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

In some cases, operating a motor past the bottom pole speed is feasible and presents system advantages if the design is fastidiously examined. The pole pace of a motor is a function of the quantity poles and the incoming line frequency. Image 1 presents the synchronous pole pace for 2-pole through 12-pole motors at 50 hertz (Hz [common in Europe]) and 60 Hz (common in the U.S.). As illustrated, เกจวัดอาร์กอน . If the incoming line frequency doesn’t change, the pace of the induction motor shall be lower than these values by a percent to slip. So, to operate the motor above the base pole velocity, 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 use a slower rated pace motor with a lower horsepower ranking 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 to be used whereas still making certain passable management of the pump/motor over its desired operating vary. The decrease present requirement of the drive can cut back the capital price of the system, depending on overall system requirements.
The functions where the motor and the pushed pump function above their rated speeds can present further flow and stress to the controlled system. This might result in a extra compact system whereas increasing its efficiency. While it could be possible to extend the motor’s speed to twice its nameplate speed, it’s more common that the maximum speed is extra restricted.
The key to those purposes is to overlay the pump speed torque curve and motor velocity torque to ensure the motor starts and functions all through the complete operational speed vary without overheating, stalling or creating any vital stresses on the pumping system.
Several factors also have to be taken into consideration when considering such options:
Noise will improve with velocity.
Bearing life or greasing intervals may be reduced, or improved match bearings may be required.
The higher velocity (and variable velocity in general) will enhance the chance of resonant vibration because of a important speed within the operating range.
The larger velocity will lead to additional energy consumption. It is essential to contemplate if the pump and drive practice is rated for the higher power.
Since the torque required by a rotodynamic pump will increase in proportion to the sq. of velocity, the opposite major concern is to ensure that the motor can provide enough torque to drive the load at the elevated speed. When operated at a velocity below the rated velocity of the motor, the volts per hertz (V/Hz) can be maintained because the frequency applied to the motor is elevated. Maintaining a continuing V/Hz ratio retains torque manufacturing secure. While it might be perfect to increase the voltage to the motor as it’s run above its rated velocity, the voltage of the alternating current (AC) power supply limits the utmost voltage that is obtainable to the motor. Therefore, the voltage supplied to the motor can not proceed to increase above the nameplate voltage as illustrated in Image 2. As shown in Image three, the out there torque decreases beyond 100 percent frequency as a outcome of the V/Hz ratio isn’t maintained. In an overspeed scenario, the load torque (pump) should be beneath the out there torque.
Before working any piece of apparatus outdoors of its rated velocity vary, it is important to contact the producer of the gear to discover out if this can be done safely and efficiently. For extra info on variable velocity pumping, discuss with HI’s “Application Guideline for Variable Speed Pumping” at pumps.org.
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