In some instances, working a motor past the bottom pole speed is possible 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. Image 1 presents the synchronous pole speed for 2-pole by way of 12-pole motors at 50 hertz (Hz [common in Europe]) and 60 Hz (common within the U.S.). As illustrated, further poles cut back the bottom pole velocity. If the incoming line frequency doesn’t change, the velocity of the induction motor will be lower than these values by a percent to slide. So, to operate 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 velocity motor with a lower horsepower ranking and operate it above base frequency to get the required torque at a lower current. This enables the choice of a VFD with a decrease current rating for use whereas still ensuring satisfactory management of the pump/motor over its desired operating vary. The lower current requirement of the drive can reduce the capital value of the system, depending on overall system requirements.
The applications where the motor and the driven pump operate above their rated speeds can provide additional flow and stress to the managed system. This could end in a more compact system while increasing its effectivity. While it could be potential to increase the motor’s pace to twice its nameplate velocity, it is more common that the utmost velocity is more limited.
The key to these purposes is to overlay the pump speed torque curve and motor speed torque to ensure the motor starts and capabilities throughout the complete operational pace range without overheating, stalling or creating any vital stresses on the pumping system.
Several factors additionally have to be taken into consideration when contemplating such solutions:
Noise will improve with velocity.
Bearing life or greasing intervals could also be reduced, or improved fit bearings may be required.
The larger speed (and variable pace in general) will improve the risk of resonant vibration as a end result of a important speed throughout the working vary.
The higher speed will end in additional power consumption. It is important to assume about if the pump and drive prepare is rated for the higher energy.
Since the torque required by a rotodynamic pump increases in proportion to the square of speed, 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 below the rated velocity of the motor, the volts per hertz (V/Hz) can be maintained as the frequency utilized to the motor is elevated. Maintaining a continuing V/Hz ratio retains torque manufacturing secure. While it will be perfect to increase the voltage to the motor as it is run above its rated velocity, the voltage of the alternating present (AC) energy supply limits the utmost voltage that is available to the motor. Therefore, the voltage equipped to the motor can not continue to extend above the nameplate voltage as illustrated in Image 2. As shown in Image 3, the available torque decreases beyond 100% frequency because the V/Hz ratio is not maintained. In an overspeed scenario, the load torque (pump) should be below the out there torque.
Before operating any piece of kit outdoors of its rated speed vary, it is important to contact the producer of the tools to discover out if this can be done safely and effectively. For เกจวัดแรงดันภาษาอังกฤษ on variable speed pumping, check with HI’s “Application Guideline for Variable Speed Pumping” at pumps.org.
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