Running 230v single phase from 208 3 phase

[cs2371]

Need to run 230 volt single phase pumps from a generator that simultaneously produces 480v and 208v 3 phase power.
Can I hook pumps up to 2 legs of the 208 side and adjust voltage up. I am thinking that as long as single leg of 208v side is no more than 130v and my high voltage side is no more than 500v I should be able to run whatever we need to run. Thanks

 

[DanDel]

If you are not using the 480V taps, and the generator allows you to adjust the 208V up, you should be ok.
(Just remember to distribute the pumps on the three phases as equally as possible. You indicated multiple pumps but not how many; if you have three, connect one to 'A' and 'B', one to 'B' and 'C', and the last to 'C' and 'A', etc)

 

[jbartos]

Suggestion: The pump motors may be connected to 208V 3Ph; however, the motors better be rated for 200V 1ph with the shaft HP sufficient to meet the pump input HP.

 

[UKpete]

If the total power of the pumps is not far off the rated power of the generator then it is very important to balance the load on all three phases as much as possible, the greater the imbalance then the greater the rotor heating in the generator due to negative sequence currents.

If there is any doubt it would be worth checking the currents in all three phases.

 

[busbar]

Are 480V loads being served concurrently with 208V loads? For the usual 12-lead low-voltage generator stator, excitation is adjusted for 120V per coil for nominal 208V, but 139V per coil {480V/{sqrt3)/2} for 480V service. Note with 139V/coil, generated voltage will be 480V ø-ø, but 240V [not 208V] at the ungrounded stator-coil taps. Typically the stator is connected 480V T1-T2-T3, neutral connected to T10/T11/T12, but it sounds like mid-winding taps may also be serving load using additional connections to T4/T7, T5/T8 and T6/T9. When operated in this mode, understand that the nominal “208V” [“240V”] output may be quite high—139V ø-n in place of the anticipated/desired 120V. Be aware that 130V/coil on the typical 12-lead stator corresponds to 225 and/or 450V ø-ø.

Generator loading is a little more complex, in that the rated coil current cannot safely/reliably be exceeded in the steady state, so coils connected to the neutral point will be loaded by equipment served at both voltages, and overloading of that coil set may occur without appropriate monitoring and protection.

 

[jbartos]

Suggestion: The motor sizes with respect to the generator rating need to be evaluated for proper starting. If the motor sizes are relatively small with respect to the generator size, and reasonably distributed between phases a, b, c, then, there will not be any major problem. However, if some motors have very high ratings with respect to the generator rating, then the generator power supply will be experiencing voltage unbalance, in transient conditions as well as in the steady state conditions, and other loads/motors may become damaged by the voltage unbalance.