinery ............................. .............................. ........................... 4

CHAPTER 2: ELECTRICAL INSTALLATIONS ................................................................................................. 8

2.1 INSTALLATION ASSEMBLY BLOCK DIAGRAM ............................ ................................ ..................... 8

2.2 DIAGRAM SHOWING THE ONE LINE DIAGRAM OF THE INSTALLED SUBSTATION ........................... 9

2.3 THE SUBSTATION ............................ ........................ ................................ ...................... ............ 10

2.3.1 Overhead Bus Bars.................... ........................... .............................. ............................. ..... 10

2.3.2 Voltage Transformer ............................ ................................ ...................... .......................... 10

2.3.3 Protective devices........................................... ................................ ...................... ............... 11

2.3.4 Power Transformers ........................... ................................ ....................... .......................... 12

2.3.5 Earthing of the Substation ........................ ................................ ...................... ..................... 14

2.3.6 Practical Work Done ............................ ................................ ...................... .......................... 14

2.4. THE LV MAIN SWITCH BOARD ........................ ................................ ...................... ...................... 19

2.4.1 Purpose of the Main Switch Board ........................ ................................ ....................... ...... 19

2.4.2 Components of the Main Switch Board ............................ ............................. ...................... 19

2.4.3 Practical Work Done ............................ ................................ ...................... .......................... 22

2.5 THE DISTRIBUTION CABINET ............................ ................................ ...................... ..................... 24

2.5.1 Purpose of the distribution cabinet .......................... ................................ ........................... . 24



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2.5.2 Components of the distribution cabinet ............................. .......................... ........................ 25

2.6 WIRING OF THE PRODUCTION BAY ........................... ................................ ...................... ............ 27

2.6.1 Practical work done ........................ ................................ ...................... ............................... 28

2.7 MOTOR SPECIFICATION AND CONNECTION ............................. ................................ ................... 30

2.7.1 Water Circulation Unit ......................... ................................ ...................... .......................... 30

2.7.2 Entry Coil Car ............................ ............................ ....................... ............................... ......... 30

2.7.2 Slitter Motor ............................. ............................ ....................... ............................... ......... 30

2.7.4 Exit Coil Car ............................ ......................... ........................... ................................ ......... 31

2.7.5 Entry Hydraulic Power Unit ............................ ................................ ...................... ................ 31

2.7.6 Exit Hydraulic Power Unit ......................... ................................ ...................... ..................... 32

2.8.0 POWER SUPPLY IN THE MAIN PRODUCTION BAY ............................ .......................... ............... 33

2.8.1 The one line diagram of power distribution in the production bay ............................. .......... 33

2.8.2 Generator .............................. .......................... ............................ ............................... ......... 35

CHAPTER 3: ELECTRICAL MAINTENANCE ......................... ................................ ...................... ................. 37

3.1 MOTORS ...................................................................................................................................... 37

3.1.1 Types of Motors .................................................................................................................... 37

3.1.2 Methods of Starting Electric Motors ............................. ............................. .......................... 41

3.1.3 Factors Considered when selecting a starter ................................ ...................... .................. 44

3.1.4 Tools Used In Troubleshooting Motors ................................................... ...................... ....... 45

3.1.5 Procedure for Trouble Shooting Single Phase Motors ............................................ .............. 47

3.1.6 Trouble Shooting guide for Single phase Motors .............................. ....................... ............. 49

3.1.7 Procedure for Troubleshooting Three-Phase Motors.................................. ....................... ... 54

3.1.8 Troubleshooting Guide for Three-Phase Motors ................................................. ................. 55

3.2 PROGRAMMABLE LOGIC CONTROLLER (PLC) ......................... ................................ ...................... .. 58

3.2.1 Uses of PLCs .............................. ................................ ...................... ................................ .... 58

3.2.2 Ladder Logic .............................. ................................ ...................... ................................ .... 58

3.2.2 Components of PLC Hardware .......................... ................................ ...................... ............ 59

3.2.3 Principle of Operation of PLCs ........................ ................................ ...................... ................ 59

CHAPTER 4:............................................................................................................................................ 61

CONCLUSION AND RECOMMENDATIONS ....................... ................................ ....................... ................. 61

4.1 CONCLUSION ................................ .......................... ........................... ................................ ......... 61

4.1.1 Achievements ........................... ........................... ........................... ................................ ......... 61



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4.1.2 Challenges Faced During Training ........................... ................................ ...................... ........... 61

4.1.3 Danger and health hazards ........................... ................................ ...................... ..................... 62

4.1.4 Safety precautions ......................... ................................ ...................... ................................ .... 62

4.2 RECOMMENDATIONS ............................ .......................... .......................... ............................ ..... 62



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List of Figures

Figure 1.1 Organisation structure of company««««««««««««3

Figure 1.2 Organisation structure of the maintenance department««««.3

Figure 2.1: Installation assembly block diagram«««««««««««.8

Figure 2.2: One line diagram of bay 11««««««««««««««...9

Figure 2.3: Picture of the voltage transformer««««««««««««.11

Figure 2.4: Picture of the drop out fuses««««««««««««««.12

Figure 2.5: Transformers installed at the substation«««««««««...13

Figure 2.6: Picture of the cables laid«««««««««««««««...16

Figure 2.7: Front part the main switch board««««««««««««..20

Figure 2.8: A picture of the current transformers«««««««««««21Figure 2.9: Showing the bus bars«««««««««««««««««22

Figure 2.1.0: A picture of the distribution cabinet««««««««««..24

Figure 2.1.1: A picture of the cable markers««««««««««««...29

Figure 2.1.2: One line diagram of the old production bay«««««««.34

Figure 2.1.3: A picture of the back up generator«««««««««««36

Figure 3.1: Star-Delta motor starting circuit««««««««««««...43

Figure 3.2: PLC Hardware«««««««««««««««««««..60



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List of Tables

Table 3.1: Trouble shooting guide for single phase motors if motor fails to start««««««.49

Table 3.2: Trouble shooting for single phase motors if protective device re-trips after

service............................................................................................................................................50

Table 3.3: Trouble shooting guide for single phase motors incase motor produces an electric

shock«««««««««««««««««««««««««««««««««««..51

Table 3.4: Trouble shooting guide for single phase motors incase motor over heats«««««52

Table 3.5: Trouble shooting guide for single phase motors incase motor produces excess

noise...............................................................................................................................................53

Table 3.6: Trouble shooting guide for 3-phase motors incase motor fails to start«««««....55

Table 3.7: Trouble shooting guide for 3-phase motors incase protective device re-trips after service«««««««««««««««««««««««««««««««««........56

Table 3.8: Trouble shooting guide for 3-phase motors in case the motor overheats«««««.57



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1

CHAPTER ONE:

INTRODUCTION

1.1 INDUSTRIAL TR AININGIndustrial training is a program organised and designed by the university. It is key and importantrequirement for one to graduate, and therefore has to be taken seriously.Industrial training has a number of objectives aimed at benefitting the student, training firm andthe university.

Below are some of the objectives of industrial training;

y To see the application of scientific principles learnt in engineering school in the field.y To acquire practical knowledge relating to the design, use and maintenance of electrical

equipmenty To get exposed to machinery and new technological advancementsy To get exposed to the working environment, the dangers, hazards and precautions/safety

measures taken at the work place.y To get hands on experience and learn how to work with the different tools used in the

field.y To achieve interpersonal relationships so as to create a network of professional contacts

that could help the student at a further date to access opportunities in the field.y To build proactive public relations and corporate responsibility.y To allow students to develop the spirit of teamwork, and Solidarity in order to satisfy a

certain cause.

y To enable the student to acquire basic skills and techniques of the Practical work performed in the field by the experts. Through co-creating with those alreadyexperienced, we are able to develop our practical capabilities as well.

y To acquire developmental ideas like starting up small scale firms/ industries and are ableto manage them with an insight of self employment.

y To make a professional development contribution to the upcoming professionals by providing both hands on skills and theoretical knowledge of the different engineeringaspects.

y To help in talent management thus nurturing young, dynamic individuals to propel intheir career aspiration thus a professional development



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1.2 COMP ANY PROFILE

1.2.1 Company Background

Roofings Limited is located on Plot 126 Lubowa Estate; Entebbe Road 6km from Kampala city

centre on a 39 acre expanse of land. Roofings Limited is among the leading manufacturers of quality steel products in Uganda. The company was established in 1994 under the license of theUganda Investment Authority, it commenced operation in December, 1995.

