Motors over 500 HP

[Zolam]

Table 430.150 provides the full load current for certain motors up to 500 HP. How do I find the current (for sizing conductors) if the motor is larger than 500 HP?

 

[stardelta]

Ask the Makers of the machine for the info you require. Tell them you are considering buying another one and chances are you will find them to be "extremely helpful" in all respects.

 

[jraef]

General "rules-of-thumb" for estimating motor FLA above 500HP is as follws, from the EASA handbook:

208V = 2.75A/HP
230V = 2.4A/HP
460V = 1.2A/HP
575V = .96A/HP
2300V = .24A/HP
4160V = .14A/HP

Note that these are for ESTIMATING only. NEVER use anything other than the motor nameplate FLA for protection device settings etc.

Eng-Tips: Help for your job, not for your homework Read faq731-376

 

[aolalde]

Use the general formula for current.

Ifl = HP*0.746 / ( 1.732*kVll*EFF*PF)

Assume EFF = 0.90 and PF=0.87, for instance 1000 HP at 4160 or 2300 Volts.

Ifl = 1000*.746 / ( 1.732*4.16*0.90*0.87) = 132.23 Amps @ 4160 V.

Ifl = 1000*.746 / ( 1.732*2.3*0.90*0.87) = 239.17 Amps @ 2300 V

For accurate calculation you need the EFF and PF from the manufacturer for each specific motor and load. Those figures (EFF & PF) change when the load changes and from different model or manufacturer.