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

In some situations, working a motor beyond the bottom pole velocity is feasible and offers system advantages if the design is carefully examined. The pole speed of a motor is a operate of the number poles and the incoming line frequency. Premiere presents the synchronous pole speed for 2-pole by way of 12-pole motors at 50 hertz (Hz [common in Europe]) and 60 Hz (common within the U.S.). As illustrated, additional poles cut back the base pole pace. If the incoming line frequency does not change, the velocity of the induction motor might be less than these values by a % to slip. So, to operate the motor above the bottom pole speed, the frequency needs to be elevated, which can be done with a variable frequency drive (VFD).
One cause for overspeeding a motor on a pump is to use a slower rated speed motor with a lower horsepower rating and function it above base frequency to get the required torque at a decrease present. This permits the number of a VFD with a decrease present score for use while still ensuring passable management of the pump/motor over its desired working range. The decrease present requirement of the drive can reduce the capital price of the system, relying on overall system requirements.
The functions where the motor and the pushed pump operate above their rated speeds can provide further circulate and stress to the controlled system. This could result in a extra compact system while growing its efficiency. While it might be possible to extend the motor’s speed to twice its nameplate velocity, it’s extra widespread that the utmost velocity is extra limited.
The key to these applications is to overlay the pump speed torque curve and motor pace torque to make sure the motor begins and features throughout the whole operational speed range with out overheating, stalling or creating any vital stresses on the pumping system.
Several factors additionally have to be taken into consideration when considering such solutions:
Noise will improve with velocity.
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 improve the chance of resonant vibration due to a important speed throughout the operating vary.
The higher pace will end in extra energy consumption. It is necessary to assume about if the pump and drive prepare is rated for the upper energy.
Since the torque required by a rotodynamic pump will increase in proportion to the square of pace, the other major concern is to ensure that the motor can present sufficient torque to drive the load on the increased speed. When operated at a speed beneath the rated velocity of the motor, the volts per hertz (V/Hz) may be maintained because the frequency utilized to the motor is elevated. Maintaining a relentless V/Hz ratio retains torque production steady. While it will be perfect to increase the voltage to the motor as it is run above its rated speed, the voltage of the alternating current (AC) energy source limits the maximum voltage that is available to the motor. Therefore, the voltage supplied to the motor can’t continue to extend above the nameplate voltage as illustrated in Image 2. As proven in Image 3, the available torque decreases past 100% frequency because the V/Hz ratio isn’t maintained. In an overspeed state of affairs, the load torque (pump) must be under the obtainable torque.
Before working any piece of apparatus exterior of its rated speed range, it’s important to contact the manufacturer of the gear to discover out if this can be done safely and efficiently. For more info on variable speed pumping, refer to HI’s “Application Guideline for Variable Speed Pumping” at pumps.org.
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