how to select a generator set? what are the factors need to be consider? formula?

Question

my total motor power = 800kw
these motors run under generator supply.
3 phase, 415v, 365A.

how to calculate?

Answer 1

415 V x 365 A x √3 = 262 kW

If the generator is rated at 262 kW, then you will not be able to operate 800 kW of motors simultaneously.

Another factor to consider is the inrush requirements of the motor(s). It is not uncommon for a motor to require 5 or more times its nameplate amperage while starting. This inrush can damage the windings of a generator if things are sized too close.

Answer 2

The only thing i can add to Thomas C is to check the nameplate for FLA Full load amps...a good starting point is 2.5 times the FLA ..the reason i would mention this is that the idling amperage and the Full Load Amps can vary and will I'm sure you get the idea......Also over current protection for these types of motors is somewhat critical as Circuit breakers tend to be over rated in AIC and Underrated in actual load thermal time values...350hp motors like these should have a fused system with motors as their primary usage A SLO-BLO Bussman is typical...the formula for calculation is ..
P(watts)= I(amps) x E(volts) x SqRt 3(1.732) x Sf(service factor:optional) <-----this is the 2.5 i was telling you about..
Good luck with you motors From the E....

Answer 3

P=1.732 x V x I x pf
P=1.732 x 415 x 365 x 0.76 (assumed value for pf) since you did not specify it from the nameplate of the motor
P=200 kW
1.732 x V x I is the apparent power which is in kVA

if your total motor power is 800kW then you are running 4 motors drawing 200kW each. you should consider the starting current (not the inrush current 'coz inrush is for transformers) which is ten times the rated current in the motor's nameplate.you will need to exceed the 800kW margin and the generators' ampacities must be capable to handle such amount of starting current, that is if you are using multiple generators in synchronism. for much safer operation try to place protective relays to your generators and motors. also use motor starter connections to avoid damages during start up and operation.