In some cases, working a motor beyond the bottom pole velocity is possible and presents system benefits if the design is fastidiously examined. The pole velocity of a motor is a operate 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, further poles reduce the base pole velocity. If the incoming line frequency does not change, the pace of the induction motor might be less than these values by a % to slide. So, to operate the motor above the base pole velocity, the frequency must be elevated, which can be done with a variable frequency drive (VFD).
One cause for overspeeding a motor on a pump is to use a slower rated speed motor with a lower horsepower ranking and function it above base frequency to get the required torque at a decrease current. This permits the choice of a VFD with a lower current score for use while nonetheless ensuring passable control of the pump/motor over its desired operating vary. The decrease current requirement of the drive can scale back the capital price of the system, relying on overall system requirements.
The functions where the motor and the driven pump function above their rated speeds can present extra flow and pressure to the controlled system. This could lead to a extra compact system whereas increasing its efficiency. While it might be attainable to increase the motor’s speed to twice its nameplate pace, it’s more frequent that the maximum pace is extra limited.
The key to those purposes is to overlay the pump speed torque curve and motor pace torque to make sure the motor begins and capabilities all through the entire operational speed vary with out overheating, stalling or creating any vital stresses on the pumping system.
Several factors additionally need to be taken into consideration when contemplating such solutions:
Noise will enhance with pace.
Bearing life or greasing intervals could also be lowered, or improved match bearings may be required.
The larger velocity (and variable pace in general) will improve the danger of resonant vibration due to a critical pace within the working range.
The greater speed will result in additional power consumption. It is essential to consider if the pump and drive practice is rated for the upper energy.
Since the torque required by a rotodynamic pump increases in proportion to the sq. of speed, the other main concern is to make sure that the motor can provide enough torque to drive the load at the elevated pace. When operated at a pace under the rated pace of the motor, the volts per hertz (V/Hz) can be maintained as the frequency utilized to the motor is increased. Maintaining a relentless V/Hz ratio keeps torque production steady. While it might be best to extend the voltage to the motor as it’s run above its rated pace, the voltage of the alternating present (AC) power source limits the maximum voltage that is out there to the motor. Therefore, the voltage supplied to the motor can not continue to increase 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 is not maintained. In ตัววัดแรงดันน้ำ , the load torque (pump) have to be below the out there torque.
Before working any piece of kit outdoors of its rated speed vary, it is important to contact the manufacturer of the gear to discover out if this might be carried out safely and efficiently. For extra information on variable speed pumping, check with HI’s “Application Guideline for Variable Speed Pumping” at pumps.org.