Soft Starters have an initial attraction because of their low unit price. For a few thousand dollars, operators can add better start and stop control to their pumping units.
They are also simple devices, tasked mainly with softening the startup process. There is not much work to do to install a Soft Starter and begin receiving its benefits. What can be better than that?
Unfortunately, like so many other quick fixes in life, Soft Starters have a considerable hidden cost. Before choosing Soft Starters as your solution, consider these three control limitations that can make this cheap device more expensive than other options.
Limited in-rush current control. Soft Starters can reduce the in-rushing current but they do not eliminate it. Typically the current is reduced by 50% from what it would otherwise be with a full voltage starter, which is still 2-4 times the full rated amperage of the motor. This electrical shock causes additional wear and tear on pumping equipment that leads to earlier workovers. The in-rush current can also cause catastrophic failure that takes the well offline, incurring workover costs and lost production. Soft Starters themselves can burn out and have a relatively short life.
No pump off control. Soft Starters can be set for start and stop but they do not monitor well conditions and shutdown based on pump off conditions. This leaves the equipment vulnerable to excessive stresses, downtime and workover.
No speed control. Soft Starters provide full current and voltage to pumping equipment following startup. Rarely is that optimal. Changing conditions in the well and differences in upstroke and downstroke leave the system unbalanced if the pump is always running full speed ahead. This leads to equipment fatigue, fluid pound, shutdown and workovers. Production is lost. Electricity is wasted and peak load demand is high.
Because of these control deficits, Soft Starters incur additional costs beyond their initial purchase price. Here are a few differences between SoftStarters and variable frequency drives that have an impact on the total return on investment.