resin rich are normally called "cast coil" units..search any leading transformer manufactuer's website and you should find related literature.
Cast coils are encapsulated in resin hence are much more robust, impervious to outside elements like moisure and dirt. Generally considered more reliable than VPI (Vaccum Pressure Impregnated) type.
I will have a look but in the meantime I will pass on what I was told on the subject by an old-timer. Resin-rich was better than VPI in terms of consolidation (this was apparent judging by the sectioned HV coils I have seen), but my former employer stopped using resin-rich windings because of health & safety considerations. It was very messy and difficult for the winder to stay clean.
However, I'm not experienced on HV insulation systems, maybe these B-stage tapes get enough resin in there where it counts for good consolidation. I have been a bit disappointed with the results of VPI of LV motor windings using un-impregnated tapes, on sectioned coils you can often push the individual conductors out very easily. It was usually proper VPI too, modern equipment with very low vacuum followed by high pressure.
Thx UKpete. It is my view too that resin rich (RR) is better than VPI for I have handled too many premature failures in VPI machines (failures within 1 to 3 years). I personally have been using RR for over 20 years with very good winding life (over 15 years).
Of late, there seems to be much hype about VPI and I wanted to know whether any serious study has ever been made comparing the two systems.
B-stage Resin rich coils have been used extensively in Europe and global VPI in America.
For high voltage machines (10kV+) the resin rich have many advantages as compared to global VPI.
Each individual coil or bar can be tested for void content before assembled in the winding. The manufacture cost and winding procedure certainly are increased with resin-rich pressed coils due to the rigid condition.
For medium voltage motors (6kV>Vll) the VPI has better performance.
The coils cost much less.
The assembly of the winding is easy.
The heat transfer is improved.
Medium voltage resin rich pressed coils are too fragile due to the very thin ground insulation. This makes them very susceptible to insulation fractures during the winding process.
For VPI process the initial investment is high and a good vacuum system, accurate control of the vacuum, pressure time, winding temperature and resin condition are mandatory to get the required penetration of resin.
At our plant we have had much better luck with vpi than "resin rich" = B-stage = hard coils. This applies both to results during predictive maintenance (including partial discharge) and to failures.
My general impression is most OEM's have moved to vpi and repair shops use resin rich for reasons that have more to do with cost and manufacturability than reliability of the finished product. I may be wrong but that's what I believe. I was unaware that there are European OEM's using resin rich as mentioned in earlier post.
I have a few epri documents which discuss it in brief details but not much more than a few sentences comparing the methods.
VPI is generally believed more resistant to moisture and contamination. More resistant to loosening or movement of coils. Also more difficult to strip for rewind.
B-Stage was mentioned better ability to test individual coils wherease reduced voltage needs to be used for testing uncured vpi coils.
Certainly either method can be done poorly to produce bad winding but my belief is vpi is superior and if quality is built in through process control the disadvantages of inability to test coils is not so much.
Wish I had more info. I know there are many different opinions and I have not found a lot of hard data on reliability. Let me know if you find some more.
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My experience with VPI windings is opposite of yours. I have replaced a few prematurely failed VPI windings with resin rich ones and they have all been working well. As you say, it is all in the process control. Our RR coils have passed all tests including PD and Tan delta tests without any issues.
My theory of OEM's adapting to VPI is that RR coils, being rigid and fragile, requires skilled winders which they lack. (All the old hands have retired and it takes a long time to train new winders).
You mentioned about some epri documents. Could you possibly mail them to me ?
I think for both systems the results depend on the process control. That is the combination of materials, equipment, procedures and people skills.
For VPI; materials, equipment and procedure are the key of success; people skill is not that important since the coils are quite flexible and the optimum impregnation process is programmed in a modern system. That implies a large initial investment out of small repair shops budget.
The resin rich hot pressed coils are kind of forgiven and success depends on the coil manufacturer quality and the winders skill not to damage the coil insulation during the assembly process.
I have been involved in both systems but to be competitive 90% or more of our rewinding are VPI type. We have VPI rewound several motors , 5000 HP,890rpm, 6.6 kV and 2500 HP,225 rpm, 6.6 kV which are working after 15 years.
