I am using an AutoTransformer to start a 300hp 4160V motor. The FLA of the motor is 41A and the LRC of the motor is 256A. The AutoTransformer is tapped at 50% voltage and the time between switching from Autotransformer contacts to across the line contacts is 9 seconds.
I have recently had some trouble when trying to start this motor on several occasions. The motor relay keeps tripping on overload and I am having trouble understanding why.
The one thing that I have noticed is that when I start the motor, the current draw is 153 A for the first nine seconds while the motor is running across the autotransformer at 50%. However after nine seconds when the across the line contact kicks in the current draw goes up to 324A, and the motor is tripping out due to the fact that this is 9X FLA.
The thing that I dont understand is why we are seeing 324A on the start when the LRC of the motor is only 256A. Also I dont understand why we are seeing this current while we are reduce voltage starting the motor. The starting acceleration of the motor is about 13.5s. Any reason why we are seeing this high current when the across the line contact kicks in?
I have recently had some trouble when trying to start this motor on several occasions. The motor relay keeps tripping on overload and I am having trouble understanding why.
The one thing that I have noticed is that when I start the motor, the current draw is 153 A for the first nine seconds while the motor is running across the autotransformer at 50%. However after nine seconds when the across the line contact kicks in the current draw goes up to 324A, and the motor is tripping out due to the fact that this is 9X FLA.
The thing that I dont understand is why we are seeing 324A on the start when the LRC of the motor is only 256A. Also I dont understand why we are seeing this current while we are reduce voltage starting the motor. The starting acceleration of the motor is about 13.5s. Any reason why we are seeing this high current when the across the line contact kicks in?