In some instances, working a motor past the bottom pole pace is possible and provides system advantages if the design is carefully examined. The pole speed of a motor is a perform of the quantity poles and the incoming line frequency. Image 1 presents the synchronous pole speed for 2-pole via 12-pole motors at 50 hertz (Hz [common in Europe]) and 60 Hz (common in the U.S.). As illustrated, further poles scale back the bottom pole velocity. If the incoming line frequency does not change, the pace of the induction motor shall be lower than these values by a p.c to slip. So, to operate the motor above the base pole pace, the frequency needs to be increased, which could be carried out with a variable frequency drive (VFD).
One cause for overspeeding a motor on a pump is to use a slower rated pace motor with a decrease horsepower score and operate it above base frequency to get the required torque at a lower current. This allows the number of a VFD with a decrease present ranking for use while nonetheless ensuring satisfactory control of the pump/motor over its desired working vary. The lower present requirement of the drive can reduce the capital value of the system, depending on general system requirements.
The functions the place the motor and the pushed pump function above their rated speeds can present additional circulate and pressure to the controlled system. This may end in a extra compact system whereas increasing its efficiency. While it could be potential to extend the motor’s pace to twice its nameplate pace, it is more frequent that the utmost speed is more limited.
เกจแรงดัน to those applications is to overlay the pump speed torque curve and motor velocity torque to ensure the motor starts and capabilities all through the entire operational velocity range with out overheating, stalling or creating any significant stresses on the pumping system.
Several factors also have to be taken into account when considering such options:
Noise will improve with velocity.
Bearing life or greasing intervals may be lowered, or improved match bearings may be required.
The larger speed (and variable velocity in general) will improve the danger of resonant vibration due to a crucial speed within the operating vary.
The higher velocity will end in extra energy consumption. It is necessary to suppose about if the pump and drive prepare is rated for the upper power.
Since เกจวัดความดันpressuregauge required by a rotodynamic pump increases in proportion to the square of velocity, the other major concern is to make certain that the motor can present sufficient torque to drive the load at the increased velocity. When operated at a velocity below the rated pace of the motor, the volts per hertz (V/Hz) may be maintained as the frequency utilized to the motor is elevated. Maintaining a continuing V/Hz ratio keeps torque manufacturing secure. While it would be ideal 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 maximum voltage that’s obtainable 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 three, the out there torque decreases past one hundred pc frequency because the V/Hz ratio just isn’t maintained. In an overspeed situation, the load torque (pump) must be under the obtainable torque.
Before operating any piece of apparatus exterior of its rated velocity range, it is important to contact the producer of the tools to determine if this may be accomplished safely and effectively. For more data on variable velocity pumping, check with HI’s “Application Guideline for Variable Speed Pumping” at pumps.org.
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