An adjustable speed drive is a device that allows for manual or automatic adjustment of its fixed operating speed to control a process or save energy. It can be electric or non-electric, and can take many different forms including mechanical, hydraulic, and electrical. Adjustable speed drives aid in process control and can save energy by decreasing fan speed in HVAC systems. Electrically powered drives can use direct current, eddy current, or alternating current.
Adjustable speed drive is a term used to describe any type of energy transmission device that allows manual or automatic adjustment of its fixed operating speed to control a process or save energy. The fixed speed of a variable speed drive motor can be increased or decreased depending on the type of application for which the device is being used. Adjustable speed drive devices can be electric or non-electric. Non-electrical drives can be mechanical or hydraulic. Electrically powered drives can use direct current, eddy current, or alternating current.
Electric motors operate at a fixed speed governed by the number of internal windings they contain. Regulating the speed of a motor using multiple sets of windings would be cumbersome and expensive. A separate motor speed control mechanism is typically required to operate a fixed speed motor at variable speeds. This type of speed control mechanism is commonly known as an adjustable speed drive. These drive mechanisms were originally intended for use in process control, but are also frequently used to save energy.
An adjustable speed drive aids in process control by providing a different operating speed for each process being performed. This mechanism also offers smoother engine operation along with acceleration and torque control. Adjustable speed drives can be used to save energy by decreasing fan speed in heating, ventilation and air conditioning systems. During heating cycles, the reduced fan speed provides better circulation of warm air in a room. Better air circulation reduces the number of heating cycles required by the system and reduces energy consumption.
Adjustable speed drives can take many different forms, including mechanical, hydraulic, and electrical. Mechanical drives can be a variable pitch, belt and pulley design or a traction type, metal roller system. Hydraulic methods typically take the form of a hydrostatic or hydrodynamic drive. Hydrostatic drives regulate speed through the use of fluid pumps and motors. Hydrodynamic drives change the speed of the engine via an input shaft driven by an impeller and an output shaft driven by a rotor.
An electrically powered adjustable speed drive can use direct, parasitic, or alternating current. DC drives regulate the speed of the motor by changing its field current or armature voltage. Eddy current drives use a device known as an eddy current clutch to regulate a motor at a fixed speed. AC drives work by decreasing the applied voltage of the motor or increasing its winding resistance. Both AC and parasitic current drives are generally considered an inefficient adjustable speed drive mechanism.
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