panel boards and wiring

EMP Group of Companies (PVT) LTD Industrial Training Report

ACKNOWLEDGEMENT

Firstly, I am grateful to Dr. Nayana Alagiyawanna, Dean, Faculty of Engineering and

Dr. Priyankara, Director, Engineering Educational Center, Faculty of Engineering,

University of Ruhuna. Also I take this opportunity to extend my gratitude to National

Apprentice and Industrial Training Authority (NAITA) for making necessary

arrangements to provide me a valuable training period.

Also I am so Indebted to Mr. Chandranandana Diyunuge, Chairman of EMP Group of

Companies (PVT) LTD & Mr. T. Suresh Kumara, Managing Director of EMP Group

of Companies (PVT) LTD for providing us all the facilities in order to have a valuable

training. Next, my sincere gratitude is extended to Mr. Ravi Rupasinghe, General

Manager of EMP Group of Companies (PVT) LTD for extending us his kind co-

operation. I take this opportunity to extend my profound thanks to the Director Board

of EMP Group of Companies (PVT) LTD.

And Also I am so indebted to Mr. Thusitha Gunasekara, Head of Electrical &

Assembly Section, for dedicating his valuable time on behalf of our own goodness &

for providing us a faculty of knowledge. Next I am thankful to all the employees of

electrical & assembly section for giving us their kind co-operation.

I take this opportunity to express my profuse thanks to Mr. Indika De Silva, Director

of EPL, for giving us a huge knowledge on project handling. And also I’m so thankful

to all the staff of EPL for extending their friendly hands towards us. And finally I

extend my regards to all the employees of EMP group for all the supports given to

have a valuable training.

Thank you!

Wijeweera D.A.P.

RU/E/2007/194

Faculty of Engineering,

University of Ruhuna.

Faculty of Engineering, University of Ruhuna. 1


PREFACE

This report on industrial training prepared by myself was done so not only as an

exercise to fulfill a part of the training requirements set out by NAITA, but also as a

testimony on the actual industrial training I had. Hereby, a detailed account of my

training programmed at EMP Group of Companies (PVT) LTD is included.

The idea behind this compilation is that anyone going through this report should get a

comprehensive understanding of all technical aspects of my training. In making this a

reality, I tried my best to keep to the guidelines stipulated by NAITA. This is

succeeded by my own training experience, which is detailed to the most possible

extent.

This report contains the entire experience and knowledge I’ve achieved from EMP

Group. The first chapter introduces the company overview where as the second and

third chapters focus on switch gears & protective devices. Next two chapters are used

to describe the knowledge of cables & panel boards.

I finally hope that this humble and honest effort of mine will meet the expectations of

the University training engineer.



CONTENTS

ContentsACKNOWLEDGEMENT ............................................................................................. 1

PREFACE ...................................................................................................................... 2

CONTENTS ................................................................................................................... 3

LIST OF FIGURES ........................................................................................................ 6

LIST OF TABLES ......................................................................................................... 8

CHAPTER 1 ................................................................................................................... 9

INTRODUCTION .......................................................................................................... 9

1.1 EMP Group of Companies...................................................................................9

Figure 1.1 – EMP Group Logo.................................................................................10

1.1.1 Range of Service of EMP, EPL & EMP Engineering.................................10

1.1.2 Range of Services of Other Members..........................................................10

1.2 The Vision & Mission.....................................................................................11

1.2 Organization Structure....................................................................................11

1.2.1 Organization Structure of EMP Group........................................................11

Figure 1.2- Organization Structure...........................................................................11

1.2.2 Structure of the Engineering & Assembly Section......................................12

CHAPTER 2 ................................................................................................................. 13

Switch Gears & Protective Function ............................................................................ 13

2.1 Introduction – Switch Gears...............................................................................13

2.1 Circuit Breakers..................................................................................................14

2.2.1 MCB.............................................................................................................14

2.2.2. Tripping Curves..........................................................................................15

2.3.1. MCCB.........................................................................................................16



2.3.2. Technical data of a MCCB.........................................................................16

2.3.3. Tripping Accessories..................................................................................17

2.4.1. ELCB & RCCB..........................................................................................18

2.5.1. ACB............................................................................................................20

CHAPTER 3 ................................................................................................................. 22

Protective Relays & Protective Devices ....................................................................... 22

3.1 Introduction........................................................................................................22

3.2. ELR....................................................................................................................22

3.3. EFR....................................................................................................................23

3.4. PFR....................................................................................................................24

3.5. Surges and Surge Arresters...............................................................................26

3.5.1 Introduction..................................................................................................26

3.5.2 Operating Terminology................................................................................26

3.6 Lightning rods....................................................................................................29

3.6.1 Introduction.....................................................................................................29

3.6.2 Installation of a Lightning Rod....................................................................29

3.6.3. Grounding...................................................................................................30

3.6.4 Other accessories.........................................................................................30

CHAPTER 4 ................................................................................................................. 31

Cables, Wiring & Circuits ............................................................................................ 31

4.1. Cable Specifications..........................................................................................31

4.2.1. Cable Anatomy...........................................................................................32

4.2.2. Selection of Cables.....................................................................................33

4.2.3 Steps of Calculating the Cable for a given load...........................................34

4.3 Cable Lying........................................................................................................35

4.4 Ring Circuits & Other Special Circuits..............................................................36

4.4.1 Ring Circuit..................................................................................................36

4.4.2 Converting 4 Pole MCCB for a Single Phase Supply or DC Supply..........37

4.5 Bimetal lugs........................................................................................................38

Figure 4.5 – Bimetal LugsCHAPTER 5 ...................................................................... 39



CHAPTER 5 ................................................................................................................. 40

Panel Boards & Distribution Boards ............................................................................ 40

5.1 Introduction - Panel Board.................................................................................40

5.2 IP Protection (Ingress Protection) of a Panel......................................................41

5.3 Motor Control Circuits.......................................................................................43

5.4 Capacitor Banks..................................................................................................49

5.4.1 Design..........................................................................................................49

5.4.2 Uses of HRC Fuses......................................................................................51

5.4.3 Uses of Capacitor Contactors.......................................................................51

5.5 ATS (Automatic Transfer Switch).....................................................................52

CHAPTER 6 ................................................................................................................. 55

CONCLUSION ............................................................................................................ 55

REFERENCES ............................................................................................................. 56

