Select a Variable Speed Drive for Centrifugal Fan
Selecting a variable speed drive (VSD) for a centrifugal fan application is a complex decision that should take into account a number of factors:
Motor type: Is it a new or retrofit installation? Some older motors don't have the proper insulation to withstand the pulse-width-modulation output of a variable speed drive. Select an inverter-duty motor if possible. Determine if an output line reactor and filter is required to protect the motor.
Distance limitations between the variable speed drive and motor.
Motor data: voltage, HP or kW, full load amps (always make certain that rated variable speed drive amps exceed motor full load amps), and base speed data.
Control method: local control (keypad), remote control via terminal strip, or serial communications.
Minimum and maximum allowable speed.
Acceleration and deceleration time.
May the load be reversed? (Does the unit require reverse lockout?)
Will the variable speed drive need to "catch" a spinning fan when it starts?
Will DC injection braking be required to stop the fan before starting or at the end of the stop ramp?
Environment: A variable speed drive is designed to withstand a standard industrial environment. Sometimes, however, extra precautions must be taken - such as use of an enclosure that includes climate control based on worst-case environmental conditions. Protection of the variable speed drive isn't the place to cut corners if you want to ensure long, trouble-free life of the variable speed drive system.
Power quality: It's good practice to perform a harmonics analysis to ensure that sensitive electronic equipment elsewhere in the building isn't affected. variable speed drives and other non-linear loads (e.g., uninterruptible power supplies and electronic ballasts) can cause harmonic line distortion that could impact this equipment. A number of harmonics estimation programs are available on the Internet or from your vendor. If the analysis reveals high levels of harmonic distortion, you can install devices such as input line reactors, harmonics filters or isolation transformers directly before the variable speed drive.
Trained fan professionals and variable speed drive vendors can provide guidance on these matters.
Motor type: Is it a new or retrofit installation? Some older motors don't have the proper insulation to withstand the pulse-width-modulation output of a variable speed drive. Select an inverter-duty motor if possible. Determine if an output line reactor and filter is required to protect the motor.
Distance limitations between the variable speed drive and motor.
Motor data: voltage, HP or kW, full load amps (always make certain that rated variable speed drive amps exceed motor full load amps), and base speed data.
Control method: local control (keypad), remote control via terminal strip, or serial communications.
Minimum and maximum allowable speed.
Acceleration and deceleration time.
May the load be reversed? (Does the unit require reverse lockout?)
Will the variable speed drive need to "catch" a spinning fan when it starts?
Will DC injection braking be required to stop the fan before starting or at the end of the stop ramp?
Environment: A variable speed drive is designed to withstand a standard industrial environment. Sometimes, however, extra precautions must be taken - such as use of an enclosure that includes climate control based on worst-case environmental conditions. Protection of the variable speed drive isn't the place to cut corners if you want to ensure long, trouble-free life of the variable speed drive system.
Power quality: It's good practice to perform a harmonics analysis to ensure that sensitive electronic equipment elsewhere in the building isn't affected. variable speed drives and other non-linear loads (e.g., uninterruptible power supplies and electronic ballasts) can cause harmonic line distortion that could impact this equipment. A number of harmonics estimation programs are available on the Internet or from your vendor. If the analysis reveals high levels of harmonic distortion, you can install devices such as input line reactors, harmonics filters or isolation transformers directly before the variable speed drive.
Trained fan professionals and variable speed drive vendors can provide guidance on these matters.