Soft starting is the energy efficient green option
Energy conscious plant operators are installing soft starts at an unprecedented rate, so that they save energy by stopping intermittent duty motors when they are actually not in use. Until recently it has been conventional practice to leave motors idling between duty cycles, but increasingly this is now seen as wasteful of energy - especially with recent rapid rises in electricity prices. Idling motors also exhibit very poor power factor, contributing to kVAr charges.
"In the past there were sound engineering reasons for doing this," explains Philip Larkin of Softstart UK, one of the beneficiaries of the change of practice. "The wear and tear on the electrical and mechanical elements of a drive system at start-up is quiet considerable, so you were offsetting this against the energy consumption."
However, the growing emphasis on reducing carbon emissions has made plant engineers re-examine many of their business practices. Soft starts reduce the electrical and mechanical shock loads and consequential damage by bringing a motor up to speed far more smoothly than direct-on-line starting. This means the motor can be stopped when not in production and started smoothly and efficiently when required, without concerns over electrical and mechanical system stresses.
Larkin says that it is very easy to make a financial case for installing a soft start on a large drive system and so his company has seen a massive upswing in orders for medium voltage soft starts.
"For instance we are just completing a repeat order for a 6.6KV 1.2MW system for a Russian metal shredder, we are building a 6.6kV 2.3MW four-motor multi-start system for a pumping station at Gadansk in Poland, an 11KV 5.5MW system for dry dock pumps in Dubai and a 6.6kV MW ATEX certified explosion-proof soft start for starting 3 off 670kW motors on a Russian mining conveyor system."
The trend is almost as pronounced in the smaller off-the-shelf soft starts. Larkin reports that sales of 4KW-600kW units have quadrupled in less than 15 months. "This includes a couple of big call-off orders for OEMs, one-off sales and ongoing projects where we are working our way through a customer's plant to improve the energy efficiency of one machine after another."