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

In some cases, working a motor past the bottom pole speed is possible and offers system benefits if the design is rigorously examined. The pole velocity of a motor is a operate of the number poles and the incoming line frequency. Image 1 presents the synchronous pole velocity for 2-pole via 12-pole motors at 50 hertz (Hz [common in Europe]) and 60 Hz (common in the U.S.). As illustrated, further poles cut back the bottom pole speed. If the incoming line frequency does not change, the velocity of the induction motor might be lower than these values by a p.c to slip. So, to operate the motor above the bottom pole velocity, the frequency must be increased, which can be carried out with a variable frequency drive (VFD).
One purpose for overspeeding a motor on a pump is to make use of a slower rated velocity motor with a lower horsepower rating and function it above base frequency to get the required torque at a decrease current. This permits the choice of a VFD with a decrease present ranking for use while still ensuring satisfactory management of the pump/motor over its desired operating vary. The lower present requirement of the drive can cut back the capital value of the system, depending on total system necessities.
The applications where the motor and the driven pump operate above their rated speeds can present extra circulate and stress to the controlled system. This might end in a extra compact system while growing its efficiency. While it might be potential to extend the motor’s pace to twice its nameplate speed, it is extra common that the utmost pace is extra limited.
The key to these applications is to overlay the pump velocity torque curve and motor pace torque to ensure the motor starts and capabilities all through the entire operational speed vary without overheating, stalling or creating any vital stresses on the pumping system.
Several factors additionally need to be taken under consideration when contemplating such solutions:
Noise will increase with velocity.
Bearing เพรสเชอร์เกจวัดแรงดันน้ำ or greasing intervals could additionally be lowered, or improved fit bearings could additionally be required.
The higher velocity (and variable velocity in general) will increase the danger of resonant vibration because of a important speed inside the working vary.
The greater pace will end in extra power consumption. It is essential to contemplate if the pump and drive train is rated for the higher power.
Since the torque required by a rotodynamic pump will increase in proportion to the sq. of speed, the other major concern is to ensure that the motor can provide sufficient torque to drive the load at the elevated pace. When operated at a speed beneath the rated velocity of the motor, the volts per hertz (V/Hz) can be maintained as the frequency utilized to the motor is elevated. Maintaining a continuing V/Hz ratio retains torque production steady. While it will be best to extend the voltage to the motor as it is run above its rated speed, the voltage of the alternating current (AC) energy supply limits the utmost voltage that’s obtainable to the motor. Therefore, the voltage equipped to the motor cannot continue to increase above the nameplate voltage as illustrated in Image 2. As shown in Image three, the available torque decreases beyond one hundred pc frequency as a result of the V/Hz ratio isn’t maintained. In an overspeed scenario, the load torque (pump) must be below the obtainable torque.
Before working any piece of equipment outdoors of its rated pace range, it’s essential to contact the manufacturer of the tools to find out if this can be carried out safely and efficiently. For more data on variable speed pumping, check with HI’s “Application Guideline for Variable Speed Pumping” at pumps.org.
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