VSD technology has come a long way in a little time. 
VSD Development
Exhibit A: The ParaJust VSD, which was distributed in Australia by Charles and Hunting back in the 1970s.
The original ParaJust VDS series was available in five sizes, although the straightness of their catalogue left a lot to be desired! DC drives had long held sway in the industrial speed control sector (some would argue that they remain very competitive to this day).
The development of AC drives focused mainly on bridging existing 415 volt three phase motors for operation with 240 volt three phase.
Another featured claim of the ParaJust was the relatively low speed drift of .25% over sustained periods. Nowadays, we routinely expect speed to remain constant from 0.1% right down to 0.01%!
Exhibit B: The WEG CFW500, available in 16 individual sizes, is the modern evolution of the original variable speed drive.
With both single phase and three phase input options, standard inputs up to 7.5kW and various feedback options, the CFW500 is WEG’s cost-effective variable speed drive for everyday applications. The CFW500 also accommodates various plug-in modules to support a range of outputs – outputs that weren’t around back in the day of the ParaJust.
It is also intriguing to see how the efficiencies of electric motors have changed over time. The ParaJust 15 Amp drive was rated as the equivalent of 4kW, whilst the CFW500 has 4kW rated at 10 Amps.
One feature that both the ParaJust and the CFW500 share is a sexy, sleek design. It’s just that the definition of sleek has evolved over the years.
