How long till it burns up?

[dpeter]

If you have a partial power failure and single phase a lighting transformer how long would it take to realy harm it?

 

[jumper]

If you have a partial power failure and single phase a lighting transformer how long would it take to realy harm it?

Can you clarify what you mean? Many controlers only break one line of a ballast. I have never seen a 3 phase ballast. Am I way off?

 

[dpeter]

To be more clear.

To be more clear.

Our retail stores experience complete and partial power failures for any number of reasons and that is to be expected. Stuff happens. What I am concerned about are the partial failures where our equipment still trys to run and burns up coils and motors if the overloads do not work. Small dollars in the scheme of things and to be sure a pain. The lighting transformers I refere to are for general lighting both flourescent and incandescent and in general are 150 and 175 KVA in size 480 to 120/208 3phase. There can be upwards of 30 in some stores. I want to shut them down as soon as possible but powers that be (management) will take whatever light that can be had to remain open despite damage and cost to equipement.
We have emergency generators and yes they work very well and so far very reliable.

 

[bob]

In a 3 phase delta configuration the center transformer is sometimes referred to as "the lighting pot". Is that what you are speaking of?

 

[iwire]

No one can say how long the equipment may or may not last.

A simple way to protect the equipment is the use of phase loss / low voltage relays that trip out certain loads or all loads.

You say you have generator back up so I suggest just putting the phase loss / low voltage monitor right at the main disconnect and have it trip the entire facility, the generator will pick up the required loads.

 

[dpeter]

No. The ones I speak of are dry type transformers in our electric rooms that supply a main distribution panel that serves six to eight MLO panels.

 

[rcwilson]

The transformers are not harmed by single phasing, its the three phase motors that get damaged quickly. A phase monitor relay that tripps just the motor loads might be the compromise answer.

 

[dpeter]

Say you have a transformer loaded to 80 percent and you lose a phase, do you then have 2/3 capacity? Does it then become unballanced and cause heat to build? All information I have says it is best to ballance the loads between phases and the more loaded it is the more criticle it becomes. Yes?

 

[dpeter]

rcwilson, and others,We are addressing motor loads with building automation but have no means to shut down lighting loads reliably (never know which phase may leave). If single phasing these for long priods of time does not harm them then I will not get so excited and insist they get powered down.

 

[jumper]

Say you have a transformer loaded to 80 percent and you lose a phase, do you then have 2/3 capacity?

Delta or Wye? I think it makes a difference.

 

[dpeter]

I believe wye

 

[iwire]

I have never seen a transformer damaged by single phasing or brown out.

What I do see damaged are contactor / relay coils and motors.

I just ordered an new coil kit for an ASCO 920 lighting contactor, the store it was controlling lights in had a phase loss last Sunday. The motors survived as they did have phase loss protection.

Another thought is if these stores have a building automation system already you could have it monitor for phase loss and shut things down if need be.

 

[dpeter]

Iwire, yes phase monitors in place but not working. Seems I recall something about no money in budget to replace. No one wants to plan to spend money but will spend lots of unplanned money.

 

[dpeter]

From the responses I am reading it would seem that I am overly concerned about a problem that does not exist. I will now focus on my motor loads.
Thanks to all,
Doug

 

[kwired]

Maybe the best thing to do is to address why you are having frequent phase losses, get POCO on it if it is their problem.