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In some situations, working a motor beyond the bottom pole velocity is feasible and presents system benefits if the design is fastidiously examined. The pole speed of a motor is a operate of the quantity poles and the incoming line frequency. Image 1 presents the synchronous pole pace for 2-pole by way of 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 velocity. If the incoming line frequency does not change, the pace of the induction motor might be lower than these values by a percent to slip. So, to function the motor above the base pole velocity, the frequency must be elevated, which can be accomplished with a variable frequency drive (VFD).
One cause for overspeeding a motor on a pump is to make use of a slower rated velocity motor with a lower horsepower rating and operate it above base frequency to get the required torque at a decrease current. This allows the number of a VFD with a lower current rating to be used while still making certain passable control of the pump/motor over its desired working range. The lower current requirement of the drive can scale back the capital price of the system, relying on general system necessities.
The purposes the place the motor and the driven pump operate above their rated speeds can provide further circulate and pressure to the controlled system. This could result in a extra compact system whereas increasing its efficiency. While it might be potential to increase the motor’s velocity to twice its nameplate speed, it is more widespread that the utmost velocity is more limited.
The key to those applications is to overlay the pump speed torque curve and motor velocity torque to ensure the motor begins and functions throughout the whole operational velocity range with out overheating, stalling or creating any significant stresses on the pumping system.
Several factors additionally have 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 higher pace (and variable velocity in general) will increase the risk of resonant vibration due to a critical pace throughout the operating range.
The larger pace will end in further energy consumption. It is important to consider if the pump and drive prepare is rated for the higher energy.
Since the torque required by a rotodynamic pump increases in proportion to the sq. of velocity, the opposite major concern is to ensure that the motor can present enough torque to drive the load on the elevated velocity. When operated at a velocity under 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 constant V/Hz ratio keeps torque production stable. While it will be perfect to extend the voltage to the motor as it is run above its rated speed, the voltage of the alternating present (AC) power source limits the utmost voltage that is out there to the motor. Therefore, the voltage supplied to the motor can’t proceed to extend above the nameplate voltage as illustrated in Image 2. As shown in Image three, the available torque decreases beyond 100% frequency because the V/Hz ratio just isn’t maintained. In ไดอะแฟรม , the load torque (pump) must be beneath the out there torque.
Before working digital pressure gauge of equipment outside of its rated velocity range, it’s important to contact the manufacturer of the tools to determine if this can be done safely and efficiently. For extra information on variable velocity pumping, check with HI’s “Application Guideline for Variable Speed Pumping” at pumps.org.
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