REYMSA COOLING TOWERS, INC.
www.reymsa.com
The
All-Fiberglass
Cooling Towers
57
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C. OPERATION
C.1 FAN CONTROL - VFD
Variable Frequency Drives (VFDs) are the preferred method for both fan motor and capacity control on
Cooling Towers. Using a VFD in Cooling Tower applications has advantages over traditional single or two
speed motor control. The primary purpose of controlling a motor with a VFD is to save energy and operating
cost. In addition, it reduces the mechanical and electrical stress on the motor and mechanical equipment.
Applications utilizing variable frequency drives (VFDs) for the fan motor control must use inverter duty
motors built in compliance with NEMA Standard MG-1, part 31. All Premium efficiency motors used by
REYMSA Towers allow to work with VFDs.
When using a Variable Frequency Drive, REYMSA recommends a Motor Shaft Grounding Ring (optional
accessory) to prevent damage on the motor bearing. See section “A.2.8.5. MOTOR SHAFT GROUNDING
RING” for more information.
C.1.1 PARAMETERS FOR VFD OPERATION
Most VFD brands include protections for overcurrent, overheating, unexpected failures, in addition to a soft
starting processes by means of acceleration and deceleration ramps, which offers an increase of the life of
the motor and fan.
REYMSA recommends using the following basic operation
parameters on their Cooling Towers to ensure a long life
expectancy.
Maximum Frequency
Usually 60 Hz. This data is shown on the motor data plate.
Minimum Frequency
REYMSA recommends operating motor at 25% of nominal
speed.
Minimum speed for gear driven models must be 450 RPM.
Minimum operating frequency can be calculated:
TEFC and TEAO motors used for typical Cooling Tower applications may lose
proper cooling at very low fan or VFD speeds. REYMSA recommends
a minimum fan operation at 25% of nominal speed.
CAUTION
▪ If the motor is operated below 25% of nominal speed.
▪ If gear box is operated with motors working below 450 RPM.
WARRANTY VOID
OPERATION RANGE
FREQ
MAX
FREQ
MIN
FREQ
Figure C-1: VFD operation range.
Nominal Vel * 0.25 = Min Vel
(RPM on motor plate) (RPM)
60 Hz * Min Vel
Min Freq =
Nominal Vel
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