this ppt is mainly based on the power systems related topic and in this ppt mainly consists of ac and dc weldings and which welding is used mainly and the importance of arc welding and electric welding and the techniques are also discussed in this and it is so helpful .and the safety requirements and the equipment used is also discussed in this topic

1. Department of Electrical & Electronics Engineering
Raghu Engineering College (Autonomous)
CASE STUDY
ON
POWER SYSTEMS -I
BACHELOR OF TECHNOLOGY
IN
ELECTRICAL AND ELECTRONICS ENGINEERING
Under the Supervision of
Ms.D.Anusha Sree
ASST.PROFESSOR
Mr P.Eswar sai 18981A0237
Mr P.Mohan 18981A0238
Ms P.Supriya 18981A0239
Mr.P.Nithesh kumar 18981A0240
Mr.P.Sanjay Kumar 18981A0241
By
Head of the department
Dr.P.SASI KIRAN
Professor

2. Topic : Case study on Arc welding and Electric welding equipment and
comparision between dc welding and ac welding.

3. What is Arc welding?
• Arc welding is a welding process that is used to join metal to metal by
using electricity to create enough heat to melt metal, and the melted metals
when cool result in a binding of the metals. It is a type of welding that uses
a welding power supply to create an electric arc between a metal stick
("electrode") and the base material to melt the metals at the point of contact.
• Arc welders can use either direct (DC) or alternating (AC) current, and
consumable or non-consumable electrodes.
• The welding area is usually protected by some type of shielding gas, vapor, or
slag.
• Arc welding processes may be manual, semi-automatic, or fully automated.
• First developed in the late part of the 19th century, arc welding became
commercially important in shipbuilding during the Second World War.
• Today it remains an important process for the fabrication of steel structures and
vehicles.

4. Safety Issues
Welding can be a dangerous and unhealthy practice without the proper precautions; however, with the
use of new technology and proper protection the risks of injury or death associated with welding can be
greatly reduced.
Heat,Fire And Explosion Hazard
Because many common welding procedures involve an open electric arc or flame, the risk of burns from
heat and sparks is significant. To prevent them, welders wear protective clothing in the form of
heavy leather gloves and protective long sleeve jackets to avoid exposure to extreme heat, flames, and
sparks. The use of compressed gases and flames in many welding processes also pose an explosion and
fire risk; some common precautions include limiting the amount of oxygen in the air and keeping
combustible materials away from the workplace.

5. Eye Damage
Exposure to the brightness of the weld area leads to a condition called arc eye in which ultraviolet
light causes inflammation of the cornea and can burn the retinas of the eyes. Welding
goggles and helmets with dark face plates—much darker than those in sunglasses or oxy-fuel
goggles—are worn to prevent this exposure. In recent years, new helmet models have been
produced featuring a face plate which automatically self-darkens electronically.To protect bystanders,
transparent welding curtains often surround the welding area. These curtains, made of a polyvinyl
chloride plastic film, shield nearby workers from exposure to the UV light from the electric arc.

6. Electric Welding
Electric welding is the joining of metal using an electrical arc and a filler metal stick electrode or wire. Welding is
done by creating an arc between the base metal (the metal being welded) and the filler metal. The arc melts the
base metal and filler metal, combining them into one material to join the base metals. The filler metal is
consumed in the process.
Types of Electric Welding
Below are some types of electric welding:
• Stick Welding
• Wire Feed Welders
• TIG Welding
• Resistance Spot Welding

8. Stick welding
Stick welding (also called SMAW or Shielded Metal Arc Welding) is the process of melting and
joining metals by heating them with an arc between a covered metal electrode (rod/stick) and
the workpiece. Shielding gas is obtained from the electrode outer coating (called flux).
The advantages of stick welding include:
• Welds steel, stainless steel, cast iron, hard surfacing, and aluminum.
• The only electric process that can weld cast iron.
• Suited for windy, outdoor conditions.
• Can be used for welding on dirty or rusty metals with select filler metals.
• Economical.
• DC good for out-of-position welding.
The disadvantages of stick welding include:
• Not good for metals thinner than 16 gauge.
• Tends to have more spatter than other processes.

