In some situations, working a motor beyond the base pole velocity is possible and provides system benefits if the design is fastidiously examined. The pole pace of a motor is a perform of the quantity 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 shall be less than these values by a % to slide. So, to function pressure gauge ดิจิตอล above the bottom pole pace, the frequency needs to be elevated, which may be accomplished with a variable frequency drive (VFD).
One purpose for overspeeding a motor on a pump is to make use of a slower rated pace motor with a decrease horsepower rating and operate it above base frequency to get the required torque at a decrease current. This permits the number of a VFD with a lower present score to be used while nonetheless guaranteeing satisfactory management of the pump/motor over its desired working vary. The lower current requirement of the drive can scale back the capital price of the system, relying on total system requirements.
The functions the place the motor and the pushed pump function above their rated speeds can provide further flow and pressure to the controlled system. This might end in a extra compact system whereas growing its effectivity. While it could be possible to extend the motor’s velocity to twice its nameplate velocity, it is more frequent that the maximum velocity is extra limited.
The key to these purposes is to overlay the pump velocity torque curve and motor velocity torque to ensure the motor starts and features all through the whole operational pace range with out overheating, stalling or creating any important stresses on the pumping system.
Several factors also must be taken under consideration when considering such solutions:
Noise will improve with pace.
Bearing life or greasing intervals could additionally be reduced, or improved match bearings may be required.
The larger velocity (and variable velocity in general) will increase the danger of resonant vibration due to a critical pace throughout the operating range.
The higher speed will lead to extra power consumption. It is important 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 pace, the other main concern is to ensure that the motor can provide enough torque to drive the load at the increased pace. 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 constant V/Hz ratio retains torque production steady. While it would be best to extend 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 obtainable to the motor. Therefore, the voltage supplied 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 percent 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 beneath the available torque.
Before operating any piece of kit exterior of its rated velocity range, it is essential to contact the manufacturer of the tools to determine if this can be carried out safely and effectively. For extra data on variable pace pumping, refer to HI’s “Application Guideline for Variable Speed Pumping” at pumps.org.
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