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DURAPULSE AC Drive Introduction
Purpose of AC Drives
AC drives are generally known by many different names: Adjustable Frequency
Drives (AFD), Variable Frequency Drives (VFD), and Inverters. Drives are used
primarily to vary the speed of three phase AC induction motors, and they also
provide non-emergency start and stop control, acceleration and deceleration, and
overload protection. By gradually accelerating the motor, drives can reduce the
amount of motor startup inrush current.
AC drives function by converting incoming AC power to DC, which is then
synthesized back into three phase output power. The voltage and frequency of
this synthesized output power is directly varied by the drive, where the frequency
determines the speed of the three phase AC induction motor.
Selecting the Proper Drive Rating
A. Determine motor full-load amperage (FLA)
Motor FLA is located on the nameplate of the motor.
Note: FLA of motors that have been rewound may be higher than stated.
B. Determine motor overload requirements
Many applications experience temporary overload conditions due to starting
requirements or impact loading. Most AC drives are designed to operate at 150%
overload for 60 seconds. If the application requires an overload greater than
150% or longer than 60 seconds, the AC drive must be oversized.
NOTE: Applications that require replacement of existing motor starters with AC
drives may require up to 600% overload.
C. Installation altitude
AC drives rely upon the cooling properties of air for cooling. As the altitude
increases, the air becomes less dense, and this decrease in air density decreases
the cooling properties of the air. Therefore, the AC drive must be oversized to
compensate for the decrease in cooling. Most AC drives are designed to operate
at 100% capacity up to altitudes of 1000 meters. Above 1000m, the AC drive
must be derated.
D. Determine max enclosure internal temp
AC drives generate a significant amount of heat and will cause the internal
temperature of an enclosure to exceed the rating of the AC drive, even when the
ambient temperature is less than 104 °F (40 °C). Enclosure ventilation and/or
cooling may be required to maintain a maximum internal temperature of 104 °F
(40 °C) or less. Ambient temperature measurements/calculations should be made
for the maximum expected temperature.
Chapter 1: Getting Started
DURAPULSE AC Drive User Manual
1st Ed. Rev. D 05/2013
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