No liquid rheostats needed with SPR

Industrial systems manufacturer Quad Plus Inc. of Chicago, Illinois, USA, has developed the so-called Slip Power Recovery (SPR) drive to replace liquid rheostats in automobile shredders. This system increases a shredder’s productivity, lowers energy costs and reduces maintenance, according to Quad Plus. At the same time, it adds, the system eliminates the need for a cooling tower as well as capacitors, and does not require the maintenance associated with a liquid rheostat.
Liquid rheostats are commonly used to start and control large AC wound rotor motors but SPR drives carry out the same functions more efficiently, says Quad Plus. The drives can improve productivity by keeping the motor speed near to its synchronous speed throughout load hits. The speed drops when the motor current reaches a pre-defined limit but recovers faster with a SPR drive compared to a liquid rheostat, Quad Plus contends.
An SPR drive also regenerates the energy it consumes such that the energy can be sold back to the power company, the company continues. In contrast, the energy consumed by a liquid rheostat is converted to heat and is wasted.