In some situations, operating a motor past the bottom pole velocity is feasible and provides system advantages if the design is rigorously examined. The pole pace of a motor is a function of the number 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, additional poles reduce the bottom pole velocity. If the incoming line frequency does not change, the velocity of the induction motor will be lower than these values by a p.c to slip. So, to operate the motor above the base pole pace, the frequency must be elevated, which can 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 speed motor with a decrease horsepower ranking and function it above base frequency to get the required torque at a lower present. This allows the selection of a VFD with a lower present rating to be used whereas still making certain satisfactory management of the pump/motor over its desired operating range. The lower current requirement of the drive can scale back the capital cost of the system, depending on overall system requirements.
The applications the place the motor and the pushed pump function above their rated speeds can present additional move and stress to the managed system. This might lead to a more compact system whereas increasing its effectivity. While it may be attainable to increase the motor’s velocity to twice its nameplate pace, it’s more common that the utmost velocity is more limited.
เกจวัดแรงดัน10bar to these functions is to overlay the pump pace torque curve and motor velocity torque to ensure the motor starts and functions throughout the entire operational velocity vary with out overheating, stalling or creating any significant stresses on the pumping system.
Several points also need to be taken under consideration when contemplating such solutions:
Noise will improve with pace.
Bearing life or greasing intervals could also be decreased, or improved fit bearings may be required.
The greater pace (and variable pace in general) will increase the chance of resonant vibration because of a important velocity within the operating vary.
The greater speed will result in further energy consumption. It is essential to consider if the pump and drive practice is rated for the upper power.
Since the torque required by a rotodynamic pump increases in proportion to the sq. of velocity, the opposite main concern is to make certain that the motor can provide sufficient torque to drive the load on the elevated velocity. When operated at a speed beneath the rated velocity of the motor, the volts per hertz (V/Hz) could be maintained as the frequency applied to the motor is increased. Maintaining a relentless V/Hz ratio keeps torque manufacturing steady. While it will be perfect to increase the voltage to the motor as it’s run above its rated velocity, the voltage of the alternating present (AC) power source limits the maximum voltage that’s obtainable to the motor. Therefore, the voltage provided to the motor can’t proceed to increase above the nameplate voltage as illustrated in Image 2. As shown in Image 3, the out there torque decreases past 100% frequency because the V/Hz ratio is not maintained. In an overspeed state of affairs, the load torque (pump) should be under the out there torque.
Before working any piece of equipment outdoors of its rated velocity range, it is essential to contact the manufacturer of the tools to discover out if this might be accomplished safely and efficiently. For extra info on variable pace pumping, discuss with HI’s “Application Guideline for Variable Speed Pumping” at pumps.org.
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