The factory produces a wide range of steel products for the building industry. These comprise of roofing sheets, expanded metal, barbed wire, chain link, wire nails, welded mesh, binding wire,hollow tubings and open profiles.

The factory imports its raw materials from reputed steel mills in Japan and South Africa coiledwire and coiled steel sheets and using cold forming machinery turns these raw materials intofinished products. It has an installed capacity of 185410.8 MT per annum. The factory is batch-

type operation, where different machines are run depending on the supply orders /marketdemand.



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The company structure and hierarchy

Figure 1.1 Organisation structure of company

The maintenance structure and hierarchy

Figure 1.2 Organisation structure of the maintenance department

General Manager

Product Manager Materials

manager

Administration

Managers

Commercial

Manager

Electricians Mechanics



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1.2.2 Production Sections and Machinery

1.2.2.1 Galvanised Wires Section

a) Chain link

Two machines from Bergandi a manufacturer from USA, automated with Allen Bradley PLC,with greater efficiency and output have enabled the decommissioning of one old machine (chainlink 1) and reduced usage of another with low efficiency machine (chainlink2).

b) Barbed wire

Five new barbed wire machines 3.73kW have also been installed. These new machines fromBergandi (USA) consume far less energy for higher output which enables us to utilise less of theold inefficient machines (20kW machines) with high rate of failure and high power consumption.

c) Razor Wire

Bergandi was also the supplier for the razor wire machine, the only machine of its kind inUganda. This machine basically utilizes raw material from the galvanised wires

1.2.2.2 Hot Rolled Coils Section

a) Door frame Machines.

In order to enhance customer satisfaction, this fast moving product on open profile is now readilyin stock thanks to the installation of the new door frame forming machine from Long year

machinery (Taiwan). The quality of the product has also been greatly improved and a variety of thicknesses is also possible. Machine changeovers on Open profile 1 have reduced therebyallowing enough time to produce and stock the wide range of products on the same machine.



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b) Cut To Length MS.

Two Cut To Length machines have been installed with Cut to Length MS 1(one) able cut up to2mm thickness.A revamped cut to length machine for thicker mild steel plates Model Marianni CTL 2000x6 has

been installed and has a capacity to cut plates of 6mx2mx6mm which make operations like tank fabrication cheaper, easier and safer due to reduced weld joints.

c) Slitting Line.

A new slitting line from Braner (USA) for coil thickness up to 6mm is to be installed. This line isfully automated with a double rotary slitter head which greatly reduces change over time.

d) Tube Mill.

We have currently installed 2(two) tube mills and a third one is still under installationTube mill 3, to be supplied by Meccanica Adda fer Italy will increase steel tube productioncapacity up to diameters of 8 inches (~200mm) and add a production turnover of up to 4000 tons.

1.2.2.3 Wire drawing section

a) EVG 1This heavy duty welded mesh machine produces and supply the construction industry withinUganda and the Great Lakes Region with high volume BRC A66, A98, A142 in customisedlength and standard length of 30m and 48m. It can produce any welded mesh up to a wirediameter of 12.00mm

b) EVG 2

This newly installed welded mesh machine from Austria is a state of art machine application of

Intelligent Logic Controllers to ensure high production of quality welded mesh with lower power consumption and fewer people manning the whole production line. The machine has anautomated cross wire pay off and does not require an additional cutting machine (Rebar machine) for cross wires. The Intelligent Logic controllers ensure high quality welding andtrimmers give a neat product finish. Mesh of wire diameter of up to 4.00mm can be produced

With EVG 1 and EVG 2, we have maintained a steady and reliable supply of light and heavyduty welded mesh of varying gauges



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c) Nail machines

There was a big market demand for 4´ Wire Nails which was hard to satisfy but with theacquisitions of more two fast and easy-to-set Wire Nails machines from National Wire products(India), we were able to satisfy the 4´ Nails Market Demand. The machines improved our quality

and production of 4´, 3´ and 2.5´ because of it¶s flexibility to produce different sizes at the samehigh efficiency and made our customers boasts of our improved supply reliability of ultimatequality wire nails. We have Nail machines from different suppliers like Vitari, National, Moroni,Ajit and Tanisaka, giving us the product benefit of all the suppliers.

d) Wire Drawing Machines.

We have embarked on efficiency improvement of these machines which has seen the old and lessefficient slip ring motors being replaced with AC Induction motors which are more efficient inenergy usage with less maintenance cost. Also improvement in production by changing coupling

to belt drives which are at lower costs has increased machine availability.

e) Electric Furnace

The increased in demand saw installation of the second furnace, which all together enhancedcustomer satisfaction. The decision to replace the control panel of the first furnace, saved a lot of energy because it follows the annealing cycle in a manner that optimizes energy saving. Thefurnace being programmable, gives flexibility that the heating cycle can be synchronized onlyduring off peak hours to minimise energy consumption.

f) Over Head Moving Cranes

We have installed 1(one) 12T crane, 11(eleven) 10T cranes, and 9(nine) 5T cranes from twomain suppliers i.e. Stalh, and Demag.Currently we have decided to procure all the crane fromdemag because of the efficiency and lower maintenance cost

1.2.2.3 Roofings Section

a) Cut To Length Machines

These are high precision, high speed machines from Yodokawa Japan for cutting of thingalvanized and pre-painted roofing iron sheets from thicknesses of about 0.14mm to 0.60mm.(Coded CTL I, II and III) with capacities of up to 3500tons



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They are coupled with forming units of various profiles (ordinary corrugation, IT4 and IT5) tosuit customer taste and requirements.

The company is also underway to install an additional cut to length machine (CTL 4) with wider cover width and stronger profile to meet the ever changing customer demands and aspirations.

b) Expanded Metal machines

These expanded a pre-cut sheet of length 1.83m to obtain up to 12pcs of expanded mesh of 2x6ft from a 0.43mm galv. Sheet thickness. Coded EM1 and EM2 from Osaka Japan.We also have mild steel expanded metal machine (coded EM3) installed in 2008 which expandsMS sheets of up to 3mm thickness with two pitch sizes of ½´ x 1´ and 1´x2´with mesh size4x8ft.

c) Tile machinesWe have installed two tile sheet machine i.e. Eco tile machines that makes iron sheet that look like the traditional clay tiles and super tile machine that make tile sheets of superior quality &latest profile



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CHAPTER 2: ELECTRICAL INST ALL ATIONS

2.1 INST ALL ATION ASSEMBLY BLOCK DIAGR AM

Figure 2.1 Installation assembly block diagram

Main switch board

Distribution Cabinet

Production Unit

Substation



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2.2 DIAGR AM SHOWING THE ONE LINE DIAGR AM OF

THE INST ALLED SUBST ATION

UMEME

metering unit

33KV Bus

Drop out fuse Drop out fuse25A, 33KV

25A, 33KV

T1 T2

1200A 1200A

800A

Figure 2.2 One line diagram of bay 11

S p a r e s

A uxi l i a r y

T u b e mi l l

S l i t t i n gl i n e

HM w e l d e r

C om pr e s s or

A C m o t or

C o ol i n g

A uxi l i a r y

H y d r a ul i c



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2.3 THE SUBST ATION

The substation is made up of;y Two transformers

y Over head bus barsy Voltage transformer y Protective device

2.3.1 Overhead Bus Bars

These provide the substation with the power from the distribution client, for this case UMEME.The overhead bus bars provide 33KV. The overhead bus bars are made of stranded aluminumconductor. Aluminum and not copper is used because the transmission current is low, since thevoltage is high.