ABBREVIATIONS ...................................................................................................... 57



LIST OF FIGURES

Figure 1.1 – EMP Group Logo………………………………………………………10

Figure 1.2- Organization Structure …………………………………………………..11

Figure 1.3 – Structure of Electrical & Assembly Section …………………………...12

Figure 2.1 – Tripping Curve ‘B’ of a MCB & its Operating Regions ………………15

Figure 2.2 Wiring Diagram of a RCCB ……………………………………………..19

Figure 3.1 – Control Diagram of an ELR ……………………………………………23

Figure 3.2 – Connection Diagram of an EFR.………………………………………. 24

Figure 3.3 – PFR with a UVT coil …………………………………………………..25

Figure 3.4 – PFR with a shunt coil …………………………………………………..26

Figure 3.5 - Construction Concept of a Surge Arrester ……………………………...27

Figure 3.6 - Anatomy of a Surge …………………………………………………….28

Figure 3.7 – Rod Type Lightning Arrester …………………………………………..29

Figure 3.8 – Earthing Chamber ……………………………………………………...30

Figure 4.1.a,b,c,d,e,f – Cable Types …………………………………………………32

Figure 4.2 – Cable Radii Variation with Cable Diameter …………………………...35

Figure 4.3 – Ring Circuit …………………………………………………………….37

Figure 4.4 – Wiring Diagram of DC or Single Phase

AC Supply to a 3 Phase MCCB …………………………………….38

Figure 4.5 – Bimetal Lugs …………………………………………………………39

Figure 5.1 – Distribution System of a Four Story Building …………………………40

Figure 5.2 – Inside view of a panel with cover plates ……………………………….43

Figure 5.3 – Terminal Connections of Motors ………………………………………44

Figure 5.4 – Power & Control Circuit Diagram of a DOL Starter………………….. 44

Figure 5.5 – Power Diagram of Star Delta Starter…………………………………...45



Figure 5.6 – Control Diagram of a Star Delta Starter ………………………………46

Figure 5.7 – Control Diagram of an Auto Transformer Starter ……………………...47

Figure 5.8 – Power Diagram of an Auto Transformer Starter ……………………….48

Figure 5.9 – Phase Diagram ……………………………………………...………….49

Figure 5.10– Wiring Diagram of a Capacitor Bank …………………………………50

Figure 5.11 – Capacitor Contactors …………………………………………………51

Figure 5.12 – Typical Control Diagram of ATS ……………………………………53

Figure 5.13 – Complete ATS Control Diagram ……………………………………54



LIST OF TABLES

Table 4.1 – Approximated Current Ratings According to the Wire Size ……………34

Table 4.2 – Selecting appropriate cable according to the phase wire ……………….35

Table 4.3 – Approximated Current Ratings According to the Wire Size ……………35

Table 5.1 – IP Protection against Solid Bodies ……………………………………...41

Table 5.2 – IP Protection against Liquid …………………………………………….42



CHAPTER 1

INTRODUCTION

As my first compulsory session of industrial training of the Engineering degree

program, I was appointed at EMP Group of Companies (PVT) LTD, Panagoda. This

training was arranged for 12 weeks from 07-07-2009 to 26-09-2009. During this

period I was assigned in EMP main factory & EMP Projects Lanka (PVT) LTD which

is a group member of EMP Group. This report consists of the experience &

knowledge that I got during the training period.

1.1 EMP Group of Companies

EMP Group of Companies was found in Templeburge industrial Estate in 1992 and it

was first known as Electro Metal Pressings (PVT) LTD. In year 2002 it was taken

over by present management and on 28th July 2006 it was incorporated as EMP Group

of Companies. Today EMP is a group with 6 members which are spreading their

hands all over the business and manufacturing world. The groups of members are as

follows.

1. Electro Metal Pressings (PVT) LTD (EMP)

2. EMP Projects Lanka (PVT) LTD (EPL)

3. EMP Engineering (PVT) LTD

4. AKLAN (PVT) LTD

5. EMP PVC (PVT) LTD

6. OMATA Water Management (PVT) LTD

7. SENAS plywood (PVT) LTD

The mother company EMP, EPL & EMP engineering together addresses the

market related to the electrical field. They have professional experience in

manufacturing electrical switch boards & relevant cable light systems & accessories.



Figure 1.1 – EMP Group Logo

1.1.1 Range of Service of EMP, EPL & EMP Engineering

As mentioned above these 3 companies are specialized in electrical field &

generally the designing part is done by EMP Engineering & EPL. Then the whole

manufacturing part including the fabrication is done by EMP & again the installation

part is done by EPL. Brief summary of EMP services are as follows.

1. Turnkey electrical projects for high rise buildings, garment

industries & apartment buildings

2. Designing & installation of turnkey electrical projects

3. Supply & installation of low voltage main switch board up to

6000A

4. Supply & installation of motor control centers

5. Supply & installation of power factor correction capacitor banks

6. Supply & installation of cable management systems (cable

ladders, cable trunkings & floor boxes)

7. Supply of 19” equipment rack systems

8. Tea & rubber factory electrification

9. Mini hydro projects

10. Generator installation & commissioning

1.1.2 Range of Services of Other Members

Among other companies, AKLAN is the sole agent for LS Industrial Systems which

manufactures & distributes all type of circuit breakers, PLC control units, and

electronic equipments all over the world. EMP PVC manufactures quality conduits &

UPVC pipes in mass scale. OMATA designs the water management systems &



provides ideal solutions for the market. SENAS plywood manufactures plywood

boards to the Sri Lankan market.

1.2 The Vision & Mission

Vision

To be the provider of total electrical engineering solutions & be switch board

manufacturer in compliance with evolving standards to supply globally

Mission

In keeping with the commitment to continuous improvement of our engineering

products, to deliver high quality expected by the customer

1.2 Organization Structure

1.2.1 Organization Structure of EMP Group

Figure 1.2- Organization Structure


EMP

GROUP

EMP EPLEMP

EngineeringAKLAN OMATA

Chairman

Managing

Director

General

Manager

EMP PVCSENAS


The academically qualified, committed and trained professionally-oriented Electrical

Engineers and Skilled Electricians along with the trained sales team dedicated to

maintain a satisfied customer base always strive to find the right electrical solutions

that are economical and practical. They are dedicating to assure optimum safety

standards in keeping with international standards. The chairman, Mr.

Chandranandana Diyunuge (B.Sc. Eng. (Hons), AMIE (SL) AMIEE (UK)) & the

managing Director, Mr. T. Suresh Kumara (B.Sc. Eng. (Hons), AMIE (SL)AMIEE

(UK)) initiated and sustained the EMP group. The General Manager Mr. H. P. Ravi

Rupasinghe (MBA, Sc. Eng. (Hons) CMEMA (SL), AMIE (SL), AMIEE (UK),

MMBAAA) is dedicating to take the group toward a quality production.

1.2.2 Structure of the Engineering & Assembly Section

Figure 1.3 – Structure of Electrical & Assembly Section


Head of Electrical & Assembly Section

Electrical & AssemblyTeam Leader

Electrical & Assembly Team

Quality Team Leader

Quality Team


CHAPTER 2

Switch Gears & Protective Function

2.1 Introduction – Switch Gears

A Switch gear is defined as a switching/ interrupting device used in connection with

generation, transmission, distribution and conversion of electric power for controlling,

metering protecting and regulating devices. Switch gears can be categorized to main

two areas, protective devices and Non-protective devices. The reaction time is

typically between 30 ms and 150 ms depending upon the age and construction of the

device. According to the requirements & other external factors, some switch gear may

not ideal for the requirement. Although sometimes the switch gear is selected as

above, there may be some mismatching because of the variable factors of the switch

gears such as breaking capacity, impulse voltage, etc.

Several different classifications of switchgear can be made according to the below

factors.

By the current rating.

By breaking capacity (maximum short circuit current that the device can

safely interrupt)

By voltage class:

o Low voltage (less than 1000 volts AC)

o Medium voltage (1000-35,000 volts AC)

o High voltage (more than 35,000 volts AC)

By insulating medium:

o Air

o Oil

o Vacuum

By construction type:

o Indoor (further classified by IP (Ingress Protection) class or NEMA

enclosure type)

o Outdoor



o Industrial

o etc

By operating method:

o Manually-operated

o Motor-operated

o Solenoid/stored energy operated

By type of current:

o Alternating current

o Direct current

By application:

o Transmission system

o Distribution.

