1. SUMMER INTERNSHIP REPORT
(22/05/2015 – 25/07/2015)
ON
BUSBAR TRUNKING SYSTEM
UNDER THE GUIDANCE OF
Mr. UDIT SHARMA
Assistant Manager
Switchgear Design and Development Centre
Electrical & Automation Independent Company
AT
LARSEN AND TOUBRO
SUBMITTED BY
AMAN LONARE
ROLL NO – 13085
DEPARTMENT OF MECHANICAL ENGINEERING
INDIAN INSTITUTE OF TECHNOLOGY KANPUR

2. ABOUT THE ORGANISATION
Larsen & Toubro Limited, also known as L&T, is an Indian multinational
company head quartered in Mumbai, Maharashtra, India. It was founded by
Danish engineers taking refuge in India, as well as an Indian financing partner.
The company has business interests in engineering, construction, manufacturing
goods, information technology, and financial services,and also has an office in
the Middle East and other parts of Asia.
L&T is India's largest engineering and construction company. Considered to be
the “bellwether of India's engineering & construction sector", L&T was
recognized as the Company of the year in Economic Times 2010 awards.
L&T has delivered Engineering, Procurement and Construction (EPC) services
for many projects in the upstream hydrocarbon sector over the last two decades,
in India, Middle East, Africa, South East Africa and Australia.
L&T Power has set up an organization focused on coal-based, gas-based and
nuclear power projects. L&T has formed two joint ventures with Mitsubishi
Heavy Industries, Japan to manufacture super critical boilers and steam turbine
generators.
The design wing of L&T ECC is called EDRC (Engineering Design and
Research Centre). EDRC provides consultancy, design and total engineering
solutions to customers. It carries out basic and detailed design for both
residential and commercial projects.

3. ABOUT THE PROJECT
I was assigned to the Busbar Trunking Team, where I and my fellow interns
were assigned work on the design of the three phase Busbars that L&T is
currently in the stage of developing, improving upon the work of their recently
acquired partner Henikwon’s S-Line busduct systems for low and medium
voltages.
BUSBAR TRUNKINGSYSTEM
In electric power distribution a Busbar is a metallic strip or bar (typically copper,
brass or aluminium) that conducts electricity within switchgear, distribution
board, substation, battery bank, or other electrical apparatus. Its main purpose is to
conduct a substantial current of electricity, and not to function as a structural member.
The material composition and cross-sectional size of the busbar determine the
maximum amount of current that can be safely carried.
Busbar trunking system in compact design is the most efficient, safe and ideal system
for electricity supply to industrial installations and high rise structures, offering a
wide current range from 125A to 2000A in type CBC (Copper conductor) and 160A
to 1250A in type CBA (Aluminium conductor). The system has been designed
especially for installations and projects where power supply has to be made available
rapidly. These are most suitable for applications where exact location and power
consumption is not sure and possible changes in physical distribution of loads are
envisaged.
BUSDUCT SYSTEM
Busduct system is an assembly comprising a system of conductors with one or more
bars separated or supported by insulating material and contained in a conduit or
similar casing
There are mainly two types of Busduct system:
1. Conventional System.
2. Sandwich System.
Busduct is manufactured into totally enclosed, pre-fabricated sections consisting of
copper or aluminium busbars. Power is simply tapped off by plug-in points
positioned at required intervals. Typically, a Busduct system will consist straight
lengths, elbows, end feed boxes, end covers, tap-off units and other special
components.
Busduct system has several key advantages over conventional forms of power
distribution:

4. • Reduced on site installation time when compared to hard wired system, thus leading
to costsaving.
• Increased flexibility in design and versatility for future modifications.
• Increased safety features brought about by the use of high-quality manufactured
components, which provide greater safety and peace of mind for specifies,
contractors and end users.
Sandwich Busduct System
The Sandwich system is a lightweight, low impedance, non-ventilated, naturally
cooled and totally-enclosed system. The system is available with 50% internal
earthing, 50% or 100% neutral busbar. To address harmonics, 200% neutral busbar is
also available.
99.99% pure copper Busbars are tin/silver coated to protect them from water and
moisture that can cause reduction in dielectric strength. Likewise, aluminium Busbars
are made of high-conductivity electrical grade aluminium (99.96% pure aluminium).
All joints are direct contact joints, which ensures total and higher surface area
contact, results in less power-loss and cooler performance. A maintenance-free lock
nut is provided where the outer head will be twisted off, once it reaches the
appropriate torque.
The housing is of galvanized steel or aluminium with epoxy power-coated by an
automated process to achieve fire resistance. The housing also gives integral ground
as standard requirement where it acts as an earth conductor. Due to its compact,
sandwich type construction, it does not require an internal fire-stop barrier.
Conventional System
This is a totally metal-enclosed air insulated Busduct system and are low-capacity
power supply systems which are widely used for various factories, machine shops,
school laboratories and commercial buildings. For most indoor locations where there
is a need for small blocks of conveniently available power, the conventional system
serves as a highly rationalized solution with various features.
The bus conductor is available in tin-plated 99.99% pure copper. Busbar is
supported with fibreglass reinforced SMC insulator which withstands above 180

