Power Disruptions

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sirbph

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Hi Guys,

I am called in to investigate power disruption problems in an industrial facility. Apparently, strange power failures occur without any notice. Certain portions of the building will suddenly go out without any breakers tripping. Voltage is not detected when tested. After some time things come back on again with proper voltage. They have 480/240V.

The electrician believes the 3 (75kVa) single-phase transformers servicing the facility are faulty and wants to replace them with one 225 KVa 3-phase transformer.

Are the transformers the problem? And is this replacement a better alternative to the existing setup for this type of facility?
 
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sirbph said:
Hi Guys,

I am called in to investigate power disruption problems in an industrial facility. Apparently, strange power failures occur without any notice. Certain portions of the building will suddenly go out without any breakers tripping. Voltage is not detected when tested. After some time things come back on again with proper voltage. They have 480/240V.

The electrician believes the 3 (75kVa) single-phase transformers servicing the facility are faulty and wants to replace them with one 225 KVa 3-phase transformer.

Are the transformers the problem? And is this replacement a better alternative to the existing setup for this type of facility?
Click to expand...

The electrician is wrong..if the transformers were bad the entire building would suffer outages.

The problem is more likely a bad connection in the feeders serving the parts of the building that go out...since after some time elapses the power comes back on it's a classic loose connection heating up enough to interrupt power, then when it cools down it allows current to flow again.

The bad connection could be at:

Breaker lugs;
Breaker bus connections;
Bus duct joints;
Disconnect switches;
Any splices or junctions;
Main lugs of subpanels;
Main lugs at the service (if only one or two phases drops out);

In any event, you have a very dangerous situation that needs some serious examination to find that loose connection before a fire starts..or worse.
 
Wow. Perhaps you can see if any of the switchgear is hot. Do you have an IR camera?

add: scan the switchgear and junction boxes
 
sirbph said:
... Apparently, strange power failures occur without any notice. Certain portions of the building will suddenly go out without any breakers tripping. Voltage is not detected when tested. After some time things come back on again with proper voltage. They have 480/240V....
Click to expand...
Couple of questions:
1. I'm not familiar with 480/240. Is this single phase?

2. "certains portions go out" Certain portions of what? Lights only? Industrial machinery? Data servers? What goes out? What stays on?

Once you figure what is going out and what panels it (they?) are fed from, then get your one-line out. Figure which panels are going down and which are not. Shouldn't be too hard from there.

I don't know how anyone could guess about the transformers being the problem without looking at a one-line.

cf
 
I haven't been given much information and I don't really know what goes out in the building- except that it seems to be the same things or the same leg.

I am wondering if it is a loose connection and not a transformer problem. I understand that even if one of the single-phase transformers went out they would still have power off of the two remaining transformers.
 
"the electrician believes" Statement explains to me that he is guessing and is suggesting to purchase an expensive transformer "on a guess"! Proper troubleshooting of this problem requires a simple tool called a voltage tester. Your electrician should carry one of these for his personnel safety. Normally on a power failure you start at the service or power source and work yourself out thru the distribution until you find the problem source. This way he doesn't have you buying a 225 kva transformer, while the original problem might be in your power company's network. Good service contractors own data loggers, which can not only pinpoint a problem , but document it in writing.
 
sirbph said:
I haven't been given much information and I don't really know what goes out in the building- except that it seems to be the same things or the same leg.

I am wondering if it is a loose connection and not a transformer problem. I understand that even if one of the single-phase transformers went out they would still have power off of the two remaining transformers.
Click to expand...


See Post #2...:roll:
 
Isolate and conquer.

Try to break the system into sections and see what is affected and what is not.

IR
PQ meter or multiple Fluke's with Min Max function
VISUAL inspection, take a look at everything USE YOUR PPE.

Nothing beats your eyes for locating many issues.
 
A 34 story hotel began to loose power to the upper third of the building--maybe 5 minutes and then would come back on. Their maintainance staff began checking and quickly narrowed it down to the bus duct feeder that fed this section of the building. Now the bus duct ran to the top floor distribution room and was enclosed in a concrete block chase up the building from the third floor. They began at the top cutting holes to inspect the enclosed bus duct and after a week they reached the horizontal run across the parking garage which was enclosed in wire lathe and stucco. Thats when we were called to find it using infrared. We found it in less than 15 minutes by just scanning the stucco horizontal chase. It was caused by a section that was never torqued. We shut it down - torqued the joint -- re-enegized and ordered two replacement sections to be changed out at a later date. And when we removed the original sections the fingers were burnt from the poor connection -- almost crispy! They had us infrared the building every two years after that.
 
480d/240v

480d/240v

240/480V 3-phase 4-wire is a common rural utility service for pumps and agricultural loads. Three 7200V-240/480V single phase transformers are connected ungrounded wye on primary and 480V delta on secondary. One (and only one) of the mid-sides is grounded. This provides 480V 3-phase for motors and 240V for some small single phase load AND is much safer than ungrounded 480V 3-phase 3-wire delta.

There is also a more common 240D/120V service where one transformer provides 120/240V single-phase (lighter) and one 240V transformer provides the open-delta for 240V 3-phase 3-wire loads.
 
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