2.3.2 Voltage Transformer

Voltage transformers also known as potential transformers are used for measuring voltage and current inelectrical power systems, and for power system protection and control.Where a voltage or current is too large to be conveniently used by an instrument, it can be scaled down toa standardized, low value.Voltage transformers isolate measurement, protection and control circuitry from the high currents or

voltages present on the circuits being measured or controlled.

Potential transformers (PTs) are designed to have an accurately known transformation ratio in both magnitude and phase, over a range of measuring circuit impedances.A voltage transformer is intended to present a negligible load to the supply being measured. Thelow secondary voltage allows protective relay equipment and measuring instruments to beoperated at a lower voltage.At the substation, the voltage transformer is connected to a meter which is mounted on its pole.The meter is used by UMEME to bill the roofing company.



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Figure 2.3 Picture of the voltage transformer

2.3.3 Protective devices

All electrical circuits must be protected against over current therefore a protective device has to be installed in order to isolate the fault from the supply so as to protect the equipment andappliances from being damaged. Damage can be cased by voltage sags, short circuits, highvoltages etc. Protection of the substation and its components is provided by the drop out fuses.

Drop out fuse (d.o.f) are complete with fuse carrier of fiber glass tube with both end heavilytinned non ferrous metal parts.The brush type phosphor bronze contacts provide positive high pressure multilane connectionand wiping and cleaning action on closing.The pressure exerted by the contacts initiates the opening movement of the fuse carrier copper &copper alloys high pressure heavily tinned metal contacts for fix top contacts assembly and bottom contact assembly. The drop out fuse units are manufactured up to and including 33KVsystem.The fuses are located just before the input to the primary side of the transformer.

The drop out fuses that are installed at the substation are rated 12A.



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Figure 2.4 Picture of the drop out fuses

2.3.4 Power Transformers

The major purpose of power transformers is to step down high voltages to low voltages or stepup low voltages to high voltages.The substation consists of two similar medium voltage transformers. The transformers weremanufactured by Pauwels trafo international, in Ireland.The transformers have the following specifications;

y Step down transformer, which is 33KV to 415V.y Power rating is 630KVA and frequency 50Hz.

Transformer connection

There are two types of transformer connections, namely;y Series connectiony Parallel connection

The two transformers installed at the substation were connected in parallel. For any two or moretransformers to be connected in parallel, the following conditions must be fulfilled;

y The transformers should have the same KVA.y The transformers should have the same turns ratio.y The transformers should have the same impedances



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y The transformers should have the same voltage ratio.

Connecting transformers in parallel have a number of advantages some of which include,;

y It enables more power to be drawn and delivered to the load.y It prevents transformer overload incase one transformer is used.y In case of failure by one of the transformer, repairs can be done without disrupting power

supply, since the other transformer will still be running.

Transformer Terminations

The terminations were made to the transformers in such away that the primary was connected in

delta and the secondary connected in star.

This form of connection has a number of advantages, these include;

y It makes it possible for a neutral wire to be picked from the transformer secondary due tothe star connection in the secondary.

y It ensures a high current to be drawn from the transformer since the star connection inthe secondary ensures low voltages and high current.

Figure 2.5 Transformers installed at the substation



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Cable cutter Protective hand gloves

Procedure

The process of laying cables involved the following processes;

y Uncoiling a line of the cable, driving it a long the tray until it reaches the entrance of the bay to which it is to supply the power.

y We then left some length that will enter the production bay. We then cut the cable on thecoil side using cable cuter such that the cut piece can both reach the transformer terminalsand also enter the production bay.

y We then marked the cut cable using masking tape in various colors from either ends todistinguish it from the other pieces that had to follow. The procedures above were

repeated to make it a total of 14 cables laid connected the substation to the production bay.



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Figure 2.6 Picture of the cables laid.



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Terminating cables

Tools

Cable lags Crimping tool (hydraulic) Masking tape in colors red, yellow, and blue Open spanners Hole bore Cable stripper Protective hand gloves

Procedure

The activity of terminating the cables on the transformers included the following processes;

y We opened the transformer terminal box using open spanners.y We bored seven holes in the steel plate that covers the termination point to allow the

seven cables to be terminated to the transformer.y With one of the cables, we stripped and exposed some part off its tip using««..

With the help of the crimping tool, we then connected a cable lag to the exposed end,with the purpose of helping us terminate the cable to the transformer by just screwing it

on the terminal contact.y We then marked the cable using masking tape which is in the colors red, yellow, blue and

black.y The above procedures were repeated other six cables and then seven cables for the other

transformer. The markings on the cables were symbolic of the phases, that is, red, yellowand blue for the three phases and black for the neutral cable.

y Finally the steel plate cover to the terminal point was replaced.



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2.4. THE LV MAIN SWITCH BOARD

2.4.1 Purpose of the Main Switch Board

The main purposes of the main switch board include;

y It provides a means of isolating the high voltage from the transformer from the industrialappliances hence providing protection from power surges.

y The main switch board provides a means of measuring the current and voltage from thesubstation through the current transformers installed in them.

y The main switch boards through the buccholz relay helps protect the installation from theoverheating cased by the power supplied by the substation transformers.

The structure of the main switch board, the various components, the purpose of the variouscomponents and their mode of operation, how they are handled during the installation.

2.4.2 Components of the Main Switch Board

Components include;

y The buccholz relay.y The current transformers.y The transformer isolating breakers.y The bus bars.

The main switch board used in the installation had a capacity to hold power a maximum of threetransformers. The main switch board was designed to supply power to a number of loads,namely;

y Slitting line feeder y Tube mill feeder y Compressor feeder y Welder feeder y Cooling tower feeder y Cooling tower feeder

Other specifications of the main switch board include;



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Rated operating voltage 433V

Rated isolation voltage 690V

Short time current for one second 70KA

Bus bar current 2500A

Figure 2.7: Front part the main switch board

a) The current transformers

These are installed on the bus bars inside the main switch board. They have specific currentratios, in which they step down current and transfer it to a digital meter from which readings of current and voltage are taken. These values reflect the value of current and voltage supplied bythe substation transformers.



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Figure 2.8: A picture of the current transformers

b) The bus bars

A bus bar is a strip of thick copper that conducts electricity within a switch board, distribution board or any other electrical apparatus. These act so as to allow the flow of large currentsthrough them. They are bare and supported by insulators.They are also used to distribute current to multiple devices through switch gear.For the main switch board installed, the bus bar current is 2500A

Power from the transformer is connected to the bus bars via a circuit breaker.For this arrangement, power from all the two transformers was delivered onto a common bus bar.This arrangement ensured that the two transformers were connected in parallel.

Reasons for connecting the transformers in parallel include;

y To make available enough power for the load that is to be supplied by the main switch board.

y Reliability, that is, incase of breakdown in one transformer, the other transformer cancontinue supplying power while the faulty one is isolated and worked on.



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Figure 2.9: Showing the bus bars

c) The transformer isolating breakers

These exist in between the main bus bar and the terminal points for the cables from thetransformers. They are accessed from the front part of the main switch board.They serve the purpose of isolating the main power from the transformer from the machineinstallation hence protecting it from power surges.Three circuit breakers exit after each terminal point of the three transformers.

The circuit breakers are rated 2500A.

