Transformer Oil Analysis

[wirenut1980]

A DGA samples the gasses in the transformer, the 9 key gasses will tell you if you have arcing, celluose breaker down, over heating, etc.... It is like a blood sample at the doc. Normal oil sample just checks the dielectric strength of the oil and if there are any contaminates present. Alway do a DGA. There is no way you had high C2H4 and then it was gone, someone messed up a sample.

Zog, I've been reading the IEEE/ANSI standard and did read that the acetalyne PPM can be higher on distribution transformers than in substation transformers due to there being less oil in the tank (obviously). The transformer I am dealing with is a distribution transformer, only 500 KVA. Does 14 PPM still seem high in this case?

I was wondering if a bayonet fuse blows in a pad mount oil filled transformer, will that give you elevated acetalyne readings? According to what I read in the IEEE standard, I think it does. This transformer has had multiple bayonet fuses blow. The transformer is tested, all tests come back good, so it is put back in service. Anywhere between 3 months to 2 years later, the fuse blows again. This is happening at multiple car wash locations.

I'll have to request a DGA analysis since only a regular oil analysis was done.

 

[mxslick]

Zog, I've been reading the IEEE/ANSI standard and did read that the acetalyne PPM can be higher on distribution transformers than in substation transformers due to there being less oil in the tank (obviously). The transformer I am dealing with is a distribution transformer, only 500 KVA. Does 14 PPM still seem high in this case?

I was wondering if a bayonet fuse blows in a pad mount oil filled transformer, will that give you elevated acetalyne readings? According to what I read in the IEEE standard, I think it does. This transformer has had multiple bayonet fuses blow. The transformer is tested, all tests come back good, so it is put back in service. Anywhere between 3 months to 2 years later, the fuse blows again. This is happening at multiple car wash locations.

I'll have to request a DGA analysis since only a regular oil analysis was done.

Ok, time to put on your thinking cap. Forget the transformer DGA for now, why are you having multiple repeated fuse blowouts in more than one location?

Are these three-phase transformers? Is it the same phase fuse that fails every time at all locations?

What equipment is common to the phase that keeps blowing fuses?

Is the overall load on the service at each location balanced as closely as possible?

Have you tried putting data recorders on the secondary to see if there are loading issues?

Is it the same brand, size and type of transformer in all cases? Are they of the same "age" , i.e. possibly a bad batch of trannys from that manufacturer?

There are a lot of facts that need to be discovered or you will never end this problem.

 

[wirenut1980]

Ok, time to put on your thinking cap. Forget the transformer DGA for now, why are you having multiple repeated fuse blowouts in more than one location?

Are these three-phase transformers? Is it the same phase fuse that fails every time at all locations?

What equipment is common to the phase that keeps blowing fuses?

Is the overall load on the service at each location balanced as closely as possible?

Have you tried putting data recorders on the secondary to see if there are loading issues?

Is it the same brand, size and type of transformer in all cases? Are they of the same "age" , i.e. possibly a bad batch of trannys from that manufacturer?

There are a lot of facts that need to be discovered or you will never end this problem.

I have many facts.

There are 3 car wash locations out of 11 total served that are having this issue. I have monitored at locations blowing fuses and at locations not blowing fuses. The loads are nearly identical (the customer is Mikes Carwash and the electrical design is cookie-cutter). All transformers are 3 phase 12,470 V Y-480Y/277 V 500 KVA and loaded up to around 400-450 KVA during business hours. Inrush currents amount to about 1/10th of what it would take to reach the minimum melt curve of the fuse (for the magnitude and duration of the inrush currents). I have not been lucky enough to be monitoring when a fuse blows. The vast majority of the load is 3 phase motors/compressors, so everything is balanced, and the monitoring data supports this claim.

In all occurrances where the phase is documented, B phase fuse is the one to blow. On the most recent occurrance, the trouble person attempted to replace the blown fuse and the fuse blew again almost immediately. The transformer and service conductors were tested for a fault, but nothing was found. Several hours later, the blown fuse was replaced again and this time it held (and has held for a few weeks now). To me, this points to heating, which points to something mechanical, like a connection issue. From monitoring data collected, the heating does not appear to be from loading. I have learned that the fuses are typically not properly torqued. Over- or under-torqueing can cause the fuse link connection to heat up and possibly blow prematurely.

