Electronically enhanced low voltage motor protection and control

By examining the true operating characteristics of motors, a motor protection system is designed that closely models the effects of motor currents on the winding and housing temperatures. Experimentally determined parameters allow this model to track thermal performance, even when the motor is sitting still after tripping. This protection and control system, using the power of a microcomputer, can provide other modes of protection not available with the common thermal overload relay. Ground fault protection, phase unbalance and loss of phase protection, jam and loss of load protection are all included in the software. The system can eliminate most of the control wiring and relaying necessary for complex motor starter circuits.<>