In some cases, operating a motor beyond the base pole speed is possible and provides system advantages if the design is fastidiously 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 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 cut back the base pole velocity. If the incoming line frequency does not change, the pace of the induction motor will be less than these values by a % to slip. So, to function the motor above the bottom 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 use a slower rated speed motor with a lower horsepower ranking and function it above base frequency to get the required torque at a lower current. This allows the number of a VFD with a decrease present ranking to be used whereas nonetheless ensuring satisfactory management of the pump/motor over its desired operating vary. The lower present requirement of the drive can reduce the capital price of the system, depending on overall system requirements.
เกจวัดแรงดันคือ and the pushed pump operate above their rated speeds can provide further flow and pressure to the managed system. This may lead to a more compact system while increasing its efficiency. While it may be possible to extend the motor’s pace to twice its nameplate pace, it is extra widespread that the maximum pace is extra limited.
The key to these functions is to overlay the pump speed torque curve and motor velocity torque to ensure the motor starts and capabilities throughout the entire operational pace range with out overheating, stalling or creating any vital stresses on the pumping system.
Several factors additionally have to be taken into account when contemplating such solutions:
Noise will enhance with velocity.
Bearing life or greasing intervals may be reduced, or improved match bearings could also be required.
The larger pace (and variable pace in general) will improve the chance of resonant vibration because of a critical pace inside the operating range.
The greater velocity will result in further energy consumption. It is necessary to contemplate if the pump and drive train is rated for the upper power.
Since the torque required by a rotodynamic pump will increase in proportion to the square of pace, the opposite major concern is to ensure that the motor can present enough torque to drive the load at the increased pace. When operated at a velocity below the rated speed of the motor, the volts per hertz (V/Hz) may be maintained as the frequency utilized to the motor is elevated. Maintaining a relentless V/Hz ratio keeps torque manufacturing steady. While it will be perfect to increase the voltage to the motor as it is run above its rated speed, the voltage of the alternating current (AC) power source limits the maximum voltage that’s available to the motor. Therefore, the voltage equipped to the motor can’t continue to extend above the nameplate voltage as illustrated in Image 2. As shown in Image 3, the obtainable torque decreases past 100% frequency as a result of the V/Hz ratio just isn’t maintained. In an overspeed situation, the load torque (pump) must be under 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 may be carried out safely and effectively. For extra information on variable velocity pumping, discuss with HI’s “Application Guideline for Variable Speed Pumping” at pumps.org.
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