In some situations, working a motor past the bottom pole velocity is feasible and provides system advantages if the design is rigorously examined. The pole pace of a motor is a perform of the quantity 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, further poles cut back the bottom pole pace. If the incoming line frequency doesn’t change, the velocity of the induction motor shall be lower than these values by a percent to slide. So, to function the motor above the base pole velocity, the frequency must be elevated, which can be accomplished with a variable frequency drive (VFD).
One cause for overspeeding a motor on a pump is to use a slower rated speed motor with a decrease horsepower rating and operate it above base frequency to get the required torque at a lower current. This allows the selection of a VFD with a lower current rating to be used whereas still ensuring passable management of the pump/motor over its desired working range. The lower present requirement of the drive can reduce the capital price of the system, depending on overall system necessities.
The applications where the motor and the pushed pump function above their rated speeds can provide further flow and strain to the managed system. This could end in a more compact system while growing its efficiency. While it may be potential to increase the motor’s velocity to twice its nameplate velocity, it’s more widespread that the utmost velocity is extra restricted.
The key to those purposes is to overlay the pump velocity torque curve and motor pace torque to ensure the motor begins and functions all through the whole operational pace range with out overheating, stalling or creating any important stresses on the pumping system.
Several factors also have to be taken into consideration when contemplating such solutions:
Noise will improve with velocity.
Bearing life or greasing intervals could additionally be reduced, or improved fit bearings may be required.
The larger velocity (and variable pace in general) will enhance the risk of resonant vibration as a end result of a crucial speed inside the working range.
The higher speed will result in further power consumption. It is important to contemplate 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 square of speed, the other major concern is to ensure that the motor can provide enough torque to drive the load at the elevated speed. When operated at a velocity below the rated velocity of the motor, the volts per hertz (V/Hz) may be maintained because the frequency applied to the motor is increased. Maintaining a constant V/Hz ratio retains torque manufacturing stable. While it will be best to extend the voltage to the motor as it’s run above its rated pace, the voltage of the alternating current (AC) power supply limits the utmost voltage that is available 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 three, the out there torque decreases past 100 percent frequency as a outcome of the V/Hz ratio is not maintained. In an overspeed state of affairs, the load torque (pump) must be under the available torque.
Before operating pressure gauge น้ำมัน of equipment exterior of its rated speed vary, it is essential to contact the producer of the equipment to discover out if this can be done safely and effectively. For more data on variable velocity pumping, discuss with HI’s “Application Guideline for Variable Speed Pumping” at pumps.org.
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