26-07-2012, 12:45 PM
AC Adjustable Speed Drives
Adjustable-Speed-Drives-Tutorial.pdf (Size: 737.94 KB / Downloads: 55)
Variable Speed Control
The simplest and least expensive way to control the speed of a process or piece of equipment is to
operate all the equipment at full speed.
C Many applications require the speed of a process or piece of equipment to be varied.
C Prior to the advent of the AC Adjustable Speed Drive, many technologies have been used,
although each has its inherent advantages and disadvantages.
Types of Variable Speed Control:
Control Valves, Dampers and Vanes
Fossil Fuel Engines
Eddy Current Clutches
Hydraulic Couplings
Variable Pitch Sheaves
DC Solid State Controllers
AD Adjustable Speed Drives
(ASD’s)
AC Adjustable Speed Drives (ASD’s)
AC Adjustable Speed Drives (ASD’s) have become very
popular variable speed control devices used in industrial,
commercial and some residential applications.
C These devices have been available for about 20
years and have a wide range of applications
ranging from single motor driven pumps, fans and
compressors, to highly sophisticated multi-drive
machines.
C They operate by varying the frequency of the AC voltage supplied to the motor using solid
state electronic devices.
C These systems are fairly expensive but provide a higher degree of control over the operation
and in many cases, reduce the energy use enough to a least offset if not more than pay for the
increased cost.
C ASD’s allow precise speed control of a standard induction motor and can result in significant
energy savings and improved process control in many applications.
C Can control the speed of a standard squirrel cage NEMA type B induction motor.
C Suitable not only for new applications, but also for retrofit on existing motors.
Synchronous Speed ' 120 X Frequency
Number of Poles
Adjustable Speed Drive (ASD) Function
AC Adjustable Speed Drives can be
thought of as electrical control devices
that change the operating speed of a
motor.