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

In some situations, working a motor past the base pole pace is feasible and offers system advantages if the design is rigorously examined. The pole speed of a motor is a function 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 in the U.S.). As illustrated, extra poles cut back the base pole speed. If the incoming line frequency doesn’t change, the velocity of the induction motor shall be lower than these values by a % to slip. So, to function the motor above the bottom pole pace, the frequency needs to be increased, which could be done with a variable frequency drive (VFD).
One purpose for overspeeding a motor on a pump is to use a slower rated pace motor with a decrease horsepower rating and operate it above base frequency to get the required torque at a decrease present. This allows the number of a VFD with a lower current score for use while nonetheless making certain passable management of the pump/motor over its desired operating range. The decrease current requirement of the drive can reduce the capital value of the system, depending on general system necessities.
The purposes where the motor and the pushed pump operate above their rated speeds can provide further circulate and strain to the controlled system. This might end in a extra compact system whereas rising its efficiency. While it might be possible to extend the motor’s speed to twice its nameplate velocity, it’s extra frequent that the maximum velocity is more restricted.
The key to those applications is to overlay the pump speed torque curve and motor pace torque to make sure the motor begins and features throughout the complete operational pace range without overheating, stalling or creating any vital stresses on the pumping system.
Several points additionally must be taken into account when contemplating such solutions:
Noise will improve with velocity.
Bearing life or greasing intervals may be reduced, or improved fit bearings could additionally be required.
The higher speed (and variable velocity in general) will improve the danger of resonant vibration as a end result of a crucial pace inside the operating range.
The larger velocity will end in further energy consumption. It is necessary to contemplate if the pump and drive train is rated for the upper energy.
Since the torque required by a rotodynamic pump increases in proportion to the square of pace, the opposite major concern is to ensure that the motor can provide sufficient torque to drive the load at the increased velocity. When operated at a speed under the rated pace of the motor, the volts per hertz (V/Hz) can be maintained because the frequency utilized to the motor is increased. Maintaining a relentless V/Hz ratio keeps torque production steady. While it will be perfect to increase the voltage to the motor as it’s run above its rated pace, the voltage of the alternating present (AC) energy source limits the maximum voltage that is obtainable to the motor. Therefore, pressure gauge หน้าปัด 4 นิ้ว supplied to the motor can’t proceed to increase above the nameplate voltage as illustrated in Image 2. As shown in Image 3, the out there torque decreases past one hundred pc frequency as a result of the V/Hz ratio isn’t maintained. In an overspeed scenario, the load torque (pump) must be under the available torque.
Before operating any piece of equipment outdoors of its rated pace vary, it is essential to contact the manufacturer of the tools to find out if this can be accomplished safely and efficiently. For more data on variable speed pumping, check with HI’s “Application Guideline for Variable Speed Pumping” at pumps.org.
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