In some cases, working a motor beyond the base pole pace is possible and provides system advantages if the design is fastidiously examined. The pole speed of a motor is a operate of the quantity poles and the incoming line frequency. Image 1 presents the synchronous pole speed 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 scale back the bottom pole pace. If the incoming line frequency does not change, the velocity of the induction motor shall be lower than these values by a p.c to slip. So, to function the motor above the bottom pole pace, the frequency needs to be increased, which can be done 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 score and operate it above base frequency to get the required torque at a lower present. This permits the choice of a VFD with a decrease current ranking to be used whereas nonetheless guaranteeing satisfactory management of the pump/motor over its desired operating vary. The lower current requirement of the drive can reduce the capital cost of the system, relying on total system necessities.
The applications where the motor and the pushed pump function above their rated speeds can present further move and stress to the controlled system. This may result in a extra compact system whereas growing its efficiency. While it might be potential to increase the motor’s speed to twice its nameplate pace, it’s more frequent that the maximum speed is extra restricted.
The key to these functions is to overlay the pump velocity torque curve and motor speed torque to ensure the motor begins and capabilities throughout the complete operational pace range without overheating, stalling or creating any important stresses on the pumping system.
Several points also have to be taken into consideration when considering such options:
Noise will improve with velocity.
Bearing life or greasing intervals could also be decreased, or improved fit bearings may be required.
The larger pace (and variable pace in general) will enhance the risk of resonant vibration due to a important speed inside the working range.
The larger speed will result in further power consumption. It is necessary to think about if the pump and drive train is rated for the higher power.
Since the torque required by a rotodynamic pump will increase in proportion to the sq. of pace, the other main concern is to ensure that the motor can present enough torque to drive the load at the increased velocity. When operated at a velocity under the rated pace of the motor, the volts per hertz (V/Hz) could be maintained because the frequency utilized to the motor is increased. Maintaining a relentless V/Hz ratio keeps torque manufacturing steady. While it would be best to increase the voltage to the motor as it is run above its rated velocity, the voltage of the alternating current (AC) power source limits the maximum voltage that’s obtainable to the motor. Therefore, the voltage equipped to the motor can’t continue to extend above the nameplate voltage as illustrated in Image 2. As shown in Image three, the out there torque decreases past 100% frequency because the V/Hz ratio is not maintained. In เพรสเชอร์เกจ , the load torque (pump) must be under the available torque.
Before operating any piece of equipment outdoors of its rated velocity vary, it is essential to contact the producer of the gear to discover out if this might be done safely and effectively. For extra info on variable velocity pumping, check with HI’s “Application Guideline for Variable Speed Pumping” at pumps.org.
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