In some cases, working a motor beyond the bottom pole velocity is possible and offers system advantages if the design is carefully examined. The pole velocity 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 within the U.S.). As illustrated, additional poles scale back the bottom pole speed. If the incoming line frequency doesn’t change, the velocity of the induction motor shall be less than these values by a % to slip. So, to operate the motor above the bottom pole speed, the frequency must be elevated, which may be accomplished with a variable frequency drive (VFD).
One purpose for overspeeding a motor on a pump is to make use of a slower rated pace motor with a lower horsepower rating and operate it above base frequency to get the required torque at a lower current. This enables the selection of a VFD with a decrease current ranking for use while still guaranteeing satisfactory management of the pump/motor over its desired working range. The lower present requirement of the drive can scale back the capital price of the system, depending on total system requirements.
The purposes the place the motor and the pushed pump function above their rated speeds can present extra move and stress to the controlled system. This may lead to a extra compact system whereas growing its effectivity. While it might be potential to increase the motor’s pace to twice its nameplate pace, it’s more frequent that the utmost pace is extra limited.
The key to those purposes is to overlay the pump velocity torque curve and motor velocity torque to make sure the motor starts and capabilities all through the entire operational speed range without overheating, stalling or creating any important stresses on the pumping system.
Several factors additionally have to be taken into account when considering such options:
Noise will enhance with velocity.
Bearing life or greasing intervals could additionally be decreased, or improved match bearings may be required.
ความหมายของเครื่องวัดความดัน (and variable velocity in general) will enhance the risk of resonant vibration because of a crucial pace within the operating range.
The higher velocity will end in additional energy consumption. It is essential to contemplate 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 sufficient torque to drive the load at the elevated pace. When operated at a speed under the rated pace of the motor, the volts per hertz (V/Hz) may be maintained as the frequency applied to the motor is increased. Maintaining a continuing V/Hz ratio keeps torque production steady. While it would be best to increase the voltage to the motor as it’s run above its rated speed, the voltage of the alternating present (AC) energy source limits the utmost voltage that’s available to the motor. Therefore, the voltage supplied to the motor can’t continue to increase above the nameplate voltage as illustrated in Image 2. As proven in Image 3, the obtainable torque decreases past one hundred pc frequency as a result of the V/Hz ratio is not maintained. In an overspeed situation, the load torque (pump) should be below the out there torque.
Before working any piece of apparatus outside of its rated pace range, it’s essential to contact the producer of the tools to discover out if this could be accomplished safely and effectively. For extra data on variable pace pumping, discuss with HI’s “Application Guideline for Variable Speed Pumping” at pumps.org.