HV failure in EHV cables manufactured by MDCV Proc

We manufacture ehv cables upto 230kv in MDCV line. Recently we have observed HV failures due to ingres of sharp protrusions from conductor screen into insulation.

Request any suggestion for its cause,

SKD

Dear SKD,

Unfortunately, I am one of the very few on the planet who has built and started a very reliable, fully computerized MDCV line using what we believed at the time to be the very best extrusion equipment (extruders and crossheads) in the world for MDCV.

As I am sure you are well aware, there is a great deal of secrecy about these machines and this prevents licensees from discussing mutual (Or even unique processing MDCV problems such as you have described.) with each other. This is naturally all rigidly enforced by Mitsubishi.

I have of course personally signed secrecy agreements both with Mitsubishi and my former employer and I am well familiar with the equipment Mitsubishi proposes for a typical MDCV line. Perhaps this is what you have but for goodness sake, do not tell me or make this public.

If you are a senior engineer with your company then I am sure we have both visited the same plant and seen the same machines running in Japan. We will also know the same Mitsubishi engineering and licensing people at the plant and in Tokyo. The MDCV world is very small and I was previously aware that your company was an MDCV licensee. Our license was negotiated some short period of time after yours.

Saying all that, an inner shield problem of the type you have described is not particularly a problem associated only with an MDCV line but rather with triple extrusion in general (All voltages) and that is where you should be looking. Perhaps you should contact the supplier of your extruders and the MDCV process designed triple crosshead. You may also wish to discuss this with your polymer supplier(s).

Likewise you should make sure your inner shield, semi-conducting, super-smooth compound is fully dried with a desiccant type drier before extrusion, that the dryer is actually functioning properly and that there is no pre-curing in that inner shield extruder or in the transfer tube equipment (if any). Make sure that all your temperature controllers are working properly and that all thermocouples are properly positioned and in good contact in the various thermocouple wells in the equipment. Finally, make sure that your crosshead and tooling are in really good shape so that there are no minor hang-up points or small dead zones where the compound could crosslink before being applied to the conductor.

Apart from the above very generalized information appropriate to any triple extrusion system, the only other legal way you could possibly deal with us for full process analysis and correction I believe would be to contract with us as a consulting engineer, place us under your secrecy agreement for suppliers and contractors and have me visit your plant. You would first however have to get a legal opinion on this from your attorneys and provide us with a "hold harmless" agreement.

I am truly sorry but I cannot say any more than this but as you can well understand, this is the way it is.

Hopefully others using different EHV cable manufacturing equipment such as a Sumitomo CCV EHV line can give you more proper advice here at the WAI Forums.

Good luck with the resolution of your problem.

Peter J. Stewart-Hay
Principal
Stewart-Hay Associates
www.Stewart-Hay.com

If you have knit lines check your crosshead and temperature profile.

JA

Hello there Santa,

I think I know your machine and I guess it is pretty old by now. No doubt it has been overhauled once or twice. Glad to hear that it is still working well although I was advised of an initial installation problem your company had. (Only so we wouldn't make the same error.)

Your company contacted me about 12 years ago when I was still employed by Canada Wire re the pollution control system I developed with a chemical consulting engineering company and installed on our new technology machine. Our machine was a completely closed system for the heating/cooling water. Anyway, at that time and because your machine was so old, we could not discuss any new technology with your company. I'm sure you know why if you indeed are intimately involved with MDCV. The environmental technology was never patented and now I can discuss it with your company. Contact me privately if you want to know more.

Peter J. Stewart-Hay
Principal
Stewart-Hay Associates
www.Stewart-Hay.com