Specifications

MedWeld 3000 Catalog Revision 8
July 2002 Page 41 of 72
Benefits of MFDC Welding Systems
There are applications and situations where the MFDC resistance welding is the best
choice available. Although there are significantly higher initial prices, the overall
cost of using MFDC over single and three-phase SCR control may actually be
significantly lower. Consider these advantages:
Significant Energy Savings:
- for plants that cannot purchase more electrical power, the
MFDC approach may allow you to do more projects with less energy
.
Improved and Consistent Power Factor:
- the MFDC load appears to have unity power
factor, which would then reduce penalties assessed by the power company.
Automatic Load Distribution:
- the MFDC load is evenly distributed across all three
phases. The bank of capacitors that are found on the MFDC system allows for current to draw from the
bank as well as from the line thus reducing peak line currents.
Welding is Tolerant of Electrical Line Disturbances:
- the energy reserve of the
capacitor banks will smooth out line notches and line spikes even while welding is taking place.
Eliminates Need and Maintenance of Expensive Kickless Cables:
- because of
the higher operating frequencies (400 to 1600Hz), the welding transformer can be as much as 74%
smaller than the traditional line frequency (50 / 60 Hz). This allows the user to locate the transformer
much closer to the welding gun thus eliminating the use of expensive Kickless cables that need to be
maintained and monitored.
Precise Welding Current Control:
- the MFDC utilizes IGBTs for switching. These are
turned on and off at the rate of 400 to 2000 times per second. By controlling both the turn on and turn
off, the MFDC can determine the current to control. Conventional controls utilize SCRs for switching.
These are turned on by the weld control but then remain conducting until the line voltage crosses the
zero point during the base frequency line cycle. Because of this, conventional controls must use a
predictive algorithm rather than a deterministic approach. Also, if an under or over compensation
occurs on one of the cycles, the conventional will have to wait until the next period of the base
frequency whereas the MFDC need only wait a fraction (1/20
th
nominal) of that time.
Attains Target Current Immediately:
- DC systems of the SCR type have a rise time
prior to its steady state. Since the MFDC is so responsive, it is possible to create full phase firing
during the natural rise time to lessen that period of time.
More Process Friendly:
- the MFDC eliminates undesired inter-cycle cooling periods that
exist in AC resistance welding processes. Welding therefore can occur faster which would then reduce
heat waste and the problems associated to eliminating that waste.