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Topic Title: Transformer insulating oil
Topic Summary: Mixing two oils of the same type from different manufacturers
Created On: 16 January 2014 12:23 AM
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 16 January 2014 12:23 AM
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bswales

Posts: 3
Joined: 09 May 2012

I have a need to mix transformer insulation oil manufactured by two different manufacturers (Shell & Nynas). Both are ASTM D3487 TYPE II inhibited insulation oil.

I know it can be done but i am having difficulty convincing the end user that this is OK. Does anyone have experience with this and, in particular can anyone cite any reference stating that is is acceptable?

Thanks
 17 January 2014 02:57 PM
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jarathoon

Posts: 1040
Joined: 05 September 2004

Why should your customer accept a product without a certificate of conformity? I don't think they should.

If you mix the two oils from the two different manufacturers the onus must be on you to get the necessary tests done to prove that the mixture you make up still meets the standard; otherwise what is the point of having the standard in the first place.

The problem is if you mix up a small sample for testing, and it passes, how can you guarantee to you're customer that you have used exactly the same proportions when mixing up the full batch of supplied oil? If you mix up a complete batch for sample testing and it fails, you potentially have mixed a comlete batch of waste oil. Therefore you would in practice need to test a trial sample and then test a batch sample, once the full batch is mixed.

But what happens if you run out of this formulation and more needs to be mixed up later, for maintenance or refurbishment work say?

You would then need to produce some more of your product from two new batches of oil from the two different manufacturers. The question is would the original tests you made still be valid for this later mixture? I would say no. Therefore the onus would be on you to get some new tests done, so you can supply your customer with a certificate of conformance.

Therefore once you have created your new formulation, you then faced with the question of how your firm or indeed another firm would support this formulation in the future. e.g. What happens if your customer wants to use a new supplier in a few years time? Your customer will presumably need a copy of the procedure you used for mixing up the oil and getting it tested.

Alternatively forget about becoming a oil manufacturer, and keep things clear and simple for your customer.


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James Arathoon
 17 January 2014 03:35 PM
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OMS

Posts: 19468
Joined: 23 March 2004

If you are mixing two graded, inhibited oils to the same standard then there is usually no problem.

There can be, and often are, mixed with no problems as they are highly miscible.

If you actually look in the standard, you'll find :

"............a mineral insulating oil that is functionally interchangeable and miscible with existing oils, is compatible with existing apparatus and with appropriate field maintenance, and will satisfactorily maintain its functional characteristics in its application in electrical equipment."



Regards

OMS

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Failure is always an option
 17 January 2014 03:56 PM
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jarathoon

Posts: 1040
Joined: 05 September 2004

So presumably Nynas and/or Shell will be duty bound to confirm to bwales on request (and for the benefit of his/her customer) that their two oils when mixed can meet this provision in the standard.

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James Arathoon
 17 January 2014 04:10 PM
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Drawde

Posts: 1
Joined: 10 January 2003

Should an issue arise with the operation of the transformer and it is subsequently identified as an oil problem e.g. moisture ingress and reduction in dielectric value, which oil company will pick up the tab? The conclusions depend on the choices made.
 17 January 2014 05:41 PM
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Zuiko

Posts: 521
Joined: 14 September 2010

OMS is 100% correct.

Oil is reguarly mixed: when the conservator of the power transformer needs topped up; it is never topped up with oil from the same batch (because of the time frame); and not necessarily with oil from the same manufacturer (the transformer owner may have changed suppliers) or of the same "type" (for example, most DNOs now use reclaimed oil instead of "new" oil.) The same goes for switchgear maintenance (although the oil is often replaced rather than topped up in that case, there will always be residue from the earlier oil).

This is the entire point of the standard, as pointed out by OMS. It is a practical impossibility to ensure a particular piece of plant will always contain oil of the same type, from the same manufacturer, from the same batch, throughout its life.




However, the obvious question is are you mixing in the first instance? Whilst it is unavoidable during the several decades the transformer will be running; in the first instance, I can't see the point?

Edited: 18 January 2014 at 11:05 AM by Zuiko
 17 January 2014 05:50 PM
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OMS

Posts: 19468
Joined: 23 March 2004

Mmmm - let me ask you both one question.

For engineering reasons, it's decided to replace the oil in a transformer.

You have no details of the original oil manufacturer or supplier, only the type (or standard to which it was manufactured) - so you intend to drain down and refill

How much original oil is left in the windings and core following drain down ? - that then mixes with the new oil.

From experience, both the named suppliers compliant ASTM D3487 TYPE II inhibited oils can be mixed, and usually both Nynas and Shell will confirm very similar ratios of additivies (the inhibitors) in thier base high grade mineral oil

You'll find similar statements to the one I posted in IEC 60296 regarding mixing of oils to the same standards.

All that's needed is a simple check on the compatibility of the inhibitors.

To be clear, I wasn't suggesting rushing off and doing it - just that it can easily be done with a few simple checks, and it's done frequently - if the OP's client won't accept it, then that's a contractual matter - technically, its perfectly feasible to do - indeed one of the points in the standards referenced is that it must be able to be done.

Regards

OMS

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Failure is always an option
 06 February 2014 08:40 AM
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bswales

Posts: 3
Joined: 09 May 2012

Thanks for all comments. The issue has only come about as a matter of urgency to get a spare 875 MVA GSU online rapidly but the end user is a few thousand litres short, and the alternative oil is the only one available quickly.

Since I posted, the transformer manufacturer has come back and supports mixing the two products as proposed, so this will proceed.
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