In some cases, working a motor beyond the bottom pole pace is possible and presents system advantages if the design is rigorously examined. The pole velocity of a motor is a perform of the number poles and the incoming line frequency. Image 1 presents the synchronous pole pace for 2-pole through 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 speed. If the incoming line frequency doesn’t change, the velocity of the induction motor shall be lower than these values by a % to slide. So, to function the motor above the base pole velocity, the frequency needs to be elevated, which can be done with a variable frequency drive (VFD).
One purpose for overspeeding a motor on a pump is to make use of a slower rated velocity motor with a decrease horsepower ranking and function it above base frequency to get the required torque at a decrease present. This allows the number of a VFD with a decrease current score for use while still making certain satisfactory management of the pump/motor over its desired operating vary. The decrease present requirement of the drive can scale back the capital price of the system, depending on total system necessities.
The purposes the place the motor and the driven pump function above their rated speeds can provide additional move and stress to the managed system. This may lead to a more compact system whereas increasing its effectivity. While it might be potential to increase the motor’s velocity to twice its nameplate velocity, it’s extra frequent that the utmost velocity is extra limited.
The key to these applications is to overlay the pump pace torque curve and motor velocity torque to ensure the motor starts and features throughout the complete operational speed range with out overheating, stalling or creating any significant stresses on the pumping system.
Several factors additionally have to be taken into consideration when considering such solutions:
Noise will enhance with velocity.
Bearing life or greasing intervals may be lowered, or improved fit bearings could additionally be required.
The greater velocity (and variable speed in general) will enhance the danger of resonant vibration as a end result of a crucial speed throughout the operating range.
The larger velocity will result in further energy consumption. ราคาpressuregauge is necessary to consider if the pump and drive practice is rated for the upper energy.
Since the torque required by a rotodynamic pump will increase in proportion to the square of pace, the other main concern is to ensure that the motor can present sufficient torque to drive the load on the elevated velocity. When operated at a pace under the rated pace of the motor, the volts per hertz (V/Hz) may be maintained as the frequency utilized to the motor is increased. Maintaining a continuing V/Hz ratio keeps torque production steady. While it would be best to extend the voltage to the motor as it is run above its rated speed, the voltage of the alternating present (AC) power supply limits the maximum voltage that is available to the motor. Therefore, the voltage equipped to the motor cannot proceed to extend above the nameplate voltage as illustrated in Image 2. As shown in Image three, the obtainable torque decreases past one hundred pc frequency because the V/Hz ratio just isn’t maintained. In an overspeed scenario, the load torque (pump) should be under the out there torque.
Before working any piece of apparatus outdoors of its rated pace vary, it is important to contact the manufacturer of the equipment to determine if this might be done 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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