In some instances, operating a motor beyond the base pole pace is possible and presents system benefits if the design is rigorously examined. The pole velocity 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 in the U.S.). As illustrated, further poles scale back the base pole pace. If เกจ์วัดแรงดันแก๊ส does not change, the velocity of the induction motor will be less than these values by a p.c to slide. So, to operate the motor above the bottom pole velocity, the frequency needs to be elevated, which could be carried out 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 score and operate it above base frequency to get the required torque at a lower current. This permits the choice of a VFD with a lower present score for use whereas nonetheless ensuring passable management of the pump/motor over its desired operating vary. The lower present requirement of the drive can scale back the capital value of the system, depending on total 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 result in a extra compact system while growing its efficiency. While it might be potential to increase the motor’s velocity to twice its nameplate speed, it’s more widespread that the utmost speed is extra limited.
The key to these functions is to overlay the pump pace torque curve and motor pace torque to ensure the motor starts and capabilities all through the complete operational pace range without overheating, stalling or creating any significant stresses on the pumping system.
Several points also must be taken into consideration when considering such solutions:
Noise will enhance with pace.
Bearing life or greasing intervals could also be lowered, or improved fit bearings could also be required.
The higher speed (and variable pace in general) will increase the chance of resonant vibration because of a critical pace within the working vary.
The larger pace will end in extra energy consumption. It is necessary to consider if the pump and drive practice is rated for the higher energy.
Since the torque required by a rotodynamic pump will increase in proportion to the sq. of velocity, the opposite major concern is to guarantee that the motor can provide sufficient 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 utilized to the motor is increased. Maintaining a relentless V/Hz ratio retains torque production stable. While it would be ideal to increase the voltage to the motor as it’s run above its rated speed, the voltage of the alternating present (AC) power source limits the maximum voltage that is out there to the motor. Therefore, the voltage supplied to the motor can not continue to extend above the nameplate voltage as illustrated in Image 2. As shown in Image three, the available torque decreases past 100% frequency as a end result of the V/Hz ratio isn’t maintained. In an overspeed scenario, the load torque (pump) have to be beneath the obtainable torque.
Before operating any piece of kit outside of its rated speed range, it’s essential to contact the manufacturer of the gear to find out if this can be accomplished safely and effectively. For extra information on variable pace pumping, discuss with HI’s “Application Guideline for Variable Speed Pumping” at pumps.org.
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