In some cases, operating a motor beyond the bottom pole pace is feasible and presents system advantages if the design is fastidiously examined. The pole pace of a motor is a function 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 within the U.S.). As illustrated, additional poles reduce the bottom pole velocity. If the incoming line frequency doesn’t change, the velocity of the induction motor will be lower than these values by a p.c to slip. So, to operate the motor above the bottom pole velocity, the frequency must be increased, which may be carried out with a variable frequency drive (VFD).
One reason for overspeeding a motor on a pump is to make use of a slower rated speed motor with a decrease horsepower ranking and function it above base frequency to get the required torque at a decrease current. This enables the choice of a VFD with a lower present ranking to be used while nonetheless making certain passable management of the pump/motor over its desired operating vary. The decrease current requirement of the drive can reduce the capital value of the system, relying on overall system necessities.
The functions where the motor and the pushed pump operate above their rated speeds can present extra flow and strain to the managed system. This might end in a extra compact system whereas growing its effectivity. While เกจวัดแรงดันลม may be attainable to increase the motor’s speed to twice its nameplate velocity, it’s extra frequent that the maximum velocity is extra limited.
The key to those purposes is to overlay the pump pace torque curve and motor velocity torque to make sure the motor begins and features all through the whole operational speed vary without overheating, stalling or creating any significant stresses on the pumping system.
Several points additionally must be taken into account when considering such solutions:
Noise will increase with speed.
Bearing life or greasing intervals could also be reduced, or improved match bearings could additionally be required.
The greater speed (and variable velocity in general) will improve the risk of resonant vibration due to a critical pace throughout the working range.
The greater velocity will result in further power consumption. It is important 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 opposite major concern is to ensure that the motor can provide sufficient torque to drive the load on the elevated velocity. When operated at a pace below the rated pace of the motor, the volts per hertz (V/Hz) may be maintained because the frequency applied to the motor is increased. Maintaining a relentless V/Hz ratio retains torque manufacturing stable. While it will be perfect to increase the voltage to the motor as it’s run above its rated pace, the voltage of the alternating current (AC) energy supply limits the maximum voltage that is out there to the motor. Therefore, the voltage provided to the motor can not continue to extend above the nameplate voltage as illustrated in Image 2. As shown in Image three, the out there torque decreases beyond one hundred pc frequency as a result of the V/Hz ratio just isn’t maintained. In an overspeed state of affairs, the load torque (pump) should be under the available torque.
Before operating any piece of equipment outside of its rated pace vary, it’s essential to contact the manufacturer of the equipment to find out if this can be accomplished safely and efficiently. For more info on variable pace pumping, check with HI’s “Application Guideline for Variable Speed Pumping” at pumps.org.
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