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7/28/2019 Arc Welding Power Source
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Arc Welding Power Source
By: Nanaksharan Singh
Welding Technology
CBL
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Introduction
Welding is a process of joining two metals. To make ajoint of two metals immense heat is required. This
heat is created in the form of an electric arc. To create
this arc a Power Source is required
.An arc welding power source is designed to changehigh voltage low amperage current into a safe lowvoltage (between 50 and 100 volts) heavy currentsupply (even above 500 Amperes) suitable for arcwelding. Power source is required to supply thecurrent that supports the arc column for fusion
welding
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power sources can be divided into three main categories
AC Power Source
e.g. Transformers and Alternator
DC Power Source
e.g. generator and Rectifier
Combination AC & DC Power Source
e.g. AC transformers with DC rectifiers.
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AC- Power Source
A welding transformer changes high voltage, low
amperage power to low voltage, high amperagewelding power.
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For a Transformer, the significant
relationship between voltages and
current and the turns in the primary
and secondary winding are as follows:-
N1/N2= E1/E2 = I1/I2
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DC Power SourceThe This type of power source is operated from the mains supply.
transformer steps down the mains voltage to a suitable weldingvoltage,
The rectifier changes the alternating current into direct current.
Very often this type of machine can be switched to give eitheralternating or direct current as required.
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ELECTRIC MOTOR DRIVEN
GENERATOR
The d.c. generator is a rotating
machine which can be driven by
an electric motor, petrol or diesel
engine.
DEISEL ENGINE DRIVEN
The engine driven type is
generally used for site work.
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Inverter Power Source
An inverter power source is different from a
transformer-rectifier type in that inverter
rectifies ac line current, uses an inverter
circuit to produce high frequency ac,reduces that voltage with an ac transformer,
and rectifies that to obtain the required dc
output.
Changing the ac frequency to a much higherfrequency allows a greatly reduced size of
transformer & reduced transformer losses.
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Basic relationship that applies to all
transformers:
V=NAfK
Where:-The magnitude of voltage to be transformed (V) is proportional to the
no. of turns of wire on the transformer coil (N), the cross-sectional
area of the transformer core (A), the frequency of the AC Voltage to
be transformed (f) and various design constants (K)
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Duty Cycle
Fundamentally, the Duty Cycle is a ratio of the Load- On
Time allowed in a specified time interval time.
National Electrical Manufacturers Association (NEMA)
specifies duty cycle based on a test interval of 10
minutes in an ambient temp. of 400C.
A 60%NEMA duty cycle means that the power source
can deliver its rated output for 6 out of every 10
minutes without overheating
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Duty Cycle at other than rated outputs as
follows:-
Ta = (I/Ia)2 X T
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Volt-Ampere Characteristics
Types of Welding Power Source
Constant Current Power Source Constant Voltage Power Source
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Constant Current Power Source
A welding power source which will produce a relatively small
change in amperage despite changes in voltage caused by a
varying arc length. Used mostly for welding with coated
electrodes.
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Constant Voltage Power Source
A welding power source which will produce a relatively small change
in voltage when the amperage is changed substantially. Used mostly
for welding with solid or flux cored electrodes.
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Polarity
The term Polarity is used to describe the electrical
connection of the electrode in relation to the terminal of a
power source. With direct current (DC), when the
electrode is connected to the +Ve terminal, the polarity is
designated as a direct current electrode positive (DCEP).When electrode is connected to theVe terminal, the
polarity is designated as a direct current electrode
negative (DCEN).
When alternating current (AC) is used, the polarity changesevery half cycle of 50Hz
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DCEN (Straight Pol.) DCEP (Reverse Pol.)
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Safe practice and accident avoidance
Make Sure all insulation is tight & secure before turning on Power.
Dont touch electrically live parts with bare skin, Do Not work withwet gloves, shoes or clothing.
Welding leads and return leads should be insulated and thickenough to carry the current safely; connectors should also beinsulated to avoid inadvertent access to live conductors andadequate for the current being carried.
The welding return lead should be connected as near as practicableto the welding arc; metal rails, pipes and frames should not be usedas part of the welding circuit unless they are a part of the workpieceitself.
The welding leads, connection devices and electrode holder or torchshould be checked at regular intervals for 'fitness for use'; repair orreplace damaged or worn components.
Inspect frequently and immediately replace worn or damaged parts. Always disconnect power source before performing any
maintenance.
Recommended Welding Cable Size
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Recommended Welding Cable SizeTotal length of copper cable in weld Ckt.
AMPS 15 m 30m 45m 60m
100 16 mm2 25 mm2 25 mm2 25 mm2
150 25 mm2 25 mm2 25 mm2 35 mm2
200 35 mm2 35 mm2 35 mm2 50 mm2
250 50(mm)2 50 mm2 50 mm2 70 mm2
300 70 mm2 70 mm2 70 mm2 95 mm2
350 95 mm2 95 mm2 95 mm2 105 mm2
400 95(mm)2
95 mm2 95 mm2 105 mm2500 105 mm2 105 mm2 105 mm2 ------
Reference : WELSPRING UNIVERSAL
(Govt. Recognized Export House)
New Delhi (INDIA)
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