The question remains: why is this only happening at 3 out of 11 seemingly identical locations both in terms of the customer load, and electrical system?

I need to try and run down information on the manufacture and age of the transformers. The locations having the issue were built at different years with a few years in between, same as the ones not having the problem.

We also have seen this issue come up at saw mills. The running theory is that there is something with a repetitive inrush current banging on those fuses, coupled with probable improper torquing, causing heating and possibly arcing and eventually fuse failure. At this point we are probably going to put in a 750 KVA transformer and call it a day.

I would appreciate any ideas at all.:-?

 

[dbuckley]

On the most recent occurrance, the trouble person attempted to replace the blown fuse and the fuse blew again almost immediately.

Unless you had a duffer replacement fuse, that points to a genuine significant overcurrent. "Almost immediately" doesn't provide time for it to be a little overcurrent

 

[zog]

Your C2H2 levels could very well be from the fuses arcing, I think the transformer issues are the result, not the cause of your problems. I would start with a megger test of the motors, including DAR/PI. It is possible you have 2 motors with a low phase insulation resistance that when they operate at the same time they create a short. Has any motor and cable testing been done?

 

[BJ Conner]

Bay-o-net fuses

Bay-o-net fuses

Wirenutz1980
Things to check.
Are all the transformers fused the same? In my experience some "Identical" assemblies may have designed by different engineers and the fuses may be one size different.
Are the transformers all Y-Y? IF so is H-O and X-O connected on all of them?

Oil analysis is usually a tool for monitoring and preventive maintenance of larger transformers. 400 KVA distribution transformers are usually replaced "off the shelf".

Have you interviewed the operators? Are the outages coorelated with some event in the operation of the carwash?
Do they happen in winter, summer, cold weather, hot?

IS the primary feed to the transformers the same - Are some overhead and some underground?
How far are they from the distribution sub?
IS the underground cable the same? Do some have a bare concentric neutral and some have covered concentric neutral?

I would do a coordination study and take it all they way back to the transformer in the distribution substation.
Transformer fuses should be blowing to protect transformer internals and service conductors. Any event down stream of the service point should be handled by the customers system.

 

[mxslick]

In all occurrances where the phase is documented, B phase fuse is the one to blow. On the most recent occurrance, the trouble person attempted to replace the blown fuse and the fuse blew again almost immediately. The transformer and service conductors were tested for a fault, but nothing was found. Several hours later, the blown fuse was replaced again and this time it held (and has held for a few weeks now).

Ok now I have an idea.

Call the POCO and talk to an engineer (Most troubleman wouldn't know what to do about this) and ask them to investigate the possibility of ferroresonace happening on those locations. Try to see if the time of the fuse blowing happens to be about the same time the POCO is switching and power factor correction capacitors on or off line.

If you have been doing data recording , look for strange peaks of voltage on your 'B" phase sceondaries, as well as any unusual looking waveforms that only last for a moment or two.

 

[mxslick]

So what happened qith this?

So what happened qith this?

Been a while on this thread so bumping it up..

wirenut1980, what was the outcome of this problem? Was a cause found? Did the POCO find any issues like ferroresonance like I suggested?

 

[wirenut1980]

Wirenutz1980
Things to check.
Are all the transformers fused the same? In my experience some "Identical" assemblies may have designed by different engineers and the fuses may be one size different.
Are the transformers all Y-Y? IF so is H-O and X-O connected on all of them?

Yes, all transformers that have had the fuses blow are all fused the same, which as the correct fuse size from my utility's the design manual. They are all Y-Y and I have not checked to see if H0 is connected to X-0, but that is what is always done. I'll have to check on this at some of the problematic locations.

Have you interviewed the operators? Are the outages coorelated with some event in the operation of the carwash?
Do they happen in winter, summer, cold weather, hot?

Yes, the outages happen at different times of day in winter and summer although I am not sure if it always happens when they are very busy. I work for the utility, so I am not that familiar with the operation of the carwash.

IS the primary feed to the transformers the same - Are some overhead and some underground?
How far are they from the distribution sub?
IS the underground cable the same? Do some have a bare concentric neutral and some have covered concentric neutral?

All locations are fed with pad mount transformers, and all are in an underground loop feed. The underground loop is relatively small in all locations and usuallly has about 5 or less transformers in it. Not sure about distance to the sub, or what difference that would make?