2.4.3 Practical Work Done

Termination of power cables from the transformer to the main switch board

Tools;y Cable lagsy Masking tape in colors red, yellow, blue and black y Crimping tool (hydraulic)y Open spannersy Cable stripper



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y Earth thread

Procedure

y First, using an open spanner, we opened the terminal box of the cables at the back of themain switch board.

y Beginning with one of the cables, we exposed a little portion of its end using a cablestripper.

y Using a cable crimping tool, we connected a cable lag to the terminal end of the cable toallow easy termination through screwing.

y We then marked the cable by tying masking tape of a given color to represent the phase.y We terminated the cable on the terminal of the main switch board by screwing, in the

correct order of phase.y The above procedures were repeated for the other cables so that all the cables from both

the transformers are terminated in the main switch board, terminating them in the right positions and observing the color codes for the various phases. That is red, yellow and blue, and black for the neutral cable.y Finally, we concluded our work by connected aluminum armoring of each cable to an

earth thread and then connecting the earth thread to the earth.



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2.5 THE DISTRIBUTION CABINET

From the LV main switch board, the power is delivered to the distribution cabinet.The distribution cabinet serves the general purpose of distributing power to the various machinecomponents such as the motors, hydraulic and water pumps, sensors, solenoid valves and other components.

2.5.1 Purpose of the dist ribution cabinet

The distribution cabinet serves the following purposes;

It separates and develops the control circuit that is used to control the machines.

The distribution cabinet distributes power both control and actual power that is used torun the machine components to the machine components. The distribution cabinet contains protective devices such as the isolator and fuses that

protect the various machine components. The distribution cabinet has a system for automation of the machines installed in it such

as the Programmable Logic Controllers (PLC), motor drives. The distribution cabinet provides a reference point for earthing the machine units which

are connected to it.

Figure 2.1.0: A picture of the distribution cabinet



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2.5.2 Components of the dist ribution cabinet

A distribution cabinet consists of various components to manage and control the power flow,some of these include;

a) An isolator

The disconnectors / isolators are used for electrical isolation of a system / equipment for maintenance.

b) Transformers

These are mainly tap transformers. They have a primary voltage of 415V and taps of 110V and240V.

The main purpose of the tap transformer is to step down voltage from 415V which is the runningvoltage to either 110V or 240V which are control voltages that are fed into the control circuit

c) Contactors

These vary in size, depending on the rating and type of load to which it has to be connected.Contactors are used in control circuits to switch on and off the power flow to the machines, usingsmall control voltages of about 110V or 240V. In this respect, contactors are used in motor startup and automation.

d) Programmable Logic Controllers (PLC)

These form the heart and core of automation of the machine. They are programmed and performthe logic control of the machine. For more information about the PLCs go to page 56.

e) Motor drives

An adjustable speed drive is a device that controls speed, and direction of an AC or DC motor.

There are two types of motor drives namely;

y DC motor drive

The function s of the dc motor drive which must be controllable for practical use is thespeed, the torque delivered, and the direction of rotation. Speed is proportional to



26

armature back e.m.f and inversely proportional to field flux. Direction of rotation issimply a matter of the relative polarities of the armature and field voltages.

y AC motor drive

This is installed to control speed and direction in ac motors. The speed of an AC motor isdetermined for the most part by two factors: The applied frequency and the number of poles.

f) Fuses

These are protective devices that are installed in the distribution cabinet to protect the other components such as the contactors, relays, PLCs etc from damage as a result of high currentflowing due to short circuits and voltage surges.

The fuses installed within the distribution cabinet have different ratings depending on the devicethey are protecting.Other components of the distribution cabinet include; Overload relays Timers Motor drives

Etc.



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2.6 WIRING OF THE PRODUCTION BAY

The process of wiring the production bay involved the build up of two types of circuits lay outs,these include;

a) The power circuit installation

This involves the cable installation which carries the medium voltage necessary for actualrunning of the machine, in terms of running the motors. For industrial case, the voltage of the power circuit layout is 415V.

Cabling

Cables used in this installation have diameters within given ranges including 4.0mm2, 2.5mm2.Since the power circuit cables supply mainly motors, the color coding has to be observed.This means each cable in this power circuit moving from one point to another is a four corecable. The colors are in the colors Red, Yellow, Blue and the neutral wire, which can also beused as the earth wire.The colors Red, Yellow and blue represent the 3 phases. Any excess core is left as a spare coreand made use of in the future.The order of termination of cables is indicated and described by a chart shown in the attached atthe end of the report.

b) The control circuit installation

This is a cable installation which carries the control current and voltage necessary for controllingand automating the machine.This installation connects to various installations such as relays, contactors, timers, sensors,solenoid valves, PLCs, push buttons, inductors, motor drives, etc.The control circuit installation serves the main purpose of controlling and switching the power circuit which actually runs the machines through the various devices such as those listed above.In industries the control voltage is 110V, single phase, and frequency of 50Hz for Uganda.The control voltage is obtained from the power circuit voltage using a tap transformer which is

normally installed inside the distribution cabinet.Cables used in this installation are of diameter 2.5mm2.Further details about the cables used and their termination points are given by the table««««



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2.6.1 Practical work done

a) Passing cables through the trucking¶s

Tools

y Wire draw tapey Side cutter y Protective hand glovesy Protective head gear y Cell tapey Installation Charty Grease

Procedure

y Using the installation charts, we identified the position of the entry and exit of anunderground trouncing.

y Using the installation charts, we further obtained the specifications of the cable that ha sto pass through that given trouncing. Specifications included, The voltage rating of the cable(where it is for control or the power circuit), The sizes of the cable, in terms of cross sectional area and its length.

The points between which the cable should connect.

y We then ordered for right cables from the factory store as indicated by the installationchart.

y So as to pass the cables through the trouncing, we first stripped and exposed a littlelength, tied the exposed cores firmly to the draw wires that were left in the trouncingduring the ground construction to help in passing cables through these truncings.

y We then smeared grease on the cable to enable it run smoothly through the truncing withminimum resistance to the outlet as indicated by the installation chart.

y We finally physically pulled the draw wire from the outlet side of the truncing until the

cable finally emerged.



29

b) Termination of cables

Tools

y Cable stripper

y Screw driversy Installation charty Multimeter y Cable markers

Procedure

y Termination of cables was done with the aid of the installation charts. The installationchart contained information about the two points between which the cables should beconnected, plus actual termination points on the terminal blocks through the numbersattached to the terminal blocks on either sides of termination.

y During the termination, we stripped both ends of the cores of a given cable using cable astripper.

y We marked each core of the cable with its termination code which consists of letters andnumbers, as indicated by the installation chart using cable markers. This we did for proper identification of the cable cores so as termination and maintenance easy.

y Using screw drivers, we terminated the cable cores by screwing them on the respectiveterminal block positions.

NB. During the termination, we made sure that the cable terminations were firm enough to avoidloose connection.

For cables with very many cores, we used the multimeter to single out and identify the coreon both sides of the cable through the continuity test.

Figure 2.1.1: A picture of the cable markers



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2.7 MOTOR SPECIFICATION AND CONNECTION

2.7.1 Water Circulation Unit

Motor Specifications;

y AC induction motor y 3 phase, 50Hzy 2750 RPMy 1.0 (0.75KW) HPy 415V

y 65A

We connected the motor in a delta configuration.

2.7.2 Ent ry Coil Car


y 3 phase, 50 Hzy 1460 RPMy 7.5 HPy 415Vy 12.8A

We connected the motor in delta configuration.

2.7.2 Slitter Motor

Motor Specifications



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y 3 phaseHP RPM AMP VOLTS Hz

150 885 232 365 36

150 1035 205 415 35

150 2550 193 415 86.4

The slitter motor is a variable speed motor. Its speed and direction are controlled by the PLCinstalled in the distribution cabinet. This control of made possible by variation of the frequency producing different operation of the motor as shown in the table above.The motor was connected in the direct on line configuration.

