In Which Applications Can a Pump Motor Be Operated Above Base Speed?

In some instances, working a motor past the bottom pole pace is possible and presents system benefits if the design is rigorously examined. The pole speed of a motor is a operate of the number poles and the incoming line frequency. เกจแรงดันสูง presents the synchronous pole pace for 2-pole through 12-pole motors at 50 hertz (Hz [common in Europe]) and 60 Hz (common within the U.S.). As illustrated, extra poles reduce the bottom pole velocity. If the incoming line frequency does not change, the speed of the induction motor might be lower than these values by a percent to slip. So, to function the motor above the bottom pole speed, the frequency must be increased, which can be accomplished 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 decrease horsepower rating and operate it above base frequency to get the required torque at a decrease current. This permits the choice of a VFD with a decrease present score for use whereas nonetheless ensuring satisfactory control of the pump/motor over its desired working vary. The lower present requirement of the drive can reduce the capital cost of the system, depending on general system necessities.
The applications the place the motor and the pushed pump function above their rated speeds can provide extra circulate and pressure to the managed system. This might result in a extra compact system while increasing its efficiency. While it could be attainable to increase the motor’s pace to twice its nameplate velocity, it is more frequent that the utmost pace is extra limited.
The key to these functions is to overlay the pump speed torque curve and motor pace torque to make sure the motor begins and capabilities throughout the whole operational pace range with out overheating, stalling or creating any significant stresses on the pumping system.
Several factors additionally need to be taken into account when considering such solutions:
Noise will improve with velocity.
Bearing life or greasing intervals could additionally be decreased, or improved fit bearings could also be required.
The greater velocity (and variable speed in general) will enhance the risk of resonant vibration due to a critical velocity within the working range.
The higher velocity will lead to additional power consumption. It is important to assume about if the pump and drive practice is rated for the higher power.
Since the torque required by a rotodynamic pump increases in proportion to the square of velocity, the other main concern is to make sure that the motor can present enough torque to drive the load on the increased speed. When operated at a pace below the rated pace of the motor, the volts per hertz (V/Hz) can be maintained because the frequency utilized to the motor is increased. Maintaining a relentless V/Hz ratio retains torque manufacturing stable. While it would be perfect to increase the voltage to the motor as it is run above its rated velocity, the voltage of the alternating present (AC) energy source limits the utmost voltage that’s obtainable to the motor. Therefore, the voltage provided to the motor can’t continue to extend above the nameplate voltage as illustrated in Image 2. As proven in Image three, the obtainable torque decreases past one hundred pc frequency as a outcome of the V/Hz ratio just isn’t maintained. In an overspeed situation, the load torque (pump) must be below the obtainable torque.
Before operating any piece of apparatus exterior of its rated velocity range, it’s important to contact the manufacturer of the equipment to discover out if this can be carried out safely and effectively. For extra data on variable speed pumping, check with HI’s “Application Guideline for Variable Speed Pumping” at pumps.org.
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