TanDelta test in Formed coils

[petronila]

Dear All,

We are manufacturing a new formed coils for a 6.6 KV machine, all coils are tested by tan delta test using a Doble M4100 equipment and the test was mede in acordance with the EN 50209 so we apply 5 steps of 20% up to reach the rated voltage.

The test readings was 0.00642(20%)-0.00656(40%)-0.00737(60%)-0.01292(80%) and 0.02132(100%) are this a good values?

Thanks for the inputs

Regards

Petronila

 

[edison123]

Per BS 4999

Initial tan delta at 0.2U must be less than 0.03

Tan delta tip up (0.6U - 0.2U) < 0.05

Delta tan delta for other steps of 0.2U< 0.05

Your (1.0U - 0.8U) is about 0.084 seems to be above this limit.

Muthu

http://www.edison.co.in

 

[electricpete]

The 20% value is supposed to indicate the quality of the resin. (0.6% sounds pretty good to me... but best comparison is against similar coils).

The tipup is supposed to be an indication of voids (in absence of interfering effects. FWIW, a GENERAL thumbrule I recall was less than 1% tipup (difference 100% and 20% readings) for coils with no stress coatings or with slot section guarded. Looks like yours is 2%-0.6% = 1.4% which doesn’t meet that particular thumbrule.

** DISCLAIMER... I am no expert. Typically this type evaluation is done by coil manufacturer considering the history / characteristics of the insulation and condition (impregnated or not) in consultation with their customers to ensure concerns on both sides are satisfied.

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[electricpete]

It sounds like those international standards have specific quantitative limits. There are no hard limits in IEEE 281.

I wanted to highlight that if stress control coatings are present, then guarding technique is important.

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[edison123]

Decimal Correction

Tan delta tip up (0.6U - 0.2U) < 0.005 (0.5%)

Delta tan delta for other steps of 0.2U < 0.005 (0.5%)


Muthu

http://www.edison.co.in

 

[petronila]

Hello Muthu and Electripete thanks for the answers.

I would like to know the possible causes for this bad readings in steps 4 and 5. The coils are manufactured with hot presses, 7 mica layers and 1 semiconductive tape layer, 10 turns with two wires in hand and the wire is enamelled and glass covered.

Thanks for the inputs

Carlos

 

[edison123]

Can't say much without knowing your process. Insufficient resin, poor taping process, bad quality tapes come to mind.

Muthu

http://www.edison.co.in

 

[Younsi]

Carlos
Good points from all. Please check your process capability for similar coils as well. Check the distribtion of DF and TU across all your coil population. Outliers are often difficult to explain without very carefull inspection or even coil dissection. Plot separate histograms for each of DF at 20% and DF at 80% or 100% and check how they look like.
A customer spec is typicall what OEMs follow. A given batch can be OK with customer A and unacceptable for customer B.
Just as Electricpete suggested we follow the ~0.5%DF at low voltage and 1% TU bsic rule. This rule is harder for higher voltage coils though. In general I don't see in your values shockingly high levels. Although I am not recommending to use them or scrap them.
Karim