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

In some situations, operating a motor beyond the base pole pace is possible and provides system benefits if the design is fastidiously examined. The pole velocity of a motor is a function of the quantity poles and the incoming line frequency. pressure gauge presents the synchronous pole velocity for 2-pole via 12-pole motors at 50 hertz (Hz [common in Europe]) and 60 Hz (common within the U.S.). As illustrated, extra poles reduce the base pole speed. If the incoming line frequency doesn’t change, the velocity of the induction motor might be lower than these values by a percent to slide. So, to function the motor above the base pole pace, the frequency must be elevated, which could be accomplished with a variable frequency drive (VFD).
One purpose for overspeeding a motor on a pump is to make use of a slower rated pace motor with a decrease horsepower ranking and operate it above base frequency to get the required torque at a lower current. This allows the choice of a VFD with a lower current score to be used whereas still guaranteeing passable control of the pump/motor over its desired working range. The lower current requirement of the drive can reduce the capital cost of the system, depending on general system requirements.
The purposes where the motor and the driven pump operate above their rated speeds can provide further move and stress to the managed system. This might end in a more compact system while increasing its efficiency. While it might be possible to increase the motor’s speed to twice its nameplate velocity, it’s more frequent that the utmost pace is more limited.
The key to these purposes is to overlay the pump pace torque curve and motor velocity torque to ensure the motor starts and capabilities all through the complete operational velocity range without overheating, stalling or creating any important stresses on the pumping system.
Several points also have to be taken under consideration when considering such options:
Noise will enhance with speed.
Bearing life or greasing intervals could also be decreased, or improved match bearings could also be required.
The higher velocity (and variable velocity in general) will improve the risk of resonant vibration because of a important speed within the working range.
The higher velocity will lead to additional energy consumption. It is necessary to consider if the pump and drive train is rated for the higher 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 at the elevated velocity. When operated at a velocity under the rated pace of the motor, the volts per hertz (V/Hz) can be maintained as the frequency applied to the motor is elevated. Maintaining a constant V/Hz ratio retains torque manufacturing stable. While it would be best to extend the voltage to the motor as it is run above its rated pace, the voltage of the alternating current (AC) energy supply limits the utmost voltage that’s obtainable to the motor. Therefore, the voltage equipped to the motor can not continue to increase above the nameplate voltage as illustrated in Image 2. As proven in Image 3, the out there torque decreases past 100% frequency as a outcome of the V/Hz ratio just isn’t maintained. In pressure gauge of affairs, the load torque (pump) should be under the obtainable torque.
Before working any piece of kit exterior of its rated pace vary, it’s important to contact the manufacturer of the gear to determine if this can be done safely and effectively. For extra information on variable speed pumping, check with HI’s “Application Guideline for Variable Speed Pumping” at

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