In Which Applications Can a Pump Motor Be Operated Above Base Speed?

In some situations, operating a motor past the bottom pole speed is feasible and provides system advantages if the design is carefully examined. Bonanza of a motor is a perform of the quantity poles and the incoming line frequency. Image 1 presents the synchronous pole pace for 2-pole through 12-pole motors at 50 hertz (Hz [common in Europe]) and 60 Hz (common within the U.S.). As illustrated, extra poles reduce the base pole velocity. If the incoming line frequency does not change, the speed of the induction motor might be less than these values by a p.c to slide. So, to operate the motor above the bottom pole speed, 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 make use of a slower rated velocity motor with a lower horsepower ranking and operate it above base frequency to get the required torque at a lower current. This enables the choice of a VFD with a lower current rating for use while nonetheless guaranteeing passable control of the pump/motor over its desired working vary. The lower current requirement of the drive can reduce the capital cost of the system, relying on overall system necessities.
The purposes the place the motor and the driven pump function above their rated speeds can provide extra move and pressure to the managed system. This may lead to a extra compact system whereas rising its effectivity. While it may be potential to extend the motor’s speed to twice its nameplate speed, it is extra common that the maximum velocity is extra restricted.
The key to those applications is to overlay the pump velocity torque curve and motor speed torque to make sure the motor starts and functions all through the complete operational speed range with out overheating, stalling or creating any important stresses on the pumping system.
Several points additionally must be taken into account when contemplating such solutions:
Noise will enhance with speed.
Bearing Skyrocket or greasing intervals could also be decreased, or improved match bearings may be required.
The greater speed (and variable velocity in general) will improve the risk of resonant vibration as a outcome of a important pace throughout the operating range.
The larger speed will lead to extra power consumption. It is important to consider if the pump and drive train is rated for the higher energy.
Since the torque required by a rotodynamic pump increases in proportion to the sq. of pace, the other main concern is to ensure that the motor can provide enough torque to drive the load at the increased pace. When operated at a pace under the rated pace of the motor, the volts per hertz (V/Hz) could be maintained because the frequency applied to the motor is elevated. Maintaining a continuing V/Hz ratio keeps torque production secure. While it will be ideal to increase the voltage to the motor as it’s run above its rated velocity, the voltage of the alternating current (AC) power source limits the maximum voltage that’s out there to the motor. Therefore, the voltage provided to the motor cannot continue to extend above the nameplate voltage as illustrated in Image 2. As shown in Image 3, the out there torque decreases past one hundred pc frequency because the V/Hz ratio is not maintained. In an overspeed state of affairs, the load torque (pump) must be under the out there torque.
Before working any piece of apparatus outside of its rated speed vary, it’s essential to contact the manufacturer of the gear to determine if this might be accomplished safely and efficiently. For extra information on variable pace pumping, refer to HI’s “Application Guideline for Variable Speed Pumping” at pumps.org.
Share

Leave a Comment