2.7.4Ex

it Coil Car


y 3 phase, 50 Hzy 1460 RPMy 7.5 HPy 415Vy 12.8A

We connected the motor in delta configuration

2.7.5 Ent ry Hydraulic Power Unit


y AC induction motor y 3 phase, 50Hzy 1460 RPM

y 25 HP, 18.5KWy 190/380-415Vy 72.8/36.4-33.8A



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2.7.6 Exit Hydraulic Power Unit


y AC induction motor y 3 phase, 50Hzy 1460 RPMy 25 HP, 18.5KWy 190/380-415Vy 72.8/36.4-33.8A

We connected motor in delta configuration.



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2.8.0 POWER SUPPLY IN THE MAIN PRODUCTION BAY

The main production bay is supplied power by a substation consisting of four transformers. Allthe transformers are rated 33KV/415V.

2.8.1 The one line diagram of power dist ribution in the

production bay



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Figure 2.1.2: One line diagram of the old production bay



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2.8.2 Generator

In case of power failure, the alternative source of power is a generator installed near the oldsubstation.

The specifications of the generator include.

Rated power prime 250KVA, 200KW

Rated voltage 400/230V

Phase 3 phase

Rated frequency 50Hz

Rated current 360.9A

Rated R.P.M 1500

Considerations before starting the generator

The generator installed at has provisions of being installed both manually and automatically.However, very many machines are connected to the substation and only a few of them have to beconnected to the generator. This therefore leaves the technicians with the choice of starting the

generator manually.Below are the steps that have to follow before starting a generator.

y Check the level of fuel in the tank. The level of the fuel should be past the minimum leveland enough to run the generator for the required time.

y Check the level of the water which acts as the coolant. This should however be donewhen the engine of the generator is not hot.

y Check the level of the battery fluid. The level should be lower the minimum level andhigher than the maximum level as indicated on the battery.

y Check the oil level. The level of the oil should not be less than the minimum level andnot higher the maximum level as indicated on the dip stick.



36

Figure 2.1.3: A picture of the back up generator



37

CHAPTER 3: ELECTRICAL MAINTENANCE

3.1 MOTORS

In a motor, electrical power forces the armature to turn, and the moving armature, through amechanical system of belts or gears, turns a mechanical load.

3.1.1 Types of MotorsThere are two types of motors these include;

a) DC. Motor

D.C motors consist of six basic parts; axle, rotor (armature), stator, commutator, field magnet(s),and brushes. In most common DC motors, the external magnetic field is produced by high-strength permanent magnets. The stator is the stationary part of the motor. This includes themotor casing, as well as two or more permanent magnet pole pieces. The rotor (together with theaxle and attached commutator) rotates with respect to the stator. The rotor consists of windings(generally on a core), the windings being electrically connected to the commutator.The commutator thus plays a very important part in the operation of the d.c. motor. Itcauses the current through the loop to reverse at the instant unlike poles are facing each other.This causes a reversal in the polarity of the field; repulsion exists instead of attraction; and theloop continues to rotate.

In order to change the direction of rotation of motor, remember that, to do this, you must reversethe connections of either the armature or the field, but not both.On larger machines, manufacturers usually provide some means of easily reversing the fieldconnections.

Types of DC motors

Series motorsThe series motor has its field connected in series with the armature and with the load, as shown below. The field coil consists of a few turns of heavy wire; and since the entire armature



38

current flows through it, the field strength varies with he armature current. If the loadincreases, the motor slows down and the back- e.m.f. decreases, which allows the current toincrease and so supply the heavier torque needed.The series motor runs very slowly with heavy loads and very rapidly with light loads.

If the load is completely removed, the motor will speed dangerously and fly apart; for thecurrent required is very small and the field very weak, so that the motor cannot turn fastenough to generate the amount of back e.m.f needed to restore balance. Series motors mustnever be run under no-load conditions, and they are therefore seldom used with belt drivesfrom which the load can be removed.

Shunt Motor

In a shunt-connected motor, the field is connected directly across the voltage source, and istherefore independent of variations in load and armature current. So the torque developed varies

directly with the armature current. If the load on the motor increases, the motor slows down,reducing the back-e.m.f. (which depends on the speed as well as on the constant field strength).The reduced back-e.m.f, allows the armature current to increase, thereby furnishing the heavier torque needed to drive the increased load.When a shunt motor is started, the starting current is small, by reason of the added startingresistance; so the starting torque will also be small. Shunt motors are normally used whereconstant speed under varying load is desired, and where it is possible for the motor tostart under light or no-load conditions.

D.C. Motor Starters

i. The Elementary Starter

An elementary starter consists of a resistance with taps on it. This resistance can be progressivelyshorted out by a knife switch whose contacts connect to the taps on the resistor. When the motor is first started, the switch contacts the end of the resistor, so that all of the resistance is in serieswith the armature. As the motor speeds up, the blade is slowly closed-shorting out more andmore of the resistance until, when the switch is completely closed, all of the resistance is shortedout.The disadvantage of the elementary starter is that if the operator forgets to open the startingswitch when the main switch is opened to stop the motor, the armature will have no limitingresistance connected to it when the motor is next re-started.



39

Also, the elementary starter does not protect the motor from excessive speed if a break in thefield circuit occurs.The elementary starter has therefore, no practical application.

ii. Shunt Motor Starters

One type of shunt motor starter has three terminals. When starting the motor, the arm is movedto the first contact, and the entire resistance is placed in series with the armature circuit. Thefield coil is connected in series with an electromagnet across the supply. As the motor builds upspeed and the back e.m.f increases, the arm is moved to each of the contacts in turn, decreasingthe resistance in steps. As the arm moves across the starter, some of the resistance is also inseries with the field and the electromagnet coil.When the arm is all the way to the right, in the "run-position," the armature is directly across the

supply, and the motor is operating at full speed.In the run position, a small piece of iron on the arm is held by the electro-magnet through whosecoil the field current flows. If the supply voltage fails or is switched off, or if the field circuit is broken, the magnet no longer attracts the iron, and a return spring pulls the arm back to the "off" position-thus disconnecting the motor from the supply, and preventing it from being startedwithout any starting resistance when the supply voltage is applied once again.The return spring can also be set to return the arm if the voltage drops by a certainamount. This is called "IOW-voltage" protection.Overload protection is provided by a second electromagnet connected so that the armaturecurrent flows through its coil. It is adjusted so that when the current the armature current flowsthrough its coil. It is adjusted so that when current exceeds a predetermined safe value, a pieceof iron attached to a spring-loaded arm is attracted to the magnet. At the end of this arm is a link which then connects two terminals and shorts-out the coil of the electromagnet holding thestarter arm in the run position. The starter arm is thus released, and disconnects the motor fromthe supply.When it is desired to obtain variable speed-control of the motor by varying the field current,the electromagnet which holds the starter arm in the run position may be connected directlyacross the supply, This type of connection allows variation of field current without alteringthe pull of the electromagnet; but it does not give protection against an open- circuited

field.



40

b) A.C. Motors

A.C. motors can be designed to operate from a single-phase a.c. supply or from a multi-phasea.c. supply. Whether the motor is single-phase or multi-phase, it operates on the same principle.

