Download Electricity - Olds High School

120102b
Welder
Electricity
Welding Technology and Properties of Metals
First Period
Table of Contents
Objective One ............................................................................................................................................... 2 Definitions................................................................................................................................................. 2 Objective Two............................................................................................................................................. 11 Atoms and Molecules.............................................................................................................................. 11 Electron Flow .......................................................................................................................................... 12 Objective Three ........................................................................................................................................... 13 Single-Phase Power................................................................................................................................. 13 Three-Phase Power ................................................................................................................................. 13 Objective Four ............................................................................................................................................ 15 AC Transformers and AC-DC Transformer-Rectifiers ........................................................................... 15 Objective Five ............................................................................................................................................. 20 Generator and Alternator Construction ................................................................................................... 20 AC Alternators ........................................................................................................................................ 21 DC Generators......................................................................................................................................... 23 Objective Six............................................................................................................................................... 27 Inverters .................................................................................................................................................. 27 Objective Seven .......................................................................................................................................... 30 Welding Machine Installation and Maintenance..................................................................................... 30 Self-Test ...................................................................................................................................................... 31 Self-Test Answers ....................................................................................................................................... 38 NOTES
Electricity
Rationale
Why is it important for you to learn this skill?
Arc welding current relies on an electrical circuit. You must understand the principles of
electricity and its related terms before you attempt any arc welding. Learning these
principles and terms will assist you in understanding the effects the current has on the arc
welding process and how it applies to the welding power source. You must also
understand the proper operating, installation and maintenance procedures for the wide
variety of welding machines available on the market
Outcome
When you have completed this module, you will be able to:
Describe electrical concepts.
Objectives
1.
2.
3.
4.
5.
6.
7.
Define electrical terms.
Describe electron flow.
Describe single-phase and three-phase power.
Describe AC and AC-DC rectified power sources.
Describe AC and DC generator power sources.
Describe multi-process inverter power sources.
Describe welding power source installation and maintenance.
Introduction
In this module, you will learn electrical terms as they apply to arc welding and welding
machines. You will learn about welding power sources: AC, AC-DC rectified, AC and
DC generators and multi-purpose inverters and the advantages, disadvantages and uses of
each.
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Objective One
When you have completed this objective, you will be able to:
Define electrical terms.
Definitions
To gain an understanding of basic electricity and welding power sources, you must first
understand some basic terms.
Alternating Current
Current that flows in one direction during any half cycle, then reverses and flows in the
opposite direction during the next half cycle is called alternating current (AC). The rate
at which this alternating occurs is measured as cycles per second; 60-cycle AC is the
most common in North America.
Amperage
Amperage is also known as the heat setting. The strength of a current of electricity is
measured in amperes. This is the electrical property that causes the electrode and/or the
parent metal to be melted. Amperage in arc welding is responsible for the metal
deposition rate and penetration.
Metal deposition rate is also known as burn-off rate. If the amperage is increased, there is
a proportionate increase in the metal deposition rate of the electrode. A decrease in
amperage results in a decrease in the metal deposition rate.
Increasing the amperage causes the arc to penetrate (burn deeper) into the parent metal;
lowering the amperage causes a decrease in penetration.
Arc
In welding, an arc is created when there is enough amperage and voltage available at the
electrode tip to overcome the natural resistance to the flow of electricity. This resistance
is usually caused by the air gap between the electrode and the work.
Arc Blow
Arc blow is a condition encountered during DC welding when the arc flares
uncontrollably from side to side. Arc blow is caused by magnetic fields being set up
around the work. This is due to current travelling in the same direction for a prolonged
period of time.
Arc blow is not a problem when welding with AC because the reversals in the direction
of current flow prevent the accumulation of magnetic fields being set up around the work.
If it is not possible for you to change to an AC power source, then arc blow can be
minimized or eliminated by doing any of the following.
 Change the position of the ground clamp.
 Use a different electrode angle or electrode inclination.
 Weld toward a heavy tack or existing weld.
 Use a lower current setting.
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Arc Voltage
Arc voltage is the voltage output of the machine during welding. It is the force that
maintains the arc between the electrode and the workpiece.
Buzz Box
The term buzz box describes AC transformer welding machines because of the typical
buzzing sound made when welding with them. Figure 1 illustrates an inexpensive AC
transformer welding machine. Settings tend to be rather coarse, typically ten to twenty
amps per step. Each step or tap is connected to a fixed position on the secondary coil in
the machine.
Figure 1 - AC transformer welder with step controls (taps).
Circuit
Any system of conductors that is designed to complete the path of an electric current is
called a circuit. Current flows in the conductor when voltage is applied to it.
Core
The core is the magnetic link between the primary and the secondary coils of a welding
transformer. The core can be moved into or out of the coil as a method of current control.
This type of current control is called movable shunt. A movable shunt means that the core
can be moved into different positions which will alter the magnetic link between the
primary and secondary coils. The shunt is usually moved mechanically by an external
hand crank that controls its movement on a slide assembly. This allows for any setting
between minimum and maximum of the machine's output potential.
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Coil
A coil is usually made of insulated copper wire and is designed to have a certain number
of turns of wire. The coil can be moved closer to or away from the core as a method of
adjusting the welding current. Figure 2 illustrates an AC transformer welding machine
with a fixed primary coil, a fixed secondary coil and a movable shunt.
