Energy saving aspects of welding machines

One of the most common questions asked when considering the procurement of welding equipment is: “What is it going to cost me?”

The later generation Inverter based welding equipment are more compact, more lightweight, more versatile, producing better welding quality. Above all they are MORE POWER EFFICIENT.

An Inverter-based welding power source with benefits galore. Inverter technology can bring significant reduction in input power consumption.

Inverter Technology Enables Lighter, More Powerful Welding Machines
In the past, welding power supplies have been based on transformers. The power supply taken was in 50 Hz 230, or 415-volt power. A metallic transformer changed it from the relatively high input voltage to 50 Hz current at a lower voltage. This low voltage current was then rectified by some sort of Rectifier Bridge to get direct current (DC) welding output. Some sort of relatively slow magnetic amplifiers usually performed control of this output.

Transformers are relatively inefficient operating at 50 or 60 Hz. A lot of heat is generated in the transformer, and the transformer must be relatively large and heavy. A significant part of the power cost goes into heating the transformer and the surrounding air. Most such welding power supplies weigh around 100 Kgs and have a shape something like a 800 – 1000 mm cube. Additionally, if 50 Hz is used, control signals are limited to being issued at no more than 100 per second, so it’s impossible to pulse the welding current any faster than this.

In inverter controlled power supplies, the same incoming 50-Hz power is used. However, instead of being fed directly into a transformer, it is first rectified to 50 Hz DC. Then it is fed into the inverter section of the power supply where it is switched on and off by solid-state switches at frequencies as high as 50,000 Hz. This pulsed, high voltage, high frequency DC is then fed to the main power transformer, where it is transformed into low voltage 20,000 Hz DC suitable for welding. Finally it is put through a filtering and rectifying circuit. Output control is performed by solid-state controls, which modulate the switching rate of the switching transistors.

A basic premise of welding power source design states that a faster operating frequency enables the power source to use fewer copper windings and a smaller core in its transformer and inductor (the heaviest components of a welder.

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 50-Hz ripple. This results in a much smoother, more stable DC welding arc.).

For industrial equipment, inverter technology can bring significant reduction in input power consumption

Low Stress Leads to Long Life
It is anticipated that products based on Inverter technology will exceed the reliability rating of existing Thyristor controlled machines. High Frequency Inverters increase reliability because it reduces the stress on the power-switching semiconductor, called an IGBT.

New technology minimizes heat generation by ramping the total power to zero before switching. This lowers the IGBT’s operating temperature and enables manufacturers to increase switching frequency by 40,000 Hz over its existing design. As a result of operating at high frequencies, the transformer and inductor in the Inverters will weigh much less than earlier designs. Heat sinks are also smaller because of their efficient design.

Inverter Advantages
Compared to conventional power sources, inverter-based welding power sources offer the following advantages:

• Lightweight and portable
• Able to obtain superior Stick welding performance with all electrode types
• Multi-process welding output without sacrificing arc performance in any mode
• Quick response to changing arc conditions (e.g., maintains a steady weld output even if the operator’s handshakes)
• Superior control over pulsed welding processes
• Line voltage independent – uses single- or three-phase input power and multiple input voltages without any manual relinking mechanism
• Better power factor (more efficient use of power from the utility)
• Less susceptibility to primary voltage fluctuations (e.g., “dirty power”)

There is another advantage of the inverter power supplies – power cost. The inverter equipment is much more efficient than transformer equipment. For instance, the current draw at 200 amperes for the typical Inverter type Welder is 29 amperes on 230 Volt single- phase Supply. The current draw of an older transformer welder is typically 50 to 60 amperes on 230 Volt single-phase Supply when welding at similar currents. While the cost savings in switching to inverters is often overstated, under normal circumstances, it is safe to say that annual power savings are approximately 10% of the power supply purchase price.

For industrial equipment, inverter technology provides the advantage of being able to connect and utilize more machines for the same welding application at the same Connected KVA of the manufacturing unit

The ability to generate AC is what really makes the inverter shine for welding aluminium using GTAW. The fact that the arc voltage never truly goes through zero means that the AC arc is much more stable than previously. Most inverter – based GTAW power supplies do not need the high frequency to be on continuously for stability. It will automatically be extinguished as soon as the arc starts. The elimination of continuous high frequency drastically reduces the amount of RFI generated by the power supply.

Second, the fact that we can send control signals at 20 KHz means that we can vary the frequency of the AC welding output. Older machines were 60 Hz AC output only. The new design can put out AC at anywhere 20 and 150 Hz. Higher frequencies can be beneficial in welding thin materials. As the frequency is raised, the arc cone, and the weld, becomes narrower, resulting in deeper penetration.

Weld penetration comes from the electrode negative part of the AC cycle. During the part of the cycle when the electrode is positive, weld penetration is reduced and more heat goes into the tungsten electrode. However, during the electrode positive part of the cycle, the arc actually acts to remove the oxides from the surface of the aluminium, making welding easier. It is for this reason that, although most other materials are GTA welded using direct current, aluminium is usually welded using AC. Very early GTAW power supplies supplied a simple sine wave output where equal amounts of electrode positive and electrode negative were generated. However, this was inefficient. We didn’t need that much electrode positive to get adequate cleaning. Later power supplies allowed us to vary the proportion of electrode negative to electrode positive. It was found that approximately 65% electrode negative and 35% electrode positive gave adequate arc cleaning and good penetration. However, a lot of the arc energy was still going to heat the tungsten electrode, so that large diameter tungsten electrodes were required.

SAVINGS IN ELECTRICITY BILLS !
For industrial equipment, inverter technology can bring significant cost savings due to lower power consumption and hence lower energy charges.

Conclusion
The inverter power supplies provide adequate arc cleaning with as little as 15% electrode positive. Reducing the amount of electrode positive makes the process more efficient, increases weld penetration, and reduces the amount of heat going into the tungsten electrode, which means smaller diameter, pointed electrodes can be used. This further concentrates and narrows the weld.
(Contributed by Ador Welding Ltd.)