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

In some instances, operating a motor beyond the base pole velocity is feasible and presents system benefits if the design is carefully examined. The pole pace of a motor is a perform of the number poles and the incoming line frequency. differential pressure gauge ราคา presents the synchronous pole velocity 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, extra poles reduce the base pole velocity. If the incoming line frequency doesn’t change, the speed of the induction motor shall be lower than these values by a % to slip. So, to function the motor above the base pole velocity, the frequency must be increased, which may be carried out with a variable frequency drive (VFD).
One reason for overspeeding a motor on a pump is to use a slower rated speed motor with a lower horsepower rating and function it above base frequency to get the required torque at a lower present. This allows the choice of a VFD with a decrease present score to be used whereas nonetheless ensuring satisfactory control of the pump/motor over its desired working vary. The decrease current requirement of the drive can scale back the capital cost of the system, relying on total system requirements.
The purposes where the motor and the pushed pump function above their rated speeds can present further move and stress to the managed system. This may end in a extra compact system while rising its efficiency. While it may be potential to increase the motor’s speed to twice its nameplate velocity, it is more widespread that the utmost velocity is extra restricted.
The key to these functions is to overlay the pump velocity torque curve and motor pace torque to ensure the motor begins and features all through the whole operational speed vary with out overheating, stalling or creating any important stresses on the pumping system.
Several factors also need to be taken into account when considering such solutions:
Noise will increase with velocity.
Bearing life or greasing intervals may be decreased, or improved match bearings could also be required.
The higher velocity (and variable speed in general) will increase the risk of resonant vibration because of a important speed within the working vary.
The higher velocity will result in further energy consumption. It is essential to contemplate if the pump and drive prepare is rated for the upper power.
Since the torque required by a rotodynamic pump will increase in proportion to the sq. of velocity, the opposite major concern is to guarantee that the motor can provide sufficient torque to drive the load at the increased pace. When operated at a velocity below 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 continuing 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 velocity, the voltage of the alternating current (AC) energy supply limits the maximum voltage that is obtainable to the motor. Therefore, the voltage provided to the motor can’t proceed to extend above the nameplate voltage as illustrated in Image 2. As proven in Image 3, the available torque decreases beyond one hundred pc frequency as a outcome of the V/Hz ratio is not maintained. In an overspeed state of affairs, the load torque (pump) must be under the available torque.
Before working any piece of apparatus outdoors of its rated pace range, it is essential to contact the producer of the equipment to discover out if this can be carried out safely and efficiently. For extra information on variable speed pumping, discuss with HI’s “Application Guideline for Variable Speed Pumping” at pumps.org.
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