An integrated on-line motor protection system

Motor protection equipment is typically aimed at protecting the motor insulation against overheating. Additional protection can be gained by applying expensive equipment based on sensing vibration and/or the current spectra of the motor to predict incipient failures. These systems, which have only recently been introduced, have limited application because of the cost and expertise required to operate them. This article proposes a single, low-cost, microprocessor-based unit to protect the motor against-or to alert the user to-the majority of motor failure modes. The proposed system includes thermal modeling for overload protection and variable ground fault protection. Mechanical failure prediction using current spectral analysis is also provided using a frequency selective expert system and a neural network to distinguish potential fault conditions from unknown online operating conditions.