Teardown: The nuances of variable-frequency drives


Posted on Feb 7, 2014

An ac drive controls ac induction motors and, like its dc counterparts, controls speed, torque, and horsepower. A dc drive typically controls a shunt-wound dc motor, which has separate armature and field circuits. This teardown of the Schneider Electric Altivar 12 variable-frequency drive details the key features that define these drives. Rotating


Teardown: The nuances of variable-frequency drives
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equipment, including fans, blowers, compressors, and pumps, consumes more than one-third the total electrical energy generated in the United States. This equipment may use variable-speed-drive technology, in which motor speed adjusts to meet the load requirements, yielding an advantage in both improved productivity and reduced energy consumption. For example, lowering fan or pump speed by 15 to 20% enables a decrease in shaft power of as much as 30%. Properly applied variable-frequency drives are affordable, reliable, and flexible, and they offer a significant amount of savings through reduced electric bills. Electronic variable-frequency drives vary the voltage and frequency to induction motors using pulse-width modulation. The drives use insulated-gate bipolar transistors to convert the fixed-frequency ac supply voltage to a variable-frequency, variable-voltage ac supply to the motor and can regulate the speed of an induction motor from approximately 10 to 200%; wider ranges are possible. The drives also regulate the output voltage in proportion to the output frequency to provide a relatively constant ratio of voltage to frequency to produce adequate torque. The Altivar 12 manual recommends that you remove the vent covers for IP (ingress protection) Type B and C mounting when IP20 protection is adequate but that you leave them on the housing in Type A mounting (Figure 1). ANSI/IEC 60529-2004 describes the degrees of...




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