DC Motor Duty Meter

Compared to other machines, DC machines are relatively complex, since they require a commutator to mechanically rectify large armature currents. This mechanical commutation is inherently a source of maintenance and lost time. However, the robustness and simplicity of control of DC machines, together with the vast experience accumulated within the industry, make them an attractive solution for mining applications, such as rope shovels and draglines. Hence, although AC motor technology is gaining an increasing market share, DC machines will continue to be used for up to several decades. Aging of the motor fleet will intensify maintenance problems during this transition period. To assist in maintenance and reduce the downtime of the production critical DC machines, it has been proposed to develop an online condition monitoring and life prediction system called a 'DC Motor Duty Meter'.

Traditional on-line condition monitoring is based on identification of early signs of faults or malfunctions. The approach proposed is different in that: (a) it tracks causes rather than the signs of motor deterioration; (b) it gives a recommendation for DC motor maintenance needs based on the cumulative duty estimation.

This report concludes the final stage 3 of the ACARP C16030 project. The main objectives of this stage were: (a) to develop a prototype Duty Meter suitable for installation with a full size electric rope shovel DC motor; and (b) to validate this prototype on a scaled version of the DC motor under conditions matching those experienced by a rope shovel DC motor.

Note that the laboratory DC motor design, the grade of the brushes, the type of the drive, etc. were carefully selected to be as close as possible to those of the full scale DC motor. The operating conditions were obtained by field

measurements on a rope shovel DC motor, scaled in proportion to the ratings of the laboratory DC motor, and exactly reproduced by using a programmed laboratory dynamometer.

This report provides a detailed description of the DC Motor Duty Meter prototype, its underlying principles, algorithms and results. The report is structured in the following way. Chapter 1 explains about the project history and objectives, summarises the main findings, outlines application and directions for future research. Chapter 2 describes the laboratory equipment used to build the Duty Meter prototype. Chapter 3 presents results of the additional experiments conducted within the final stage of the project. Chapters 4 described the Duty Meter models developed throughout the project. Chapter 5 explains how the Duty Meter models were implemented in the algorithm of the National Instrument CompactRIO system, and presents validation results. Chapter 6 briefly explains the software, and how to install and use the Duty Meter. Chapter 7 discusses technology transfer activities.