an induction motor always getting trip

Circuit breakers operate off a time-current curve, if you have not installed a circuit breaker with the correct curve (such as a D-curve circuit breaker designed for protecting motors and other high inrush current loads) then you will likely experience problem circuit breaker tripping.

Check your circuit breaker is the correct type and current rating for your application.

You failed to adequately state how you are starting the motor, but by virtue of your saying it is "change over to Delta" I can assume you are using a Star-Delta motor starting scheme. One of the big problems with Star-Delta as a starting method is exactly what you are experiencing; sometimes if the transition happens at the wrong point in the sine wave, there can be a very high current spike, upwards of 2000 times the motor FLC! There really is nothing you can do about it without changing the starter. Open Transition Star-Delta is really an inappropriate starting method for a high inertia load such as that because during transition, the motor slows down which can exacerbate the problem.

You have 2 choices: 1) Convert that starter to what is called a "Closed Transition Star-Delta", which means adding a 4th contactor and an external resistor bank. the resistors will get red hot during the moment or two they are in the circuit, so you must have free air flow around them to prevent over heating. this makes it a bad choice for dirty environments such as pulverisors. 2) Get rid of the Star-Delta starter and buy a Solid State Soft Starter. it is MUCH better for your motor and mechanical power train components because there is no transition spike of torque, and it will not cause your breaker to trip and cause a loss of production. In the long run, it will end up less expensive to own.

What is your incoming MCCB amps rated and it KA rated?

What is your star delta timer setting, how many second you set for it to changeover.

Is your motor direct drive the pendulum pulvarizor or by belts.

We need this information for your answer. Sometime, we do have some problem with the start delta during changeover.