In Which Applications Can a Pump Motor Be Operated Above Base Speed?

In ที่วัดแรงดัน , operating a motor beyond the base pole velocity is possible and offers system advantages if the design is carefully 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 speed for 2-pole via 12-pole motors at 50 hertz (Hz [common in Europe]) and 60 Hz (common within the U.S.). As illustrated, extra poles reduce the base pole velocity. If the incoming line frequency doesn’t change, the pace of the induction motor might be less than these values by a percent to slide. So, to operate the motor above the base pole pace, the frequency needs to be increased, which may be carried out with a variable frequency drive (VFD).
One reason for overspeeding a motor on a pump is to use a slower rated speed motor with a lower horsepower ranking and operate it above base frequency to get the required torque at a lower current. This permits the choice of a VFD with a decrease present score for use whereas nonetheless guaranteeing satisfactory control of the pump/motor over its desired operating vary. The lower present requirement of the drive can scale back the capital cost of the system, relying on general system necessities.
The functions the place the motor and the pushed pump operate above their rated speeds can present extra circulate and pressure to the managed system. This could end in a extra compact system while increasing its efficiency. While it might be attainable to increase the motor’s speed to twice its nameplate pace, it’s extra common that the maximum pace is more limited.
The key to these applications is to overlay the pump pace torque curve and motor pace torque to ensure the motor begins and functions all through the complete operational velocity range without overheating, stalling or creating any vital stresses on the pumping system.
Several points additionally need to be taken into consideration when contemplating such options:
Noise will improve with velocity.
Bearing life or greasing intervals may be decreased, or improved match bearings may be required.
The higher velocity (and variable pace in general) will enhance the chance of resonant vibration as a result of a important pace inside the working vary.
The higher velocity will result in extra power consumption. It is necessary to contemplate if the pump and drive train is rated for the upper energy.
Since the torque required by a rotodynamic pump will increase in proportion to the sq. of pace, the other major concern is to make certain that the motor can present sufficient torque to drive the load on the elevated speed. When operated at a speed under the rated speed of the motor, the volts per hertz (V/Hz) can be maintained as the frequency applied to the motor is increased. Maintaining a relentless V/Hz ratio keeps torque manufacturing stable. While it will be ideal to extend the voltage to the motor as it’s run above its rated velocity, the voltage of the alternating present (AC) energy source limits the maximum voltage that is obtainable 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 obtainable torque decreases past 100% frequency because the V/Hz ratio is not maintained. In an overspeed state of affairs, the load torque (pump) must be below the available torque.
Before working any piece of apparatus exterior of its rated speed range, it is essential to contact the producer of the tools to determine if this can be accomplished safely and efficiently. For extra data on variable velocity pumping, discuss with HI’s “Application Guideline for Variable Speed Pumping” at pumps.org.
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