2.1 Circuit Breakers

A circuit breaker is an automatically-operated electrical switch designed to protect an

electrical circuit from damage caused by overload or short circuit. Its basic function is

to detect a fault condition and, by interrupting continuity, to immediately discontinue

electrical flow. Unlike a fuse, which operates once and then has to be replaced, a

circuit breaker can be reset (either manually or automatically) to resume normal

operation. Circuit breakers are usually able to terminate all current flow very quickly:

Circuit breakers can be categorized to several types.

1. MCB

2. MCCB

3. ELCB & RCCB

4. ACB

5. OCB

6. VCB

Among above all types 1-4 types are commonly used.

2.2.1 MCB

MCB (Miniature Circuit Breaker) is a circuit breaker with optimum protection

facilities of over current and short circuit only. These are manufactured for fault level



of up to 10KA only with operating current range of 6 to 125 Amps (the ranges are

fixed). It is available as single pole, double pole, three pole, and four pole MCB’s.

These are used for smaller loads -electronic circuits, house wiring etc. As MCB reacts

for both over current & short circuit, it avoids over heating in case of excess current &

provides fire protection.

2.2.2. Tripping Curves

Every MCB have a specified tripping curve, B,C,D or sometimes very specialized

curve that varies from MCB brand to brand (e.g. -: K & Z curves of ABB breaker). B,

C & D curves are defined in IEE regulations.

The relationship between current and tripping time is usually shown as a curve,

known as the MCB's trip characteristic. The most important curves are B, C and D.

Type B MCBs react quickly to overloads, and are set to trip when the current passing

through them is between 3 and 5 times the normal full load current. They are suitable

for protecting incandescent lighting and socket-outlet circuits in domestic and

commercial environments (resistive loads), where there is little risk of surges that

could cause the MCB to trip.

Type C MCBs react more slowly, and are recommended for applications involving

inductive loads with high inrush currents, such as fluorescent lighting installations.

Type C MCBs are set to trip at between 5 and 10 times the normal full load current.

This type is generally used.


Over current region

Short circuit region

Figure 2.1 – Tripping Curve ‘B’ of a MCB & its Operating Regions


Type D MCBs are slower still, and are set to trip at between 10 and 20 times the

normal full load current. They are recommended only for circuits with very high

inrush currents, such as those feeding transformers and welding machines.

K curves can also be used for motors and transformers but have improved thermal

characteristics at 1.05 to 1.2 times the rated current. The Z curves provide protection

to semiconductors, with instantaneous trip values at two to three times the rated

current.

2.3.1. MCCB

MCCB’s (Moulded Case Circuit Breakers) are designed for protection of low voltage

distribution systems. They are suitable for application as main breakers & for

protection of branch & feeder circuit & connected equipment. MCCB’s provide

protection of short circuit & overload protection. For all circuit elements including

cables, motors etc. They are designed for used in control centers, panel boards &

switch boards. They suit the requirement of lighting distribution & other power

circuits. Main two types of MCCBs are

2.3.2. Technical data of a MCCB

It is vitally important to know the parameters of a MCCB that are essential when we

selecting a proper MCCB. All the technical data of a MCCB is printed in the face

plate and it is vitally important to know the meanings of them.

1. Rated Current (In) -: The current which the circuit breaker will carry

continuously under specified conditions and on which the time/current

characteristics are based. Unless otherwise stated In is based on a reference

ambient temperature of 30 degrees centigrade.

2. Rated Operational Voltage (Ue) -: The nominal line to line voltage of the

system should not exceed Ue

3. Rated insulation Voltage (Ui) -: .The highest operating voltage that will not

cause a dielectric strength failure. The rated insulation voltage is used as a

parameter for dielectric strength tests. The rated insulation voltage must

always be higher than the rated operating voltage (Ue).



4. Rated Impulse Withstand Voltage (Uimp) -: The voltage on which

clearance distances are based. The value of transient peak voltage the circuit

breaker can withstand from switching surges or lighting strikes imposed on the

supply .e.g. Uimp = 8kV, Tested at 8kV peak with 1.2/50µs impulse wave.

5. Ultimate Breaking Capacity (Icu) -: The maximum fault current which can

flow through without damaging the equipment. The calculated prospective

fault current at the incoming terminals of the circuit breaker should not exceed

Icu.

6. Service Breaking Capacity (Ics)-: The maximum level of fault current

operation after which further service is assured without loss of performance.

7. Let Through Energy (I2t) -: A measure of energy required to blow the fuse

element and so a measure of the damaging effect of over current on protected

devices; sometimes known as the let-through energy. Unique I2t parameters

are provided by charts in manufacturer data sheets for each fuse family. The

energy is mainly dependent on current and time for fuses. When a fault is

occurred, fault energy will flow through the protective device. That energy is

known as the let through energy. So a good quality protective device must

have a lesser value of let through energy

8. Utilization Category of a MCCB -:

Every MCCB has a utilization category, “Cat. A” or “Cat. B”.

Cat. A -: Category A designates circuit breakers not specifically intended for

selectivity with devices on the load side. In other words circuit breakers will

discriminate only up to certain fault levels, above which discrimination with

devices on the load side cannot be guaranteed.

Cat. B -: Category B designates circuit breakers specifically intended for

selectivity with devices on the load side. Such circuit breakers will incorporate

some form of time delay.

2.3.3. Tripping Accessories

Unlike RCDs (Residual Current Devices) MCCB has a tripping method, which can

operates fully mechanically. Even though power is not supplied to the breaker, if it is

in on position it can be tripped using the trip button. But RCD cannot be tripped when

the power isn’t supplied as its tripping method works from residual current (through



an electrical signal mechanical system is energized). There is also a method to do the

tripping function of a MCCB by using electrical signals (current). For this we have to

use the tripping accessories, shunt coil & UVT coil which is normally mounted in the

right hand seat of the case of the MCCB. Protection relays are connected to these

coils.

Shunt Coil -: When a current passes through the shunt coil it passes tripping signal to

the MCCB. In the normal operation no current must be gone through shunt coil. If

power flow continuously through a shunt coil, it will burn. So current to the shunt coil

is supplies from out going of the breaker.

UVT coil -: When current doesn’t pass through the UVT coil it passes tripping signal

to the MCCB. So to switch on a breaker with UVT coil, the coil must be provided a

voltage. So it must be connected to the incoming of the breaker.

2.4.1. ELCB & RCCB

There are two types of ELCB, the voltage operated device and the differential current

operated device. For the convenience of further explaining voltage operated ELCB

will be referred as vELCB and differential current operating ELCB will be referred as

iELCB.

The principle of operation of the vELCB is as follows. Under normal conditions the

closed contacts of the vELCB feed the supply current to the load. The load is

protected by a metal frame. The vELCB also has a relay coil, one end of which is

connected to the metal frame and one end connected directly to ground. A shock risk

will arise if a breakdown in the insulation occurs in the load which causes the metal

frame to rise to a voltage above earth. A resultant current will flow from the

metalwork through the relay coil to earth and when the frame voltage reaches a

dangerous level, e.g. 50 volts, the current flowing through the relay coil will be

sufficient to activate the relay thereby causing opening of the supply contacts and

removal of the shock risk.

