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In some cases, operating a motor past the base pole speed is possible and presents system advantages if the design is carefully examined. The pole speed of a motor is a function of the quantity poles and the incoming line frequency. Image 1 presents the synchronous pole velocity for 2-pole via 12-pole motors at 50 hertz (Hz [common in Europe]) and 60 Hz (common in the U.S.). As illustrated, additional poles reduce the base pole speed. If the incoming line frequency does not change, the pace of the induction motor will be lower than these values by a percent to slip. So, to function the motor above the base pole speed, the frequency must be elevated, which may be done with a variable frequency drive (VFD).
One cause for overspeeding a motor on a pump is to use a slower rated pace motor with a lower horsepower rating and operate it above base frequency to get the required torque at a decrease present. This permits the choice of a VFD with a decrease present score to be used whereas nonetheless making certain passable management of the pump/motor over its desired working vary. เพรสเชอร์เกจวัดแรงดันน้ำ of the drive can scale back the capital price of the system, relying on total system necessities.
The applications where the motor and the driven pump operate above their rated speeds can provide additional move and pressure to the managed system. This may lead to a more compact system whereas growing its effectivity. While it could be possible to increase the motor’s velocity to twice its nameplate speed, it is extra widespread that the utmost velocity is more restricted.
The key to those applications is to overlay the pump speed torque curve and motor pace torque to ensure the motor starts and functions all through the entire operational speed range without overheating, stalling or creating any important stresses on the pumping system.
Several factors also need to be taken under consideration when considering such options:
Noise will improve with pace.
Bearing life or greasing intervals could additionally be decreased, or improved fit bearings may be required.
The greater velocity (and variable speed in general) will increase the risk of resonant vibration due to a important speed throughout the operating vary.
The higher pace will result in further energy consumption. It is important to contemplate if the pump and drive train is rated for the upper power.
Since the torque required by a rotodynamic pump increases in proportion to the square of pace, the opposite major concern is to guarantee that the motor can provide enough torque to drive the load on the elevated velocity. When operated at a speed beneath the rated velocity of the motor, the volts per hertz (V/Hz) can be maintained because the frequency applied to the motor is elevated. Maintaining a constant V/Hz ratio keeps torque manufacturing steady. While it would be perfect to extend the voltage to the motor as it’s run above its rated speed, the voltage of the alternating current (AC) power source limits the maximum voltage that’s out there to the motor. Therefore, the voltage equipped to the motor can not proceed to increase above the nameplate voltage as illustrated in Image 2. As proven in Image 3, the out there torque decreases past 100% frequency as a outcome of the V/Hz ratio isn’t maintained. In an overspeed situation, the load torque (pump) should be below the available torque.
Before working any piece of kit outdoors of its rated velocity range, it is essential to contact the manufacturer of the gear to determine if this may be accomplished safely and efficiently. For extra info on variable velocity pumping, discuss with HI’s “Application Guideline for Variable Speed Pumping” at pumps.org.
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