In some instances, working a motor beyond the bottom pole velocity is feasible and offers system advantages if the design is carefully examined. The pole pace of a motor is a function of the quantity poles and the incoming line frequency. pressure gauge 10 bar presents the synchronous pole velocity for 2-pole via 12-pole motors at 50 hertz (Hz [common in Europe]) and 60 Hz (common within the U.S.). As illustrated, further poles scale back the base pole pace. If the incoming line frequency does not change, the pace of the induction motor might be less than these values by a % to slip. So, to function the motor above the bottom pole velocity, the frequency needs to be increased, which could be carried out with a variable frequency drive (VFD).
One purpose 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 allows the choice of a VFD with a decrease current rating for use while nonetheless making certain satisfactory control of the pump/motor over its desired working vary. The lower current requirement of the drive can cut back the capital value of the system, depending on general system requirements.
The applications the place the motor and the driven pump function above their rated speeds can provide extra flow and pressure to the controlled system. This could result in a extra compact system while growing its effectivity. While it could be potential to increase the motor’s pace to twice its nameplate pace, it’s extra frequent that the maximum pace is more limited.
The key to those applications is to overlay the pump velocity torque curve and motor pace torque to ensure the motor starts and capabilities all through the whole operational speed range without overheating, stalling or creating any important stresses on the pumping system.
Several points also must be taken into account when considering such solutions:
Noise will improve with velocity.
Bearing life or greasing intervals may be decreased, or improved match bearings could also be required.
The larger velocity (and variable speed in general) will increase the danger of resonant vibration as a end result of a important speed inside the working vary.
digital pressure gauge will end in additional power consumption. It is necessary to consider if the pump and drive prepare is rated for the higher energy.
Since the torque required by a rotodynamic pump will increase in proportion to the sq. of velocity, the opposite major concern is to make certain that the motor can present enough torque to drive the load at the elevated speed. When operated at a velocity beneath the rated velocity of the motor, the volts per hertz (V/Hz) may be maintained as the frequency utilized to the motor is increased. Maintaining a continuing V/Hz ratio keeps torque manufacturing steady. 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) energy source limits the utmost voltage that’s available to the motor. Therefore, the voltage supplied to the motor can’t proceed 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 just isn’t maintained. In diaphragm seal of affairs, the load torque (pump) must be beneath the out there torque.
Before working any piece of kit exterior of its rated speed vary, it is important to contact the producer of the tools to determine if this may be done safely and effectively. For extra information on variable speed pumping, refer to HI’s “Application Guideline for Variable Speed Pumping” at pumps.org.
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