In some instances, 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 operate of the number poles and the incoming line frequency. Image 1 presents the synchronous pole pace 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, additional poles cut back the bottom pole speed. If the incoming line frequency doesn’t change, the pace of the induction motor shall be less than these values by a % to slide. So, to function the motor above the bottom pole pace, the frequency needs to be elevated, which can be accomplished with a variable frequency drive (VFD).
One cause for overspeeding a motor on a pump is to make use of a slower rated velocity motor with a lower horsepower score and operate it above base frequency to get the required torque at a decrease current. This allows the number of a VFD with a lower current ranking to be used while still ensuring passable control of the pump/motor over its desired working vary. เกรดวัดแรงดัน of the drive can cut back the capital cost of the system, relying on overall system necessities.
The purposes the place the motor and the driven pump function above their rated speeds can present further flow and stress to the managed system. This may lead to a more compact system while increasing its effectivity. While it may be possible to increase the motor’s pace to twice its nameplate speed, it’s extra widespread that the maximum pace is extra limited.
The key to these purposes is to overlay the pump speed torque curve and motor pace torque to ensure the motor starts and features all through the entire operational pace range with out overheating, stalling or creating any important stresses on the pumping system.
Several factors additionally have to be taken into account when considering such options:
Noise will improve with velocity.
Bearing life or greasing intervals could also be decreased, or improved fit bearings could also be required.
The greater velocity (and variable pace in general) will increase the chance of resonant vibration due to a important speed within the operating range.
The larger velocity will lead to further energy consumption. It is important to contemplate if the pump and drive prepare is rated for the higher power.
Since the torque required by a rotodynamic pump increases in proportion to the sq. of velocity, the opposite major concern is to ensure that the motor can provide enough torque to drive the load at the increased speed. When operated at a velocity below the rated speed of the motor, the volts per hertz (V/Hz) may be maintained as the frequency applied to the motor is elevated. Maintaining a constant V/Hz ratio keeps torque manufacturing stable. While it might be perfect to extend the voltage to the motor as it’s run above its rated speed, the voltage of the alternating current (AC) energy supply limits the maximum voltage that is available to the motor. Therefore, the voltage equipped to the motor can’t proceed to increase above the nameplate voltage as illustrated in Image 2. As proven in Image three, the out there torque decreases past one hundred pc frequency as a result of the V/Hz ratio isn’t maintained. In an overspeed state of affairs, the load torque (pump) have to be beneath the available torque.
Before operating any piece of equipment outside of its rated velocity range, it’s essential to contact the producer of the gear to find out if this can be done safely and efficiently. For more info on variable speed pumping, discuss with HI’s “Application Guideline for Variable Speed Pumping” at pumps.org.
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