5. degree Celsius.
The indoor Busduct is totally enclosed in non-ventilated housing made of 1.6mm
thick epoxy powder-coated electro-galvanized steel sheet.
We were assigned three broad tasks (two minor and one major) which will
be outlined in this report. The first minor task, which would later form a subset
of the major task, was to find an alternative method for the computation of the
AC resistance of the conductors as affected by skin and proximity effects, in
order to verify the previously assembled data by the engineers at Henikwon.
The second minor task was to collate data collected from L&T’s competitors
and assemble it into a coherent and user friendly format so that it may be easily
subjected to quick analysis. Where necessary we were also required to perform
numerical analysis on this data and calculate certain data that was not
mentioned. This task had the added benefit of allowing us to familiarize
ourselves with busbar trunking and the considerations involved in its design.
The third, major task assigned to us, which may be said to have formed the bulk
of our training, was to develop a system to design busbars and present their
dimensions, keeping in mind the various factors that come into play so that the
most efficient use may be got out of it while keeping physical conditions in
mind.
SKIN EFFECT
Skin effect is the tendency of Alternating current (AC) to become distributed within
a conductor such that the current density is largest near the surface of the conductor,
and decreases with greater depths in the conductor. The electric current flows mainly
at the "skin" of the conductor, between the outer surface and a level called the skin
depth. The skin effect causes the effective resistance of the conductor to increase at
higher frequencies where the skin depth is smaller, thus reducing the effective cross-

6. section of the conductor. The skin effect is due to opposing eddy currents induced by
the changing magnetic field resulting from the alternating current.
An alternating current in a conductor produces an alternating magnetic field in and
around the conductor. When the intensity of current in a conductor changes, the
magnetic field also changes. The change in the magnetic field, in turn, creates an
electric field which opposes the change in current intensity. This opposing electric
field is called counter-electromotive force (back EMF). The back EMF is strongest at
the centre of the conductor, and forces the conducting electrons to the outside of the
conductor, as shown in the diagram.
PROXIMITY EFFECT
In the foregoing consideration of skin effect it has been assumed that the conductor is
isolated and at such a distance from the return conductor that the effect of the current
in it can be neglected. When conductors are close together, particularly in low voltage
equipment, a further distortion of current density results from the interaction of the
magnetic fields of other conductors.
In the same way as an e.m.f. may be induced in a conductor by its own magnetic flux,
so may the magnetic flux of one conductor produce an e.m.f. in any other conductor
sufficiently near for the effect to be significant.
If two such conductors carry currents in opposite directions, their electro-magnetic
fields are opposed to one another and tend to force one another apart. This results in a
decrease of flux linkages around the adjacent parts of the conductors and an increase
in the more remote parts, which leads to a concentration of current in the adjacent
parts where the opposing e.m.f. is a minimum. If the currents in the conductors are in
the same direction the action is reversed and they tend to crowd into the more remote
parts of the conductors.

