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

In some situations, working a motor beyond the base pole speed is feasible and provides system benefits if the design is fastidiously examined. The pole pace of a motor is a function of the quantity poles and the incoming line frequency. เกจวัดแรงดันต่ำ presents the synchronous pole speed for 2-pole through 12-pole motors at 50 hertz (Hz [common in Europe]) and 60 Hz (common within the U.S.). As illustrated, additional poles reduce the bottom pole velocity. If the incoming line frequency doesn’t change, the velocity of the induction motor might be lower than these values by a % to slip. So, to function the motor above the bottom pole speed, the frequency must be elevated, which could be done with a variable frequency drive (VFD).
One reason for overspeeding a motor on a pump is to use a slower rated velocity motor with a decrease horsepower score and operate 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 to be used while nonetheless making certain passable management of the pump/motor over its desired operating vary. The lower present requirement of the drive can scale back the capital cost of the system, relying on total system requirements.
The applications where the motor and the driven pump function above their rated speeds can provide additional flow and stress to the managed system. This could lead to a more compact system whereas rising its efficiency. While it might be possible to increase the motor’s pace to twice its nameplate velocity, it is extra common that the utmost speed is more limited.
The key to these purposes is to overlay the pump pace torque curve and motor pace torque to ensure the motor starts and features all through the entire operational velocity range without overheating, stalling or creating any important stresses on the pumping system.
Several points also must be taken under consideration when contemplating such solutions:
Noise will enhance with pace.
Bearing life or greasing intervals could also be reduced, or improved fit bearings may be required.
The greater velocity (and variable pace in general) will enhance the risk of resonant vibration due to a critical velocity throughout the working range.
The higher speed will lead to further power consumption. It is necessary to suppose about if the pump and drive train is rated for the upper power.
Since the torque required by a rotodynamic pump increases in proportion to the sq. of velocity, the other major concern is to ensure that the motor can present enough torque to drive the load on the increased speed. When operated at a pace beneath the rated speed of the motor, the volts per hertz (V/Hz) can be maintained as the frequency utilized to the motor is elevated. Maintaining a relentless V/Hz ratio retains torque production steady. While it will be best to increase the voltage to the motor as it’s run above its rated speed, the voltage of the alternating present (AC) energy supply limits the maximum voltage that’s out there to the motor. Therefore, the voltage provided to the motor can’t proceed to extend above the nameplate voltage as illustrated in Image 2. As proven in Image three, the available torque decreases past 100 percent frequency as a outcome of the V/Hz ratio is not maintained. In an overspeed situation, the load torque (pump) must be beneath the available torque.
Before working any piece of kit outside of its rated pace vary, it is essential to contact the manufacturer of the equipment to determine if this can be done safely and efficiently. For extra data on variable velocity pumping, check with HI’s “Application Guideline for Variable Speed Pumping” at pumps.org.
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