In Which Applications Can a Pump Motor Be Operated Above Base Speed?

In some cases, working a motor past the bottom pole pace is feasible and provides system advantages if the design is rigorously examined. The pole speed of a motor is a perform of the number poles and the incoming line frequency. Image 1 presents the synchronous pole pace for 2-pole via 12-pole motors at 50 hertz (Hz [common in Europe]) and 60 Hz (common within the U.S.). As illustrated, extra poles cut back the bottom pole speed. If the incoming line frequency does not change, the pace of the induction motor might be lower than these values by a % to slip. So, to operate the motor above the bottom pole velocity, the frequency needs to be increased, which can be carried out with a variable frequency drive (VFD).
One reason for overspeeding a motor on a pump is to make use of a slower rated speed motor with a decrease horsepower score and operate it above base frequency to get the required torque at a decrease current. This enables the selection of a VFD with a decrease present score for use whereas nonetheless making certain passable management of the pump/motor over its desired operating range. The lower present requirement of the drive can reduce the capital cost of the system, depending on total system necessities.
The purposes where the motor and the pushed pump function above their rated speeds can provide further move and stress to the managed system. This could end in a more compact system whereas rising its efficiency. While it could be potential to increase the motor’s velocity to twice its nameplate pace, it is more common that the utmost velocity is extra restricted.
The key to those applications is to overlay the pump pace torque curve and motor velocity torque to ensure the motor starts and functions all through the complete operational pace range without overheating, stalling or creating any significant stresses on the pumping system.
Several points additionally must be taken into account when considering such solutions:
Noise will increase with pace.
Bearing life or greasing intervals could additionally be lowered, or improved fit bearings could additionally be required.
The higher pace (and variable pace in general) will increase the danger of resonant vibration as a result of a important speed within the working range.
The greater velocity will end in further energy consumption. It is necessary to consider if the pump and drive prepare is rated for the higher power.
Since the torque required by a rotodynamic pump increases in proportion to the square of velocity, the other main concern is to ensure that the motor can provide sufficient torque to drive the load at the increased pace. When operated at a pace under the rated velocity of the motor, the volts per hertz (V/Hz) may be maintained because the frequency applied to the motor is increased. Maintaining a continuing V/Hz ratio keeps torque manufacturing stable. While it would be best to increase the voltage to the motor as it’s run above its rated pace, the voltage of the alternating present (AC) power supply limits the utmost voltage that’s obtainable to the motor. Therefore, the voltage equipped to the motor can not continue to increase above the nameplate voltage as illustrated in Image 2. As proven in Image 3, the obtainable torque decreases past 100% frequency as a result of the V/Hz ratio isn’t maintained. In เพรสเชอร์เกจ , the load torque (pump) must be below the obtainable torque.
Before operating any piece of equipment outdoors of its rated speed range, it is important to contact the manufacturer of the tools to determine if this may be accomplished safely and effectively. For more info on variable pace pumping, discuss with HI’s “Application Guideline for Variable Speed Pumping” at pumps.org.
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