As can be seen from the above description, this type of ELCB is essentially a voltage

sensing device intended to detect dangerous touch voltages. The level of shock

protection provided by the vELCB was somewhat limited as these devices would not

provide shock protection in the event of direct contact with a live part. An additional



problem with the vELCB was its tendency to be tripped by earth currents originating

in other installations.

The principle of operation of the vELCB is as follows. Under normal conditions the

closed contacts of the iELCB feed the supply current to the load. The load conductors

are passed through a current transformer (CT). The load conductors act as primary

windings of the transformer. The CT is fitted with a secondary winding. Under

normal conditions, the total current flowing from the supply to the load will be the

same as the total current flowing back to the supply from the load. As the currents in

both directions are equal but opposite, it has no effect on the CT. However, if some

current flows to earth after the iELCB, possibly due to an earth fault, the current

flowing to the load and from the load will be different. This differential current will

cause a resultant output from the CT. This output is detected and if above a

predetermined safe level, it will cause the iELCB to trip and disconnect the supply

from the load.

Now differential current operating ELCB is referred as RCCB and provides 3 types of

protection.

1. Basic Protection- Protective measure against direct contact

2. Fault Protection - Protective measure against indirect contact

3. Additional Protection – Maximum current allowable for a fault

Figure 2.2 Wiring Diagram of a RCCB



2.5.1. ACB

ACB(air circuit breaker) is an electric protecting apparatus which is installed between

an electric source and load units in order to protect a load unit and a load line from an

abnormal current generated on an electric circuit and to perform distribution function

for changing the electric power line to another line. The electrical systems in

residential, commercial and industrial applications usually include a panel board for

receiving electrical power from a utility source. The power is then routed through

over current protection devices to designated branch circuits supplying one or more

loads. Electrical power distribution systems and their components need protection

from numerous types of malfunctions, including over current conditions, overvoltage

conditions, under voltage conditions, reverse current flow, and unbalanced phase

voltages. If a MCCB is used instead of an ACB it is essential to connect protection

relays to protect load from above malfunctions. Generally ACB is available from

1200A to 6400A for low voltage applications.

Air circuit breakers include operating mechanisms that are mainly exposed to the

environment. Since the air circuit breakers are rated to carry several thousand amperes

of current continuously, the exposure to convection cooling air assists in keeping the

operating components within reasonable temperature limits. A typical air circuit

breaker comprises a component for connecting an electrical power source to electrical

power consumer or load. The component is referred to as a main contact assembly. A

main contact is typically either opened, interrupting a path for power to travel from

the source to the load, or closed, providing a path for power to travel from the source

to the load. In many air circuit breakers, the force necessary to open or close the main

contact assembly is provided by an arrangement of compression springs.

In many air circuit breakers, the mechanism for controlling the compression springs

comprises a configuration of mechanical linkages between a latching shaft and an

actuation device. The actuation device may be manually or electrically operated. In a

common construction of a low voltage air circuit breaker, the movable contact is

mounted on a contact arm that is pivoted to open the contacts by a spring powered

operating mechanism triggered by a trip unit responsive to an over current condition

in the protected circuit. Various accessory devices are used with such air circuit

breakers to provide auxiliary function along with over current protection. One such



accessory is the bell alarm accessory that provides local and remote indication as to

the occurrence of circuit interruption.



CHAPTER 3

Protective Relays & Protective Devices

3.1 Introduction

When manufacturing a panel board it is essential to have some protective methods

other than breakers which provide additional protection to the panel board,

equipments that are connected to the panel board and the user. For this case protective

relays and other protective devices such as surge arresters and fuses can be used.

When considering about protective relays, it doesn’t act a protective function alone. It

needs some tripping accessories mounted in a MCCB such as described in chapter

2.3.3, to provide the protective function. As panel board is the heart of the distribution

system of building it is vitally important to have protective methods.

3.2. ELR

ELR (Earth Leakage Relay) ensures the protection of electrical installations and

person against direct and indirect contacts. ELR is designed on an electronic basis,

which ensures the monitoring of earth fault currents. When the fault current rises

above the selected level, the outputs of the product operate depending on the relay

selected, it can have either fixed or adjustable settings for selectivity purposes. Both

minimum leakage current and also the tripping current can be adjusted in an ELR.

This is an advantage of an ELR than a RCCB.

To operate an ELR it must be connected to a CBCT (Core Balance Current

Transformer).The function of an ELR is as below (Figure 3.2.1). It is known that at

any instant the algebraic sum of currents in 3 phase balanced supply is equal to zero.

So at normal condition, total algebraic sum of currents in four wires (3 phases and

neutral) must be zero. So at normal conditions no current should be generating in the

CBCT. When a leakage happens then there will be a leakage current and ultimately

algebraic sum of current through CBCT will not be equal to Zero and as a result of

that the current will be induced in the CBCT. This current provides a signal to ELR

and it begins to operate and closes its normally open contact. Then there will be a



current through the shunt coil and then shunt coil passes a tripping signal to the

MCCB. (It is known that if there is a current through a shunt coil it will provide a

tripping signal to a MCCB). ELR is used with MCCBs with current rating less than

250A.

Figure 3.1 – Control Diagram of an ELR

3.3. EFR

EFR (Earth Fault Relay) is used for protecting from earth faults and use with MCCBs

with current rating greater than 250A. The function of EFR is as same as ELR, but

more sensitive than ELR. Instead of a CBCT, four separate CT’s are used to connect

an EFR. It is an Electronic Trip Unit, designed to protect the Electrical installation in

case of faults or leakage currents beyond a preset level. The trip delay is adjustable.



Figure 3.2 – Connection Diagram of an EFR

3.4. PFR

PFR (Phase Failure Relay or Phase Voltage Balance Relay) is a three-phase voltage

sensing device that trips on phase loss, phase reversal, over voltage, or under voltage.

Voltage unbalance trips the device when any voltage drops certain percentage (around

10%) below the average. Under voltage is externally adjustable from 75–100% of the

rated voltage (Depends upon the brand and type). The LED on the front of the device

lights when the device is energized. For the protection of 3 phase loads tih can be

installed.

Generally a PFR is used along with an UVT coil. But a disadvantage of this is when

incoming supply cuts off, PFR considers it as a fault and trips the circuit. Then

somebody has to switch on the breaker after power comes. To avoid this disturbance


NO

EFR

Auxiliary Supply

Shunt Coil

Fuse 1

CTs

L1 L2 L3 N

MCCB

Fuse 2


sometimes shunt coil is used instead of a UVT. But it has some disadvantages also.

When a failure of a phase which provides voltage to the shunt coil, occurs then PFR

cannot send the tripping signal. Of course this matter can be avoided but it is a little

bit expensive.

Figure 3.3 – PFR with a UVT coil



Figure 3.4 – PFR with a shunt coil

3.5. Surges and Surge Arresters

3.5.1 Introduction

The lightning arresters and ground wires can well protect the electrical system against

direct lightning strokes but they fail to provide protection against travelling waves,

which may reach the terminal apparatus. The surge arresters or surge diverters

provide protection against such surges. A lightning arrester or a surge diverter is a

protective device, which conducts the high voltage surges on the power system to the

ground.

3.5.2 Operating Terminology

Generally Surge arrester is assembled at the incoming side of an every main

distribution board. The construction concept of a surge arrester is as shown below.



