Message Board Thread - "Cast Coil Transformers"

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Cast Coil Transformers shockwave48 7/14/2005
I'm going to scan a dry type, cast coil transformer (4 MW, 34.5kV/782V)that tripped a "transformer lockout" alarm. What if anything would I be able to see on the transformer, and what should I be looking for?
Any idea on the maximum temperature to be considered dangerous?
Re:Cast Coil Transformers shockwave48 7/27/2005
Would ultrasound be better for detecting arcing sounds to indicate early signs of failure?
Re:Cast Coil Transformers Michael 7/28/2005
If you wnat ot spend the money, there is a camera that will see te "arcing" and energy emmision. It should apply to your situation. If I remember correctly, it's called Corona imaging.

Re:Cast Coil Transformers Tony Holliday (HAWK IR) 7/31/2005
There are a couple of major points to check with Transformers, but it does depend on their configuration as to how much you can see.

I guess that at the 34.5kV Primary side, the cable terminations will be at high level and exposed, which is good for IR as you have direct line of sight to the target. Beware of solar reflection though, especially if you are using a shortwave system as you may find that you "see" problems that are not really there.

On the 782V Secondary - kind of a strange voltage, I would be interested in what your plant does if you could email me offline! - the terminations will either be cable or direct copper bus. Eitherway, these will most probably be enclosed in a heavy steel box which you cannot scan with IR our UV (corona) without removing the covers, I don't think ultrasound will be effective in this case either unless you can find an airgap in the box, which if it is outdoor will not be present. The only option here is to install IR Sightglasses into the box in order to view the connection point (picture attached with resultant image below). If the equipment is outdoor, make sure you select a product with the correct NEMA test certificate in order that you do not derate your equipment.

Another interesting point to perhaps look at would be the taps themselves. These are bolted connection points on the transformer windings which short out sections of the windings to alter the secondary voltage. Again, you would need to install IR Sightglasses to view these points UNLESS the transformer is part of an indoor package substation which sometimes have ventilation louvres which are partially transmissive.

Hawk IR have generated various application specific literature documents to help with the scanning of different electrical equipment. If you would like a copy of the Transformer document, just drop me an email and we will send a copy out to you.

As for "critical" temperatures, this is more difficult, especially when you consider transformers generate heat as part of their normal mode of operation. I would definately look for delta-T changes across phases - assuming balanced loads, which it should be - but do bear in mind load. This is the most important point when scanning any piece of electrical equipment, check the downstream main breaker directly off the xfrmr which will have a metering panel showing the current load through the breaker at that time. Note this down each time you scan the xfrmr and take it into account when comparing images over time.

I hope this helps, I know its a little generalised (difficult without a picture of the xfrmr!!). If I can help any further, please do let me know.

Best regards!

Tony Holliday
Hawk IR International Ltd.
Tel. 1-877-4-HAWKIR
Re:Cast Coil Transformers Falcon 8/4/2005
Try to find an identical transformer that is functioning properly and infrared it. Compare these thermograms to the transformer in question. Rremember to consider transformer bank loading in your comparison and try to themogram under the same ambient conditions.

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