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

In some situations, working a motor beyond the bottom pole speed is possible and offers system advantages if the design is fastidiously examined. The pole speed of a motor is a function of the number poles and the incoming line frequency. Image 1 presents the synchronous pole velocity 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, extra poles cut back the bottom pole speed. If the incoming line frequency does not change, the pace of the induction motor will be lower than these values by a percent to slip. So, to function the motor above the bottom pole velocity, the frequency must be elevated, which may be done with a variable frequency drive (VFD).
One reason for overspeeding a motor on a pump is to use a slower rated speed motor with a lower horsepower score and operate it above base frequency to get the required torque at a lower present. This allows the selection of a VFD with a lower present score to be used whereas still making certain passable management of the pump/motor over its desired working range. The lower present requirement of the drive can cut back the capital cost of the system, depending on general system requirements.
เกจวัดแรงดัน4นิ้วราคา and the pushed pump function above their rated speeds can provide further move and strain to the managed system. This could end in a extra compact system while growing its effectivity. While it may be possible to extend the motor’s velocity to twice its nameplate pace, it’s extra frequent that the utmost velocity is more restricted.
The key to those applications is to overlay the pump speed torque curve and motor speed torque to ensure the motor starts and functions throughout the entire operational speed range with out overheating, stalling or creating any vital stresses on the pumping system.
Several points additionally must be taken under consideration when contemplating such solutions:
Noise will improve with velocity.
Bearing life or greasing intervals may be reduced, or improved fit bearings could additionally be required.
The larger pace (and variable velocity in general) will improve the danger of resonant vibration because of a critical speed inside the working range.
The higher velocity will lead to further power consumption. It is necessary to contemplate if the pump and drive practice is rated for the higher energy.
Since the torque required by a rotodynamic pump increases in proportion to the square of speed, the opposite main concern is to ensure that the motor can present enough torque to drive the load on the elevated pace. When operated at a pace beneath the rated pace of the motor, the volts per hertz (V/Hz) could be maintained because the frequency applied to the motor is increased. Maintaining a relentless V/Hz ratio retains torque manufacturing secure. While it will be perfect to increase the voltage to the motor as it is run above its rated velocity, the voltage of the alternating present (AC) power source limits the utmost voltage that is out there to the motor. Therefore, the voltage provided to the motor can’t proceed to increase above the nameplate voltage as illustrated in Image 2. As shown in Image 3, the available torque decreases beyond one hundred pc frequency as a end result of the V/Hz ratio isn’t maintained. In an overspeed scenario, the load torque (pump) should be beneath the out there torque.
Before operating any piece of equipment exterior of its rated velocity range, it’s essential to contact the manufacturer of the gear to discover out if this can be done safely and effectively. For more data on variable pace pumping, check with HI’s “Application Guideline for Variable Speed Pumping” at pumps.org.
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