primary resistance reduced voltage motor starting question
primary resistance reduced voltage motor starting question
(OP)
Having a little trouble finding a solution to this question.
The DOL starting current of a motor is 90A at 400V. If a primary resistance starter is used, what must the voltage across the motor fall to if the starting current is to be reduced to 30A?
Any help would be much appreciated.
The DOL starting current of a motor is 90A at 400V. If a primary resistance starter is used, what must the voltage across the motor fall to if the starting current is to be reduced to 30A?
Any help would be much appreciated.





RE: primary resistance reduced voltage motor starting question
Where VL-L it is the line voltage Rst is the stator resistance R’rot it is the rotor resistance referred to stator, Xsst is the stator leakage magnetic flux reactance and X’srot it is the rotor leakage reactance referred to stator.
If the frequency is constant then the denominator is constant and the current is proportional with the supply voltage.
In order to produce 30 A then the supply voltage has to be 400/3=167 V.
But the motor produced torque will drop with the square of voltage. If at rated voltage the start toque is 1.5 times the rated torque now will be 1.5/9=0.167 times the rated. I wonder if the motor could start now.
Only if you would reduce the frequency in the same time you could maintain the torque as was before.
RE: primary resistance reduced voltage motor starting question
"Will work for (the memory of) salami"
RE: primary resistance reduced voltage motor starting question
RE: primary resistance reduced voltage motor starting question
RE: primary resistance reduced voltage motor starting question
RE: primary resistance reduced voltage motor starting question
1947 is calling and wants its RV technology back perhaps?
"Will work for (the memory of) salami"