In some cases, operating a motor past the bottom pole velocity is possible and provides system advantages if the design is fastidiously examined. The pole velocity of a motor is a function of the number 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, extra poles scale back the base pole pace. If the incoming line frequency doesn’t change, the speed of the induction motor might be lower than these values by a percent to slide. So, to operate the motor above the bottom pole velocity, the frequency needs to be increased, which could be done with a variable frequency drive (VFD).
One reason for overspeeding a motor on a pump is to use a slower rated pace motor with a lower horsepower ranking and function it above base frequency to get the required torque at a decrease current. This enables the selection of a VFD with a decrease current ranking for use while nonetheless guaranteeing passable control of the pump/motor over its desired operating vary. The lower present requirement of the drive can scale back the capital value of the system, depending on overall system requirements.
The functions where the motor and the driven pump operate above their rated speeds can provide additional circulate and stress to the controlled system. ชนิดของpressuregauge might end in a extra compact system while increasing its efficiency. While it may be attainable to extend the motor’s velocity to twice its nameplate pace, it is extra common that the maximum velocity is more restricted.
The key to these functions is to overlay the pump velocity torque curve and motor pace torque to ensure the motor starts and features throughout the entire operational speed vary without overheating, stalling or creating any vital stresses on the pumping system.
Several points also must be taken into account when considering such solutions:
Noise will increase with velocity.
Bearing life or greasing intervals may be reduced, or improved match bearings may be required.
The greater pace (and variable speed in general) will enhance the danger of resonant vibration because of a critical speed throughout the operating range.
The greater speed will end in further energy consumption. It is necessary to think about if the pump and drive practice is rated for the higher power.
Since the torque required by a rotodynamic pump increases in proportion to the square of pace, the opposite main concern is to guarantee that the motor can present enough torque to drive the load on the increased pace. When operated at a speed under the rated velocity of the motor, the volts per hertz (V/Hz) could be maintained because the frequency applied to the motor is elevated. Maintaining a relentless V/Hz ratio retains torque manufacturing secure. While it would be best to extend the voltage to the motor as it’s run above its rated speed, the voltage of the alternating current (AC) energy supply limits the maximum voltage that’s obtainable 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 3, the obtainable torque decreases beyond 100 percent frequency because the V/Hz ratio is not maintained. In an overspeed scenario, the load torque (pump) must be below the available torque.
Before operating any piece of equipment outdoors of its rated pace vary, it is important to contact the manufacturer of the equipment to determine if this may be accomplished safely and efficiently. For more information on variable speed pumping, refer to HI’s “Application Guideline for Variable Speed Pumping” at pumps.org.