A Rotor Condition Monitor for Squirrel-Cage Induction Machines

Rotor temperature is of concern in both short-term machine protection and in longer term condition monitoring systems for large induction machines. Unduly large temperatures can arise under severe operating conditions such as stall and overload. A cage rotor condition monitoring system using direct temperature measurement is described. Under running conditions, it continuously transmits temperature information about strategic points on the rotor via an optical link. Possible rotor circuit imperfections are broken bars and end rings, single or multiple, and the deterioration of bar/end ring joints. The possibility of using temperature information for the identification of these faults is also investigated.     

Transient thermal characteristics of induction machine rotor cage

Thermal analysis of an induction machine cage rotor during stall conditions forms an important part of design calculations. The study of rotor circuit thermal behavior is also useful to identify causes of failure in large cage rotor induction machines. The authors present a three-dimensional finite-element-based electrical-thermal analysis of the bar and end-ring area of a large rotor to examine its thermal characteristics during a stall. Details of temperature variations at key locations in the bar and end ring are provided. The calculations are compared to experimental results, and the advantages and limitations of the solution technique for rotor analysis are discussed     

Reliability improvement and economic benefits of online monitoringsystems for large induction machines

Microprocessor-based monitoring systems are being developed for the regular analysis of large induction machine variables and to predict possible fault conditions, so that preventive maintenance can be organized in a cost-effective manner. A method for the evaluation of the improvement of machine reliability made by such monitoring systems is presented. An economic and financial analysis to examine the viability of a condition monitoring system for a large machine using comprehensive rotor, stator, and other parameter measurements is developed. In two case studies, the costs of design, construction, mounting, and operation of condition monitoring systems are discussed, and estimates are made at current costs. These costs are balanced against the costs avoided in cases of unexpected machine failures, lost production, and repairs. Cost estimates for repairs and downtime are made using published information from previous reliability surveys on electrical machines. Information is presented for different machine sizes, which will indicate any relevance of the machine size when evaluating monitoring systems