Figure 2 - Coils and movable shunt in an AC welding machine.
Conductor
A conductor is a material or substance that is capable of transmitting electricity. Most
metals are good conductors because they offer little resistance to current flow.
Constant Current
Constant current (CC) denotes a welding machine that is used for SMAW and GTAW.
These machines typically produce a relatively high open circuit voltage to assist in
establishing a welding arc. These machines produce a steep or drooping volt-amp curve.
Constant Voltage
Constant voltage (CV) is also known as constant potential. The term denotes a welding
machine suitable for wire process welding. These machines produce a relatively stable
voltage regardless of the amperage output of the machine. These power sources produce
an almost flat volt-amp curve.
Current Flow
Current flow is the movement of electrons in an electrical circuit. It is measured in
amperes.
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Cycle
A cycle is one complete rotation of the sine wave pattern as illustrated in Figure 3. The
sine wave begins at zero, climbs to its maximum positive value, then drops back through
zero and becomes negative. It reaches its maximum negative value, then proceeds to zero
again. This movement is one full cycle of AC current. With 60-cycle AC, the current
changes direction 120 times per second.
Figure 3 - One cycle of alternating current (sine wave).
Diode
A diode is a one-way electrical valve. It allows current to flow in one direction only. In a
welding machine, diodes are used to change AC to DC. Figure 4 illustrates a silicon
diode found in some AC-DC rectifier welding machines.
Figure 4 - Silicon diode.
Direct Current
Electric current that flows in one direction only and has either a positive or negative
value is direct current (DC). There is no change of direction as there is with AC. The
electron theory states that current flows from negative to positive, since that is the
direction that electrons flow in.
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Duty Cycle
All welding machines are rated by the National Electrical Manufacturers Association
(NEMA). The rating, called the duty cycle, is based on maximum output over a tenminute time period. This rating is expressed as a percentage of the time that the machine
can run at maximum rated output current before it must be allowed to cool down.
For example, a machine rated at 300 amps with a 60% duty cycle can operate at
maximum rated amperage for six minutes out of ten without causing damage by
overheating. Also, if the machine was required to run continuously, it could safely run at
60% of 300 amps, which is 180 amps maximum. Exceeding duty cycle ratings can
damage or ruin a welding power source.
Electron
Electrons are negatively charged particles that move through a conductor when current is
flowing. Electron theory states that because electrons carry a negative charge they are
attracted by positively charged bodies, so they move from negative to positive.
Frequency
Frequency relates to the speed at which alternating current changes its direction of flow.
A high frequency current is used in some welding processes to allow for non-touch arc
starting or to provide a path for the weld current to follow.
Generator
A generator is a machine used to create electricity of sufficient volume for welding. A
shaft with an electrical conductor is rotated perpendicular to a magnetic field. Generators
produce either AC or DC depending on their internal configuration. AC generators are
often called alternators.
Inductance
Inductance is the ability of a conductor to transfer current onto a neighbouring body
without physical contact. For example, in a transformer welder, current is brought to the
primary coil where a magnetic field is created due to the wire windings on the iron core.
The magnetic field induces or creates a current flow into the secondary coil without
physical contact.
Insulator
An insulator is any material that does not allow current to flow through it.
Inverter
An inverter is a device that changes DC to AC. In welding machines, inverters are also
used to increase the frequency of AC.
Line Transformer
This is another term used to describe an AC transformer welding machine.
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Magnetic Field
A magnetic field is created when current is forced to flow through a coil that is wrapped
around an iron core. The strength of the magnetic field determines the power capacity of
the welding machine.
Open Circuit Voltage
When a welding machine is turned on, but no current is flowing in the circuit, the
machine has open circuit voltage at the output terminals. Once an arc is started, voltage is
introduced into the circuit (closed circuit), and current begins to flow immediately.
Primary Coil
The primary coil on a welding transformer takes power directly from the AC input power
line. The current flowing into the primary coil causes a magnetic field to form.
Rectifier
A rectifier is a device that changes AC to DC by allowing current to flow in one direction
only.
Relay
A relay is a switch that is operated by electro-mechanical force rather than by the
application of external mechanical force. Inverter welding machines use high-speed
relays. Other types of relays used in gas-shielded welding processes are solenoids or
contactors.
Resistance
Resistance is the property of an electrical conductor to oppose the flow of current, which
causes electrical energy to be turned into heat. Resistance is measured in ohms and is
calculated by dividing voltage by amperage (Ohms = V/A). The electrode to work gap
(arc length) offers resistance to current flow. It is this resistance to the flow of current
across the arc that creates the heat needed for welding.
Reverse Polarity
In a DC welding circuit, reverse polarity occurs when the electrode cable is connected to
the positive terminal of the welding machine. Using reverse polarity results in the
following electrode and arc characteristics as compared to straight polarity.
 The electrode melts somewhat slower, which allows slower welding speeds.
 Approximately two thirds of the arc energy is associated with the base metal
(negative terminal).
 Penetration is deeper.
 Metal flow is generally narrow.
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Figure 5 is a DC welding machine that is connected to reverse polarity.
Figure 5 - Reverse polarity (electrode positive).
Straight Polarity
In a DC welding circuit, straight polarity occurs when the electrode cable is connected to
the negative terminal of the welding machine. Using straight polarity results in the
following electrode and arc characteristics as compared to reverse polarity.
