In some situations, working a motor beyond the base pole pace is possible and offers system benefits if the design is rigorously examined. The pole speed of a motor is a function of the number poles and the incoming line frequency. Image 1 presents the synchronous pole velocity for 2-pole via 12-pole motors at 50 hertz (Hz [common in Europe]) and 60 Hz (common in the U.S.). As illustrated, additional poles scale back the base pole pace. If the incoming line frequency does not change, the velocity of the induction motor shall be lower than these values by a p.c to slide. So, to function the motor above the base pole velocity, the frequency needs to be increased, which can be carried out with a variable frequency drive (VFD).
One reason for overspeeding a motor on a pump is to use a slower rated velocity motor with a lower horsepower rating and operate it above base frequency to get the required torque at a lower 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 operating range. เกจวัดแรงดัน4นิ้วราคา of the drive can cut back the capital value of the system, depending on total system necessities.
The purposes where the motor and the pushed pump function above their rated speeds can provide additional flow and strain to the controlled system. This could lead to a extra compact system while increasing its effectivity. While it could be attainable to increase the motor’s pace to twice its nameplate pace, it is extra widespread that the utmost speed is extra restricted.
The key to those functions is to overlay the pump pace torque curve and motor velocity torque to make sure the motor starts and features throughout the complete operational speed range with out 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 velocity.
Bearing life or greasing intervals could additionally be decreased, or improved fit bearings could additionally be required.
The larger speed (and variable speed in general) will enhance the danger of resonant vibration because of a important speed inside the working range.
The greater pace will lead to additional power consumption. It is necessary to assume about if the pump and drive prepare is rated for the upper power.
Since the torque required by a rotodynamic pump increases in proportion to the sq. of pace, the other major concern is to guarantee that the motor can present sufficient torque to drive the load on the increased speed. When operated at a velocity below the rated pace of the motor, the volts per hertz (V/Hz) may be maintained as the frequency applied to the motor is increased. Maintaining a constant V/Hz ratio retains torque manufacturing steady. While it might be ideal to extend the voltage to the motor as it’s run above its rated pace, the voltage of the alternating current (AC) power source limits the utmost voltage that is out there to the motor. Therefore, the voltage equipped to the motor can not continue to increase above the nameplate voltage as illustrated in Image 2. As proven in Image three, the obtainable torque decreases beyond 100 percent frequency as a outcome of the V/Hz ratio isn’t maintained. In an overspeed state of affairs, the load torque (pump) should be below the obtainable torque.
Before operating any piece of kit exterior of its rated pace vary, it’s important to contact the manufacturer of the tools to determine if this can be accomplished safely and efficiently. For more information on variable velocity pumping, check with HI’s “Application Guideline for Variable Speed Pumping” at pumps.org.
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