A method and apparatus for detecting a stator winding fault in an induction motor includes sampling instantaneous signals from the motor and then deriving sequence components of at least some of the instantaneous signals using a power decomposition technique (PDT), one of the sequence components being a total negative sequence current component. In addition, the method includes calculating an expected negative sequence current based on at least some of the sequence components. Thereafter, the method subtracts the expected negative sequence current from the total negative sequence current to determine a fault negative sequence current, wherein the fault negative sequence current is indicative of the fault. More preferably, the method additionally includes calculating an intrinsic motor negative sequence current based on at least some of the sequence components, and subtracting the intrinsic motor negative sequence current from the fault negative sequence current generated as described above to determine a modified fault negative sequence current. Notably, the method and apparatus are capable of detecting faults that cause a modified fault negative sequence current as low as approximately 0.2% of the full load current.

The invention concerns a device for and a process for testing electric motors, in particular fan motors, for functionality, wherein electromagnetic alternating fields produced by an electric motor are received by an antenna, wherein the received signals are analyzed for signal components in the frequency range of the rotation value of electric motors or their harmonics via an analysis unit, and wherein upon determination of functionality the results are indicated by an indicator unit.

A hydraulic excavator 1 working in fields includes a controller 2 for measuring a working time for each of an engine 32, a front 15, a swing body 13, and a travel body 12, storing measured data in a memory of the controller 2, and then transferring it to a base station computer 3 via satellite communication, an FD, etc. The transferred data is stored as a database 100 in the base station computer 3. The base station computer 3 reads the data stored in the database 100 for each hydraulic excavator, calculates a working time of a part belonging to each section on the basis of the working time of that section, and compares the calculated working time with a preset target replacement time interval of the relevant part, thereby calculating a remaining time up to next replacement of the relevant part and managing the scheduled replacement timing thereof. Thus, the appropriate scheduled replacement timing of parts can be determined even in a construction machine having a plurality of sections that differ in working time from each other.

A system and method for predicting mechanical failures in machinery driven by induction motors by using the motor as a diagnostic tool to detect present mechanical disturbances. The motor is monitored during operation to avoid down-time. The motor's torque fluctuations are used as an indicator of early-stage mechanical failures in the machinery. The motor's torque fluctuations are determined using indirect sensing techniques that are less expensive and less intrusive than previously known. More specifically, torque is derived from easily and inexpensively measurable parameters, such as motor slip and phase angle. Current operation is compared to known normal operation. Variations of the motor's characteristics from the known baseline indicate an actual or approaching mechanical failure. "Experimental Fractals" are disclosed that visually represent a current state of the monitored machinery and allow for visual comparison to a baseline for detection of mechanical failures. Future failures are forecasted by extrapolating a derived trend.

An integrated motor monitoring system collects, analyzes, and stores to database(s) on-line and off-line coordinated real-time motor data for industrial AC and DC motors. On-line coordinated real-time motor data from both on-motor sensors and remote sensors at a motor control center are collected simultaneously and processed. Off-line measurements are performed with integrated stimulus and measurement apparatus. Monitoring units at the motor and motor control center each collect specific data on the motor. The database provides current and historical data on the motor for analyses conducted at the motor or at the motor control center. Additionally the motor monitoring system has the capability of relating motor system or process events with motor performance.