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

In some instances, operating a motor beyond the base pole pace is feasible and provides system benefits if the design is carefully examined. The pole velocity of a motor is a function of the number poles and the incoming line frequency. Image 1 presents the synchronous pole speed 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, additional poles reduce the base pole speed. If the incoming line frequency doesn’t change, the speed of the induction motor will be lower than these values by a % to slip. So, to operate the motor above the base pole velocity, the frequency needs to be elevated, which can be accomplished with a variable frequency drive (VFD).
เกจวัดแรงอัดกระบอกสูบ for overspeeding a motor on a pump is to make use of a slower rated pace 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 decrease present score for use while still making certain satisfactory control of the pump/motor over its desired operating vary. The lower present requirement of the drive can reduce the capital price 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 additional move and stress to the managed system. This could lead to a extra compact system while rising its effectivity. While it may be possible to extend the motor’s velocity to twice its nameplate velocity, it is extra common that the utmost speed is extra limited.
The key to those purposes is to overlay the pump velocity torque curve and motor pace torque to ensure the motor starts and capabilities throughout the complete operational pace vary without overheating, stalling or creating any important stresses on the pumping system.
Several points also must be taken under consideration when considering such options:
Noise will increase with speed.
Bearing life or greasing intervals may be decreased, or improved match bearings could additionally be required.
The larger velocity (and variable speed in general) will improve the danger of resonant vibration as a result of a important pace inside the working range.
The larger pace will end in extra power consumption. It is necessary to suppose about if the pump and drive train is rated for the upper energy.
Since the torque required by a rotodynamic pump increases in proportion to the square of pace, the other major concern is to ensure that the motor can present enough torque to drive the load at the elevated velocity. When operated at a velocity beneath the rated speed of the motor, the volts per hertz (V/Hz) can be maintained because the frequency applied to the motor is increased. Maintaining a constant V/Hz ratio keeps torque production secure. 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) energy supply limits the utmost voltage that is obtainable to the motor. Therefore, the voltage supplied to the motor cannot proceed to extend above the nameplate voltage as illustrated in Image 2. As proven in Image 3, the out there torque decreases past 100% frequency as a result of the V/Hz ratio is not maintained. In an overspeed state of affairs, the load torque (pump) should be beneath the obtainable torque.
Before working any piece of equipment outdoors of its rated velocity vary, it’s essential to contact the manufacturer of the tools to find out if this can be done safely and efficiently. For extra information on variable velocity pumping, refer to HI’s “Application Guideline for Variable Speed Pumping” at pumps.org.
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