 The electrode melts somewhat faster, resulting in faster welding speeds.
 Approximately two thirds of the arc energy is associated with the electrode
(negative terminal).
 Penetration is shallow.
 Metal flow is somewhat wider.
Figure 6 is a DC welding machine that is connected to straight polarity.
Figure 6 - Straight polarity (electrode negative).
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Secondary Coil
The secondary coil is located on the main transformer core of an AC welding machine.
The energy created in the magnetic field by the primary coil is induced into the secondary
coil.
Switch
A switch is a device with points of contact that can complete a circuit.
 When the contact points are open, no current can flow.
 When the contact points are closed, current can flow because the circuit is
complete.
Voltage
Voltage is the electrical pressure or force that causes current to flow in a conductor or to
cross an arc gap. Voltage is often called EMF, which stands for electromotive force.
Voltage in arc welding is responsible for the following:
 starting the arc,
 maintaining the arc,
 puddle fluidity and
 puddle flow.
Starting the Arc
With constant current welding machines, open circuit voltage needs to be quite high (50
to 100 volts) to initiate an arc. Once the arc is established, the voltage will drop to a
welding voltage. Both voltage and amperage are present in the circuit.
Maintaining the Arc
Arc voltage must be present to maintain the arc.
Puddle Fluidity and Flow
Arc voltage directly affects the width of the weld bead and the fluidity or wetness of the
puddle. An increase in arc voltage causes an increase in puddle width and fluidity; a
decrease in arc voltage causes the puddle to be narrower and less fluid. The amount of
voltage is determined by the type and size of the filler metal being used. Larger filler
metals generally require higher voltage to weld properly.
Volt-Amp Curve
Volt-amp curves (also known as output slopes) are graphical illustrations that indicate the
output of a welding machine. Voltage is plotted on the vertical axis and amperage on the
horizontal axis. Machines that produce a steep or drooping volt-amp curve (constant
current) are used for SMAW or GTAW.
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Machines that produce a fairly flat volt-amp curve (constant voltage) are used for most
wire feed welding processes. Figure 7 illustrates different volt-amp curves.
 The solid lines represent flat volt-amp curves that are generally used for wire
feed welding processes.
 The dotted lines represent constant current machines used for SMAW and
GTAW.
 Open circuit voltage is plotted where the graph meets the vertical axis.
Figure 7 - Volt-amp curves.
Welding Machine
A welding machine is also known as a welding power source. A welding machine is
specifically designed to deliver voltage and amperage of sufficient capacity for welding.
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Objective Two
When you have completed this objective, you will be able to:
Describe electron flow.
Atoms and Molecules
The smallest particle of any element that can exist is an atom. All material is composed
of atoms. When atoms combine, the molecules formed have entirely different
characteristics than their individual atoms. For example, if hydrogen (an explosive gas) is
combined chemically with oxygen, water molecules are formed. An atom consists of
three parts:
1. neutrons,
2. protons and
3. electrons.
Neutrons and protons are located in the nucleus and make up most of the mass of the
atom. A carbon atom, as shown in Figure 8, has six protons. Protons have a positive
charge (+). Each element has a different number of protons in its atoms. The number of
protons in an atom does not change. Atoms never gain or lose protons. Neutrons have a
neutral charge, so they are not normally considered in electrical principles.
Figure 8 - Carbon atom.
Electrons move in orbits around the nucleus. An electron carries a negative (–) charge
that is exactly equal in magnitude to the positive charge of the proton, so an atom
containing an equal number of protons and electrons has no net electrical charge. The
attraction between the positive protons and negative electrons holds the electrons in their
orbits; their speed keeps them from falling into the nucleus.
Atoms can gain or lose electrons due to electrical, mechanical or chemical activity. When
an atom gains an electron, the atom has a negative (–) charge. If an atom loses an
electron, it has a positive (+) charge because there are more protons than electrons.
Charged atoms are called ions.
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Electron Flow
After the discovery of electrons, a theory called the electron flow theory came about to
show how electrons move. The theory states that negatively charged electrons are
attracted to positively charged protons.
Direct-current electrode negative (DCEN), also called straight polarity, uses the
electrode connected to the negative terminal. The work piece is connected to the positive
terminal. The direction of electron flow is towards the base metal because the current
travels from negative to positive.
Direct-current electrode positive (DCEP), also called reverse polarity, has the electrode
connected to the positive terminal. The electron flow is toward the electrode which is
from (-) to (+).With DC, the electrons will always flow from negative to positive. There
is no change of electron direction of flow with DC as there is with AC.
Alternating current (AC) flows in one direction during any half cycle, then reverses and
flows in the opposite direction during the next half cycle. Alternating current has the
electrode and work pieces connected to the terminals designated by the welding machine
manufacturer. The welding current switches between both positive and negative half
cycles. Electron flow varies depending on which half cycle the current is on.
In North America you use a 60-cycle AC power source. This means you have 60 sine
waves each second. One sine wave will change electron flow two times, so 60 sine waves
or cycles will change direction 120 times each second.
The selection of DCEP, DCEN or AC depends on the filler metal type, the material being
welded and the welding process used.
Figure 9 shows how welding current flows depending on machine configuration and the
effect on the electron flow between the welding machine and the work piece.
Figure 9 - Welding current and electron flow.
