In some cases, working a motor beyond the bottom pole velocity is possible and offers system benefits if the design is carefully examined. The pole speed of a motor is a perform of the quantity poles and the incoming line frequency. Image 1 presents the synchronous pole speed for 2-pole through 12-pole motors at 50 hertz (Hz [common in Europe]) and 60 Hz (common in the U.S.). As illustrated, extra poles reduce the bottom pole speed. If the incoming line frequency does not change, the speed of the induction motor might be lower than these values by a percent to slide. So, to function the motor above the base pole speed, the frequency must be elevated, which may be accomplished 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 ranking and operate it above base frequency to get the required torque at a lower current. This allows the selection of a VFD with a decrease present ranking for use whereas still making certain passable control of the pump/motor over its desired operating range. The decrease current requirement of the drive can scale back the capital price of the system, relying on overall system necessities.
The purposes the place the motor and the driven pump operate above their rated speeds can provide further circulate and pressure to the managed system. This may lead to a extra compact system while rising its efficiency. While it could be attainable to extend the motor’s velocity to twice its nameplate pace, it’s more common that the utmost speed is extra restricted.
The key to those functions is to overlay the pump velocity torque curve and motor velocity torque to make sure the motor starts and functions throughout the complete operational velocity range with out overheating, stalling or creating any important stresses on the pumping system.
Several factors additionally need to be taken into account when considering such options:
Noise will enhance with speed.
Bearing life or greasing intervals may be decreased, or improved match bearings could additionally be required.
The higher pace (and variable speed in general) will improve the risk of resonant vibration as a end result of a important velocity within the working range.
The greater speed will result in extra energy consumption. It is important to contemplate if the pump and drive prepare is rated for the upper power.
Since the torque required by a rotodynamic pump will increase in proportion to the square of speed, the other main concern is to make sure that the motor can provide enough torque to drive the load at the elevated velocity. When operated at a speed under the rated velocity of the motor, the volts per hertz (V/Hz) could be maintained because the frequency applied to the motor is elevated. Maintaining a continuing V/Hz ratio retains torque production steady. While it would be ideal to extend the voltage to the motor as it is run above its rated velocity, the voltage of the alternating current (AC) power source limits the maximum voltage that is out there to the motor. Therefore, เกจวัดแรงดันภาษาอังกฤษ supplied to the motor can not proceed to increase above the nameplate voltage as illustrated in Image 2. As proven in Image three, the out there torque decreases beyond 100% frequency as a end result of the V/Hz ratio isn’t maintained. In an overspeed state of affairs, the load torque (pump) should be beneath the available torque.
Before working any piece of apparatus exterior of its rated velocity range, it’s important to contact the producer of the gear to find out if this might be done 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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