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

In some instances, working a motor past the bottom pole pace is possible and provides system advantages if the design is rigorously examined. The pole speed of a motor is a operate 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 in the U.S.). As illustrated, extra poles reduce the base pole velocity. If เกจ์วัดแรงดันแก๊ส does not change, the speed of the induction motor might be less than these values by a % to slide. So, to function the motor above the bottom pole speed, the frequency must be elevated, which can be accomplished with a variable frequency drive (VFD).
One reason for overspeeding a motor on a pump is to use a slower rated pace motor with a lower horsepower rating and operate it above base frequency to get the required torque at a decrease current. This enables the number of a VFD with a decrease current ranking for use while nonetheless guaranteeing satisfactory control of the pump/motor over its desired operating vary. The lower current requirement of the drive can reduce the capital value of the system, relying on overall system requirements.
The purposes where the motor and the pushed pump function above their rated speeds can present additional flow and pressure to the controlled system. This could end in a more compact system whereas growing its efficiency. While it may be attainable to increase the motor’s speed to twice its nameplate pace, it is extra common that the maximum pace is extra limited.
The key to these purposes is to overlay the pump velocity torque curve and motor velocity torque to make sure the motor starts and features throughout the whole operational speed range without overheating, stalling or creating any vital stresses on the pumping system.
Several factors additionally must be taken into account when considering such options:
Noise will improve with velocity.
Bearing life or greasing intervals may be decreased, or improved match bearings could additionally be required.
The greater pace (and variable velocity in general) will increase the risk of resonant vibration due to a crucial speed throughout the operating range.
The higher speed will lead to extra power consumption. It is necessary to contemplate if the pump and drive practice is rated for the upper energy.
Since the torque required by a rotodynamic pump increases in proportion to the square of velocity, the other main concern is to make certain that the motor can provide enough torque to drive the load on the increased velocity. When operated at a pace below the rated velocity of the motor, the volts per hertz (V/Hz) can be maintained because the frequency applied to the motor is elevated. Maintaining a relentless V/Hz ratio keeps torque production steady. While it will be best to increase the voltage to the motor as it is run above its rated speed, the voltage of the alternating current (AC) power source limits the maximum voltage that’s obtainable to the motor. Therefore, the voltage supplied to the motor can not continue to extend above the nameplate voltage as illustrated in Image 2. As shown in Image 3, the available torque decreases past 100 percent frequency because the V/Hz ratio is not maintained. In an overspeed situation, the load torque (pump) must be beneath the obtainable torque.
Before working any piece of kit outside of its rated speed range, it is important to contact the producer of the gear to discover out if this might be accomplished safely and effectively. For extra data on variable speed pumping, discuss with HI’s “Application Guideline for Variable Speed Pumping” at pumps.org.
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