This principle is that the a.c. applied to the motor generates a rotating magnetic field, and thisrotating magnetic field causes the rotor of the motor to turn.A.C. motors are generally classified into two types.

a) Synchronous Motor

The synchronous motor is so called because its rotor is synchronized with the rotating field setup by the stator. The application of three-phase a.c. to the stator causes a rotating magnetic fieldto be set up around the rotor. But since the rotor is energized with d.c., it will act like a bar magnet.The speed of rotation of the magnetic field depends on the frequency of the three-phase a.c.supply; and since the supply frequency is fixed, synchronous motors are, in practice, single-speed motors. They are used for Loads which require constant speed from no-load rightthrough to the full-load condition.One of the disadvantages of a synchronous motor is that it cannot be started from a standstill byapplying three-phase a.c. to the stator.The instant a.c. is applied to the stator, a high-speed rotating field appears.In other words, a synchronous motor in its pure form has no starting torque. It is usually started,

therefore, with the help of a small induction motor, or with windings equivalent to thisincorporated in the synchronous motor. When the rotor has been brought near to synchronousspeed by the starting device, it is energized by connecting it to a d.c. voltage source. The rotor then falls into step with the rotating field,

b) Induction Motors

Construction

The two main components of the induction motor include;

i. Stator It is the outer part of an induction motor. It consists of steel frame that encloses a hollowcylindrical core made up of thin laminations of silicon steel. It provides suitable slots in its inner

periphery for winding purposes.



41

ii. Rotor

It is the inner part of the motor, which moves during running. Rotor receives energy from thestator by a process of induction.

Types of induction motors

i. Squirrel cage rotor

It consists of a highly laminated cylindrical core having parallel slots on its outer surface. Thick copper bars are placed on each slot and metal rings (end rings) short these bars.It is used for low and medium starting torque motor.

ii. Wound rotor

This is used for high starting torque. It consists of a laminated cylindrical core and carries athree-phase double layer distributed winding.The resistances can be varied by suitable switchgear and finally short-circuited when motor runsat rated speed.

3.1.2 Methods of Starting Elect ric Motors

Due to their simplicity, robustness and cost effectiveness, squirrel-cage motors are the preferredchoice of industry.During start-up, they develop currents of up to approximately eight times the rated current andthe high starting torque linked to this.The high starting currents often lead to unwelcome voltage drops in the supply network and thehigh starting torque put the mechanical elements under considerable strain. Therefore, theelectricity companies determine limiting values for the motor starting currents in relation to therated operational currents. The permissible values vary from network to network and depend on

its load-bearing capacity.Various starters and methods can be used to reduce currents and torque:



42

a) Normal star-delta starters

To enable the motor to start, the motor windings are configured in a star formation to the supplyvoltage. The voltage applied to the individual motor windings is therefore reduced by a factor of 1¥3 = 0.58 this connection amounts to approximately 30% of the delta values.The starting current is reduced to one third of the direct starting current, i.e. typically to 2...2.5Ie.Due to the reduced starting torque, the star-delta-connection is suitable for drives with a highinertia mass but a resistance torque which is low or only increases with increased speed. It is preferably used for applications where the drive is only put under a load after run-up, i.e. for presses, centrifuges, pumps, ventilators, etc.

After motor run-up, in most cases an automatic timing relay controls the switch-over from star todelta. The run-up using star connection should last until the motor has reached the approximate

operational speed, so that after switching to delta, as little post-acceleration as possible isrequired. Post-acceleration in delta connection will instigate high currents as seen with direct-on-line starting. The duration of start in star connection depends on the motor load. During deltaconnection, the full mains voltage is applied to the motor windings.The contactors of a star-delta starter switch over the windings accordingly.Starting in star, the main contactor connects the mains to winding endings U1, V1, W1.The star contactor shorts winding endings U2, V2, W2. After successful run-up, the star contactor switches itself off and the delta contactor connects terminals U1/V2, V1/W2, W1/U2.When changing from star to delta, attention has to be paid to the correct phase sequence, i.e. thecorrect connection of the conductors to motor and starter.

Incorrect phase sequence can lead to very high current peaks during the cold switch-over pause,due to the easy torque reduction following re-start.These peaks can damage the motor windings and stress the control gear unnecessarily. Therotation of the motor has to be considered as well.



44

The autotransformer reduces the current in the mains supply line further and in accordance withits ratio. Like the star delta connection, the autotransformer starter has a favorable torque-currenttake-up ratio.In order to adapt the motor start characteristics to the torque requirement, auto-transformers areusually equipped with three selectable tapings (e.g. 80%, 65%, and 50%).

When the motor has almost reached its rated torque, the star connection on the transformer isopened. The transformer¶s partial windings act as chokes in series to the motor windings, andtherefore, like the uninterrupted star delta connection, the motor speed does not drop duringswitch over.After the main contactor has been switched in, the motor windings are applied to the full mains

voltage. Finally, the transformer is disconnected from the mains.Depending on tapping and the motor¶s starting current ratio, the starting current amounts to 1 - 5x Ie. The available torque is reduced in ratio to the starting current.

c) Start via resistors

In this case, cost-efficient resistors are used instead of the above-mentioned chokes.This method is less helpful in reducing the starting current for the same torque requirement, because the motor torque reduces as a value of the square of the voltage and the voltage appliedto the motor increases only due to the motor¶s reduced current consumption during increasingspeed.

It is better to reduce the ballast resistor step by step during start. But this requires considerablymore switch gear.Another possibility is the use of encapsulated wet (electrolytic) resistors. For these resistors, theohmic resistance reduces in line with the temperature increase caused by the starting current¶sheating capability.

3.1.3 Factors Considered when selecting a starter

The power for the machine installation will normally be supplied by the Regional ElectricityCompany, and the user will need to comply with any local regulations. The Regional ElectricityCompany will normally limit DOL starting to a maximum motor rating. If the motor is belowthe DOL starting limit, determine the peak starting current which it would draw if started direct-on-line. Check that this peak starting current is within the capacity of the supply.



45

The installation will normally be fed from a step down power transformer. Check that the peak starting current will not initiate a circuit breaker trip on the high- voltage (primary) side of the transformer. Check that the supply line will not introduce unacceptable voltage drops when the peak current is taken. If this is a problem, the choice lies between installing larger cables or selecting

a starting method other than DOL. If the above conditions are all satisfied, DOL starting will provide an economical solution, provided that the mechanical load can handle the peak starting torque produced. If the above conditions are all satisfied, DOL starting will provide an economical solution, provided that the mechanical load can handle the peak starting torque produced. If any of the conditions are not satisfied, use the table to choose an alternative method of starting. Be particularly careful to ensure that the starting torque produced by the method of starting chosen is adequate for the application.

3.1.4 Tools Used In Troubleshooting Motors

Troubleshooting is the systematic elimination of various parts of a system, process, or piece of equipment to locate a malfunctioning part. To locate and correct a motor malfunction quickly,troubleshooting is best performed using the proper test tools, these include

i. Non-contact voltage detector

A non-contact voltage detector is a test tool that gives a visual indication when voltage is presentin a conductor, or other metal parts. The tester glows red if voltage is present. The red glow can be used to indicate if voltage is present in an insulated conductor, or that a non-insulated metal part is energized (hot, live) by a hot conductor touching an improperly grounded system or part.Touching an energized metal part can cause an electrical shock.

ii. Digital multimeter (DMM)

A DMM is a test tool that measures several different electrical quantities, such as voltage,resistance, or current. Some models also include special features for taking minimum/maximum,and relative measurements and/or testing diodes and capacitors. A DMM is required when performing troubleshooting tasks such as testing for power loss from blown fuses, excessivecurrent levels from overloaded circuits, and improper resistance from damaged insulation or equipment.



46

iii. Clamp-on ammeter

A clamp-on ammeter is a test tool that measures current in a circuit by measuring the strength of the magnetic field around a conductor. Most clamp-on ammeters measure AC, others canmeasure both AC and DC. The clamp-on ammeter allows current measurements without openinga circuit.The jaws of a clamp-on ammeter are opened and enclose the conductor under test. Themeasurement displayed indicates the amount of current drawn by loads connected to theconductor.

iv. Megohmmeter

A megohmmeter is a test tool that detects insulation deterioration by measuring high resistancevalues under high voltage conditions.

