Recently, some customers have asked us to quote for xlpe cables made with water tree retardant xlpe compound.
Our contention was that since we use hot nitrogen in our CV tube for curing xlpe compound, this requirement was superfluous and that the compound was necessary for steam cure lines only.

Please let me have your comments in the matter please

Hello there,

I am sorry to tell you that your premise is incorrect as there are a number of reasons for the generation of electrical trees in XLPE insulation. They include damage to the inner shield - insulation interface from pre-cure particles, bad plastic flow, poor tooling, impurities and so on. Insulation impurities and voids can also be starting spots for electrical trees.

You are correct in that electrical trees were originally associated with XLPE steam curing hence the name water trees. In today's world however, the term water trees should be replaced with the term electrical trees.

We always offered and still offer our customers the choice of super-clean XLPE or super-clean tree retardant XLPE on low, medium and high voltage XLPE cable. (Say 138 kV and below.)

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

Thank you for the clarification

With best regards

Hello again,

This is my understanding of how the term "water tree" came about.

In the early days of steam curing, it was determined that, once extruded and inside the steam pressure tube environment, the not yet cured polyethylene was particularly transparent to water vapor. The water vapor goes into solution in the polyethylene and, after cross linking and initial cooling, some water vapor gets back out via the conductor and the outside surface of the cable. Many millions of small water droplets however condense inside and towards the radial center of the insulation. The water then evaporates when the insulation is left to degas at room temperature or in degassing ovens, leaving millions and millions of very small holes in the insulation. There are so many of these little holes that they can be seen with the naked eye and they are often referred to as a "halo" inside the insulation because they look like a milky ring or "halo".

Electrical trees can and will form from flash overs across these holes (Keeping in mind that there is a voltage gradient radially outwards in the insulation.). Thus the term "water trees" was born.

Regards
Peter J. Stewart-Hay
Principal
Stewart-Hay Associates
www.Stewart-Hay.com
519 641-3212

Thank you again..
...do not know if you remember... we met at Borivali..Mumbai.
Heard you were at Nashik...sorry could not meet you as I am away from Mumbai nowadays.

With Best Regards,

ngkotecha

naren kotecha

Hello again Naren,

Yes of course I remember you although I'm afraid I would not have made the connection without your advice. That meeting was two years ago from last April. I still have your former business card and I had asked about you to keep our business contact list up to date.

I'm sorry as well we did not meet while I was there this time but then India is such a large and busy country. When I was at Nashik, I had the weekends free and was at the Gateway Resort Hotel so there was time.

I do indeed hope you are having good success with your new company. It is a very small world.

With best personal regards
Peter J. Stewart-Hay
Principal
Stewart-Hay Associates
www.Stewart-Hay.com
519 641-3212