Considerations in the Selection and Application of AC and DC Motors for Cement Plants

There are several types of motors to choose from when selecting motors for large HP (2000 HP - 10.000 HP) cement plant applications including; squirrel cage induction motors, wound rotor induction motors, PAM induction motors, synchronous motors, and DC motors, all of which have their own advantages and disadvantages. This paper will compare the operational characteristics of the induction, synchronous and DC motors to demonstrate how to apply the different speed-torque-current characteristics of each when driving typical cement plant loads. This paper will compare several different starting methods for AC motors such as across the line starting, autotransformer, solid state starting, and Adjustable Speed Drive (ASD) and discuss the limiting factors of each method such as starting current requirements and cage heating. A comparison of the operating characteristics of induction and synchronous motors will demonstrate how the power factor and efficiency advantage of synchronous motors can be applied to lower the energy cost of a cement plant. The variable speed operation of induction and synchronous motors operating on adjustable speed drives will be compared with the operational characteristics of DC motors which vary speed without the use of a drive.