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

In some instances, operating a motor past the base pole velocity is feasible and presents system benefits if the design is rigorously examined. The pole velocity of a motor is a function of the quantity 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 in the U.S.). As illustrated, further poles reduce the base pole velocity. If the incoming line frequency doesn’t change, the speed of the induction motor might be lower than these values by a % to slide. So, to function the motor above the base pole velocity, the frequency needs to be increased, which may be accomplished with a variable frequency drive (VFD).
One cause for overspeeding a motor on a pump is to make use of a slower rated speed 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 present ranking for use while nonetheless guaranteeing satisfactory control 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, relying on total system necessities.
pressure gauge where the motor and the driven pump operate above their rated speeds can provide further circulate and pressure to the managed system. This could end in a extra compact system whereas increasing its effectivity. While it might be possible to increase the motor’s speed to twice its nameplate speed, it is extra common that the utmost pace is more restricted.
The key to those functions is to overlay the pump velocity torque curve and motor velocity torque to ensure the motor starts and functions throughout the whole operational speed range without overheating, stalling or creating any vital stresses on the pumping system.
Several factors also need to be taken into consideration when contemplating such options:
Noise will enhance with pace.
Bearing life or greasing intervals could additionally be lowered, or improved match bearings could additionally be required.
The higher pace (and variable velocity in general) will increase the danger of resonant vibration as a result of a crucial velocity inside the working vary.
The greater velocity will result in extra energy consumption. It is necessary to consider 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 speed, the other main concern is to guarantee that the motor can provide enough torque to drive the load at the increased pace. When operated at a pace beneath the rated velocity of the motor, the volts per hertz (V/Hz) could be maintained because the frequency utilized to the motor is increased. Maintaining a continuing V/Hz ratio retains torque manufacturing stable. While it will be best to extend the voltage to the motor as it’s run above its rated speed, the voltage of the alternating present (AC) energy source limits the utmost voltage that is out there to the motor. Therefore, the voltage supplied to the motor can’t continue to increase above the nameplate voltage as illustrated in Image 2. As shown in Image 3, the obtainable torque decreases beyond 100% frequency because the V/Hz ratio just isn’t maintained. In an overspeed scenario, the load torque (pump) must be below the obtainable torque.
Before operating any piece of apparatus exterior of its rated pace range, it is important to contact the producer of the gear to discover out if this can be carried out safely and efficiently. For more info on variable pace pumping, refer to HI’s “Application Guideline for Variable Speed Pumping” at pumps.org.
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