In some cases, operating a motor past the bottom pole speed is feasible and offers system advantages if the design is carefully examined. The pole speed 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, further poles scale back the bottom pole velocity. If เกจวัดแรงดันเบนซิน doesn’t change, the speed of the induction motor might be less than these values by a % to slip. So, to operate the motor above the base pole velocity, the frequency must be increased, which may be accomplished with a variable frequency drive (VFD).
One cause for overspeeding a motor on a pump is to use a slower rated pace motor with a decrease horsepower rating and function it above base frequency to get the required torque at a decrease present. This enables the selection of a VFD with a decrease present rating for use whereas still ensuring satisfactory control of the pump/motor over its desired working range. The decrease current requirement of the drive can reduce the capital cost of the system, depending on overall system necessities.
The functions where the motor and the pushed pump function above their rated speeds can provide extra move and strain to the controlled system. This could lead to a more compact system while rising its effectivity. While it may be attainable to extend the motor’s speed to twice its nameplate pace, it’s more widespread that the maximum pace is more restricted.
The key to those functions is to overlay the pump pace torque curve and motor pace torque to ensure the motor starts and capabilities all through the complete operational speed vary with out overheating, stalling or creating any vital stresses on the pumping system.
Several factors additionally need to be taken under consideration when considering such options:
Noise will enhance with velocity.
Bearing life or greasing intervals may be reduced, or improved match bearings could additionally be required.
The larger pace (and variable speed in general) will enhance the danger of resonant vibration due to a critical pace throughout the working range.
The larger pace will lead to further power consumption. It is essential to consider if the pump and drive train is rated for the upper power.
Since the torque required by a rotodynamic pump increases in proportion to the square of pace, the other major concern is to ensure that the motor can provide sufficient torque to drive the load on the increased velocity. When operated at a speed under the rated speed of the motor, the volts per hertz (V/Hz) can be maintained because the frequency applied to the motor is elevated. Maintaining a continuing V/Hz ratio keeps torque production secure. While it would be best to increase the voltage to the motor as it is 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 not proceed to increase above the nameplate voltage as illustrated in Image 2. As proven in Image 3, the out there torque decreases beyond one hundred pc frequency as a end result of the V/Hz ratio is not maintained. In an overspeed state of affairs, the load torque (pump) must be below the obtainable torque.
Before operating any piece of kit outdoors of its rated speed vary, it’s essential to contact the producer of the gear to discover out if this could be carried out safely and effectively. For extra info on variable velocity pumping, refer to HI’s “Application Guideline for Variable Speed Pumping” at pumps.org.
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