In some instances, working a motor beyond the bottom pole pace is feasible and presents system advantages if the design is carefully examined. The pole pace of a motor is a function of the number poles and the incoming line frequency. Image 1 presents the synchronous pole pace 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 reduce the base pole pace. If the incoming line frequency does not change, the velocity of the induction motor will be less than these values by a percent to slide. So, to function the motor above the base pole velocity, the frequency must be increased, which may be done with a variable frequency drive (VFD).
One purpose for overspeeding a motor on a pump is to use a slower rated speed motor with a lower horsepower ranking and operate it above base frequency to get the required torque at a decrease present. This enables the choice of a VFD with a decrease present rating for use while nonetheless guaranteeing passable management of the pump/motor over its desired working vary. The decrease present requirement of the drive can reduce the capital price of the system, depending on general system requirements.
The purposes the place the motor and the pushed pump function above their rated speeds can present further move and pressure to the managed system. This might result in a more compact system while growing its effectivity. While it may be potential to increase the motor’s speed to twice its nameplate velocity, it is extra frequent that the utmost velocity is extra limited.
The key to those applications is to overlay the pump velocity torque curve and motor pace torque to make sure the motor starts and capabilities throughout the complete operational speed range with out overheating, stalling or creating any important stresses on the pumping system.
Several points also must be taken into consideration when considering such options:
Noise will enhance with speed.
Bearing life or greasing intervals may be decreased, or improved fit bearings could also be required.
The greater velocity (and variable velocity in general) will increase the risk of resonant vibration as a end result of a important pace within the operating range.
The higher velocity will result in additional power consumption. It is essential to contemplate if the pump and drive train is rated for the upper power.
Since the torque required by a rotodynamic pump increases in proportion to the square of velocity, the opposite main concern is to make sure that the motor can provide enough torque to drive the load on the elevated velocity. When operated at a pace beneath the rated pace of the motor, the volts per hertz (V/Hz) can be maintained as the frequency applied to the motor is increased. Maintaining a continuing V/Hz ratio retains torque manufacturing stable. While it would be best to increase the voltage to the motor as it’s run above its rated velocity, the voltage of the alternating present (AC) energy supply limits the maximum voltage that’s out there to the motor. Therefore, เกจวัดแรงดันน้ำมันเบนซิน supplied to the motor can’t proceed to extend above the nameplate voltage as illustrated in Image 2. As shown in Image 3, the out there torque decreases beyond one hundred pc frequency as a end result of the V/Hz ratio isn’t maintained. In an overspeed situation, the load torque (pump) should be beneath the out there torque.
Before operating any piece of apparatus outdoors of its rated speed vary, it is important to contact the manufacturer of the tools to determine if this can be done safely and efficiently. For extra info on variable pace pumping, check with HI’s “Application Guideline for Variable Speed Pumping” at pumps.org.
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