Figure 3.5 - Construction Concept of a Surge Arrester

Fig 3.5.(i) shows the basic form of a surge arrester. It consists of a spark gap in series

with a non-linear resistor. One end of the arrester is connected to the terminal of the

equipment to be protected (generally a distribution board) and the other end is

effectively grounded. The length of the gap is so set that normal voltage is not enough

to cause an arc but a dangerously high voltage will break down the air insulation and

form an arc. The property of the non-linear resistance is that its resistance increases as

the voltage (or current) increases and vice-versa. This is clear from the voltage current

characteristic of the resistor shown in Fig 3.5.(ii).

Under normal operation, the lightning arrester is off i.e. it conducts no current to earth

or the gap is non-conducting. On the occurrence of over voltage, the air insulation

across the gap breaks down and an arc is formed providing a low resistance path for

the surge to the ground. In this way, the excess charge on the line due to the surge is

harmlessly conducted through the arrester to the ground instead of being sent back

over the line. It is worthwhile to mention the function of non-linear resistor in the

operation of arrester. As the gap sparks over due to over voltage, the arc would be

short-circuited on the power system and may ground the surge. Since the


http://electricalandelectronics.org/wp-content/uploads/2009/03/lightning-arrestor.png


characteristic of the resistor is to offer low resistance to high voltage (or current), it

gives the effect of short-circuit. After the surge is over, the resistor offers high

resistance to make the gap non-conducting.

But though a lightning has the strength about 200kA, generally a surge arrester of

10kA is assembled in a main panel & 5kA for a branch panel for the protection (or

otherwise only one 20kA surge arrester for the main panel & no surge arresters for

branch panel). This is a contradiction. Let’s clear this, consider below figure.

Figure 3.6 - Anatomy of a Surge

Suppose a surge of 210kA occurs on a 3 phase transmission line. Then for a single

phase the surge will be70kA. In the transmission line it can flow through both

directions. So the surge for one side will be 35kA. The arrester of distribution

transformer then diverts about 20kA to the ground. When the rest of the surge, 15kA

meets the main panel surge arrester, it will be diverted to the earth (if possible

capacity of a surge arrester) or the rest part of the surge will be grounded by branch

panel surge arresters.



3.6 Lightning rods

3.6.1 Introduction

Lightning is an unpredictable event that can affect our electrical system any time

which has the high current capacity & high voltage capacity. Direct effects are from

resistive (ohmic) heating, arcing and burning. Indirect effects are more probable. On a

building without lightning protection, those same millions of volts of electricity still

have to get to the ground. Lightning will use the electrical wiring, telephone or cable

wiring, structural elements of the building, or anything else it can find as a path to

ground. None of these building elements is designed to safely carry this amount of

electricity. The result is a build-up of resistance, which leads to fire and explosive

damage to the building. Still it is impossible to guarantee 100% about a lightning

protection. But some percentage of protection can be taken from installing lightning

arresters. There are various types of lightning arresters. Among that finial rod type

lightning arrester is the most common type. This is made out of pure copper.

Lightning rod is the equipment that directly acts with a lightning.

Figure 3.7 – Rod Type Lightning Arrester

3.6.2 Installation of a Lightning Rod

The lightning rod must be installed in an appropriate angle to protect the building.

This protection angle varies according to the capacity of the lightning. Generally,

lightning arrester is fixed in a height that includes the building in 45 degrees of angle.



According to top area of the building multiple arresters may be used. Lightning rods

must be placed at regular intervals, preferably 20 feet apart, at most. The end rods

should be installed within at least one foot of the end of the roof, though two feet, at

most, is acceptable. The most suitable, but most cost way of fixing over head shield is

the Faraday cage, copper plate net with 2x2 square feet squares. But as this is very

high in cost, a copper tape is run around the top of the building & bottom of the

building. Then these two rounds are connected with copper tape (by all four sides or

at least two sides).

3.6.3. Grounding

After proper grounding is connected, the earth resistance must be smaller than 10

ohms. Depending on the earth resistance numbers of grounding rods are varied. At

least 2 rods are grounded at a distance same as the depth of the rod for grounding.

Depending on the size of your house, at least 2 groundings will be needed. If the

building is larger in perimeter than 250 feet but less than 350, the building needs three

groundings. If the perimeter is between 350 and 450 feet, it needs four, and so on. The

groundings should be at opposite corners of the house, if possible. If the copper rods

are not enough for decreasing resistance then a copper plate have to be used. It must

be laid in the ground such that the copper plate will make 30 degrees angle to vertical

axis.

3.6.4 Other accessories

A yellow bow must be kept to disconnect the grounding rod with the lightning rod to

measure the ground resistance time to time. And also earthing chamber must also be

kept

Figure 3.8 – Earthing Chamber



CHAPTER 4

Cables, Wiring & Circuits

In electrical systems, cables are used for carrying electrical currents. Most times core

of these cables are made of copper or Aluminum to conduct current with minimum

voltage drop. Most cables have a protective insulation to protect the cable & also to

protect living beings from dangerous voltages. Types of cables are differ according to

the,

1. Current go through (cable size)

2. Purpose they are used

3. Place (indoor or outdoor)

4. Protection level required

5. Etc.

Mainly the cable types can be categorized to below groups.

1. General Cables (cables which are used for general purposes)

2. Flexible Cables

3. Aluminum Cables (Bare conductors)

4. Armored Cables

5. Unarmored Cables

6. Auto Cables

7. Coaxial Cables

8. Telecommunication Cables

4.1. Cable Specifications

As previously said types of cables that are used is differs from various reasons.

Generally bare conductors are used for the transmission & distribution of low,

medium & high voltage. Armored & unarmored cables are used for the distribution of

electricity with in cities, factories & buildings. They are directly laid in ground where

excessive mechanical stresses likely to occur. Though the armored cables don’t need

any excess protection, unarmored cables must be provided some additional protection.

Other major type of cable used in low voltage distribution in rural & semi urban areas

is ABC (Arial Bundled Conductors) Cables. These are only few things about cables



4.2.1. Cable Anatomy

Below are some types of cables that have explained above.

4.1.a 4.1.b

4.1.c 4.1.d

4.1.e 4.1.f

Figure 4.1.a,b,c,d,e,f – Cable Types



From above figures it can be seen that some cables are consists of several strands. It

can be observed that though the cables have same cross sectional area if the number

of strands of cable is higher than the other it can carries a larger current than other

one. This incident happens because of electrons. Normally charges (here electrons)

stays in the surface of any conductive element. The numbers of strands are increased

means that the surface area of the cable is increased. That means it can take more

electrons (current). So, than other cables of same size flexible cables can take larger

currents.

4.2.2. Selection of Cables

Voltage Drop

Voltage drop is the reduction in voltage in an electrical circuit between the source and

load. When a cable is being selected for taking current for a specified machine, as per

IEEE regulations it is required to have the voltage drop of the cable less than 4% of

the nominal supply. This voltage drop must be included all the voltage drops in series.