9. Metal inert gas welding
MIG (Metal Inert Gas) Welding (also called GMAW or Gas Metal Arc Welding) joins metals by heating them
with an arc between a continuously fed wire (filler metal electrode) and the workpiece. Externally supplied
gas or gas mixtures provide shielding(available through the Thoroughbred Industrial Cylinder Exchange).
The type of shielding gas depends on the type of wire. For mild steel wire, the gas is C25 (that is, 75% Argon
and 25% CO2) or CO2. For aluminum wire, the gas is Argon. For stainless steel wire, the gas is called "tri-mix"
(a mixture of Argon, CO2 and helium).
The advantages of MIG welding include:
• Welds steel, stainless steel, and aluminum.
• Continuous wirefeed makes it the easiest process to learn.
• Produces cleaner welds than other processes.
• Can be used for high-speed welding.
The disadvantages of MIG welding include:
• Must not be used in windy conditions.
• All paint and rust needs to be cleaned off the material before welding.

10. Tungsten inert gas welding
TIG Welding (also called GTAW or Gas Tungsten Arc Welding) joins metals by heating them with an arc
formed between the tungsten electrode and the base metal. (The tungsten electrode, unlike a stick
electrode, does not become part of the completed weld). Filler metal is sometimes used and Argon inert
gas or inert gas mixtures are used for shielding.
The advantages of TIG welding include:
• AC TIG welds aluminum and magnesium alloys.
• DC TIG welds brass, copper, steel, stainless steel, and titanium.
• Provides the highest quality and most precise welds.
• Ability to weld thin materials.
The disadvantages of TIG welding include:
• Requires more skill and experience than any other method.

11. Resistance spot welding
Resistance spot welding (also called simply spot welding) joins two pieces of metal by passing current
between electrodes positioned on opposite sides of the pieces to be welded. There is no arc with this
process and it is the resistance of the metal to the current flow that causes the fusion.
The advantages of spot welding include:
• Welds steel and stainless steel.
• Relatively easy to use.
• No shielding gas required.
The disadvantages of spot welding include:
• Primarily used for sheet metal work.

12. Comparision between AC welding and DC welding machines
Comparison # A.C. Welding Machine:
1. A.C. welding machine is cheaper, small in size, light in weight and simple to operate.
2. Maintenance of A.C. welding machine is easier and more economical, because there is no moving parts in
it.
3. Heat generated is equal at both the poles, so it does not require changing of polarity.
4. A.C. welding machine is not suitable for welding all metals particularly non-ferrous metals and alloys.
5. Bare electrode cannot be used. Only specially designed coated electrodes can be used.
6. A.C. welding machine is not suitable for welding of sheet metals due to difficulty in starting the arc.
7. The problem of arc-blow can be easily controlled.
8. Voltage drop in A.C. is less, hence, can be used at a large distances from the power supply.
9. It can only be used when A.C. power supply is available.
10. Less electric energy consumption per kg of metal deposited (3 to 4 kWh.).
11. A.C. Welding machine has high efficiency (0.8 to 0.85).
12. A.C. Welding machine has lower operating cost.
13. A.C. Welding machine has an disadvantage of using low power factor at the welding station, (0.3 to 0.4).

13. Comparison # D.C. Welding Machine:
1. D.C. welding machine is two to three times costlier, larger in size, heavier in weight and is
more complicated.
2. Maintenance cost is higher because of many moving parts in it.
3. Heat generated is different at the work and the electrode by changing the polarity.
4. D.C. welding machine is suitable for welding all types of metals by changing the polarity.
5. Both coated and bare electrode can be used in D.C. welding machine.
6. It is used for all sorts of work as starting of the arc is easier comparatively.
7. Arc-blow is severe and difficulty to control.
8. Voltage drop is relatively higher, it can be used only at a short distance from the power
supply.
9. It can be used anywhere with engine driven D.C. generator or by rectified A.C. supply.
10. Higher electric energy consumption per kg of metal deposited (6 to 10 kWh).
11. Efficiency of D.C. Welding machine is low only 0.3 to 0.6.
12. It has higher operating cost.
13. The motor in a D.C. Welding has an advantage of high power factor of 0.6 to 0.7.