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

In some situations, working a motor past the base pole speed is possible and presents system advantages if the design is carefully examined. The pole velocity of a motor is a operate 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, extra poles scale back the bottom pole velocity. If the incoming line frequency doesn’t change, the speed of the induction motor shall be less than these values by a p.c to slide. So, to operate the motor above the base pole speed, the frequency needs to be increased, which can be done 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 decrease horsepower score and operate it above base frequency to get the required torque at a decrease current. This permits the selection of a VFD with a decrease current 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, relying on general system necessities.
The applications where the motor and the driven pump operate above their rated speeds can provide additional circulate and stress to the controlled system. This might end in a extra compact system while rising its efficiency. While it might be possible to increase the motor’s speed to twice its nameplate pace, it is extra widespread that the maximum speed is more limited.
The key to these applications is to overlay the pump velocity torque curve and motor speed torque to make sure the motor begins and functions throughout the complete operational velocity vary with out overheating, stalling or creating any vital stresses on the pumping system.
Several points also need to be taken into consideration when considering such options:
Noise will increase with speed.
Bearing life or greasing intervals may be decreased, or improved match bearings may be required.
The larger pace (and variable velocity in general) will improve the chance of resonant vibration as a end result of a crucial pace throughout the operating vary.
The greater speed will end in further energy consumption. It is important 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 pace, the other major concern is to ensure that the motor can provide sufficient torque to drive the load on the increased pace. When operated at a velocity beneath the rated speed of the motor, the volts per hertz (V/Hz) can be maintained because the frequency applied to the motor is increased. Maintaining a continuing V/Hz ratio keeps torque manufacturing stable. While it would be best to extend the voltage to the motor as it’s run above its rated velocity, the voltage of the alternating current (AC) power source limits the maximum voltage that’s out there to the motor. Therefore, the voltage equipped to the motor can not proceed to increase above the nameplate voltage as illustrated in Image 2. As shown in Image 3, the obtainable torque decreases beyond one hundred pc frequency as a outcome of the V/Hz ratio just isn’t maintained. In an overspeed state of affairs, the load torque (pump) should be beneath the available torque.
Before operating any piece of equipment outside of its rated velocity range, it’s important to contact the manufacturer of the gear to determine if this can be accomplished safely and efficiently. For เกรดวัดแรงดัน on variable speed pumping, check with HI’s “Application Guideline for Variable Speed Pumping” at pumps.org.
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