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Adventech Explains The Maxeff Inrush Current and LRC (Locked Rotor Current) Difference

SEM, UTI | June 15, 2021

PR Newswire

FLORENCE, Ala. , June 15, 2021 /PRNewswire/ --

Inrush Current Description:
"Instantaneous peak Inrush current is a momentary current transient that occurs immediately (within half an AC cycle) after contact closure. Locked rotor current is the root-mean-square (RMS) current that is established following the peak Inrush; the current remains near the locked rotor value during acceleration until the motor approaches its operating speed. The terms Inrush current and starting current are often used to mean locked rotor current." Ref. U.S. Department of Energy

Standard Motor:

Limitation and Disadvantages:

High Inrush current can cause nuisance tripping of protective devices or cause motor damage.
It can also cause voltage dips in the supply line (which can affect other equipment), or even prevent the motor from starting properly.
High Inrush current also leads to high torque production at start up — sometimes as much as twice the rated torque — which can cause sudden, severe acceleration that damages mechanical loads.
The amount of current drawn by the motor during startup is also influenced by the resistance of the stator windings. Newer, high-efficiency motors — such as IE3 premium efficiency versions — have lower winding resistance (to reduce I 2 R losses ), so Inrush current can be an even more significant problem in these designs than in older, lower-efficiency motors.

MAXEFF Motor:
The Maxeff motor is a combination of two circuits - motor and generator. Whereas the motor circuit is directly connected to power and the generator circuit is 180 phase out. When the motor is connected DOL (Direct On Line), the motoring circuits come into action which draws a lower current since it utilizes only 2/3 rd of the winding, limiting higher Inrush current. Once the generator circuit is excited, the motor comes into a full circuit. At that point, the motor's speed is increased which does not demand a high Inrush current and still has higher LRC (Locked Rotor Current). * Refer to Advanced Energy Test Report . As the motor obtains full speed and is stabilized, LRC is settled to a normal rated current like that of a standard motor. See Figure 2 .

The switching phenomenon is exclusive to the Maxeff motor as it limits the high Inrush current and still has higher LRC (Locked Rotor Current), as well as torque, as compared to a standard premium motor.

Advantage Over a Standard Motor:

i) Protection against nuisance tripping of protective devices

ii) Voltage Dips

iii) Load Protection

iv) Maxeff motors have lower winding resistance (to reduce I²R losses ). Due to its two internal circuits (motor and generator) and its switching phenomenon, it overcomes the high Inrush current compared to that of standard premium motors.

*Advanced Energy Report can be read in its entirety at www.adventechinc.com

Media Contact: Kasidhe Pruet, 256-712-5783, sales@adventechinc.com