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Objective Three
When you have completed this objective, you will be able to:
Describe single-phase and three-phase power.
Single-Phase Power
Single-phase power systems supply residential and small business areas. In North
America, single-phase AC operates at 60 cycles where the voltage peaks in one direction
and then reverses its polarity sixty times per second. This means that the current will
change direction 120 times per second. Figure 10 illustrates a single cycle of single-phase
AC power; the AC current sine wave peaks and then reverses itself.
Figure 10 - Single phase AC sine wave.
Three-Phase Power
Three-phase power systems supply electrical services to larger commercial and industrial
facilities. Three-phase power is made by combining three single-phase lines (of the same
frequency) which are out of phase by one third of a cycle so that individual voltages peak
one after another in sequence. Figure 11 illustrates a single cycle of three-phase AC
power; the three current sine waves peak and reverse themselves in sequence resulting in
fewer gaps in the current flow.
Figure 11 - Three-phase Ac sine wave.
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Three- Phase Power Advantages
Most of the energy delivered to industrial installations is carried by three-phase
systems. This type of system offers three distinct advantages over single-phase
systems (Figure 12).
Figure 12 - Advantages of a three-phase system.
Constant Power
In a three-phase system, equipment is supplied with three voltages. This maintains
voltage to the three-phase equipment during its operation; the power is relatively
constant. In a single-phase system, with one voltage that goes through a zero value
twice in a cycle, power is pulsating. The constant power of a three-phase system
results in less vibration and better performance than from single-phase equipment.
Smaller Equipment
Three-phase power allows motors and alternators to be smaller and lighter and still
achieve the same power output. This tends to reduce the cost of three-phase
equipment compared to single-phase equipment.
Efficient Energy Transmission
The transmission of energy in a three-phase system is more efficient than in a singlephase system. Smaller transmission lines and distribution equipment result in lower
overall system costs. Approximately 25% less copper is used in a three-phase system
for feeders and equipment as compared to the equivalent capacity of a single-phase
system.
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Objective Four
When you have completed this objective, you will be able to:
Describe AC and AC-DC rectified power sources.
AC Transformers and AC-DC Transformer-Rectifiers
To select the type of welding machine that would be most suited for a specific job site,
you need to understand the advantages and disadvantages of an AC transformer versus an
AC-DC transformer rectifier.
AC Transformers
A transformer (Figure 13) takes electricity from the power grid and converts it into
welding current. It does this with two separate insulated wire coils wrapped around a
laminated steel core. The current from the power grid flows through the primary winding
and creates a magnetic field. Because AC is used in the power grid, the magnetic field
collapses. This occurs each time the alternating current changes direction from straight
polarity to reverse polarity because there is zero current flow.
The magnetic field transfers from the primary winding into the secondary winding each
time the magnetic field collapses. The magnetic field that collapses into the secondary
winding now becomes welding current. The number of turns of wire in the primary and
secondary windings are adjusted to ensure the correct welding current is obtained.
Figure 13 - Basic transformer construction.
The AC transformer welding power source converts high voltage, low amperage to low
voltage, high amperage that is suitable for welding. This process is called step down
voltage. To do this, the primary winding consists of many wraps of fine wire, and the
secondary winding has fewer wraps of much heavier wire. Both of these wire coils are
wrapped around laminated steel plates which helps to induce the current from the primary
winding into the secondary winding each time magnetic field collapses or changes
direction.
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There are variations of how different types of adjustable coils work in transformer
welders. Figure 14 shows an adjustable coil set-up transformer that moves the primary
and secondary coils closer together or farther apart. As the coils move closer together,
there is less resistance and voltage flow increases. The greater the distance between the
two coils is, the greater the resistance is. Greater resistance results in decreased voltage
flow.
Figure 14 - Adjustable coils that move together or apart.
Figure 15 shows a metal shunt adjustable coil. The adjusting screw causes a metal bar to
move up and down. As the bar moves down, it interrupts the flow of voltage from the
primary coil to the secondary coil. Just like water running out a faucet, the more the shunt
is opened, the greater the voltage flow is; as the shunt is closed, voltage flow decreases.
Figure 15 - Metal shunt adjustable coil.
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Figure 16 shows a saturable reactor that has an iron core with two or more coils of wire
wound around it. In its construction, it is similar to a transformer, but that is the only
similarity. A DC current flows from a rheostat into the coil surrounding the metal core
and creates a build-up in a magnetic field in the iron core. The more intense the DC is,
the greater the magnetic field in the core is.
NOTES
The other end of the iron core also has a coil, but with AC flowing through it from the
transformer to the rectifier. The AC creates its own magnetic field in the metal core
which creates a resistance and allows less current to flow to the rectifier.
If the DC is increased, the DC magnetic field increases in the metal core until it becomes
saturated. When the core is saturated with DC magnetic field, there is no capacity for the
AC field to form in the metal core. This causes the AC to flow at full capacity to the
rectifier. Increasing the DC from the rheostat creates a greater DC magnetic field which
causes more AC flow; decreasing the DC from the rheostat causes less AC to flow to the
rectifier.
Figure 16 - Adjustable coils with rheostat control.
Table 1 outlines some advantages and disadvantages of the AC transformer.
AC Transformers
Advantages
Low initial cost.
Low maintenance costs.
Lower operating costs.
Generally quiet operation.
No accumulative arc blow.
Disadvantages
Not portable.
