Is a buck transformer needed ???

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Re: Is a buck transformer needed ???

Thats correct too bennie . When overheasting occurs torque begins to drop and if the load remains the same overheating will continue and deteriorate the winding insulation and as a matter of fact if the heat continues to build and if the load is not reduced complete failure will occur. The paragraph you quote is a warning that you really should not run a motor fully loaded at a 10% drop in nameplate voltage however the NEMA standard for motors allows this to happen they just dont reccomend it. Neither do I. Owned my own electric motor shop for nearly 20 years and the engineers who used the service factor voltage were my freinds. Kept us in the rewind and replacement business!!!
 
Re: Is a buck transformer needed ???

A basic thought is, " are we talking service voltage or utilization voltage". A utility provides 240 volts +/- 5%. That is the service voltage range. A facility can drop that voltage another 5%, that is utilization voltage. For the longest time, equipment manufacturers talked utilization voltage, about 230 volts, and engineers and utility folks talked service voltage, 240 volts. They are the same system, just different points along the circuit. The same logic applies to 460 vs 480. Looks like there is still confusion. Because I suspect the nameplate lists utilization voltage, I don't see a violation with a motor rated at 230 volts being installed on a 240 volt system. However a motor rated only 230 volts probably should not be installed on a system rated 208 volts. That would be a listing violation.
 
Re: Is a buck transformer needed ???

:eek:
I've always heard the 10% rule from Engineers bur never really knew where it came from. I would think the 3% and 5% rulers for voltage drop would still apply. I don't have a code book handy so i cant look it up right know. What if you have 10% drop also feeding motor controls,PLC etc?????
 
Re: Is a buck transformer needed ???

Originally posted by four:
What if you have 10% drop also feeding motor controls,PLC etc?????
Click to expand...
For the most part, PLCs and controls don't care much if the voltage is off a bit. If you look at PLC power supply specs they can take a range of voltages such as 85-130V 9nominal 115V).

Relays and contactors generally function without much trouble with some under/overvoltage.

Pilot lights can have problems with over voltage but thats not real common.
 
Re: Is a buck transformer needed ???

The referrence that I have shows these general effects of voltage on induction motors at -10% voltage:
Sarting and max. torque down 19%;
% slip up 20-30%;
Efficiency FL down 2%, 3/4 about the same, 1/2 up slightly;
PF@3/4 and FL Up 1-7%, 1/2 up 3-10%;
FLA up 5-10%;
Starting current down 10%;
FL temp. rise down 10-15%;
Max. overload capacity down 19%;
magetic noise down slightly.
 
Re: Is a buck transformer needed ???

:roll:
The section in the code I was speaking of was section 210.19(a)1 fpn #4 in this section it talks about 3% drop from farthest outlet of power and 5% drop from feeder and farthest outlet. I didnt know if this section pertains to what me are discussing. This is with outlet being defined as "wiring system at which current is taken to supply utilization equipment" article 100
 
Re: Is a buck transformer needed ???

I remember reading that a 3 phase motor that is running at 208 volts and has a 1.15 service factor and is nameplated at 208-230/460 V, is now rated at 1.0 service factor when powered at 208.. overload devices (heaters or class 10 adjustable OL) should be set accordingly. Further food for thought is when that motor is wired for 480 volts (higher voltage on a 9 lead motor) , can the motor be supplied with 416 volts? That would allow for a whole lot of voltage drop provided that the motor load is not running into the service factor.
 
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