The Design And Construction Of Electric Arc Welding Machine
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TABLE OF CONTENT
Title page
Certification
Dedication
Acknowledgement
Table of content
CHAPTER ONE
1.0
Introduction
1.1 History
1.2
Aims/objective
1.3
Scope
1.4
Principle of transformer Operation
1.5
Equivalent Circuit of the Machine
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CHAPTER TWO
2.0
Literature Review
2.1
Transformer Design
2.2
Coil Design
2.3
Core Design
2.4
Specification for design
CHAPTER THREE
3.0
Construction
3.1
Lamination
3.2
Transformer former
3.3
Copper coils
3.4
Insulating Materials
3.5
Methodology
3.6
Test and Operating Conditions
3.7
Operating Conditions
3.8
Conclusion
3.9
Recommendation
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REFERENCES
CHAPTER ONE
HISTORY/INTRODUCTION
1.0
The machine is specially designed for industrial and agricultural
welding. It is only powered from A.C power source for all welding.
The unit is designed to operate on single phase 240v A.C. supply and it is
mainly a transformer unit. It is capable of operating from 25 Amps socket for
most of its output range. The current drawn form the mains supply may exceed
the 25 Amps, hence the unit must be provided with 30A switch fuse input as
those provided for electric cookers, heaters etc. this connection must be made
to the dead side of a 30A circuit. The circuit should not be shared by any other
appliance.
The unit consists of the following main components single phase
transformer (with tap changing secondary). The transformer is a step-down
transformer with different tapping at H, M and L; welding tung cables.
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The transformer is a conventional-cooled, single phase transformer
which has shell type of lamination core and insulated windings of copper cols.
In addition, the windings are given double insulation with the use of varnish
solution which helps to prevent short-circuiting in the windings.
With the help of Angle iron and lamination core, the core loss, iron loss in the
machine is reduced to minimum. They also help to reduce humming in the
machine. Hence, efficiency of the machine is greatly improved.
1.1
AIMS AND OBJECTIVES
Sequel to the vast need and use of iron rods, metal bars and pipes, right from
the domestic level up to industrial extent, the arc welding machine was built in
order to ensure that the ulterior motive of the manufacturers of these products
(iron rods, metal bars and pipes) by their manufacturers is being achieved as
part f technological advancement. With the electric Arc welding machine, the
difficulty of using iron rods, bars and pipes in construction works has been
removed.
Moreso, the Arc welding machine has also contributed a lot towards the
economy of life in such a way that when products like machine tools,
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agricultural tools, machine parts, motor parts etc get broken, they could be
restored to usage, or made functional once again through welding, by the use of
the electric Arc welding machine. In that respect, the problem has been solved
without going back to purchase a new one.
1.2
SCOPE
The machine is specially designed for industrial and agricultural welding. It is
powered from single phase, 240v 50Hz power supply. It is operated from 30A
socket.
During use; when tap changing, the entire machine should be off before tap
changing the load terminal when welding.
When there is low welding current and due to variation of power supply,
a higher tap should be used to increase the welding current.
This electric Arc welding machine is a heavy duty welding machine
which is capable of welding all or 12 gauges of electrodes, while in operation.
For material cutting, the machine should be tapped at the highest
tapping, although cutting is not very effective at low voltage supply.
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1.3
PRINCIPLE OF TRANSFORMER OPERATION
An alternating voltage applied to P circulates an alternating current through P
and this current produces an alternating flux in the iron core, the mean path of
this flux being represented by the dotted line D. if the whole of the flux
produced by P pass through S, the emf induced in each turn is the same for P
and S. hence if N1 and N2 be the number of turns on P and S respectively (refer
to fig. 2.0).
Total emf induced in S
= N2 x emf per turn = N2
Total emf induced in P
= N1 x emf per turn = N1
When the secondary S is open circuit, its terminal voltage is the same as the
induced emf. The primary current is then very small, so that the applied voltage
V1 is practically equal and opposite to emf induced in P, hence
V2 = N2
V1
N1
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Since the full load efficiency of a transformer is nearly 100 percent, I 1V1 x
primary power factor = I2V2 x secondary power factor. But, the primary and
secondary power factor at full load are nearly equal
I1 = V2
I2
V1
When a load is connected across secondary terminals (short circuited), the
secondary current
- by Lenz’s law produces a demagnetizing effect.
Consequently, the flux and the emf induced in the primary are reduce slightly.
But this small change may increase the difference between the applied voltage
and the e.m.f induced in the primary from say 0.05% to say 1%, in which case
the new primary current would be 20 times the no-load current. The
demagnetizing ampere-turns of the secondary is thus nearly neutralized by the
increase in the primary ampere-turns and since the primary ampere-turns on no
load are very small compared with the full load ampere-turns.
- full load primary ampere-turns = full load secondary ampere-turns.
i.e I1N2 = I2N2
so that I1 = N2 = V2
I2
N1
V1
It will be seen that the magnetic flux forms the connecting link between the
primary and secondary currents and that any variation of the secondary
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current is compared by a small variation of the flux and therefore of the
e.m.f induced in the primary, thereby enabling the primary current to vary
approximately proportional to the secondary current. This balance of
primary and secondary ampere-turns is an important relationship whenever
transformer action occurs.
1.4
EQUIVALENT CIRCUIT OF THE MACHINE
ZP
I1
RP
XP
Io
I1ZP
V1
Input
voltage
V1
R
Ic
X
x
Imag
Fig. 1.4
x
Zs
I2
XS
I2
RS
I2ZS
E2
V2
To
Load
Fig. 1.4
RP and RS are resistances equal to resistance of the primary and secondary
windings of the machine.
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Similarly, inductive reactance XP and XS represent the reactance of the
windings due to leakage flux in the machine. The inductance reactor X is such
that it takes a reactive current equal to the magnetizing current (I M) of the
transformer. The core losses due to hysteresis and eddy currents are allowed
for by a resistor R of such value that it takes a current IC equal to the core-loss
component at the primary current, i.e IC2R is equal to the core loss of the actual
transformer. The resultant of (IM) and IC is IO.
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