In some instances, operating a motor beyond the bottom pole velocity is feasible and provides system benefits if the design is fastidiously examined. The pole velocity of a motor is a operate of the number 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 within the U.S.). As illustrated, extra poles scale back the base pole pace. If the incoming line frequency doesn’t change, the pace of the induction motor shall be less than these values by a percent to slide. So, to function the motor above the base pole speed, the frequency needs to be elevated, which could be carried out with a variable frequency drive (VFD).
One reason for overspeeding a motor on a pump is to make use of a slower rated speed motor with a lower horsepower ranking and function it above base frequency to get the required torque at a decrease present. This permits the choice of a VFD with a lower present score to be used while still guaranteeing 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 total system necessities.
The purposes where the motor and the driven pump operate above their rated speeds can provide additional circulate and strain to the managed system. This could lead to a more compact system while increasing its effectivity. While it could be attainable to extend the motor’s velocity to twice its nameplate speed, it is extra frequent that the utmost velocity is more limited.
เกจวัดแรงดันเชื้อเพลิง to those functions is to overlay the pump velocity torque curve and motor pace torque to ensure the motor starts and features all through the entire operational speed range without overheating, stalling or creating any important stresses on the pumping system.
Several factors additionally have to be taken into account when considering such options:
Noise will enhance with speed.
Bearing life or greasing intervals could additionally be decreased, or improved match bearings may be required.
The higher pace (and variable pace in general) will enhance the risk of resonant vibration due to a critical pace inside the operating vary.
The greater speed will end in extra energy consumption. It is important to contemplate 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 sq. of velocity, the other main concern is to ensure that the motor can provide enough torque to drive the load at the elevated speed. When operated at a velocity beneath the rated speed of the motor, the volts per hertz (V/Hz) may be maintained because the frequency utilized to the motor is increased. Maintaining a relentless V/Hz ratio retains torque production secure. While it might be perfect to increase 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’t proceed to increase above the nameplate voltage as illustrated in Image 2. As shown in Image 3, the available torque decreases past 100% frequency because the V/Hz ratio just isn’t maintained. In an overspeed situation, the load torque (pump) should be beneath the obtainable torque.
Before working any piece of kit outdoors of its rated pace vary, it is important to contact the producer of the equipment to determine if this may be accomplished safely and efficiently. For more info on variable pace pumping, refer to HI’s “Application Guideline for Variable Speed Pumping” at pumps.org.
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