Electrical Motors

Motors - Erik Mertens -The scope of this document is to introduce the basic principles of motors and its important characteristics as well as the possibilities to drive equipment. The motor driven equipment on a typical industrial site accounts for approximately two thirds of the electricity consumption. Therefore, any type of measure taken to improve the efficiency of a motor system consequently can offer major energy savings - From Laborelec and Leonardo Energy.

The Following Technical Papers are from Rockwell Automation

  • A Comparison of the Characteristics of AC and DC Motors -  As AC motors continue to be used in applications traditionally served by DC motors, some comparisons of the characteristics of AC and DC motors seem appropriate. The aspects of AC and DC motors which will be reviewed include typical construction, torque production, equivalent circuits, ratings (power and torque density), speed ranges, load ranges, etc. This comparison will also highlight some of the relative advantages and disadvantages of each type of motor in variable speed applications. In addition, looking at variable speed AC motors with a “DC motor mentality” can offer a more “user-friendly” understanding of these AC machines. This point of view can also suggest ways to optimize AC motors for variable speed applications.
  • What Is Regeneration? -  When the rotor of an induction motor turns slower than the speed set by the applied frequency, the motor is transforming electrical energy into mechanical energy at the motor shaft. This process is referred to as ‘motoring’. When the rotor turns faster than the synchronous speed set by a drive output, the motor is transforming mechanical energy from the motor shaft into electrical energy. It may be a ramp to stop, a reduction in commanded speed or an overhauling load that causes the shaft speed to be greater than the synchronous speed. In any case this, condition isreferred to as "regeneration".
  • Drive and Motor Basics  - An adjustable speed drive is a device that controls speed, and direction of an AC or DC motor. Some high performance drives are able to run in torque regulation mode.
  • Motor Load Characteristics -  Motor loads are classified into two main groups depending on how their torque requirement varies with operating speed. The following paragraphs deal with the various load types found in industry.
  • Power Distribution Systems - The type of transformer and the connection configuration feeding a drive plays an important role in its performance and safety. The following is a brief description of some of the more common configurations and a discussion of their virtues and shortcomings.
  • Dealing with Power Factor Correction Capacitor switching and AC drives - There are two significant concerns regarding the existence of power factor correction capacitors being located on the input of an AC Drive. One concern is the additional current loading that may exist in the capacitor. The other concern occurs when capacitor switching is used to adjust any variations in the power factor of the motor load.

Embedded Motor Condition Monitoring, Diagnostics - Adam Krug -  Embedded condition monitoring and remote diagnostics prevent equipment failure, reduce energy consumption, improve reliability. Only a very small percentage of critical motors and motor loads in the U.S. actually are equipped with any sort of condition monitoring. This lack of adoption largely stems from the costs and complexity of conventional condition monitoring equipment.  Industry-leading solid-state, motor control technology provides customers with the ability to monitor parameters, albeit not the exact same parameters, to gain a more precise and real-time perspective on performance, far more simply than traditional condition monitoring methods - from ISA.

Baldor has released a software estimating tool that enables users to evaluate the energy efficiency of electric motors and variable speed drives. Known as BE$T, the Baldor Energy Savings Tool can be downloaded free of charge from the company’s website. The software analyses the efficiency and annual electricity usage of users’ existing motors, and calculates the cost savings that can be achieved by replacing them with equivalent higher efficiency models. Built-in motor performance and pricing information enables the software to suggest optimum replacements and to estimate the investment payback period.

Electrical Drive Reference Centre - This Excellent Reference Site provides technical information on a range of different Electrical Motors.

Electrical Motors - Technical Articles - from the Electrical Drive Reference Centre.

Motor Tree - From SMMA - The Motor & Motion Association.

Motors-NEMA Terminations and Connections - from HUPP Electric Motors.

NEMA Frame Dimensions - Foot Mounted AC Machines, Type C Face Mounting Foot or Footless AC Motors, and Type D Flange Mounting Foot or Footless AC Motors - from HUPP Electric Motors.