A megohmmeter detects insulation failure or potential failure of insulation caused by excessivemoisture, dirt, heat, cold, corrosive vapors or solids, vibration, and aging.

v. Non-contact thermometer

A non-contact thermometer is a test tool that measures temperature at a single point.Temperature is measured when troubleshooting because the resistances of most materials changeas the temperature of the material changes.An increase in temperature decreases the performance of electrical equipment and destroys

insulation.Loose, corroded, or dirty electrical connections generate unwanted resistance and heat. Thetemperature rise at a connection depends on the current flowing through the connection and theresistance of the connection.

vi. Power quality analyzer

A power quality analyzer is a test tool used to obtain and record more valuable troubleshootingdata. They can take all the basic measurements that a DMM can take, and also measure

harmonics, transients, power, and other electrical quantities.



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Troubleshooting capacitor motors

A capacitor motor is a split-phase motor with the addition of one or two capacitors. Capacitorsgive the motor more starting and/or running torque.Troubleshooting capacitor motors is similar to troubleshooting split-phase motors. The onlyadditional device to be considered is the capacitor.To troubleshoot a capacitor motor, apply the following procedure:

1. Turn the handle of the safety switch or combination starter OFF. Lock out and tag the starting mechanism per company policy.2. Using a voltmeter, measure the voltage at the motor terminals to make sure the power is OFF.3. Capacitors are located on the outside frame of the motor.Remove the cover of the capacitor. Caution: A good capacitor will hold a charge, even when power is removed.

4. Visually check the capacitor for leakage, cracks, or bulges.Replace the capacitor if present.5. Remove the capacitor from the circuit and discharge it. To safely discharge a capacitor, placea 20,000 �, 2 W resistors across the terminals for five seconds.6. After the capacitor is discharged, connect the ohmmeter leads to the capacitor terminals. Theohmmeter will indicate the general condition of the capacitor.A capacitor is good, shorted, or open.Set your voltmeter to measure capacitance. The capacitance value read should be within ± 20 %of the value on the capacitor label.



49

3.1.6 Trouble Shooting guide for Single phase Motors

a. Motor will not start

Table 3.1: Trouble shooting guide for single phase motors if motor fails to start.

Possiblecause

Suggested test tool Corrective action

Thermalcutoutswitch isopen

Reset the thermal switch. Caution: Resetting the thermal switch mayautomatically start the motor.

Blown fuseor open CB

Basic electricaltester DMM , clamp

meter,or Megohmmeter

Test the OCPD. If voltage is present at the input, but not the outputof the OCPD, the fuse is blown or the CB is open. Check the ratingof the OCPD.

It should be at least 125 % of the motor¶s FLC.

Motor overload onstarter tripped

Allow overloads to cool. Reset overloads. If reset overloads do notstart the motor, test the starter.

Low or novoltageapplied tomotor

Basic electricaltester,DMM or clampmeter

Check the voltage at the motor terminals. The voltage must be present and within 10 % of the motor nameplate voltage.If voltage is present at the motor but the motor is not operating,remove the motor from the load the motor is driving. Reapply power to the motor. If the motor runs, the problem is with the load. If the

motor does not run, the problem is with the motor.Replace or service the motor.

Open controlcircuit betweenincoming power andmotor

Basic electricaltester,DMM or clampmeter

Check for cleanliness, tightness, and breaks. Test the circuit startingwith the incoming power and moving to the motor terminals.Voltage generally stops at the problem area.

Startingwinding notreceiving

power

Basic electricaltester,DMM or clamp

meter

Check the centrifugal switch to make sure it connects the startingwinding when the motor is OFF .



50

b. Fuse, CB, or overloads re-trip after service

Possible cause Suggested test tools Corrective action

Blown fuse or

open CB

Basic electrical tester,

DMM , clamp meter,or Megohmmeter

Test the OCPD. If voltage is present at the input, but not the

output of the OCPD, the fuse is blown or the CB is open.Check the rating of the OCPD. It should be at least 125 % of the motor¶s FLC.

Motor overloadon starter tripped

Allow overloads to cool. Reset overloads. If reset overloadsdo not start the motor, test the starter.

Low or novoltage appliedto motor

Basic electrical tester,DMM or clamp meter

Check the voltage at the motor terminals. The voltage must be present and within 10 % of the motor nameplate voltage.If voltage is present at the motor but the motor is notoperating, remove the motor from the load the motor isdriving.Reapply power to the motor. If the motor runs, the problemis with the load. If the motor does not run, the problem iswith the motor.Replace or service the motor.

Open controlcircuit betweenincoming power andmotor


Check for cleanliness, tightness, and breaks. Test the circuitstarting with the incoming power and moving to the motor terminals. Voltage generally stops at the problem area.

Motor shaftdoes notturn

Disconnect the motor from the load. If the motor shaft stilldoes not turn, the bearings are frozen. Replace or service themotor.

Table 3.2: Trouble shooting for single phase motors if protective device re-trips

after service



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3.1.7 Procedure for Troubleshooting Three-Phase Motors

The extent of troubleshooting a 3ø motor is dependent upon the motor¶s application. If the motor is used in an application that is critical to the operation or production, testing is usually limited to

checking the voltage at the motor. If the voltage is present and correct, the motor is assumed to be the problem.Unless it is very large, the motor is usually replaced at this time so production can be resumed.If time is not a critical factor, further tests can be made in order to determine the exact problem.

To troubleshoot a three-phase motor, apply the following procedure:

1. Using a voltmeter, measure the voltage at the motor terminals. If the voltage is present and atthe correct level on all three phases, the motor must be checked. If the voltage is not present onall three phases, the incoming power supply must be checked.

2. If voltage is present but the motor is not operating, turn the handle of the safety switch or combination starter OFF. Lock out and tag the starting mechanism per company policy.3. Disconnect the motor from the load.

4. After the load is disconnected, turn power ON to try restarting the motor. If the motor starts,check the load.5. If the motor does not start, turn it OFF and lock out the power.

6. With an ohmmeter, check the motor windings for any opens or shorts. Take a resistancereading of the T1-T4 coil. This coil must have a resistance reading. If the reading is zero, the coilis shorted. If the reading is infinity, the coil is opened. Since the coil winding is made of wireonly, the resistance is low.However, there is resistance on a good coil winding. The larger the motor, the smaller theresistance reading.After the resistance of one coil has been found, the basic electrical laws of series and parallelcircuits are applied. When measuring the resistance of two coils in series, the total resistance istwice the resistance of one coil.When measuring the resistance of two coils in parallel, the total resistance is one half the

resistance of one coil.



55

3.1.8 Troubleshooting Guide for Three-Phase Motors

a. Motor will not start

Possible cause Suggested test tools Preventive action

Wrong motor Connections

Most three-phase motors are dual-voltage.Check for proper motor connections.

Blown fuse or open CB

Basic electrical tester,DMM , clamp meter, or megohmmeter

Test the OCPD. If voltage is present at theinput, but not the output of the OCPD, thefuse is blown or the CB is open. Check therating of the OCPD. It should be at least 125% of the motor¶s FLC.


Allow overloads to cool. Reset overloads. If reset overloads do not start the motor,test the starter.

Low or no voltageapplied to motor


Check the voltage at the motor terminals.The voltage must be present and within 10 %of the motor nameplate voltage. If voltage is present at the motor but the motor is notoperating, remove the motor from the loadthe motor is driving. Reapply power to themotor.

If the motor runs, the problem is with theload. If the motor does not run, the problemis with the motor.Replace or service the motor.

Open control circuit between incoming power and motor


Check for cleanliness, tightness, and breaks.Test the circuit starting with the incoming power and moving to the motor terminals.Voltage generally stops at the problem area.