7. This effect, known as the 'proximity effect' (or 'shape effect'), tends usually to
increase the apparent a.c. resistance. In some cases, however, proximity effect may
tend to neutralise the skin effect and produce a better distribution of current as in the
case of strip conductors arranged with their flat sides towards one another.
We were also required to familiarize ourselves with the calculations and results
of the engineers at Henikwon for their design of low and medium voltage
busbar systems. We were particularly recommended to concern ourselves with
the physical dimensions and number of conductors required for the various
generally accepted current ratings and the electrical characteristics for busbars
made of both copper and aluminium and operating at frequencies of 50 and 60
Hz. For these purposes we were given access to the data published by
Henikwon and were provided with the calculations used by the engineers and
aided in familiarizing ourselves with the methods applied by them.
This initial study of generally accepted conditions and practices allowed us an
insight on what methods the electrical industry followed and what theory,
calculations and assumptions this data is based on. A lot of the formulae and
assumptions that we came across were based on experimentally acquired data
and as the general study and understanding of the electromagnetic phenomena
is far from complete a lot of broad assumptions, neglect of certain effects and
anomalies were observed.
Thanks to our introductory studies we were armed with the basic understanding
and knowledge required for the various tasks and challenges assigned to us over
the course of our training.

8. FIRST TASK
The first task assign to us was to calculate the resistance of the three phase copper
busbars with 0.6mm spacing and verify the resistances calculated by engineers of
Henikwon. . This task was deemed necessary as Henikwon’s proposed designs had
not yet been subjected to rigorous testing.
The need to find a different method to calculate ac resistance was felt as the method
used by Henikwon’s engineers was novel and based purely on the curve tracing to
develop a formula based on experimentally acquired data. While this method was
commendable, it had no solid grounding in the numerous books and papers referred
to by us. I would like to state that there seems to be no consensus amongst the
academics about the exact numerical method to calculate the altered resistance of an
ac conductorbased on skin effect and proximity effect. Available methods for
calculating the resistance are based on graphs formed using the results of exhaustive
experimentation. The method we arrived at was based on the following, generally
accepted graph:

9. The use of d.c resistance (represented by Ro in the graph) and frequency, as well as a
ratio of the dimensions could be used to calculate the skin effect ratio. The sketching
of this graph and the approximation of intermediary curves allowed me to arrive at
satisfactory values of the skin effect ratio.
Graph of the above sort for various ratios of width to thickness were used to calculate
the proximity effect ratio for the conductors where the parameter p could be found
using the formula:
The values I calculated using these graphical methods were close enough to the
values calculated by Henikwon engineers to confirm the relative accuracy of
Henikwon’s methods. The method, while productive of desirable results, involved too
many approximations to be entirely satisfactory, and we improved on it later as can
be seen in the section dedicated to the third task, of which the first task could be
viewed as a preliminary subset.

10. SECOND TASK
The next task assigned to us involved the collecting, organizing and comparison of
data concerning the busbardesigns of the various competitors of L&T. The purpose
of this task was to give a quick overview of the current market situation and the
prevalent trends in busbardesign. It would also allow for the comparing of L&T’s
data to the data made available by industry leaders and allow L&T to determine the
position they would be likely to occupyin terms of benefits offered by and the
drawbacks of their products. This data would also be highly helpful in designing
busbars as well as it would provide a region for the calculations for an given current
rating, and outline the area within which the various parameters of a given conductor
may fall, thus providing an alternative system for verification.

11. We used the brochures supplied byABB, C&S, Eaton, Powerbar, Schneider,
Henikwon, and in addition to this we also included L&T’s projected values for their
S-Line technology. Fordifferent current ratings, we considered the busbar cross-
sectional area and the number of conductors used per phase. We compared the
weights of the trunking system for various configurations of conductors (3P, 3W; 3P,
4W; 3P, 5W; 3P, 3W+50% Earth; 3P, 4W+50% Earth, 3P, 5W+50% Earth). The
values of short time current withstand for a fault lasting one second, ac resistance at
20 deg. Celsius, ac resistance at 80 deg. Celsius, reactance, impedance and voltage
drop for different power factors were also compared. All of these parameters were
considered for both copperand aluminium and at frequencies of 50Hz and 60Hz.
In several places the data supplied was insufficient, i.e., data was not available for all
heads of comparison. In certain cases we were able to fill the gap using simple
formulae and deductions. Where voltage drop was missing, our knowledge of the
impedance and the standard formula enabled us to calculate the likely voltage drop
based on the universally accepted formula
I = Rated Current
Rc = A.C resistance
Xc = Reactance
We were also able to estimate the dimensions (width and thickness) and the number
of conductors perbundle based on the general trend for various current ratings and
the assumption that the thickness was constantly considered to be 6mm.
Upon examination of this data we were able to arrive at certain empirical conclusions
about bus bar trunking design and the electrical parameters associated with it. We
were also able to form a general idea of what considerations were involved in the
design of busbars and which parameters ought to be kept in mind while designing a
busbartrunking system.

