Download pdf - Providing Power Supply for Arc Welders by Using Rectifier (Final)

8/6/2019 Providing Power Supply for Arc Welders by Using Rectifier (Final)

1/20

Vahid Nahani

Muhammad Firdaus

Venothkumar

Theivinderan Reddy


2/20

Rectification the process of converting an alternating voltage or alternatingcurrent into direct voltage or direct current

2 types of rectifier

Constant Current

Constant Voltage

Welding power supply - device that provides an electric current to perform welding

Welding requires above 12000 amps which will take AC power from the utility

mains and convert it to DC for the welder.

Example :

Car battery

Sophisticated


3/20

Welding machines - a constant current (CC) or constant

voltage(CV).

Output Voltage - maintain steady current while constant voltage

machine will fluctuate its output current to maintain a set voltage.

Shielded metal arc welding will use a constant current source and

gas metal arc welding and flux-cored arc welding typically use

constant voltage sources.

Constant voltage it also possible with a voltage sensing wire feeder.


4/20

Transformer is used to for

the welding power supplyconverts the high voltage

and low current electricity

from the utility (AC) mains

into a high current and

low voltage , typically

between 17 to 45 volts and55 to 590 amps


5/20

Primary side of transformer is connected to AC and

the secondary part is connected to full wave diode

rectifier and the output is dc power supply for

welding.


6/20

Sometimes referred as metal inert gas (MIG).

Semi-automatic or automatic arc welding process.

Uses constant voltage supply

Thus, change in arc length results in a large change

in heat input and current.

A constant voltage, direct current power source is

most commonly used with GMAW


7/20

MIG arc welding power source has a secondary

tapped transformer.

It consists of a transformer, rectifier and output

capacitor The step down transformer winding in primary and

secondary side are separated, which means the

output of transformer is isolated from the power

line ground. The rectifier is a full wave bridge of silicon diodes

output filter smoothest the secondary voltage to

give a more consist weld.


8/20

switch is used to select step on the transformer

mechanically can control the secondary output voltage

rebus and reliable design

the output voltage cannot be controlled remotely and

input voltage fluctuations will affect the output.

The output filter capacitor is sized on the basis

permissible output ripple voltage

the capacitor supplies the maximum output current I

continuously and it charges up to the output voltage

every 1/100 s for the full wave rectifier with 50Hz line

frequency.


9/20


10/20

A bleeder resistor is connected across the output

capacitor to discharge it when the supply is turned off

and to remove the hazard of an unexpected voltage


11/20

overcome the effect of input fluctuations on the output

The welding power source opposite maintains a constant

output voltage using an SCR control circuit.

rectifier that remains in non-conductive state, even

when forward voltage is applied from anode to cathode,until a positive triggle pulse is applied to the gate and

the SCR fires.

rectifier that remains in non-conductive state, even

when forward voltage is applied from anode to cathode,until a positive triggle pulse is applied to the gate and

the SCR fires.


12/20

Two SCRs in this design are connected in anti-parallel at

the input to the transformer primary allowing power tobe controlled during each half cycle of the AC input.


13/20

requires fewer moving parts and it can be remotelycontrolled and voltage fluctuations at the input do not

affect the weld output.

poor efficiency and low speed of control.

If the dV/dt is too large , the device will begin to conductwithout a gate signal an will result in erratic circuit

operation and potential device damage.


14/20

Since the advent of high-power semiconductors

such as the insulated gate bipolar transistor(IGBT)

it is now possible to build a switching power supply

capable of coping with the high loads of arcwelding.

These designs are known as inverter welding units

first rectify the utility AC power to DC; then they

switch (invert) the DC power into a step downtransformer to produce the desired welding

voltage or current


15/20

The input power AC is rectified to DC using a power

factor correction boost converter


16/20

A full bridge MOSFET power stage convert thevoltage back to AC at high frequency typically 50Hzto 100Hz.

The transformer steps down the voltage which isthen rectified and smoothed at the output stage.

high power conversion efficiency

due to high frequency operation of the MOSFET

bridge the size of the components can be greatlyreduced specially the transformer and the outputfilter stage.

component size is inversely proportional to theoperating frequency

invertor power source maintains a constant outputvoltage regardless of changes in line input voltageand output current


17/20


18/20

Advantages

The main power transformer, which operates at 20,000Hertz

is vastly more efficient than 60Hertz transformers, which

means it can be much smaller and the huge advantage in

weight and portability in favor of the inverter based arc

welder machines


19/20

Advantages

There is another advantage of the inverter power supplies -

power cost. The inverter equipment is much more efficient

than transformer equipment.

The other significant advantage of inverter power supplies

is that, by chopping up the incoming AC so finely, we end up

with a very steady DC, without the typical 60 Hertz ripple.

This results in a much smoother, more stable DC welding

arc.


20/20

Thank You