Construction of Transformer

norzul (Mechanical)
1 Dec 05 13:41
Hi,I'm curently involved in a cogeneration plant project. We have procured few auxiliary transformer. Our technical standards specify the followings:"Oil-immersed transformers rated 1600 kVA and below shall be hermetically sealed. Transformers rated above 1600 kVA and up to 3150 kVA, may be either hermetically sealed or of the conservator type. However, hermetically sealed transformers above 3150 kVA shall be subject to Principal approval."However, the supplier requested for deviation and propose to supply the non-hermetically sealed type transformer for 250 kVA. Is this common in industry?Thanksnorzul
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ScottyUK (Electrical)
1 Dec 05 14:23
Very small conservator types are not especially common in the UK. Hermetic transformers arguably require a little less maintenance, and this is the reason why they are more popular with the distribution companies. Conservator-type transformers usually have more complex instrumentation requirements than hermetics, but that is largely a factor of size and value; on such a small transformer it may not be considered economical to fit more than the basics.
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norzul (Mechanical)
1 Dec 05 14:37
TQ ScottyUK....appreciate if you can further qualify what do yu mean by "factor of size and value". Just wonder...for this small transformer why the supplier insist to supply the conservator type. From cost point of view I think it is more expansive. From maintenance point of view, looks like we may require more maintenance. It's like loose-loose situation not win-win...?? Fyi..the contract that we have is lump sum type i.e. we are not going to pay for the additional cost incurred by the supplier.
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ScottyUK (Electrical)
2 Dec 05 2:45
The comment regarding "...size and value..." was really to suggest that although most conservator-type transformers have more instruments and protection functions, this isn't solely because they are of that design. Larger transformers tend to supply larger loads, or multiple small loads, and loss of such a transformer typically causes greater disruption than loss of a small type. They are also major capital assets, and the cost of better protection is a diminishing percentage of total cost as the transformer size increases, so it becomes economical to find sophisticated protection to, say, a GSU transformer whereas that protection might cost more than the total value of a small distribution transformer.That logic doesn't entirely apply to your excitation transformer because loss of that one small transformer will shut down the generator just as effectively as loss of the GSU transformer, unless you are very lucky and have redundant excitation transformers. It would however be a relatively small task to remove and replace the excitation transformer if it failed, and relatively inexpensive to hold one as a spare for that eventuality.So far as why so supplier wants to supply a conservator type, I can only guess that they have no experience of hermetic types, or are using a stock design rather than devloping a new one, or they have some stock of the conservator type already available.
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ScottyUK (Electrical)
2 Dec 05 2:47
Oops - I said 'excitation transformer' when should have said 'auxiliary transformer'. Thoughts from my real job spilling through into my online one!
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norzul (Mechanical)
2 Dec 05 17:09
What are the disadvantages of hermetically sealed transformer as compared to that of conservator type?
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Electic (Electrical)
2 Dec 05 17:23
Norzul,I am not sure where you are located but in the USA I have not heard of 'hermetically sealed' transformers for normal distribution duty in the size you are specifying.I would expect either a welded tank or gasketed bolted tank with a pressure relief valve, fill and drain valves, bolt on bushings, bayonet fuse etc; most of which would preclude 'hermetically sealed'.I suggest you find a brand name you trust and go to their website or catalog and seek how their transformers are constructed, maybe check a couple of them out and write a spec about what you really need after seeing this.
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norzul (Mechanical)
2 Dec 05 17:44
Dear Electic/Guys,Fyi, I'm currently involved in a cogeneration project, 120 MW (4 Gas Turbines + 4 Heat Recovery Steam Generators + 1 Steam Turbine). It is a lump sum turnkey kind of project. Now, the status is towards the end of detailed design/procurement phase. We'd issued POs for the GTs and ST. Our company's technical standards require hermetically sealed transformer for 1600 kVA and below.The GT supplier complies with our stds. Unfortunately the ST supplier doesn't comply. The problem is, we just realized about this. Contractually we could still force them to comply....but...the schedule most likely will be affected & cause project delay...1st I try to convince myself that the conservator type is perfectly OK and perhaps more technically superior as compared to that of hermetically seal...before I go to my management for explanation...Thanksnorzul
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norzul (Mechanical)
2 Dec 05 17:50
Actually I'm looking for technical justifications to have conservator type transformer...perhaps yu guys can help me...since I'm not an electrical engr by dicipline.
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Electic (Electrical)
2 Dec 05 21:05
If I understand correctly the conservator type transformer is more appropriate for larger transformers over 10MVA. Even then it is a rarity these days with most manufacturers offering a nitrogen blanket system instead.Read my previous post about standard specs for the size of transformer you anticipate. Hermetically sealled and Conservator both sound like oddballs for 1.6MVA.
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norzul (Mechanical)
3 Dec 05 4:25
TQ Electic....I do agree with yu, however what I don't understand is why conservator type is appropriate for larger transformer over 10MVA i.e. needs for technical explanation
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matwong (Electrical)
4 Dec 05 23:45
In our case, we accept both type of trxs for our distribution network and there is no preference to any one of them. Personally, I will think this is the design concept adopted by different manufacturers where they will normally stick to the type that they have sent for type-test(for that particular ranges of trxs).The hermetically sealed type as mentioned earlier by ScottyUK claims to be "less maintenance" than conservator type. For the latter, one needs to replace the silica gel for the breather more often.Electric, Just wonder what is the normal distribution size of transformer used in USA if not as mentioned by norzul (1600kVA and below) ? FYI, hermetically sealed trx can be either adopted gas cushion (I presume same as nitrogen blanket) or thinner cooling fin system for 'breathing' purposes which are both acceptable in our MV distribution system.