DC Motor For Emergency

What about talking to motor manufacturers directly?

1. In my experience, an emergency pump must provide oil for a minimum time. This is usually at least an hour, since the machinery takes 30 min or more to stop rotating. You have not clarified how long battery can supply 60 amps or stated the "end voltage" when cells are discharged.
2. But there may be an extra requirement - oil flow may be necessary to stop melting of bearing [due to heat from the prime mover hot rotor] and/or oil fire. Well-designed machines will go to stationary without oil flow - but no guarantee on damage resulting. You do not say if prime mover is steam or gas turbine and whether there is one, common, oil system for generator and turbine.
3. 15 h.p. is 11 kW and Baldor motor is rated for 240V - so you will not exceed its rated armature current at 120V 5 kW.
4. Field values for Baldor motor I interpret as 300V for 1750 rev/min, 150 for 2300 rev/min - both at 240V armature.
5. Scaling speed in proportion to armature voltage at 150V field gives 2300* 120/240 = 1150 rev/min at 120V on armature. Operation at 5 kW shaft is at about rated armature current - so rotor field is normal.
6. In absence of any saturation data (e.g. detailed speed vs field current measurements at 240V armature) the speed must be adjusted from 5. in proportion to field voltage to 1150 x 150/120 = 1440 rev/min. N.B. The weaker the field, the faster the rotor has to turn to provide a back - emf voltage equal to the armature supply.
7. Thus far, it looks as if Baldor motor would run at about 1440 rev/min with 120V on armature and field at 5 kW shaft power- a good speed for pumps.
   
8. Caution One - with DC motors you have to allow for speed variation with load. I assume figures given for motor are at full load - speed on small load will increase. But it is only a few % and is better at low flux densities below field saturation.
9. Caution Two - The temperature of the field has a big effect on its resistance. This makes the field current for a given field voltage much higher when cold than hot, I guess about 30% - this has a direct effect on speed which will be about 1/1.3 = 75% of calculated 1440 rev/min = 1100 rev/min cold - I assume any rated values given are HOT condition.
   
10. Caution Three - Your post is not clear if the Baldor machine has rated armature current for 15 hp at 2300 or 1750 rev/min - but assuming 2300, as above, machine looks OK. The machine rating plate ought to have the rated armature current on it.
11. Caution Four - Cooling of machine depends on its inbuilt fans [if there are any - you have not indicated if Baldor machine is continuous rated or very short-time]. Since cooling flow is proportional to speed squared for the typical shaft mounted fan (and the lower velocity has reduced cooling effect!) a drop of speed from 2300 to 1500 rev/min will halve the cooling or worse. Since the machine would run at about rated current at 120V/5 kW the losses are the same as at rated voltage.
12. Caution Five - You write "supplied 125 DCV, it will run with a proportional reduced speed, and Power". This is not a correct view. An ideal D.C. shunt machine, with field and armature fed in parallel, would keep the same speed whatever the voltage! Please read my procedure above for a better idea.
13. Caution 6 - makers do not usually tell you about the variation of speed of samples of a given design from nominal values!
14. Caution 7 - The torque of a DC motor depends on field current x armature current - so one could be in trouble dropping field voltage to 120V, which is less than rated -- needs clarification of rating at 1750 rev/min (i.e. is it 15 hp or a lower figure).
    
15. Summary - a) The Baldor machine looks possible, but there is uncertainty about its rated armature current and speed for rated power. The adequacy of its cooling at reduced speed is doubtful and needs careful investigation! If it is rated for 15 hp at 1750 rev/min, it may be practical for 1450 rev/min 5 kW shaft - particularly if you only need the motor to run for 1 hour and its rating is continuous. b) The battery voltage and capacity were not clearly stated and need proper comparison with the necessary motor current, time and voltage.