No choice of polarity.
Limited electrode selection.
More difficult to strike and maintain an arc.
Restricted welding processes.
Table 1 - AC transformer advantages and disadvantages.
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Figure 17 is an AC transformer welding power source that has a welding current range of
40 to 225 amperes. It produces a smooth AC arc for welding a wide variety of materials
including low carbon, low alloy and stainless steels.
Figure 17 - AC transformer welding power source.
(Courtesy of Lincoln Electric)
AC-DC Transformer-Rectifiers
AC-DC transformer-rectifier welding machines are AC transformers with an added
rectifier. The rectifier unit is made up of diodes that are capable of allowing current to
flow in one direction only, thus changing AC to DC. Since silicon diodes are small and
must carry high currents, they are mounted on copper or aluminium plates that serve as
heat sinks. The heat sinks draw the heat away from the diode. A fan also blows air
through the machine to help dissipate the heat. Figure 18 shows the internal parts of a
typical industrial quality AC-DC transformer-rectifier welding power source.
Figure 18 - AC-DC transformer-rectifier welding power source.
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Table 2 outlines some advantages and disadvantages of the AC-DC transformer-rectifier.
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AC-DC Transformer-Rectifiers
Advantages
May have AC and DC output capability.
Full selection of electrodes.
Choice of polarity.
Few moving parts (cooling fan unit and
current control system).
Machines may be CC or CV.
CC machines may be used with a voltagesensing wire feeder for GMAW.
Disadvantages
Generally more costly than transformers.
Arc blow can be a factor with DC.
Not portable.
Requires a clean, cool environment.
Table 2 - Advantages and disadvantages of an AC-DC transformer-rectifier.
The welder in Figure 19 is using an AC-DC transformer-rectifier welding power source
to lay a root bead using direct current reverse polarity with an E4310 (E6010) electrode.
Figure 19 - Transformer-rectifier power source.
(Courtesy Miller Electric Mfg. Co.)
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Objective Five
When you have completed this objective, you will be able to:
Describe AC and DC generator power sources.
Generator and Alternator Construction
Generators and alternators convert mechanical energy into electrical energy. A generator
produces DC, and an alternator produces AC. When mechanical energy is applied to a
conductor and it moves across the magnetic lines of force in a magnetic field, an
electrical current is generated or induced in the conductor. If the ends of this conductor
are connected to a complete circuit, there is a flow of electrons or current. In Figure 20,
the current flow is coming toward you.
Figure 20 - The induced voltage causes current to flow out toward the reader.
In Figure 21, the movement of the conductor is in the opposite direction as is the current
flow. The current is now going away from you.
Figure 21 - The induced voltage causes current to flow away from the reader.
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A practical application of this induced current is the generator. A basic generator consists
of a wire loop that can rotate in a stationary magnetic field (Figure 22). When the wire
loop is rotated through the magnetic lines of force in the magnetic field, a current is
induced in the conductor. As the loop rotates in the magnetic field, it continuously cuts
through the magnetic lines of force creating current.
NOTES
Figure 22 - The basic generator.
To select the type of welding machine that would be most suited for a specific job site,
you need to understand the advantages and disadvantages of the different types of
welding power sources that are available. Generator or alternator power sources may be
driven by an electric motor or petroleum driven engines. The main advantage of the
petroleum engine-driven machines is portability.
AC Alternators
The current that is induced into the armature conductor of an AC alternator as it rotates in
the magnetic field is picked up by slip rings. Figure 23 shows the connection of a slip
ring to each end of an armature conductor.
Figure 23 - Slip rings in an AC alternator.
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In a basic AC alternator, the magnetic field is fixed and the armature rotates. Welding
current is picked up directly from the rotating magnetic armature through the slip rings.
Figure 24 shows the the conductor at position A which does not cut any lines of force
because at that instant it is moving parallel to the lines of force. As the conductor moves
from position A to position B, the angle of cut increases, as does the voltage induced.
When the conductor reaches position B, the angle of cut is at right angles to the magnetic
lines of force and a maximum voltage is induced.
The generated waveform in Figure 24 shows the induced voltage to be zero at point A
and then rising to a maximum of peak value at point B. As the conductor travels from
position B to position C, the induced voltage decreases as the angle of cut reduces to
zero. At position C the induced voltage is again zero as the conductor is, at that instant,
moving parallel to the magnetic lines of force. The generated waveform moves from the
peak value at point B to the zero value at point C.
When the conductor moves from position C to position D the angle of cut again
increases, as does the induced voltage. At position D the maximum voltage is induced.
The only difference is that the conductor is cutting the force lines in the opposite
direction; the induced voltage will also be in the opposite direction and is shown as a
negative quantity on the generated waveform. The generated voltage moves from the zero
value at point C to the negative peak value at point D.
As the conductor travels from position D back to A, the value of voltage reduces as the
angle of cut reduces to zero. The generated waveform moves from the negative peak
value at point D to the zero value at point A.
Figure 24 - Voltage generated by a conductor rotated in a magnetic field.
Rotating a conductor through a magnetic field generates a current that:
 varies from zero to a maximum value depending upon the angle at which the
conductor cuts the magnetic lines of force and
 reverses its polarity for each half of the rotation of the conductor.
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AC alternators are particularly useful when work takes place at remote locations and AC
current is needed for power tools and arc welding. For example, commercial garage door
installers or commercial sign installers often equip their rigs with small engine-driven AC
alternators (Figure 25).
