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

In some situations, operating a motor past the bottom pole velocity is feasible and presents 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 in the U.S.). As illustrated, extra poles reduce the bottom pole speed. If the incoming line frequency doesn’t change, the speed of the induction motor will be less than these values by a percent to slide. So, to operate the motor above the bottom pole speed, the frequency must be increased, which could be done with a variable frequency drive (VFD).
One purpose for overspeeding a motor on a pump is to make use of a slower rated speed motor with a lower horsepower ranking and function it above base frequency to get the required torque at a lower current. This permits the selection of a VFD with a lower present rating for use while nonetheless guaranteeing satisfactory control of the pump/motor over its desired working range. The decrease present requirement of the drive can scale back the capital cost of the system, relying on overall system necessities.
The applications where the motor and the driven pump function above their rated speeds can present extra flow and stress to the managed system. This could lead to a more compact system while increasing its efficiency. While it could be attainable to extend the motor’s pace to twice its nameplate velocity, it is extra common that the utmost pace is extra limited.
The key to these functions is to overlay the pump velocity torque curve and motor speed torque to make sure the motor starts and functions throughout the whole operational speed vary with out overheating, stalling or creating any vital stresses on the pumping system.
Several factors also need to be taken into account when contemplating such solutions:
Noise will enhance with velocity.
Bearing life or greasing intervals could also be lowered, or improved match bearings could also be required.
The greater velocity (and variable speed in general) will improve the danger of resonant vibration due to a critical pace within the operating vary.
The larger speed will result in extra energy consumption. It is essential to suppose about if the pump and drive practice is rated for the upper power.
Since the torque required by a rotodynamic pump increases in proportion to the sq. of velocity, the opposite main concern is to ensure that the motor can provide sufficient torque to drive the load on the elevated pace. When operated at a velocity below the rated speed of the motor, the volts per hertz (V/Hz) may be maintained because the frequency applied to the motor is elevated. Maintaining a continuing V/Hz ratio retains torque production stable. While weksler ea14 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) power supply limits the maximum voltage that is out there to the motor. Therefore, the voltage supplied to the motor can’t continue to increase above the nameplate voltage as illustrated in Image 2. As proven in Image 3, the available torque decreases past one hundred pc frequency as a result of the V/Hz ratio is not maintained. In an overspeed situation, the load torque (pump) should be under the available torque.
Before working any piece of apparatus exterior of its rated velocity range, it is essential to contact the producer of the tools to discover out if this can be carried out safely and effectively. For more information on variable velocity pumping, discuss with HI’s “Application Guideline for Variable Speed Pumping” at

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