In some instances, working a motor past the bottom pole speed is possible and provides system benefits if the design is rigorously examined. The pole pace of a motor is a operate of the quantity poles and the incoming line frequency. Image 1 presents the synchronous pole pace 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 base pole speed. If the incoming line frequency does not change, the speed of the induction motor will be less than these values by a % to slip. So, to operate the motor above the base pole pace, the frequency must be elevated, which may be done with a variable frequency drive (VFD).
เกจวัดแรงดันไฟฟ้า for overspeeding a motor on a pump is to make use of a slower rated pace motor with a decrease horsepower ranking and function it above base frequency to get the required torque at a lower present. This permits the choice of a VFD with a lower present ranking to be used whereas still making certain passable management of the pump/motor over its desired working vary. The decrease current requirement of the drive can scale back the capital value of the system, relying on total system necessities.
The functions the place the motor and the driven pump operate above their rated speeds can present further flow and stress to the controlled system. This might lead to a extra compact system while growing its efficiency. While it may be potential to increase the motor’s speed to twice its nameplate velocity, it is more common that the maximum velocity is extra restricted.
The key to these functions is to overlay the pump pace torque curve and motor speed torque to make sure the motor begins and capabilities all through the complete operational speed range without overheating, stalling or creating any important stresses on the pumping system.
Several points also need to be taken into account when considering such solutions:
Noise will improve with pace.
Bearing life or greasing intervals may be reduced, or improved match bearings could additionally be required.
The larger velocity (and variable pace in general) will enhance the danger of resonant vibration due to a important pace throughout the working range.
The larger velocity will end in further energy consumption. It is necessary to consider if the pump and drive prepare is rated for the higher power.
Since the torque required by a rotodynamic pump increases in proportion to the square of velocity, the other major concern is to ensure that the motor can present sufficient torque to drive the load at the elevated velocity. When operated at a pace beneath the rated velocity of the motor, the volts per hertz (V/Hz) can be maintained because the frequency utilized to the motor is increased. Maintaining a continuing V/Hz ratio retains torque manufacturing secure. While it would be ideal to extend the voltage to the motor as it’s run above its rated speed, the voltage of the alternating current (AC) power supply limits the maximum voltage that is obtainable to the motor. Therefore, the voltage supplied to the motor cannot proceed to increase above the nameplate voltage as illustrated in Image 2. As proven in Image three, the obtainable torque decreases beyond one hundred pc frequency as a result of the V/Hz ratio just isn’t maintained. In an overspeed state of affairs, the load torque (pump) should be below the available torque.
Before operating any piece of apparatus exterior of its rated speed range, it is essential to contact the manufacturer of the gear to determine if this can be carried out safely and efficiently. For extra info on variable speed pumping, discuss with HI’s “Application Guideline for Variable Speed Pumping” at pumps.org.
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