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What is the reason causes motor tripped?

You might want to look at the application and see if the motor was properly designed for your application. Obtain a load curve from the pump manufacturer under your typical site conditions (ie temperature, pressure, etc.) Also obtain a curve for worst case conditions. Send both curves to the motor manufacturer and tell them that you want to start the load with a Soft Starter. First ask them if the load can be started with a 65% voltage tap. Ask for a starting torque curve for 65%. Ask if the load can be started with limiting the current to 400%(389amp x 4 = 1556amp). Ask for a starting torque curve limiting current to 400%. Compare the results and see if there is sufficient torque to start the load and sufficient torque margin. Assuming you have not found a problem with the torque. Ask for a time vs current curve under all the conditions as stated above. You will need these curves to properly setup and coordinate your relaying.

Usually overcurrent (more than the starting current) or long time with starting current can make trip in starting, for some different problems (mechanical or electrical).
Was the speed zero or no when the protection trips?
If the problem is the mechanical load (as high load torque or inertia/viscosity of the load) the starting current value will be normal, but will maintain during long time and it can be a problem, maybe adjust the time to trip. The soft-starter voltage and or current limitation settings must be in according to the required acceleration time, too.
Which device provided the command to trip? A soft starter internal protection or an external relay gives the trip? If the soft-starter gives the trip, usually it has a display and show a code number of the error on trip and you can check it in a soft-starter manual.
First I suggest you to check the settings of the protections that gives the command to trip (soft-starter or relay).

Another cause assuming reduced voltage start, star/delta, autotransformer, primary resistance, soft start etc., could be that the motor is not delivering torque sufficient to accelerate the connected load to speed. That is the starting current and starting time under RVS conditions exceeds that permissible by the overload curve. A more advanced protection strategy such as motor thermal modeling may be required. Motor thermal modeling allows the user to 'match' the curves of the protection device to the connected motor.

If the motor is taking three phase balance overcurrent than most of the time it is seeing heavy overloading. The only electrical condition in which it will take that heavy balanced overcurrent is the one in which the winding are partially burnt but showing balance resistance in all three phases, which is highly unusual. Your information is incomplete. If you give more information on current pattern and the terminal voltage then I would be able to comment on it more.

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