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Topic Title: failing of Transformer Turns Ratio Tests
Topic Summary: how to proceed when TX fails a 3 phase test, but seems to pass phase by phase?
Created On: 10 July 2013 07:01 PM
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 10 July 2013 07:01 PM
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Posts: 10
Joined: 18 January 2003

We have had a new 11000/ 400 transformer fail primary tests on turns ratio, the test facility are using a Vanguard ATRT-03B tester. Results are wildly out - like A - 98, B - 29, C - 18 .

Never seen anything like it, but interestingly when I asked them to repeat, but not as a complete 3 phase test, but phase per phase, and using a method prescribed for field testing of ratio and vector group using single phase at time :

HV side Neutral line connect and A phase side connect. B phase and C phase left open, do not connect any terminals. On LV side connect a phase and c phase, b phase leave it open. Program your automatic ratiometer to correct vector group YNd11, commence testing. use use HV/LVxSqrt3,

Then results per individual phase where ok and as expected - generally around 15.9 for a step up 0.4 to 11kV YnD11.

Questions are:

1. What does this indicate - a mis-configuration on the internal winding connections, and as a result some unknown vector group.
2. why does it seem to pass the phase by phase method, yet not when all phases connected and using the instrument in automatic mode - the unit does equally not pick up that the TX is a YnD11, and comes up with result unknown?
3. as a result we now loose confidence in the supplier, so any thoughts on what else we do to obtain piece of mind that the unit is any good?
4. what exactly is the prescribed test method - BS EN 60076-1 is pretty vague, section 10.3 does not say much at all?
5. We wanted to call on the manufacturer to open it up for inspection, but they claim not required, they have fulfilled the requirement and it is fine! What can we actually use to cite a non-conformance of the code or accepted practise etc?

Sorry, a long post, but I am a bit lost, and Interested in anyone who has had similar experience, and how the rectification process went.



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