12. THIRD TASK
The final task that formed the bulk of our training involved the development of a
method to design a busbar with near ideal dimensions that would allow it to be best
suited to its practical applications.
We were requested to start from scratch, our supervisor believing that our lack of
industry exposure may well be an advantage for us. Our initial preparation for the
task involved extensive reading on the subject of busbar trunking, and the formation
of a general picture of the calculations we would be required to do and the data that
would be required for the aforementioned calculations to be performed.
Preliminary forays into the realms of calculations illustrated the inadequacy of the
available data and formulae and the need for several assumptions. We also realised
that the only approachto calculating the dimensions (i.e., the cross-sectional area) of
the conductors was iterative. Therefore it was decided that it would be necessary to
assume values for the cross sectional area and then proceed by trial and error to arrive
at the most suitable value. The suitable value must be decided by the most
advantageous values of the parameters under consideration.
We were already supplied with certain values around which to revolve our trials
owing to the data compiled during the second task, therefore it was deemed
unnecessary by our supervisor for us to actually perform the iterations and arrive at a
value. He recommended we focus instead on developing a method by which to best
calculate the various electrical parameters (dc resistance, ac resistance, reactance,
voltage drop and losses). We were required to make these procedures as accurate as
possible, keeping considerations for practical applications in mind and allowing for
the neglect of minor deviations.
As voltage drop and losses are easily derivative of impedance, the major challenge
was finding the resistance and reactance. I had already studied an approximate
method for the calculation of ac resistance which was sufficient for the task of
verification but highly unsuitable in a scenario where some degree of accuracy was
required. We discovered a formula developed based on the curve already shown
above for the calculation of skin effect factor. Upon testing this formula with respect
to already available data, we found it provided satisfactory accuracy in the values
rendered and thus we considered it suitable to the purpose. In the formula given
below ‘a’indicates the thickness and ‘b’indicates the width of the conductor.

13. The next step was to consider the change in resistance due to proximity effect. The
available data for proximity effect on rectangular copperconductors was inadequate
and there seemed to be a general lack of consensus on methods of calculating its
effects on resistance. The methods available were highly complex and involved the
application of FEM methodology whereas we had been abjured by our supervisor to
use purely non-programming based methods of calculation. No simplified formula
presented itself. We did, however, manage to gather from our research that the
proximity effect depended on the dimensions of the conductor, inter-conductor
spacing and frequency of the current flowing through the conductor. Forlower
frequencies it was allowable to ignore the proximity effect and for the lower cross-
section of area correspondingto lower currents the proximity effect is judged to be
sufficiently low and thus may be safely neglected. Thus we proceeded on to the
considerations of reactance, judging the effects of proximity to be comparatively
unimportant.
The studies concerning skin and proximity effects of conductors onreactance took up
a considerable amount of time as again there was an insufficiency of available
material on how to calculate these effects without the application of integral
techniques or FEM, and we could consider neither method as we were limited by the
need to avoid the use of any programming techniques. However upon examining
several papers it was borne upon us that the industrial and academic researchers were
alike in stating that for the calculation of reactance, proximity effect was in general,
universally ignored, and the reactance was determined using any number of available
formulae for self and mutual inductance. After safely concluding that this was the
accepted norm, and not just an anomalous assumption, we decided to proceed with
the calculation of reactance by finding the inductance of the conductor.

15. It is also possible to calculate the inductances using the formulae developed by Piatek,
Baron, Szczegielniak, Kusiak and Pasierbek
Considering the figure:
For self-inductance:
For mutual Inductance:
The above formula can be considered keeping in mind and accounting for the phase
difference between the two conductors under consideration. It can similarly be
applied to the other phase and the sum of the three terms so obtained may give us the
total inductance at any instant.
Keeping these formulae in mind and assembling them and their results in a systematic
manner we can assemble a procedurefor calculating and comparing the parameters
for various cross sectional areas of the conductors to be used in three phase bus bars.

