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 presents system advantages if the design is fastidiously examined. The pole speed of a motor is a operate of the number poles and the incoming line frequency. Image 1 presents the synchronous pole speed 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 reduce the base pole velocity. If the incoming line frequency doesn’t change, the velocity of the induction motor will be less than these values by a % to slip. So, to function the motor above the bottom pole speed, the frequency needs to be elevated, which could be done 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 enables the number of a VFD with a lower current rating to be used while still guaranteeing passable management of the pump/motor over its desired operating range. The decrease present requirement of the drive can cut back the capital cost of the system, depending on total system necessities.
เกจวัดแรงดันลมคือ where the motor and the driven pump operate above their rated speeds can present additional flow and strain to the managed system. This may end in a extra compact system while growing its efficiency. While it could be possible to increase the motor’s pace to twice its nameplate pace, it is extra frequent that the utmost velocity is extra limited.
The key to these applications is to overlay the pump velocity torque curve and motor velocity torque to ensure the motor begins and capabilities all through the whole operational velocity range with out overheating, stalling or creating any vital stresses on the pumping system.
Several points also have to be taken into account when contemplating such options:
Noise will enhance with velocity.
Bearing life or greasing intervals may be decreased, or improved fit bearings could also be required.
The larger velocity (and variable pace in general) will enhance the danger of resonant vibration due to a crucial velocity inside the operating vary.
The larger velocity will result in extra power consumption. It is important 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 ensure that the motor can provide enough torque to drive the load on the elevated speed. When operated at a pace under the rated pace of the motor, the volts per hertz (V/Hz) can be maintained as the frequency utilized to the motor is increased. Maintaining a constant V/Hz ratio retains torque manufacturing secure. While it might be best to extend the voltage to the motor as it’s run above its rated speed, the voltage of the alternating current (AC) power source limits the maximum 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 three, the available torque decreases beyond one hundred pc frequency because the V/Hz ratio is not maintained. In an overspeed scenario, the load torque (pump) must be beneath the obtainable torque.
Before working any piece of equipment outdoors of its rated velocity vary, it’s important to contact the manufacturer of the tools to find out if this may be done safely and effectively. For extra data on variable pace pumping, refer to HI’s “Application Guideline for Variable Speed Pumping” at pumps.org.
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