That means maximum permissible voltage drop of a cable must be 4%. The factors

affecting for the voltage drop ate,

1. Resistance of the cable for 1m length (Voltage drop for 1m- [v/Am]) - Vc

2. Rated current of the cable (or carrying current) - I

3. Length of the cable - L

So Voltage drop of the cable (Vd) can be calculated as,

Vd= ILVc

Derating Factors

All the cables in the market are marked for a current that it can carry under standard

conditions. But always these standard conditions cannot be kept practically, in a

construction. So if a cable is selected according to the requirements (current)

according to our assemble method there can be variations of current. The factors that

are affecting for above variations are called as derating factors. They are,

1. Ambient temperature

2. Ground temperature

3. Depth of lying

4. Soil Thermal resistivity



So if a cable is being selected, we must consider derating factors which are mentioned

in cable catalogues.

4.2.3 Steps of Calculating the Cable for a given load

Let, we are given to calculate suitable cable size for a machine which have known

power consumption, Known input voltage. And also the distance from power supply

to load (L) is provided. Then,

Using the given data, calculate the load current I.

Select a wire that is a little bigger to carry I (Iwire > I)

Then multiply the rated current of selected wire with all the derating factors.

Find whether,

Iwire x derating factors < I

If so select next bigger wire size. If not select that wire

Then calculate the voltage drop of wire & nominal voltage drop & see whether

it is ok.

4.2.4 Normal Current Ratings for Wires

Current ratings for wires differ from manufacturer to manufacturer, though they are

almost similar. Below shows the approximated current ratings for given wire sizes

under standard conditions.


Wire size

(sq. mm)

Current Rating

(A)

1 121.5 162.5 194 246 3210 4016 6025 10035 12550 16070 20070 22595 250120 300150 350185 400

Table 4.1 – Approximated Current Ratings According to the Wire Size


According to these current ratings appropriate earth cables have to be selected.

According to IEC regulations, selection of protective earth cable is as follows.

Cross-sectional area Minimum cross-sectional area of phase conductors of the corresponding protective

S conductor (PE, PEN) Sp

mm2 mm2 S ≤ 16 S

16 < S ≤ 35 16 35 < S ≤ 400 S/2

400 < S ≤ 800 200 800 < S S/4

Table 4.2 – Selecting appropriate cable according to the phase wire

Note that the values in table are valid only if the protective conductor is made of the

same metal as the phase conductors.

4.3 Cable Lying

When a cable is being laid it is important, but generally forgotten factor is cable

bends. As per IEEE regulations according to cable diameter, the internal radii of cable

vary as follows.

Figure 4.2 – Cable Radii Variation with Cable Diameter

Cable Diameter Range (mm) Minimum internal radii (mm) - r

D < 10 D x 3

10 < D < 25 D x 4

25 < D D x 6

PVC/XLPE insulated armored circular

conductors

D x 6

PVC/XLPE insulated armored or

unarmored solid Al or shaped Cu

conductors

D x 8

Table 4.3 – Approximated Current Ratings According to the Wire Size


r

D


4.4 Ring Circuits & Other Special Circuits

4.4.1 Ring Circuit

Ring circuit is provided two independent conductors for live, neutral and protective

earth within a building for each connected load or socket. This design enables the use

of smaller-diameter wire than would be used in a radial circuit of equivalent total

current. Ideally, the ring acts like two radial circuits proceeding in opposite directions

around the ring, the dividing point between them dependent on the distribution of load

in the ring. If the load is evenly split across the two directions, the current in each

direction is half of the total, allowing the use of wire with half the current-carrying

capacity. In practice, the load does not always split evenly, so thicker wire is used.

Another advantage of ring circuits was an economy of cable and labor, as one could

connect a cable between two existing 15 A radially wired sockets to make one 30 A

ring, then adding as many sockets as were desired. This would leave the ring supplied

by two 15 A fuses, which worked well enough in practice, even if unconventional.

Rules for ring circuits say that the cable rating must be no less than two thirds of the

rating of the protective device. This means that the risk of sustained overloading of

the cable can be considered minimal. In practice, however, it is extremely uncommon

to encounter a ring with a protective device other than a 30 A fuse. The IEE Wiring

Regulations (BS 7671) permit an unlimited number of socket outlets to be installed on

a ring circuit, provided that the floor area served does not exceed 100 m2. In practice,

most small and medium houses have one ring circuit per storey, with larger premises

having more.

Ring circuits can have extra sockets added to them by adding a 'spur' onto a ring

circuit. A spur is a branch off the ring circuit, usually from an existing circuit,

although a junction box could also be used. Theoretically as many spurs as sockets

could be added, but the maximum load of the circuit (30/32amp) still exists). To

extend a spur further more a fuse must be connected. The rating of the fuse is decided

according to the power factor & the number of socket outlets.



Figure 4.3 – Ring Circuit

4.4.2 Converting 4 Pole MCCB for a Single Phase Supply or DC Supply

The protective equipments which is having over current protection, sometimes don’t

activate for an over current in one line only. It only activates if over current goes

through all 3 phases. In this case, if we wire an over current relay or a thermal

magnetic MCCB by using only 2 poles the protection system may not work properly.

To avoid this case it is wired as below.


30A Fuse

Power Supply

2.5mm wires

2.5mm wires1.5mm wires

1.5mm wires2.5mm wires

Fuse

Fuse


Figure 4.4 – Wiring Diagram of DC or Single Phase AC Supply to a 3 Phase MCCB

This connection allows equal heating in all 3 phases in case of a over current in the

provided phase.

4.5 Bimetal lugs

Whenever aluminium cable is to be terminated on copper bus bar or copper contact, if

aluminium lug is used then contact between terminal lug and copper bus bar being of

dissimilar metals, galvanic action takes place. Also if copper lug is used then contact

between aluminium cable and barrel of copper terminal lug is of dissimilar metal and

hence the galvanic action takes place. In order to prevent dissimilar contact and to

avoid galvanic action it is always advisable to use copper aluminium Bi-Metal lugs.

In Bi-Metal lugs barrel of the lug is of aluminium and the head or palm of the lug is of

copper. This ensures contact between aluminium cables to terminal lug is of

aluminium and contact between terminal lug to copper bus bar or contact is of copper.

Thus contact between dissimilar metal is avoided and contact between similar metal is

established. Thus Bi-Metallic or galvanic action is completely eliminated and hence

durable joint is achieved.

Electrolytic copper head / palm is friction welded to electrolytic aluminium barrel. At

the interface, copper molecules and aluminium molecules intermingles with each

other and form durable bond. Similarly if aluminium cable is to be joined with copper

cable then Bi-Metal in line connectors are to be used. Here for aluminium cable


L N

L N


aluminium barrel is provided and for copper cable copper barrel is provided. Copper

and aluminium barrels are friction welded. Depending upon application Bi-Metal

terminals, in line connectors, pin type connectors etc are manufactured.

Figure 4.5 – Bimetal Lugs



CHAPTER 5

Panel Boards & Distribution Boards

5.1 Introduction - Panel Board

A panel board (or distribution board) is a component of an electricity supply system

which divides an electrical power feed into subsidiary circuits, while providing a

protective fuse or circuit breaker for each circuit, in a common enclosure. Normally, a

main switch, and in recent boards, one or more Residual-current devices (RCD) or

Residual Current Breakers with Over current protection (RCBO), will also be

incorporated. Rather than providing separate protection systems, it is easier to use a

panel board. The main advantage of a panel board is, all the outgoing power circuits

& incoming power can be controlled at a single location. Since panel boards are with

protection systems it supplies overall protection to its subsidiary circuits. When a

construction of a high rise building or a factory, it is easy to use panel boards & sub

DB’s & also panel boards provides high protection & neat electric work for the

building.

