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

In some cases, working a motor beyond the bottom pole velocity is feasible and offers system benefits if the design is fastidiously examined. The pole speed of a motor is a perform of the number poles and the incoming line frequency. Image 1 presents the synchronous pole speed for 2-pole through 12-pole motors at 50 hertz (Hz [common in Europe]) and 60 Hz (common within the U.S.). As illustrated, additional poles cut back the base pole speed. If the incoming line frequency doesn’t change, the velocity of the induction motor will be lower than these values by a % to slip. So, to operate pressure gauge octa above the base pole speed, the frequency must be increased, which can be accomplished with a variable frequency drive (VFD).
One purpose for overspeeding a motor on a pump is to make use of a slower rated velocity motor with a lower horsepower ranking and function it above base frequency to get the required torque at a decrease current. This enables the choice of a VFD with a decrease current score for use whereas nonetheless making certain passable control of the pump/motor over its desired working range. The lower present requirement of the drive can reduce the capital cost of the system, relying on general system requirements.
The purposes the place the motor and the pushed pump function above their rated speeds can provide extra circulate and stress to the controlled system. This may lead to a more compact system while rising its effectivity. While it could be attainable to increase the motor’s pace to twice its nameplate pace, it’s more frequent that the utmost velocity is more limited.
The key to those applications is to overlay the pump velocity torque curve and motor pace torque to ensure the motor starts and capabilities throughout the entire operational speed vary with out overheating, stalling or creating any important stresses on the pumping system.
Several points also must be taken under consideration when considering such options:
Noise will enhance with velocity.
Bearing life or greasing intervals could additionally be decreased, or improved match bearings could additionally be required.
The higher velocity (and variable velocity in general) will enhance the chance of resonant vibration because of a crucial velocity inside the operating vary.
The larger velocity will lead to extra power consumption. diaphragm seal is essential to contemplate if the pump and drive practice is rated for the upper energy.
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 sufficient torque to drive the load on the elevated velocity. When operated at a velocity beneath the rated speed of the motor, the volts per hertz (V/Hz) can be maintained as the frequency applied to the motor is increased. Maintaining a relentless V/Hz ratio keeps 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 present (AC) energy source limits the maximum voltage that’s out there to the motor. Therefore, pressure gauge supplied to the motor can’t continue to increase above the nameplate voltage as illustrated in Image 2. As shown in Image 3, the out there torque decreases past 100% frequency as a result of the V/Hz ratio is not maintained. In an overspeed situation, the load torque (pump) must be beneath the available torque.
Before operating any piece of kit outside of its rated velocity vary, it’s essential to contact the producer of the tools to determine if this may be accomplished safely and efficiently. For extra data on variable pace pumping, discuss with HI’s “Application Guideline for Variable Speed Pumping” at pumps.org.
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