ELECTRIC MOTORS

Electric motor coverts electric energy into mechanical energy. They do this through the interaction between the motors magnetic field and the electric current flowing in the copper windings to generate rotary motion or torque to drive the motor shaft, usually connected to a load.

The basic components of an electric motor consist of the following; stator, rotor, armature, commutator, brushes, bearings, shaft, fans and sensors.

The stator is the stationary part of the motor, housing the windings and the magnetic core. The rotor is the moving part of the motor, attached to the shaft. The armature is the coil of wire (or multiple coils) wrapped around the rotor. The commutator switches current flow to the armature (in DC motors only). The brushes are spring loaded contacts riding on the commutator (in DC motors only). The bearings supports the shaft and facilitates smooth rotation. The shaft is the rotating axis of the motor. The fan cools the motor (in some design) and the sensors monitor motor parameters (temperature, speed, position).

Electric motors are classified according to their power supply source. They are alternating current (AC) motors if they are powered by the grid, inverters or electric generators. Otherwise they are called direct current (DC) electric motors, if they are powered through batteries or rectifiers to convert grid voltage to direct current.  Generally alternating current (AC) motors are more efficient and easier to control than direct  current (DC) electric motors. Also alternating current (AC) motors can run in more phases compared to direct current (DC) motors.

Electric motor is basically an electric generator running backwards; that is using current to produce motion, rather than motion to produce electric current.

Electric  motors specification involves several quantities; the voltage or the range of voltages the motor operates, the motor speed or the range of speed the motor can run, the electric power drawn by the motor (in horsepower or watts) and finally the torque or effective turning force or moment (in newton per meter( NM)) of the electric motor.

Electric motors are estimated to consume over 25% of the electricity supply from the grid. While large electric motors with power rating ranging from 10hp to 500hp or more, can be extremely efficient at converting electrical energy to kinetic energy (i.e. with efficiencies between 85% to 95%). These efficiencies are only achieved when the electric motors are well matched with their loads. Actual efficiencies in normal usage are sub optimal, for instance electric motors oversized for the load they drive. Small electric motors with power ratings of less than 10hp are inherently less efficient with efficiencies around 50%.

The main challenges of electric motors are issues relating to their thermal management due to the excessive heat generation during operation, therefore advancement in cooling technologies will be beneficial to electric motors. Also issues relating to cost reduction in their production and operation will enhance and increase their use and application.

Electric motors have found widespread use as prime mover in a variety of applications. These applications include; electric vehicles, advanced traction motors, automation and robotics, industrial machinery, consumer appliances and so on.

The following trends are expected for the future; increased adoption of electric motors in transportation, industrial automation and consumer appliances. This trend will necessitate advances in the development of new materials, incorporation of integrated sensor based control systems connected to internet of things (IoT) platform and perhaps AI optimized motor control for predictive maintenance and monitoring. Furthermore,  the development and use of high temperature superconductors, grapheme and nano-materials and wide bandgap semiconductors will increase power density, reduce thermal  stress and increase the switching speed  respectively of electric motors in the future.

 

SOURCES;

• Electric motors handbook by H. Douglass Beattie.
• Electric motors and drives by Austin Hughes.
• Electric motor design and application by William H. Yeadon.
• Principles of electrical machines by M.G Say.
• Electric motor selection and application by William C. Anderson