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Understanding Motor Drives

Posted: April 23, 2015, 11:16 am EST

Understanding Motor Drives

The electric motor was once the driving force of the industrial revolution, and it remains highly relevant today as the muscle behind technological evolution. Available in many different types for a huge variety of purposes, motor drives affect many aspects of our lives whether we recognize it or not.

Adjustable Speed Motor Drives

Used to control the speed of machinery, adjustable speed motor drives have many industrial applications including assembly lines. Typically designed with several pre-set speed ranges that can be chosen, they are available in four basic types:

  1. Mechanical
    Mechanical adjustable speed motor drives allow for the adjustment of pitch diameter on one or both pulleys. Traction drives- a type of mechanical drive- use metal rollers to transmit power, and their speed can be adjusted by changing the positioning of the rollers to alter the diameter of contact between them. There are many shapes and designs of rollers to suit a wide variety of purposes.
  2. Electromechanical
    Adjusted mechanically or automatically controlled, these drives contain both mechanical and electrical components making them useful hybrid devices.
  3. Hydraulic
    Broken down into three main types, hydraulic drives rely on hydraulic pumps and motors or oil to transfer torque. Hydrostratic drives regulate their speed by controlling the flow of fluid with a control valve while hydrodynamic drives (also known as fluid couplings) utilize oil to transfer torque from a rotor or impeller.

    These drives are most commonly seen as torque converters in cars. Finally, hydroviscous drives consist of one or more discs connected to an input shaft and pressed against one or more discs on the output shaft. A thin film of oil between the discs is used to transmit torque and protect the discs from damage.
  4. Electronic
    Controlled either manually or automatically, electronic drives include DC motor drives, eddy current drives, and AC motor drives. They typically contain both a speed control unit and an electric motor and are used for many purposes.
Variable Frequency & Variable Torque Motor Drives

Variable speed drives typically allow for more control over their exact speed than adjustable speed drives as they are not limited to pre-set ranges. These drives are used in many electro-mechanical systems from small appliances to mine mill drives in order to control motor speed and torque. In fact, up to 25% of the world's electricity is used by motors of this type employed in many industrial applications!

The three main types of variable torque and power systems include: variable torque, commonly used in centrifugal fans, pumps, and blower systems; constant torque, generally seen in conveyor and positive displacement pump applications; and constant power which is most often utilized in the form of power tools and traction applications.

Soft Start Motor Drives

Soft starters are used on AC electrical motors in order to reduce stress and damage to both mechanical and electrical systems in startup.

During startup, the inrush currents can reach levels up to 7 times higher than the standard running current while startup torque can reach levels almost 3 times higher than average. This can cause sudden stress to the system, reducing service life and causing dips in power. By utilizing soft start drives, this stress can be negated, effectively increasing the life of your equipment.