Exam 2 WE-1-DP Electricity 120102b

What is 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.

What is Core?

is the magnetic link between the primary and the secondary coils of a welding transformer. 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.

What happens when you increase the Arc voltage?

it causes an increase in the puddle width and fluidity.

Duty Cycle (DC)

percentage of time that electrical current is on in relation to entire treatment time. This is based on a maximum output over a ten minute time period. This rating is expressed as a percentage of the time that a machine can run at maximum rated output current before it must be allowed to cool down.

Advantages of Three Phase Power?

-Constant Power: of three phase system results in less vibration and better performance than from single-phase powered equipment; because equipment maintains voltage to three-phase during its operation and the power is relatively constant -Smaller equipment: Power allows motors and alternators to be smaller and lighter and still achieve the same power output. This tend to reduce the cost of three-phase equipment compare to single-phase equipment. -More efficient: 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.

Types of Relays?

-Gas-shield welding processes are solenoid or contactors -Inverter Welding machines use high-speed

What are the 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.

In reverse polarity what are the results in the electrode and arc characteristics as compared to straight polarity?

-The electrode melts somewhat slower, which allows slower welding speed. -Approximately two thirds of arc energy is associated with the base metal (negative energy) -Penetration is deeper. -Metal flow is generally narrow

Machines that produce a steep or drooping volt-amp curve (Constant current) are used for SMAW or GTAW.

-The solid lines represent flat volt-amp curve 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.

How to avoid Arc Blow?

-Use AC arc current to avoid accumulation of magnetic field because the reversal in the direction of current flow. -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.

How a generator works

1. Converts mechanical energy (turning movement) to electrical energy. 2. When a conductor is moved through a magnetic field, electric current is produced and will flow through conductor. 3. A shaft with an electrical conductor i rotated perpendicular to a magnetic field.

An atom consists of three parts?

1. neutrons, 2. protons and 3. electrons.

What happens when DC flow thru the AC transformer?

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. 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.

Difference between an alternator and a generator?

A generator produces DC, and an alternator produces AC

What is a volt-amp curve?

A graphical illustration that plots the relationship between voltage and amperage output of a welding power source. It indicates the output of a welding machine graphically. Voltage is plotted on the vertical axis and amperage on a the horizontal axis.

What current is used in welding processes to allow for non-touch arc starting?

A high frequency current to which will provide a path for the weld current to follow.

What is an insulator?

A material that does not allow heat or current to flow through it.

What is a diode?

A semiconductor device with two terminals, typically allowing the flow of current in one direction only. To regulate the potential difference in circuits. There are used to change AC to DC

Three-Phase AC sine wave

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.

What is an electron?

A subatomic particle that has a negative charge. They state that because electron carry a negative charge they are attracted by positively charged bodies, so they mace from negative to positive.

Important element affects an Arc?

Arc voltage must be present to maintain the arc. Arc voltage directly affects the width of the weld bead and the fluidity or wetness of the puddle.

What is an AC-DC Transformer-Rectifier?

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.

What are heat sinks purpose in an AC-DC transformer rectifier?

Areas of the body that can accept and dissipate great amounts of heat. Since silicone diodes are small and must carry high currents, there are mounted on copper or aluminium plates that serve as heat sinks. Drawing the heat from the diodes.

How long can a welding machine rated 300 amps with 60% duty cycle can operate at before it overheats?

At maximum rated amperage of six minutes out of ten continuously without causing damages to the welding power source, which is 180 amps maximum.

What are ions and how are they formed?

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.

What is constant current?

CC denotes a welding machine that is used for SMAW and GTAW. These machine suitable for wire process welding. These machines produce a relatively high open circuit voltage to assist in establishing a welding welding arc. These machines produce a steep or drooping volt-amp curve.

AC/DC transformer rectifiers

Convert AC power to DC power

What is Direct Current CD?

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.

A carbon atom, as shown that has six protons.

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.

How much amperage range an AC transformer current should dissipate to produce a weld?

From 40 to 225 amps to produce a smooth AC arc for welding a wide variety of materials including low carbon, low alloy and stainless steels.

What happens if DC current increases in a AC Transformer?

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.

What is a saturable reactor and what it does in AC Transformer?

In electrical engineering is a special form of inductor where the magnetic core can be deliberately saturated by a direct electric current in a control winding. Once saturated, the inductance of the saturable reactor drops dramatically. 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.

Reverse Polarity (electrode positive)

Is Dc welding machine that is connected to reverse polarity.

straight polarity (electrode negative)

Is a DC welding machine that is connected to straight polarity.

What is arc blow?

Is a condition encountered during DC welding when arc flares uncontrollably from side to side.

What is alternating current AC?

Is a current that flows in one direction during half cycle, then reverses and flows in the opposite direction during the next half cycle. The rate at which this alternating occurs is measured as cycles per second; 60-cycle, this current is the most common in North America. This means you have 60 sine waves each second. One sine waves will change electrons flow two times, so 60 sine waves or cycle will change direction 120 times each second.

What is a generator?

Is a device that converts mechanical energy into electrical energy sufficient for welding. They produce either AC or DC depending on their internal configuration. AC generators are often called Alternators.

What is 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 a contact point is closed, current can flow because the circuit is compete.

What is a rectifier?

Is a devise that changes AC to DC by allowing current to flow in one direction only and is achieved by using a diode.

What is an AC transformer

Is a passive electrical device that takes electricity from a power grid, between two or more circuits; converting it into welding current. A varying current in one coil of the transformer produces a varying magnetic flux, which, in turn, induces a varying electromotive force across a second coil wound around the same core.

What is a circuit?

