Transformers in Parallel

[jim dungar]

When they say the "switched as a unit", I take that to mean if you shut off or trip a breaker on one, it has to shut off a breaker on the other. That seams to defeat any advantage of paralleling them to start with.

If you were paralleling the transformers for more capacity then turning off one unit would overload the remaining one.

 

[steve66]

The NEC handbook also mentioned the danger to a maintenance person from the voltage from one transformer backfeeding through the other transformer. If an electrician were to open the primary breaker on one transformer, the load side of that breaker would still be hot (along with the primary winding.)

Thanks for all the help.
Steve

 

[zog]

The NEC handbook also mentioned the danger to a maintenance person from the voltage from one transformer backfeeding through the other transformer. If an electrician were to open the primary breaker on one transformer, the load side of that breaker would still be hot (along with the primary winding.)

Thanks for all the help.
Steve

And the fault would most likely still be there, whatever caused the 1st transformer to fail would affect the other transformer when it was energized.

 

[weressl]

The NEC handbook also mentioned the danger to a maintenance person from the voltage from one transformer backfeeding through the other transformer. If an electrician were to open the primary breaker on one transformer, the load side of that breaker would still be hot (along with the primary winding.)

Thanks for all the help.
Steve

Yeah, that's why we use check valves. Ooops, wrong thread......

 

[cschmid]

Steve I am curious if you could tell us a little about the situation you are working with..What is the critical load we are trying to maintain a consistant level of power too..

 

[sdv]

// xfmrs

// xfmrs

If you do parallel, also make sure you use the same manufacturer and even same production lot, because the slightest differences in impedance and voltage regulation under light loading can cause high circulating currents. It's not a problem...but a waste of energy.

 

[steve66]

This is for critical loads in a hospital expansion project. (The transformer that failed was in an existing part of the hospital).

Steve

 

[cschmid]

Now I think we understand the concern you are dealing with..Thank You

 

[barclayd]

This is for critical loads in a hospital expansion project. (The transformer that failed was in an existing part of the hospital).

Steve

Are these 'critical loads' connected to the Critical Branch?
I think JCAHO would have some standards & regulations that have to be followed.
I really think you need to reconsider the parallel transformer scenario.
Ask, instead, 'How can I provide maximum reliability within the restraints of the various pertinent NEC & JCAHO requirements?'
db

 

[zog]

You need to look at NFPA 79 (I think its 79) for health care facillities, some special requirements there.