Figure 5.1 – Distribution System of a Four Story Building


Main Panel

Sub DBFloor 1

Floor 1

Sub DBFloor 2

Floor 2

Sub DBFloor 3

Floor 3

Sub DB Floor 4

Floor 4

Electricalcomponents




Main Power Supply


5.2 IP Protection (Ingress Protection) of a Panel

A two-digit number established by the International Electro Technical Commission is

used to provide an Ingress Protection rating to a piece of electronic equipment or to an

enclosure for electronic equipment. The protection class after EN60529 is indicated

by short symbols that consist of the two code letters IP and a code numeral for the

amount of the protection. IP XX (e.g. – IP 54)

The two digits represent different forms of environmental influence:

• The first digit represents protection against ingress of solid objects.

• The second digit represents protection against ingress of liquids.

The larger value of each digit, the greater the protection. As an example, a product

rated IP54 would be better protected against environmental factors than another

similar product rated as IP42. IP rating tables are as below.

IP First number - Protection against solid objects

0 No special protection

1 Protected against solid objects up to 50 mm, e.g.

accidental touch by persons hands.

2 Protected against solid objects up to 12 mm, e.g. persons

fingers.

3 Protected against solid objects over 2.5 mm (tools and

wires).

4 Protected against solid objects over 1 mm (tools, wires,

and small wires).

5 Protected against dust limited ingress (no harmful

deposit).

6 Totally protected against dust.

Table 5.1 – IP Protection against Solid Bodies



IP Second Number – Protection against liquid

Table 5.2 – IP Protection against Liquid

According to above two charts it can be seen that there must be some ways to increase

the protection of a panel Board. They are,

Equal thickness of powder coating according to the standards – Insulate

enclosure to prevent hazards up to some level in case of a fault condition

Doors for panel boards with properly assembled & earthed

Cover plates which are tailor made for the panel – provides additional

protection after door is opened

Insulation of the Bus bars & Perspex sheets – provides additional protection

after cover plates are removed

Panel earthing – to ground in case of fault current

Using glands in cable cable entries

Sometimes, albeit rarely, the optional characters three and/or four may be used as

follows:

3rd Character – Optional access to live parts (A,B,C,D)

1. A - Back of hand


0 No protection.

1 Protection against vertically falling drops of water e.g. condensation.

2 Protection against direct sprays of water up to 15o from the vertical.

3 Protected against direct sprays of water up to 60o from the vertical.

4 Protection against water sprayed from all directions - limited ingress

permitted.

5 Protected against low pressure jets of water from all directions - limited

ingress.

6 Protected against temporary flooding of water, e.g. for use on ship

decks - limited ingress permitted.

7 Protected against the effect of immersion between 15 cm and 1 m.

8 Protects against long periods of immersion under pressure.


2. B - Finger

3. C - Tool

4. D - Wire

4th Character – Optional Supplementary Information ( H,M,S,W)

1. H - High voltage apparatus

2. M - Motion during water test

3. S - Stationary during water test

4. W -Weather conditions

Figure 5.2 – Inside view of a panel with cover plates

5.3 Motor Control Circuits

Mainly, 3 types of motor control circuits were learnt in detail during the training

period. They are,

1. Direct On Line Starter (DOL starter)

2. Star Delta Starter

3. Auto Transformer Starter

DOL Starter – This starter type is used for small motors, normally motors which

have power less than 10kW. If the motor type wanted is Star or Delta (We can

configure it), it must me manually connected. That means during the operation we



cannot change the motor type. There are 3 copper bars which are provided with the

motor, & using those, the motor can be configured as below.

Figure 5.3 – Terminal Connections of Motors

After motor is configured to star or delta, the supply should connect to the terminals

U1, V1, W1 according to the below diagram.

Figure 5.4 – Power & Control Circuit Diagram of a DOL Starter


U1 V1 W1

W2 U2 V2

Terminal connection of Motor

U1 V1 W1

W2 U2 V2

Star connection of Motor

U1 V1 W1

W2 U2 V2

Delta connection of Motor

Cu bar

Cu bars


Star Delta Starter

To decrease the starting current cage motors of medium and larger sizes are started at

a reduced supply voltage. The reduced supply voltage starting is applied in the Star

Delta methods. This is applicable to motors designed for delta connection in normal

running conditions. Both ends of each phase of the stator winding are brought out as

six terminals. For starting, the stator windings are connected in star and when the

machine is running the switch is thrown quickly to the running position by

automatically (It can be done manually also), thus connecting the motor in delta for

normal operation. The power diagram of Star Delta starter is shown below.

Figure 5.5 – Power Diagram of Star Delta Starter



When the motor is started in the star connection, the phase voltage of the motor is

reduced by a factor of √3. The starting line current of the motor will be reduced to a

1/3 value of DOL Delta starting. And ultimately power of the motor will be reduced

to a factor of 1/3. A disadvantage of this method is that the starting torque (which is

proportional to the square of the applied voltage) is also reduced to 1/3 of its delta

value.

Note that all six terminals of the motor are connected to wires. No copper bars are

used to configure the Delta connection; it is automatically done by the contactors

according to the control circuit. At the starting moment, line contactor & star

contactor are energized. After a time delay while star contactor is being de-energized,

the Delta contactor will be energized & work as a DOL Delta motor. The control

circuit of star delta starter is as below.

Figure 5.6 – Control Diagram of a Star Delta Starter


KL KS KD

Emergency Stop

KLPushON

TimerT1

T1

KD KS

T1

L

N

PushOFF


Auto Transformer Starter

This method also reduces the initial voltage applied to the motor and therefore the

starting current and torque. The motor, which can be connected permanently in delta

or in star, is switched first on reduced voltage from a 3-phase tapped auto -

transformer and when it has accelerated sufficiently, it is switched to the running (full

voltage) position. The principle is similar to star-delta starting and has similar

limitations. The advantage of the method is that the current and torque can be adjusted

to the required value, by taking the correct tapping on the autotransformer. This

method is more expensive because of the additional autotransformer and uses this

starter for motors above 80kW.

Consider figures 5.7 & 5.8. In this control system, firstly star contactor will be

energized. Soon after the transformer contactor will be energized. Then after a time

delay while main contactor is energized the star contactor will be energized. At this

moment, motor have got the full load. Then after a time delay, transformer contactor

also will be de energized.

Figure 5.7 – Control Diagram of an Auto Transformer Starter



Figure 5.8 – Power Diagram of an Auto Transformer Starter


M

U V W

Fuses

KM

MainContactor

KT

TransformerContactor

Auto Transformer

KS

StarContactor

OverCurrent

Relay


5.4 Capacitor Banks

5.4.1 Design

Capacitor banks are mainly installed to provide capacitive reactive compensation/

power factor correction. The use of capacitor banks has increased because they are

relatively inexpensive, easy and quick to install and can be deployed virtually

anywhere in the network. Its installation has other beneficial effects on the system

such as, improvement of the voltage at the load, better voltage regulation.

Normally in factories or other high power consuming places, most probably there will

be a consumption of inductive load. Inductive voltage means that there must be a

lagging power factor. In order to reduce the tariff & utilization of power the power

factor must be taken near to 1. That means power factor angle must be taken to zero.

