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In some cases, working a motor past the bottom pole pace is feasible and offers system benefits if the design is rigorously examined. The pole speed of a motor is a function of the quantity poles and the incoming line frequency. เครื่องมือที่ใช้วัดความดันคือ presents the synchronous pole speed for 2-pole via 12-pole motors at 50 hertz (Hz [common in Europe]) and 60 Hz (common in the U.S.). As illustrated, further poles reduce the base pole speed. If the incoming line frequency does not change, the pace of the induction motor will be lower than these values by a p.c to slide. So, to function the motor above the bottom pole pace, the frequency must be elevated, which may be done with a variable frequency drive (VFD).
One purpose for overspeeding a motor on a pump is to use a slower rated pace motor with a lower horsepower ranking and operate it above base frequency to get the required torque at a decrease current. This permits the choice of a VFD with a lower current rating to be used whereas still ensuring satisfactory management of the pump/motor over its desired working vary. The lower present requirement of the drive can cut back the capital price of the system, relying on total system necessities.
The applications where the motor and the pushed pump operate above their rated speeds can present additional flow and strain to the managed system. This might end in a extra compact system while increasing its efficiency. While it may be possible to increase the motor’s pace to twice its nameplate pace, it is extra widespread that the utmost pace is extra restricted.
The key to those purposes is to overlay the pump speed torque curve and motor speed torque to make sure the motor starts and capabilities all through the entire operational pace vary with out overheating, stalling or creating any vital stresses on the pumping system.
Several factors additionally must be taken into consideration when considering such options:
Noise will enhance with speed.
Bearing life or greasing intervals could also be reduced, or improved fit bearings could also be required.
The larger velocity (and variable pace in general) will improve the chance of resonant vibration because of a important velocity inside the working vary.
The higher velocity will lead to extra energy consumption. เครื่องมือที่ใช้ในการวัดความดัน is necessary to contemplate 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 square of velocity, the other major concern is to make certain that the motor can present enough torque to drive the load at the elevated pace. When operated at a pace under the rated velocity of the motor, the volts per hertz (V/Hz) could be maintained as the frequency utilized to the motor is elevated. Maintaining a continuing V/Hz ratio keeps torque manufacturing secure. While it might be best to increase the voltage to the motor as it’s run above its rated velocity, the voltage of the alternating present (AC) energy supply limits the utmost voltage that is out there to the motor. Therefore, the voltage supplied to the motor can not continue to increase above the nameplate voltage as illustrated in Image 2. As proven in Image three, the out there torque decreases past one hundred pc frequency because the V/Hz ratio is not maintained. In an overspeed state of affairs, the load torque (pump) must be beneath the out there torque.
Before working any piece of equipment outside of its rated speed vary, it is important to contact the producer of the gear to determine if this can be accomplished safely and effectively. For more information on variable speed pumping, discuss with HI’s “Application Guideline for Variable Speed Pumping” at pumps.org.