16. OTHER MINOR TASKS
We were privileged to benefit from many conversations with our supervisor on both
technical issues as well as industrial and marketing ones.
We were given an introductory tutorial in the use of the PRO Engineer and ANSYS
software. We were guided in their application to observing and quantifying the
magnetic field around a current carrying bodyand were allowed some time to
experiment and familiarize ourselves with ANSYS.
I also learned to export 3D model to PDF and editing drawings. I learnt some basic
commands and tools, design few practice models and did some very basic assemblies.
Pro-Engineer
Pro-Engineer is a 3D CAM feature-based, associative solid modelling software. It is a
collaborative applications that provide solid modelling, assembly modelling, 2D
orthographic views, finite element analysis etc for mechanical designers.
Pro-Engineer can be used to create a complete 3D digital model of manufactured
goods. Themodels consistof 2D and 3D solid model data which can also be used
downstream in finite element analysis. A productand its entire bill of materials
(BOM) can be modelled accurately with fully associative engineering drawings.

17. We even went to test station to perform tests on the busbarsample. We were given an
assignment of understanding impulse withstand test. We assisted our seniors during
testing. We learnt the testing procedure, specifications & purposeof test. Before the
test we prepared test set-up & assembled double stack busbar assembly with two joint
blocks. We also assemble the Busduct system and performed an impulse voltage test
on Busduct to check the insulation level and performance.

18. Impulse Withstand Test
Electrical equipment must be capable of withstanding overvoltages during operation.
Thus by suitable testing procedurewe must ensure that this is done.
In addition to the ordinary temporary overvoltages, usually incoming from the supply
line, the plants and the relevant assemblies are prospective victims of peak and
transient not-linear overvoltages due to atmospheric causes (fulminations) both direct,
when they affect materially the structure, as well as
indirect, when their effect is generated by the electromagnetic fields induced around
the impact point of the lightning.
High voltage testing can be broadly classified into testing of insulating materials
(samples of dielectrics) and tests on completed equipment.
The capability of the assemblies to withstand such stresses depends all on the
dielectric strength of the air between the two live parts carrying the impulse.
The test is passed if no discharges are detected

19. ACKNOWLEDGMENT:
The internship I had with Larsen and toubro was a great chance for
learning and professional development. Therefore, I consider myself as a
very lucky individual as I was provided with an opportunity to be a part of
it. I am also grateful for having a chance to meet so many wonderful
people and professionals who led me through this internship period.
I am using this opportunity to express my deepest gratitude and special
thanks to the Mr. Udit Sharma (Assistant Manager) who in spite of being
extraordinary busy with his duties, took time out to hear, guide and keep
me on the correct path and allowing me to carry out my project at their
esteemed organization and extending during the training.
It is my radiant sentiment to place on record my best regards, deepest
sense of gratitude to Mr. Nitin L. Hande, Mr. Atul Asodekar, Ms. Pooja
Deshmukh, Ms. Laxmi Priya, Ms. Jayshree Joshi, Mr. Kiran Patil and Mr.
Ketan Patil for their careful and precious guidance which were extremely
valuable for my study both theoretically and practically.
I perceive as this opportunity as a big milestone in my career development.
I will strive to use gained skills and knowledge in the best possible way,
and I will continue to work on their improvement, in order to attain desired
career objectives. Hope to continue cooperation with all of you in the
future.
Aman Lonare
20th July 2015

20. REFERENCES:
1. Industrial Power Engineering Handbook-K.C. Agarwal
2. Extra losses caused in high current conductors by skin and proximity effects- A.
Ducluzaux
3. Copperfor Busbars- Guidance for Design and Installation- CopperDevelop-
ment Association
4. Electrical Coils and Conduits- H.B. Dwight
5. Some Proximity Effect Formulas for Bus Enclosures- H.B. Dwight
6. Copperof busbars-www.apqi.org
7. Self-Inductance of long conductors ofrectangular cross-section-Zygmunt Pi-
atek, Bernard Baron, Tomas Szczegielniak, Dariusz Kusiak, Artur Pasierbek
8. Mutual Inductance of long rectangular conductors-Zygmunt Piatek, Bernard
Baron, Tomas Szczegielniak, Dariusz Kusiak, Artur Pasierbek
9. Formulas and Tables for Mutual and Self-inductance- E.B. Roas and F.W.
grover
10.Experimental and numerical evaluation of busbar trunking impedance- Y. Du, J.
Burnett, Z.C. Fu
11.Modeling Skin and Proximity effects with Reduced Reliazable RL Circuits-
Shizhong Mei & Yehea I. Ismail
12.Exact Inductance Equations for Rectangular Conductors with Applications to
More Complicated Geometries- Cletus Hoer and Carl Love