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

In some situations, working a motor beyond the bottom pole speed is possible and offers system benefits if the design is fastidiously examined. The pole velocity of a motor is a perform of the quantity poles and the incoming line frequency. Image 1 presents the synchronous pole pace for 2-pole by way of 12-pole motors at 50 hertz (Hz [common in Europe]) and 60 Hz (common in the U.S.). As illustrated, further poles scale back the bottom pole velocity. If the incoming line frequency does not change, the speed of the induction motor shall be less than these values by a percent to slip. So, to operate the motor above the bottom pole pace, the frequency needs to be increased, which may be done with a variable frequency drive (VFD).
One reason for overspeeding a motor on a pump is to use a slower rated pace motor with a decrease horsepower score and operate it above base frequency to get the required torque at a lower current. This enables the number of a VFD with a lower present rating for use while nonetheless ensuring satisfactory management of the pump/motor over its desired operating range. The decrease present requirement of the drive can scale back the capital value of the system, depending on total system requirements.
The purposes the place the motor and the driven pump operate above their rated speeds can provide extra move and strain to the controlled system. This may result in a extra compact system while rising its efficiency. While it may be potential to extend the motor’s pace to twice its nameplate pace, it’s more common that the utmost pace is more restricted.
The key to these functions is to overlay the pump speed torque curve and motor pace torque to ensure the motor begins and features throughout the whole operational pace vary with out overheating, stalling or creating any significant stresses on the pumping system.
Several factors also have to be taken into account when contemplating such options:
Noise will increase with velocity.
Bearing เกจวัดแรงดันอากาศ or greasing intervals may be decreased, or improved fit bearings may be required.
The higher speed (and variable velocity in general) will improve the danger of resonant vibration because of a important speed inside the working vary.
The larger speed will lead to additional power consumption. It is important to assume about if the pump and drive prepare is rated for the upper energy.
Since the torque required by a rotodynamic pump will increase in proportion to the sq. of velocity, the other main concern is to guarantee that the motor can present sufficient torque to drive the load at the increased speed. When operated at a speed below the rated velocity of the motor, the volts per hertz (V/Hz) may be maintained because the frequency applied to the motor is elevated. Maintaining a constant V/Hz ratio retains torque manufacturing secure. While it will be perfect to extend the voltage to the motor as it is run above its rated speed, the voltage of the alternating present (AC) power source limits the utmost voltage that’s available to the motor. Therefore, the voltage provided 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 past 100 percent frequency because the V/Hz ratio isn’t maintained. In an overspeed state of affairs, the load torque (pump) must be under the available torque.
Before operating any piece of kit outdoors of its rated velocity vary, it’s essential to contact the manufacturer of the tools to discover out if this could be carried out safely and effectively. For extra info on variable speed pumping, discuss with HI’s “Application Guideline for Variable Speed Pumping” at pumps.org.
Share

Scroll to Top