To do this we supply a capacitive load to compensate the inductive load. This is the

system of a capacitor bank.

Figure5.9 – Phase Diagram

The power factor regulator combines comprehensive operation with user-friendly

control setting. It uses numerical techniques in computing the phase difference

between the fundamentals of current and voltage, thus precise power factor

measurement is achieved even in presence of harmonics. The power factor regulator

is designed to optimize the control of reactive power compensation. Reactive power

compensation is achieved by measuring continuously the reactive power of the system



and then compensated by the switching of capacitor banks. The sensitivity setting

optimizes the switching speed. With the inbuilt intelligent automatic switching

program, the power factor regulator further improves the switching efficiency by

reducing the number of switching operations required to achieve the desired power

factor.

Figure 5.10– Wiring Diagram of a Capacitor Bank


1234

ToContactors

OfCapacitor

Bank

On Load Changeover Switch

Power Factor

Regulator

A11

A12

A13

A14

A11 A12 A13 A14

A21 A24A23A22

To Load

Generator CEB

AuxiliarySupply

Capacitor Contactors

HRC Fuses


5.4.2 Uses of HRC Fuses

In electrical system fuse acts as protection device and depending on application

different type of fuse is to select. Out of these different type of fuses HRC is also one

of the type and it stands for “High Rupture Capacity". This type of fuses normally

used where some delay is acceptable for protecting the system. it has a advantage of

current limiting feature. So it is used for protection of contactors which may melt for

higher value of current. H.R.C fuses acts as secondary protecting devices [back up

protection]. This type of fuses normally used where some delay is acceptable for

protecting the system. That means this fuse will not burn out for a current pulse & as a

result of this it identifies a fault current & an inrush current separately. So these fuses

are used in series with motors & surge arresters.

5.4.3 Uses of Capacitor Contactors

Many customers use power-factor correction capacitors to increase the efficiencies of

their overall power systems. When switching capacitors in and out of the power

system, the switching device (contactor) can experience initial in-rush currents near

180x the nominal current. This high current can reduce the life of the contactor. The

Capacitor Contactors include early-make auxiliary contacts that bring pre-charge

resistors into the circuit to handle the high in-rush currents.

Figure 5.11 – Capacitor Contactors



5.5 ATS (Automatic Transfer Switch)

Transfer switches are critical components of any emergency or standby power system.

When the normal (preferred) source of power is lost, a transfer switch quickly and

safely shifts the load circuit from the normal source of power to the emergency

(alternate) source of power. This permits critical loads to continue running with

minimal or no outage. After the normal source of power has been restored, the re-

transfer process returns the load circuit to the normal power source. Transfer switches

are available with different operational modes including:

* Manual

* Automatic

Most of the times both of above are available as one unit according to the customer

requirements. ATS is mostly a relay logic control unit, but sometimes available as

programmable logic control unit. The typical control diagram of an ATS is as below.

The main items that are used in ATS are contactors with electrical & mechanical

interlocks. Two coupled contactors with mechanical interlocks doesn’t energize at the

same time. If one contactor is energized then automatically other contactor will be de-

energized. That means at any moment path is provided for only one source, not the

both of them.

Consider figure 5.11. The task of the timer T1 is, to wait a given time to observe

whether there is any failure again in the main supply ( To avoid continuous switching

in case of a back to back failures when generator runs) T2 timer is used to provide a

delay to energize CEB side. And T3 timer is used to provide a delay to energize

generator contactor (This is in case of a little time failure. To avoid the starting of a

generator for a little time failure)



Figure 5.12 – Typical Control Diagram of ATS



Figure 5.13 – Complete ATS Control Diagram


T1

R1

T

2K

1

T3

K2

T

1

PF

R1

EP

B1 R1

Auto

Man

ual

S

elec

tor

Sw

itch P

B1

PB

2K

1T

2

K1

K2

ON

OF

F

K2

K1

ON

OF

F

K2

PB

4

PB

3

T3

Auto

Man

ual

S

elec

tor

Sw

itch

EP

B2

PF

R2

Fu

se1

Fu

se2

K2

K2

R1

CE

BG

EN

Gen

erat

or

Sta

rt

Sig

nal

R1

Fig

ure

– A

TS

Co

ntr

ol

Dia

gra

m w

ith m

anual

Co

ntr

ol

Cir

cuit


CHAPTER 6

CONCLUSION

I’ve got a good opportunity to have my first compulsory session of industrial training

in EMP Group of Companies, Panagoda Sri Lanka. EMP Group of Companies is the

Sri Lanka’s leading solution provider of electrical solutions with global presence.

EMP honored a lot of awards for its outstanding performance and robust growth in

this sector.

During this valuable period I was able to take so much of hand on experiences

installation and troubleshooting of mobile telecommunication equipment. And also I

was able to have knowledge about project handling, electrical designing, ISO

standards, IEEE regulations & store keeping

Here I should mention that I was able to get a special opportunity to work together

technicians as well as engineers and share their knowledge and experiences. Those

things gave me a really good training as an engineering undergraduate.

Since EMP involving implementation of various electrical projects in Sri Lanka, I’ve

got much experience in techniques on implementation of a electrical project, as I

involved there. This made me to interact with various industry people, not only from

EMP, but from some other companies such as Holcim (Pvt.) LTD, Textile Apparel

(PVT) LTD etc. Since the implementation of project is going on in whole Sri Lanka,

I’ve got a chance to visit lot of sites in various places. By this I’ve got a vast

knowledge not only in technical and electrical sector but also in management field.

As well as The EMP staffs are very friendly and guided me a lot in the training. So, it

helps me to gain a better experience and work made my training valuable and

successful.



REFERENCES

1. IEEE Wiring Regulations

2. http://www.emp.lk/

3. http://www.lsis.biz/

4. http://wikipedia.org/

5. http://www.sierracables.com/Product_Range-2-1.html

6. http://www.electronics-manufacturers.com/info/electrical-components/air-

circuit-breaker.html


http://www.electronics-manufacturers.com/info/electrical-components/air-circuit-breaker.html

http://www.electronics-manufacturers.com/info/electrical-components/air-circuit-breaker.html

http://www.sierracables.com/Product_Range-2-1.html

http://wikipedia.org/

http://www.lsis.biz/

http://www.emp.lk/


ABBREVIATIONS

1. AC - Alternative Current

2. ACB - Air Circuit Breaker

3. ATS - Automatic Transfer Switch

4. DB - Distribution Board

5. DC - Direct Current

6. EFR - Earth Fault Relay

7. ELCB - Earth Leakage Circuit Breaker

8. ELR - Earth Leakage Relay

9. HRC - High Rupture Capacity

10. IEEE - Institution of Electrical & Electronic Engineers

11. IP - Ingress Protection

12. MCB - Miniature Circuit Breaker

13. MCCB- Molded Case

14. OCB - Oil Circuit Breaker

15. PFR - Phase Failure Relay

16. PVC - Poly Vinyl Chloride

17. RCBO – Residual Current Circuit Breaker with Over Current Protection

18. RCCB - Residual Current Circuit Breaker

19. RCD - Residual Current Device

20. UVT - Under Voltage Trip

21. VCB - Vacuum Circuit Breaker

22. XLPE - Cross Link Poly Ethylene


panel boards and wiring

Documents