Do the power ratings on the nameplate of an AC motor indicate electrical or mechanical power?
The power that can be read on the name space is the mechanical power you can take from the shaft of the motor. What you calculated is the electrical power that you put in the motor. There has to be a difference due to mechanical/electrical losses (friction, heat etc.) in the motor.

Concerning the 30 hp: I think 1 hp = 736 W, so 30 hp =22080 Watts which is close enough to 22 kW. 

EDIT 

According to their formula: $$ HP = \frac{1,73* E *I * Eff*PF}{746} = \frac{1,73 * 380 V * 47 A * (\frac {22 kW}{24,75 kW}) * 0,8}{746} = 29,5 hp $$ That should be close enough to 30 hp.