We have moved a piece of older equipment from another location that was powered from the grid at 240VAC. The new location has 480 VAC and the plan is to power the equipment via a 480VAC Delta to 208/120VAC wye general purpose transformer. Output of said transformer will be routed through a 3 phase load center. Although the engineer says there will be "no problem", I'm not getting warm and fuzzy. Will universal motors rated for 230VAC run properly (albeit slower) at 208VAC? I'm not sure why but I seem to remember something about phase angle issues between 208 VAC derived from 3 phase supply and "normal" 240 VAC single phase. I'm not well versed in proper use of transformers but something sounds fishy here. Can someone shed some light?
Thanx,
Jim
Assumption: By "universal motors" you mean standard Design B induction motors.
Following discussion is limited to standard stuff - Design B induction motors
Adding to all of the good comments:
Yes, engineers are whiley, slippery sorts. I certainly would not trust anything one said in a blog conversation.
That aside, what you are discussing is operating 230V motors on 200V - yes, "200V". That is the standard winding voltage if one is planning on using on a 208V system.
Here is the basic model:
1. Induction motors have to run within their rated slip - generally 3% - 5%. Even if the voltage is lowered, the speed has to remain about the same.
2. The available torque drops linearly with the voltage.
3. If one wants the horsepower back up to nameplate, the current has to go up.
So, what happens if the voltage is dropped from 230V to 200V?
The motor will only produce 87% rated power at FLA. If the motor is not loaded over 87%, the application is as okay as it was before.
Supposing the motor was loaded to 100%. To make up the power the current has to go up - about 16%. And that puts the application just over the top of an sf 1.15 motor. Probably still okay, but the motors will run hot. My inclination would be to buy 200V rated spares.
If the motors are 1.0 SF, they will run hot enought to burm skin. They won't last. I'd be buying new or rewinding for 200V (and 1.15sf)
Now add in a change in ambient to from okay to hot - say 20C to 40C. This is a problem. Conventional wisdom says the motors will fail in 1/4 normal time. A twenty year motor will now last 5 years. It's an accounting decision as to replace, buy new spares now, buy new later.
:angel:
As for the phase angle change through the transformers - that's a problem. One has to make sure the Sympathetic Inrush Harmonizers are adjusted correctly, or the inrush current can easily trip the feeder CB. :huh:
ice