protection of welding machine

Well first off you find out the current rating of the welder, then you choose a suitably-rated circuit breaker to protect it.

Ahh, that's it, it's not rocket science (why don't you know this, what are they teaching students now days?).

In addition to the selecting your circuit breaker on current rating of the welder, the breaker trip curve should be a D-curve for best results. The more common C-curve and B-curve breakers will be too prone to nuisance-tripping on the inrush current of the welder, but a D-curve is designed for motors and other highly inductive loads.

thanks, but it isn't correct answer

How about a 16A D-curve MCB (assuming 400V 3-ph ac supply and medium size industrial welder).

You don't give many details so why do you expect to get anything other than a general answer, specific answers like the above are only a guess.