NOTES
Figure 25 - Engine-driven AC alternator.
(Courtesy Miller Electric Mfg. Co.)
Table 3 outlines the advantages and disadvantages of the AC generator.
AC Alternators
Advantages
No arc blow.
May be portable.
Higher duty cycle rating than many transformers.
Can run power tools.
Disadvantages
High initial cost.
Higher operating costs than stationary units.
Higher maintenance costs than stationary units.
Generally noisier than transformer designs.
Narrow electrode selection on AC.
Table 3 - Advantages and disadvantages of an AC alternator.
DC Generators
The basic principle behind generators and alternators is that current is produced by
electrical conductors when they are moved through a magnetic field. One component,
either the magnetic field or the conductor, is stationary; the other component rotates on a
shaft. It does not matter whether it is the magnetic field or the conductor that rotates; it
only matters that the magnetic coil experiences a changing magnetic intensity.
If the ends of the armature conductor are connected to a ring that is cut in half (split), and
each half is insulated from the other, a switching or rectifying action takes place and a
direct current is supplied to the load. A split ring is called a commutator.
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Figure 26 shows the connection of a split ring commutator to each end of the armature
conductor. The commutator has two half-rings, so one brush that is connected to the
commutator is always positive, and the other is always negative. The DC generator is still
producing the same AC voltage in the armature, but the commutator provides a switching
action that allows the current flow to the load in one direction only.
Figure 26 - A commutator in a DC generator.
As the armature loop rotates, the direction of the movement of each half of the loop is
reversed with respect to the magnetic field (Figure 27). The commutator, however,
switches the direction of this current to maintain the same direction of the current flow to
the load.
Figure 27 - Direct current generation.
This direct current waveform repeats for every revolution of the DC generator.
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NOTES
DC Output Alternators
Many engine-driven welding power sources use the alternator design. The AC output
current is rectified to DC. The major advantages of the alternator designs are their
capabilities for producing AC and DC output and high duty cycle ratings. Table 4 shows
advantages and disadvantages of DC generators and alternators.
DC Generators and Alternators
Advantages
Choice of polarity.
Smoother arc than with AC.
May be portable.
Full choice of electrodes.
Often have auxiliary power output.
Disadvantages
High initial cost.
Higher maintenance costs than transformer sets.
Higher operating costs than transformer sets.
Generally noisier than transformer sets.
Arc blow is a factor with DC.
Table 4 - Advantages and disadvantages of a DC generator.
The welding machine in Figure 28 is a DC generator driven by a diesel engine with dual
controls for setting voltage and amperage. This unit also has the capability of producing
3000 watts of AC auxiliary power to run power tools and other equipment by using an
internal inverter.
Figure 28 - DC generator power source driven by diesel engine.
(Courtesy of Lincoln Electric)
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NOTES
The wire feeder in Figure 29 is a portable unit that may be used with CV power sources
and CC power sources such as the DC generator shown in Figure 28. Known widely in
the industry as a suitcase wire feeder, it is designed with a voltage-sensing circuit for use
with CC power sources. Engine-driven DC generators coupled to portable voltagesensing wire feeders are used for remote location jobs where it is advantageous to use
GMAW or FCAW.
Figure 29 - Portable wire feeder unit. (Courtesy of Lincoln Electric)
Figure 30 is an example of an engine-driven alternator design that can rectify the current
to DC and has the capability of producing 3000 watts of AC auxiliary power. The control
panel features a stepped coarse current control and a fine current adjustment rheostat
arrangement.
Figure 30 - Engine-driven AC alternator design welder.
(Courtesy Miller Electric Mfg. Co.)
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NOTES
Objective Six
When you have completed this objective, you will be able to:
Describe multi-process inverter power sources.
Inverters
An inverter is an electronic circuit that is capable of transforming DC input to AC output.
The AC output waveform can be set to any desired shape, such as square, triangle or sine.
A few basic types of inverters have fixed frequency and fixed voltage output. With the
high-speed computer control available today, the inverter output voltage and frequency
are programmable.
Inverter welding power sources immediately rectify the incoming AC into DC and then
transistors convert DC voltage into a high frequency AC output. The higher frequency
AC is then rectified to extremely smooth DC welding output. Transistors can turn power
on and off at very high speeds, allowing them to dispense extremely small bits of energy
at a very high frequency. These very small units of energy result in an extremely smooth
output current. Figure 31 shows a schematic of the internal configuration of a typical
inverter welding power source.
Figure 31 - Inverter power source.
Inverter technology is based on the principle that the magnitude of voltage to be
transformed is equal to the number of turns of wire on a transformer, multiplied by the
cross sectional area of transformer core, the frequency of AC voltage to be transformed
and design constants (Figure 31).
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By manipulating the formula, designers were able to reduce the size and weight of the
transformer and to generate significant energy savings over conventional power sources.
An inverter's size and weight can be reduced, and it can still have equal current output to
a conventional power source.
 If you double the number of turns on the primary coil (N), this will allow the core
area to be cut in half.
 If you double the core area, this will allow the number of turns to be cut in half.
 By increasing the frequency by 4 times, the core area and the number of turns can
be halved.
 If the frequency is increased 10 times, 100 times, 400 times or 500 times, then
the core area and the number of turns can be reduced considerably.