Table 3.6: Trouble shooting guide for 3-phase motors incase motor fails to

start



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b. Fuse, CB, or overloads re-trip after service


Power not applied toall three lines


Measure voltage at each power line. Correctany power supply problems.

Blown fuse or openCB

Basic electrical tester,DMM , clamp meter,or megohmmeter

Test the OCPD. If voltage is present at theinput, but not the output of the OCPD, thefuse is blown or the CB is open. Check therating of the OCPD. It should be at least 125% of the motor¶s FLC.


Allow overloads to cool. Reset overloads. If reset overloads do not start the motor,test the starter.

Low or no voltageapplied to motor


Check the voltage at the motor terminals.The voltage must be present and within 10 %of the motor nameplate voltage. If voltage is present at the motor but the motor is notoperating, remove the motor from the loadthe motor is driving. Reapply power to themotor.

If the motor runs, the problem is with theload. If the motor does not run, the problemis with the motor.Replace or service the motor.

Open control circuit between incoming power and motor


Check for cleanliness, tightness, and breaks.Test the circuit starting with the incoming power and moving to the motor terminals. Voltagegenerally stops at the problem area.

Motor shaft doesnot turn

Disconnect the motor from the load. If themotor shaft still does not turn, the bearingsare frozen. Replace or service the motor.

Table 3.7: Trouble shooting guide for 3-phase motors incase protective device

re-trips after service.



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c. Motor overheats


Motor is singlePhasing

Basic electrical tester, DMMor clamp meter

Check each of the three-phase power lines for correct voltage.

Improper ventilation

Infrared temperature Clean all ventilation openings. Vacuumor blow dirt out of motor with low- pressure, dry, compressed air.

Motor is

overloaded

Basic electrical tester, clamp

meter or DMM with clampaccessory

Check the load for binding. Check shaft

straightness.Measure motor current under operatingconditions.If the current is above the listed currentrating, remove the motor.Re-measure the current under no-loadconditions. If the current is excessiveunder load but not when unloaded,check the load. If the motor drawsexcessive current when disconnected,replace or service the motor.

Excessiveharmonics

Power qualityAnalyzer

Check for the presence of harmonics inthe feeder supplying the motor,especially 5th harmonic which cangenerate heat rise.

Table 3.8: Trouble shooting guide for 3-phase motors in case the motor

overheats.



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3.2 PROGR AMMABLE LOGIC CONTROLLER (PLC)

A PLC (Programmable Logic Controllers) is an industrial computer used to monitor inputs, and

depending upon their state make decisions based on its program or logic, to control (turn on/off)its outputs to automate a machine or a process.

3.2.1 Uses of PLCs

� Cost effective for controlling complex systems.� Flexible and can be reapplied to control other systems quickly and easily.� Computational abilities allow more sophisticated control.� Trouble shooting aids make programming easier and reduce downtime.� Reliable components make these likely to operate for years before failure.

3.2.2 Ladder Logic

Ladder logic is the main programming method used for PLCs. As mentioned before, ladder logichas been developed to mimic relay logic.The decision to use the relay logic diagrams was a strategic one. By selecting ladder logic as themain programming method, the amount of retraining needed for engineers and trades people wasgreatly reduced.Modern control systems still include relays, but these are rarely used for logic.A relay is a simple device that uses a magnetic field to control a switch. When a voltage isapplied to the input coil, the resulting current creates a magnetic field. The magnetic field pulls ametal switch (or reed) towards it and the contacts touch, closing the switch. The contact thatcloses when the coil is energized is called normally open. The normally closed contacts touchwhen the input coil is not energized. Relays are normally drawn in schematic form using a circleto represent the input coil. The output contacts are shown with two parallel lines. Normally opencontacts are shown as two lines, and will be open (non-conducting) when the input is notenergized. Normally closed contacts are shown with two lines with a diagonal line through them. When theinput coil is not energized the normally closed contacts will be closed (conducting).



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3.2.2 Components of PLC Hardware

i. Power Supply

This can be built into the PLC or be an external unit. Common voltage levels required by thePLC (with and without the power supply) are 24Vdc, 120Vac, 220Vac.

ii. CPU (Central Processing Unit)

This is a computer where ladder logic is stored and processed.

iii. I/O (Input / Output)

A number of input/output terminals must be provided so that the PLC can monitor the processand initiate actions.

iv. Indicator lights

These indicate the status of the PLC including power on, program running, and a fault. These areessential when diagnosing problems.

3.2.3 Principle of Operation of PLCs

The input/output (I/O) system is physically connected to the field devices that are encountered inthe machine or that are used in the control of a process.These field devices may be discrete or analog input/output devices, such as limit switches, pressure transducers, push buttons, motor starters, solenoids, etc.The I/O interfaces provide the connection between the CPU and the information providers(inputs) and controllable devices (outputs).

During its operation, the CPU completes three processes:

It reads, or accepts, the input data from the field devices via the input interfaces, It executes, or performs, the control program stored in the memory system.



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It 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 outputsis known as scanning.

Figure 3.2: PLC Hardware

The input/output system forms the interface by which field devices are connected to thecontroller. The main purpose of the interface is to condition the various signals received from or sent to external field devices.Incoming signals from sensors (push buttons, limit switches, 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 positionvalves, are connected to the terminals of the output interfaces. The system power supply providesall the voltages required for the proper operation of the various central processing unit sections.



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CHAPTER 4:

CONCLUSION AND RECOMMEND ATIONS

4.1 CONCLUSIONIt has been an absolutely important opportunity and experience to me as both a student and asan individual.

4.1.1 Achievements

By training with roofings, I have realized and experienced a lot of achievements in my life both personally and as an engineer. Some of these achievements include;

In my quest and journey to becoming an engineer, I have been blessed with the privilege of hands on practice. Through this privilege, I have been able to relate my lecture room theoreticalknowledge to the actual practical work that is involved. This has added focus, appreciation andlove to my career and has acted as a driving and guidance in my further quest for knowledge inthe engineering field. Further more the opportunity of getting involved in the actual groundactivities has blessed me with confidence to deal with the various engineering activities.

To add to that, training with roofings has improved my relational skills. In terms of team work, Ihave been able to get an opportunity to work in a team with my fellow trainees, a training officer and other technicians.

4.1.2 Challenges Faced During Training

Despite the various benefits I realized from training with roofings, i encountered a number of challenges in my quest for knowledge.

Communication and interrelationship between some the technicians and the trainees was reallychallenging at times. This came from the selfish behavior of some of the technicians who werenot willing to extend knowledge to the trainees.

I also faced a challenge of dealing with engineering aspects in which I had no prior knowledgethat is aspects having concepts that I had yet to cover in my proceeding academic year of study.



Getting adapted to the working atmosphere had very many working ethics I had to observeRespects such as keeping time was challenging since I had to travel from campus to Lubowawhich involves encountering a lot of traffic.

4.1.3 Danger and health hazards

y Hearing impairment and disorders due to working in high noise sections.y Body injuries, which may be inform of loss of body parts due machine cutting them off.y Respiratory related problems, resulting from inhaling exhaust gases from the various

machines.

4.1.4 Safety precautions

y Using ear plugs in high noise sections to prevent ear damage.y Using the right body gear to protect the body from damage. The gear used comprises of;

Head Helmet Safety gloves Overalls Safety shoes

4.2 RECOMMEND ATIONS

I would recommend roofings to critically train both their employees and trainees on the basicsafety procedures so as on reduce on the potential risk of human damage. To this, it shouldmake sure that all the safety gear is available.

I would also recommend roofings to train their employees the art of communication and teamwork at the place. This is critical to enable trainees to benefit from the program.

Roofings Report

Documents

Transcript of Roofings Report