Is a pathway that allows electrons (electricity) to flow in a controlled electric field. Current flows in the conductor when voltage is applied to it.

What is a relay?

Is a switch that depends on current being in it's coil to switch on. It is operated by eletro-machanical force rather than by the application of external mechanical force. Inverter welding machines use high-speed relays.

What is single-phase power?

Is a when the flow is in one direction during any half cycle, then reverses and flow in the opposite direction during the next half cycle just like Alternating Current. This meaning that the current will change directions 120 times per second. This power system supply residential and small business areas.

What is metal deposition rate?

Is also know as burn-off rate. If the amperage is increased, there is a proportionate increase in the metal deposition rate of the electrode. A decrease results in a decrease in the metal deposition.

What is a welding machine?

Is also known as a welding power source. Is specifically designed to deliver voltage and amperage of sufficient capacity for welding.

What is constant volt?

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.

Why Arc Blow is caused?

Is caused by magnetic fields being set up around the work. This due to current travelling in the same direction for a prolonged period of time.

What is arc welding?

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.

What determines the amount of arc voltage?

Is determined by the type and size of the filler metal being used. Large filler metals generally require higher voltage to weld.

Where the Diode is found?

Is found in some AC-DC rectifier welding machines.

What is an electron flow?

Is how the electrons (electricity) move thru a conductor. The theory states that negatively charged electrons are attracted to positively charged protons.

What is straight polarity?

Is it when in a DC welding circuit the electrode cable is connected to the negative terminal of the welding machine.

What voltage is also called?

Is often called EMF, which stands for electromotive force.

What is a cycle?

Is one complete rotation of the sine wave pattern. 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

What is inductance?

Is the ability of a conductor to transfer current onto a neighbouring body without physical contact. For example A voltage that is induced in a coil in an AC circuit. This voltage is opposite in direction to the applied voltage, and opposes any change in the alternating current.

What is a magnetic field?

Is the area of magnetic force around a magnet. In welding is when current is forced to flow through a coil that is wrapped around an iron core.

What is a secondary coil?

Is the energy created in the magnetic field by the primary coil is induced into the secondary coil. This is located on the main transformer core of an AC welding machine.

What is amperage heat setting?

Is the measurement of the number of electrons moving through a conductor. In other word is the strength of a current of electricity. Is also the electrical property that causes the electrode and / or the parent metal to be melted, being the responsible for the metal deposition rate and penetration. Lowering the AMP causes a decrease in penetration. Increasing the AMP causes the arc to burn deeper.

What is current flow?

Is the movement of electrons in an electrical circuit. It is measured in amperes.

What is frequency?

Is the number of waves or cycles that pass a given point per second. It relates to the speed at which alternating currents changes its direction of flow.

What is voltage?

Is the pressure that pushes electricity through an electrical circuit, conductor or to cross an arc gap. This is responsible for: - Staring an arc - Maintaining the arc -Puddle fluidity -Puddle flow

What is an Atom?

Is the smallest particle of any element that can exist. 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.

What is 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.

What is 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.

What is a conductor?

Is when a material allows electrons to flow through. Most metals are good conductor because they offer little resistance to current flow.

Three phase power

Is when multiple voltage wave forms are superimposed on one another, resulting in a waveform that maintains a nearly constant high voltage. It uses three single-phases AC wave forms (lines) at the same time. of the same frequency which are out of phase by one of a cycle so that individual voltage peak one after another in sequence.

What happens if the Arc voltage deceases?

It causes the puddle to be narrower and less fluid.

What is resistance?

It is a measure of how difficult it is for an electric current to pass through a component turning the electrical energy into heat.

How is resistance measured?

It is measure in Ohms and is calculated by dividing voltage by amperage (ohms = V/A).

What the strength of current is measured in?

It is measured in Amperes

What is reverse polarity?

It occurs when the electrode cable is connected to the positive terminal of the welding machine.

What is a primary coil?

On a welding transformer takes power directly from AC input power line. The current flowing in the primary coil causes a magnetic field to form.

Open and close circuits illustration

Switch on and Off

What is step down voltage?

The AC transformer welding power source converts high voltage, low amperage to low voltage, high amperage that is suitable for welding.

How direct current electrode positive DCEP (Straight Polarity) works?

The electron flow is toward the electrode which is from (-) to (+). With DC, the electron direction of flow will always flow from negative to positive. There is no change of electron direction of flow with DC as there is with the AC

The current flow coming towards you.

The induced voltage causes current to flow out towards the reader.

Who rates the welding machine duty cicle?

The national electrical manufacturers association (NEMA)

What determines the strength of the magnetic field?

The power capacity of the welding machine.

What are neutrons and protons?

The protons are located in the nucleus and make up most of the mass of the atom. 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. Protons have a positive charge (+).

What is a 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.

How straight polarity (direct current electrode negative DCEN) works?

The work piece is connected to the positive terminal. The direction of the electron flow is towards the base metal because current travels from negative to positive.

What is a line transformer?

This is another term to describe an AC transformer welding machine.

How an ac transformer achieves 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.

AC_DC transformer-rectifier welding power source to lay a root bead using direct current reverse polarity with an E4310 (E6010)

Transformer-rectifier power source

How AC transformers work?

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 winding are adjusted to ensure the correct welding current is obtained.

What is an open circuit voltage?

When a welding machine is turned on, but no current is flowing in the circuit, the machine has an 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.

How much volts are required to Starting an arc?

With CC current welding machines, open circuits voltage needs to be quite high to start an arc (50 to 100 volts). Once the arc is established, the voltage is dropped to a welding voltage. Both voltage and amperage are present in the circuit.