Table 5 highlights advantages and disadvantages of inverters.
Inverters
Advantages
Small and lightweight.
Low input power requirements.
Excellent arc-starting characteristics.
Easily configured for automation.
May be CC or CV.
Pulse current capabilities.
Excellent control over output current.
Disadvantages
AC is very noisy.
Requires a clean, cool environment.
High initial cost.
Arc blow a factor with DC.
Electronic components are more fragile.
Expensive to repair.
Table 5 - Advantages and disadvantages of an inverter.
Figure 32 shows an inverter power source that can be used for SMAW, GMAW, FCAW,
MCAW and GTAW. It operates on single-phase or three-phase input power and is shown
with an optional wire feeder.
Figure 32 - Inverter-design power source.
(Courtesy ESAB Welding and Cutting Products)
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Figure 33 is an example of an engine-driven inverter multi-process welding power
source. This machine also has the capability of producing 12 000 watts of auxiliary
power that can used to run a second inverter welding power source.
NOTES
Figure 33 - Engine drive with inverter design.
(Courtesy Miller Electric Mfg. Co.)
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NOTES
Objective Seven
When you have completed this objective, you will be able to:
Describe welding power source installation and maintenance.
Welding Machine Installation and Maintenance
Here are some guidelines you should follow when installing electric welding machines.
 Locate the machine in an area that is as dust free as possible, outside the work
area and away from corners and walls.
 Make sure there is plenty of air movement for the fan motor unit to help keep the
machine cool.
 Installation must meet applicable electrical codes and be performed by qualified
personnel only.
DANGER
Input current for most industrial quality welding machines is
potentially deadly. Do not attempt to install the equipment unless you
are qualified to do so.



Input power must be compatible with the machine manufacturer's
recommendations.
Machines must be properly grounded to prevent electrical shock.
All electrical connections must be clean and tight.
Here are some guidelines that you should follow with respect to machine maintenance.
 Blow out internal components periodically with high-volume, low-pressure air
following the manufacturer's recommendations.
 Lubricate any bearings, bushings or mechanical controls following the
manufacturer's recommendations.
 Ensure that all electrical connections are clean and tight and that insulation is not
cracked or torn.
 On engine-driven machines, follow the engine manufacturer's recommendations
for service requirements.
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NOTES
Self-Test
1. This term describes a noisy, uncontrollable arc that flares from side to side.
a) arc voltage
b) arc blow
c) inductance
d) resistance
2. This term describes the influence exerted by a magnetic field on neighbouring bodies
without physical contact.
a) voltage
b) amperage
c) frequency
d) inductance
3. This is the fundamental unit of electricity that moves through a conductor when
current is flowing.
a) resistors
b) electrons
c) conductors
d) rectifiers
4. Which term describes the NEMA rating of a welding machine?
a) duty cycle
b) direct current
c) arc voltage
d) amperage
5. Electrode positive means:
a) straight polarity.
b) reverse polarity.
c) AC transformer.
d) alternating current.
6. The number of __________ never increases or decreases in the atom.
a) electrons
b) neutrons
c) protons
d) ions
7. Electrons have a _______ charge.
a) neutral
b) 12-volt
c) positive
d) negative
8. Which term measures the strength of a current of electricity?
a) amperage
b) voltage
c) electron
d) inductance
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NOTES
9. A charged atom is called _______.
a) a molecule
b) an amp
c) an ion
d) a volt
10. What term describes a medium that provides an electrical path for current to flow
through?
a) cycle
b) circuit
c) conductor
d) core
11. The electron flow theory states that electrons move from _______.
a) positive to negative
b) negative to positive
12. This term describes a material that can stop current flow through itself.
a) inductor
b) inverter
c) conductor
d) insulator
13. The nucleus of an atom has:
a) electrons and protons.
b) protons and neutrons.
c) neutrons and electrons.
d) only electrons.
14. Which term describes the voltage output of the machine during welding?
a) arc rectification
b) arc blow
c) arc voltage
d) inductance
15. When current flows through a coil wrapped around an iron core, what is created?
a) a magnetic field
b) reverse polarity
c) transformer rectifier
d) duty cycle
16. This device in a welding machine is designed to have a certain number of turns of
wire.
a) circuit
b) core
c) coil
d) cycle
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NOTES
17. The main function of this device is to change AC to DC.
a) resistor
b) rectifier
c) relay
d) reactor
18. Electrode negative is:
a) straight polarity.
b) reverse polarity.
c) ac transformer.
d) alternating current.
19. This current flows in one direction only and has either a positive or negative value.
a) direct current
b) alternating current
c) open circuit voltage
d) arc voltage
20. Which term describes a piece of equipment used to create electricity of sufficient
volume for welding?
a) inductor
b) resistor
c) transformer
d) generator
21. Which is a graphical illustration that plots the relationship between voltage and
amperage output of a welding power source?
a) open circuit voltage
b) volt-amp curve
c) electromotive force
d) duty cycle
22. When no current is flowing in the circuit, but the machine is turned on, you can
measure the:
a) open circuit voltage.
b) constant current.
c) alternating current.
d) volt-amp curve.
23. The speed at which AC changes direction is called the:
a) voltage.
b) amperage.
c) frequency.
d) resistance.
