Is dressing out a new oil filled transformer specialized work or can a general Contractor do it?
Is dressing out a new oil filled transformer specialized work or can a general Contractor do it?
(OP)
We are purchasing a new 15kV, 30 MVA transformer. It will come as a box, with the radiators, bushings, lightning arrestors, etc. unattached.
We're aware there are companies out there that specialize in assembling transformers, however it doesn't seem to be such a difficult job that our general Contractor couldn't handle it.
Is there a reason why we should hire a speciality Contractor?
We're aware there are companies out there that specialize in assembling transformers, however it doesn't seem to be such a difficult job that our general Contractor couldn't handle it.
Is there a reason why we should hire a speciality Contractor?






RE: Is dressing out a new oil filled transformer specialized work or can a general Contractor do it?
If the transformer is shipped dry, you will definitely want to hire a transformer maintenance outfit that has the proper equipment to vacuum fill and filter the transformer oil. Even if shipped with oil, additional oil will likely be needed after the radiators are installed.
I would not let a general contractor do this work on a 30 MVA unit unless they have prior experience and strong credentials. Some of it is straightforward, but there are a lot of potential pitfalls. You will need to test it anyway, and the general contractor will definitely not have the equipment to do that.
RE: Is dressing out a new oil filled transformer specialized work or can a general Contractor do it?
1) Have the GC tie off all tools used for internal connections. Have magnets available to retrieve any dropped hardware. Carefully control hardware inventory.
2) Carefully follow OEM instruction procedures.
3) Verify all radiator valves are open.
4) Use TyGon (or other clear type) tubing, connected to the lower drain valve, to determine proper fill level. The instruction book should have some statement of where the oil level should be and conversion factors, based on temperature. There needs to be room at the top of the radiators for proper oil circulation.
5) Consider at a minimum, testing the Dielectric strength of the make up oil. Additional field tests such as power factor can also be performed.
6) Pay particular attention to the gaskets used for radiators. Make sure surfaces are clean and dry. Use approved gasket adhesives, as recommended by the OEM.
7) At a minimum, TTR and Megger Tests should be performed. Additional tests, such as power factor / dissipation factor, bushing tests. All alarms, gauges and controls should be tested.
8) Consider a final purge with Dry Nitrogen gas when internal work is complete.
9) Perform final Oil DGA and Quality tests.
Pay close attention to grounding connections on surge arrestors.
The downside of using a GC inexperienced with this is what if they damage the unit? Can you live with the delays associated with a failure.
RE: Is dressing out a new oil filled transformer specialized work or can a general Contractor do it?
Bill
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"Why not the best?"
Jimmy Carter
RE: Is dressing out a new oil filled transformer specialized work or can a general Contractor do it?
The following IEEE standards also will be helpful.
1)C57.93-2007 Installation and maintenance of transformers
2)C57.106-2002 - Maintenance of oil.
RE: Is dressing out a new oil filled transformer specialized work or can a general Contractor do it?
Plus as DPC mentioned, there are several tests that should be done after assembly and before energizing that require special test equipment and trained techs to perform. Testing is important not only for safety concerns but also to esablish baseline data for trending over the life of the transformer.
RE: Is dressing out a new oil filled transformer specialized work or can a general Contractor do it?
Concurring with others, specialty skills and equipment are required. Your manufacturer is a good source, but in today's 'competitive' market, maybe not the best one. As a general rule for MY transformer, I'd want a 'before' oil sample tested for physical properties and dissolved gases, followed by a second sample upon completion of the work. I had a client crying copious tears when a low-ball contractor 'worked' on his transformer and left him with a tank of wet oil.
There are quite a few steps to the operations of dressing out a transformer that are not readily apparent to the average electrician/mechanic/construction wireman. Doing things wrong at this stage of the game will result in years of aggravation at the least, and early failure is not out of the question.
Expanding on 'smallgreek's' testing, a transformer this size gets the tests in the ANSI/NETA Acceptance Test Specification after work is complete. This involves power factor testing, turns ratio, winding resistance, oil, etc., and in spite of advances in easy to use test equipment, you still need a competent testing agent. Most GC's don't keep these guys on staff.
old field guy
RE: Is dressing out a new oil filled transformer specialized work or can a general Contractor do it?
We called in the experts to fill the transformers. On one fill, a sharp engineer spotted a small leak when trending vacuum levels during pump down.
Bottom line, even the experts call the experts to fill the transformer.
Bill
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"Why not the best?"
Jimmy Carter
RE: Is dressing out a new oil filled transformer specialized work or can a general Contractor do it?