Over its 100-year history, welding has become one of the most essential technical skills in manufacturing and fabrication. The process of using high-temperature, electrical-powered heat to fuse two pieces of metal or synthetic material has been incorporated throughout the industry in an increasingly wide variety of applications that rely on a range of tools and techniques. But Electrical welding machines are among the most pollutant loads due to their strong nonlinear behavior. As a result, utilities have established new criteria for connecting welding machines in the grid.
Power Quality Analysis in Welding Loads
Welding machines can reduce productivity, lower product quality, increase worker fatigue.
The action time of the spot welding machine is extremely fast, the welding duration is hundreds of milliseconds, and the welding frequency is fast;
During the welding process, according to the different welding materials, the welding current of the spot welding machine can change from a few amperes to several thousand amperes in an instant, changing at a very fast speed, which has a great impact on the power grid;
The working response time of the spot welding machine is extremely fast, the welding duration is only hundreds of milliseconds, and the welding frequency changes very quickly;
During the welding process, the spot welding machine will generate huge reactive power, which will cause the power factor of the grid to be very low and the reactive power penalty from electricity companies.
Meanwhile, there’s variability of the arc cycle-to-cycle. The first strike of the welder is especially unpredictable. This results in a difficult-to-define harmonic spectra. As the weld begins to flow, the harmonic spectra is more predictable with less amplitude of the peak current. However, the harmonic current still cannot be predicted. This unpredictabity, in addition to the very high cycle-tocycle peak currents at first strike, make selection of a harmonic mitigation method extremely difficult. If the harmonics are not mitigated, they can cause excess heat in the network, which can lead to a host of problems resulting in downtime and further productivity loss.
YTPQC Products to these power quality problems
YTPQC-ASVG Advanced Static Var Generator ASVG
YTPQC-ASVG Advanced Static Var Generator ASVG is an advanced dynamic VAR compensators. With an extremely fast response time (Instantaneous response time within 20us), SVG can perfectly compensate the reactive power of the welding machine.
YTPQC-HPFC Hybrid Power Factor Correction
An alternative to the Dynamic VAR compensator is the hybrid power factor correction with YTPQC-SVG controlling Capacitor banks, which will have a much better cost performance at site with large kVAr demand.
YTPQC-AHF Active Harmonic(Power) Filter AHF
With the same advantages as SVG, Active Harmonic Filter can filter out harmonics very well and improve the power quality of the welding sites. YTPQC-AHF is the best comprehensive power quality control device, with the functions of harmonics compensation,reactive power compensation and 3 phase unbalance compensation.
Detailed description of power quality problems of welding sites
Electric Spoting welding machinese, such as those found in heavy manufacturing facilities or used in normal plant repairs, are certainly a big problem of power quality. They have several unique operating characteristics that, if not addressed properly, can decrease productivity and product quality and increase worker fatigue–all of which can detract from your bottom line.
Electrical contractors and facility managers working in these environments should be aware of these potential problems and how to identify them in the manufacturing process. Doing so early on can save considerable time and money in the long run.
One of the major problems associated with the welding process is the sudden inrush current demand. Spot welders draw high inrush currents during their operating cycle, usually for a short duration of a few seconds. These high periodic currents cause the upstream transformer to saturate with the magnetic flux (magnetizing current). Flux saturation can cause a drastic drop in transformer output voltage, which can lead to failure or poor performance of the load. In other words: dramatically lower or lost productivity.
Flickering lighting has been shown to increase worker fatigue. When output voltage of the transformer drops, the power supply sees this drop and tries to supply the current needed to maintain the voltage of the faulty transformer, creating an additional component to the current surge within the electrical system. This current surge intermittently exacerbates the voltage drop on the power supply. If the voltage cycling is repetitive, it may appear as flickering lights.
Next, there is intermittent operation at short intervals. When welding for the first time, the welder requires several cycles of essentially infinite current. During this time, the electrical system providing the power cannot provide all the current needed. The result is welder voltage dips and poor weld quality. In an automated manufacturing plant, there are multiple welders on an electrical system powered by one electrical system. Simultaneous operation of multiple welding machines will aggravate the problem of voltage sag and greatly increase the incidence of poor product welding.
Finally, there is a difference between arc cycle and period. A welder's first strike is especially unpredictable. This makes it difficult to define the harmonic spectrum. When the weld starts to flow, the harmonics are more predictable and the peak current magnitude is smaller. However, harmonic currents remain unpredictable. This unpredictability, combined with very high cycle-to-cycle peak currents at the first stroke, makes the choice of harmonic mitigation method extremely difficult. If harmonics are not mitigated, they can cause overheating in the network which can cause a cascade of problems leading to downtime and further loss of productivity.
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