24. This term describes the property of an electrical conductor that opposes the flow of
current.
a) resistance
b) inductance
c) voltage
d) amperage
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NOTES
25. In welding, this term describes what is created when there is enough amperage and
voltage to overcome the natural resistance to the flow of the electricity.
a) amp
b) volt
c) cycle
d) arc
26. List three (3) advantages of three-phase systems over single-phase systems.
a) ____________________________________
b) ____________________________________
c) ____________________________________
27. What phase of power supplies most industrial applications?
a) single-phase power
b) two-phase power
c) three-phase power
d) four-phase phase
28. This welding machine transforms AC to DC.
a) line transformer
b) transformer rectifier
c) DC generator
d) AC transformer
29. This term describes one complete revolution of the AC alternator.
a) circuit
b) core
c) coil
d) cycle
30. What happens when mechanical energy is applied to a conductor and it moves across
the magnetic lines of force in a magnetic field?
a) Magnetism is generated.
b) Electrical current is generated.
c) Single-phase power is generated.
d) Three-phase power is generated.
31. These machines convert high voltage, low amperage to low voltage, high amperage
by the use of a primary and a secondary coil.
a) AC transformer
b) AC generator
c) DC generator
d) AC alternator
32. What does EMF stand for?
a) electron movement force
b) elementary motor force
c) electromotive force
d) electromotive factor
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33. Which term describes the typical sound of an AC transformer welding machine?
a) turbine whine
b) high-pitched scream
c) buzz box
d) whisper quiet
NOTES
34. This type of welding machine is capable of changing DC to high frequency AC.
a) AC generator
b) DC rectifier
c) DC generator
d) inverter
35. What is the function of the secondary winding on a transformer welder?
a) to induce high frequency current
b) to serve as a back-up in case the primary winding fails
c) to step down the voltage
d) to step down the amperage
36. One advantage of an AC transformer welder is freedom from:
a) undercut.
b) arc blow.
c) porosity.
d) slag inclusions.
37. What is the purpose of a silicon-controlled rectifier?
a) to change AC to DC
b) to change single-phase to three-phase
c) to increase the welding speed on aluminum
d) to change DC to AC
38. What is one advantage of an AC-DC transformer-rectifier welding machine?
a) Arc blow is not a problem.
b) The purchase price is lower than for a transformer.
c) You have a choice of polarity.
d) It does not have to be kept clean and cool.
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NOTES
39. In Figure 34 the output voltage or current waveform to a load from a generator that
uses slip rings is indicated by which diagram?
a) A
b) B
c) C
Figure 34 - Current waveform.
40. In Figure 34 the output voltage or current waveform to a load from a generator that
uses a commutator is indicated by which diagram?
a) A
b) B
c) C
41. A DC motor generator produces what type of welding current?
a) rectified
b) AC
c) DC
d) high frequency
42. How can you change the polarity on an AC alternator welding machine?
a) Switch the cables at the machine.
b) Reverse the direction of the motor.
c) Change the polarity taps on the reactor coils.
d) An AC alternator has no fixed polarity.
43. What is one advantage of an engine-driven generator welding machine?
a) lower cost
b) portability
c) less noise
d) less maintenance
36
44. What is one advantage of all transformer welding machines?
a) The maintenance costs are lower.
b) There is no choice of polarity.
c) They are not portable.
d) The choice of electrode types is narrow.
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45. These welding power sources immediately rectify the incoming AC to DC and then
transistors create a higher frequency AC. The higher frequency AC is then rectified
to extremely smooth DC.
a) transformers
b) generators
c) buzz boxes
d) inverters
NOTES
46. How did manufactures reduce the size and weight of transformers and generate
significant energy savings over conventional power sources?
a) rectifier technology
b) generator technology
c) inverter technology
d) transformer technology
47. What is an advantage of an inverter welding machine?
a) small and lightweight
b) generally cheaper to buy
c) portability
d) functions well in a dirty environment
48. What is a disadvantage of an inverter welding machine?
a) poor arc starting characteristics
b) higher input power requirements
c) higher initial cost than transformers or rectifiers
d) cannot be configured for automation
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NOTES
Self-Test Answers
1. b) arc blow
2. d) inductance
3. b) electrons
4. a) duty cycle
5. b) reverse polarity.
6. c) protons
7. d) negative
8. a) amperage
9. c) an ion
10. c) conductor
11. b) negative to positive
12. d) insulator
13. b) protons and neutrons.
14. c) arc voltage
15. a) a magnetic field
16. c) coil
17. b) rectifier
18. a) straight polarity.
19. a) direct current
20. d) generator
21. b) volt-amp curve
22. a) open circuit voltage.
23. c) frequency.
24. a) resistance
25. d) arc
26. a) constant power
b) smaller equipment
c) more efficient
27. c) three-phase power
28. b) transformer rectifier
29. d) cycle
30. b) Electrical current is generated.
31. a) AC transformer
32. c) electromotive force
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33. c) buzz box
34. d) inverter
35. c) to step down the voltage
36. b) arc blow.
37. a) to change AC to DC
38. c) You have a choice of polarity.
39. a) A
40. c) C
41. c) DC
42. d) An AC alternator has no fixed polarity.
43. b) portability
44. a) The maintenance costs are lower.
45. d) inverters
46. c) inverter technology
47. a) small and lightweight
48. c) higher initial cost than transformers or rectifiers
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Module Number 120102b
Version 6.0