I would do a coordination study and take it all they way back to the transformer in the distribution substation.
Transformer fuses should be blowing to protect transformer internals and service conductors. Any event down stream of the service point should be handled by the customers system.

There are fuses at the overhead to underground transition pole, and those have not blown at all. Not sure what doing a coordination study back to the substation will tell me. Could you please elaborate?

Thanks for the feedback!

 

[wirenut1980]

Ok now I have an idea.

Call the POCO and talk to an engineer (Most troubleman wouldn't know what to do about this) and ask them to investigate the possibility of ferroresonace happening on those locations. Try to see if the time of the fuse blowing happens to be about the same time the POCO is switching and power factor correction capacitors on or off line.

If you have been doing data recording , look for strange peaks of voltage on your 'B" phase sceondaries, as well as any unusual looking waveforms that only last for a moment or two.

Sorry if I was not clear mxslick, I work for the utility and am trying to figure this out for our customer. My understanding about ferroresonance is that it is highly unlikely to occur on a wye-wye transformer, and usually a phase is lost on the primary side, and there is no load on the secondary side of the transformer.

I have some recording data and did not see any strange distortion in the voltage waveform other than a small amount of distortion from the VFD's inside. I am planning on placing some PQ analyzers long term in a couple locations transformer secondaries in hope of catching an event.

Our power factor correction caps switch on and off all the time, so if they were somehow involved, I would think this would happen a lot more.

I have sent in some blown and unblown B phase fuses to the fuse manufacturer for analysis, but have not heard back from them.

Thanks!

 

[wirenut1980]

Your C2H2 levels could very well be from the fuses arcing, I think the transformer issues are the result, not the cause of your problems. I would start with a megger test of the motors, including DAR/PI. It is possible you have 2 motors with a low phase insulation resistance that when they operate at the same time they create a short. Has any motor and cable testing been done?

I think you are right about the fuses causing the C2H2 levels. I like your idea about the 2 motors theory, but I have a inkling that the customer is not going to want to do this. I will ask if I have any proof of a fault. The only way to do that is to catch an event. No insulation testing has been done on the motors/cables that I am aware of.

 

[mxslick]

Sorry if I was not clear mxslick, I work for the utility and am trying to figure this out for our customer. My understanding about ferroresonance is that it is highly unlikely to occur on a wye-wye transformer, and usually a phase is lost on the primary side, and there is no load on the secondary side of the transformer.

I have some recording data and did not see any strange distortion in the voltage waveform other than a small amount of distortion from the VFD's inside. I am planning on placing some PQ analyzers long term in a couple locations transformer secondaries in hope of catching an event.

Our power factor correction caps switch on and off all the time, so if they were somehow involved, I would think this would happen a lot more.

I have sent in some blown and unblown B phase fuses to the fuse manufacturer for analysis, but have not heard back from them.

Thanks!

Ok, thanks for the clarification...hope something turns up to explain this.. very strange that data logging shows nothing unusual.

 

[zog]

I think you are right about the fuses causing the C2H2 levels. I like your idea about the 2 motors theory, but I have a inkling that the customer is not going to want to do this. I will ask if I have any proof of a fault. The only way to do that is to catch an event. No insulation testing has been done on the motors/cables that I am aware of.

So your customer would rather replace a transformer than spend $100 on some basic testing?

 

[wirenut1980]

So your customer would rather replace a transformer than spend $100 on some basic testing?

Haha, no, I am sure their idea is that we (the utility) foot the bill for the new transformer.

 

[mxslick]

So your customer would rather replace a transformer than spend $100 on some basic testing?

I'm not surprised by that...my cinema customers would rather risk a $2,000+ lamp reflector and lost shows rather than replace a $400 Xenon bulb. (Bulbs can last as much as 1-2 years at 5 shows/day). They think the upcoming digital cinema conversion is gonna save them money...until they realize that the bulbs are 2-3 times more expensive and will last only 3-4 months. And a bulb explosion in a D-Cinema projector costs a minimum of $4,000 in damage (upwards of $10,000 in a 3-D machine.)

Preventative maintenance is a dirty four-letter word to most cinema owners. :grin:

Haha, no, I am sure their idea is that we (the utility) foot the bill for the new transformer.

Question here then is who owns the transformer? :grin: