In some situations, working a motor beyond the bottom pole speed is feasible and provides system benefits 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 pace 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 scale back the bottom pole speed. If the incoming line frequency doesn’t change, the speed of the induction motor shall be less than these values by a % to slide. So, to function the motor above the bottom pole speed, the frequency needs to be elevated, which can be accomplished with a variable frequency drive (VFD).
One purpose for overspeeding a motor on a pump is to use a slower rated velocity motor with a lower horsepower score and operate it above base frequency to get the required torque at a decrease current. This permits the choice of a VFD with a lower present ranking for use whereas still making certain satisfactory control of the pump/motor over its desired working range. The lower current requirement of the drive can cut back the capital value of the system, depending on general system requirements.
The purposes the place the motor and the driven pump operate above their rated speeds can present additional circulate and pressure to the managed system. This might end in a extra compact system while rising its effectivity. While it might be possible to extend the motor’s velocity to twice its nameplate speed, it is more frequent that the utmost pace is more restricted.
The key to these functions is to overlay the pump pace torque curve and motor velocity torque to make sure the motor starts and functions all through the complete operational velocity range with out overheating, stalling or creating any vital stresses on the pumping system.
Several factors also need to be taken under consideration when considering such solutions:
Noise will improve with speed.
Bearing life or greasing intervals may be lowered, or improved fit bearings may be required.
The larger speed (and variable velocity in general) will improve the danger of resonant vibration as a result of a crucial velocity within the working vary.
The greater speed will end in additional energy consumption. It is essential to consider if the pump and drive train is rated for the higher energy.
Since เกจวัดแรงดันน้ําไทวัสดุ required by a rotodynamic pump will increase in proportion to the square of pace, the other main concern is to ensure that the motor can present enough torque to drive the load at the increased velocity. When operated at a speed under the rated speed of the motor, the volts per hertz (V/Hz) can be maintained as the frequency applied to the motor is elevated. Maintaining a relentless V/Hz ratio retains torque manufacturing steady. While it might be best to increase the voltage to the motor as it’s run above its rated pace, the voltage of the alternating present (AC) energy supply limits the maximum voltage that’s out there to the motor. Therefore, the voltage equipped to the motor can’t continue to extend above the nameplate voltage as illustrated in Image 2. As proven in Image three, the available torque decreases beyond 100% frequency because the V/Hz ratio isn’t maintained. In เกจแรงดันสูง of affairs, the load torque (pump) have to be below the out there torque.
Before operating any piece of apparatus outdoors of its rated velocity range, it is essential to contact the producer of the equipment to find out if this could be accomplished safely and efficiently. For more data on variable speed pumping, refer to HI’s “Application Guideline for Variable Speed Pumping” at pumps.org.
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