http://www.electrotechnik.net/2009/07/water-trees-and-electrical-trees-and.html

http://jeen.fei.tuke.sk/index.php/JSES/article/view/291/359.

http://publications.lib.chalmers.se/records/fulltext/159090.pdf

these are two different phenomena with different mechanisms, although in certain situations both can appear simultaneously. I also suggest to consult the excellent book of Dissado and Fothergill:

http://www.amazon.com/Electrical-Degradation-Breakdown-Polymers-Materials/dp/0863411967

Water trees initiate at a point of electric stress and grow parallel to the electric field lines. The growth of a water tree causes a reduction of the effective insulation thickness below the point that is required to withstand the electric stress, after which electrical tree causes the cable to fail. It was observed that the growth rate of wet trees increases with the conductivity of water.

 Electrical tree is also found to grow in a region of high electrical stress, such as metallic asperities, conducting contaminants, and structural irregularities.

The difference between water tree and electrical treeing:

   - Water Treeing :

    ▪ already at low field strength(˂1kV/mm)

    ▪  extremely slow tree discharge recognizable

    ▪  not visible

  - Electrical Treeing :

   ▪ at high local strength

   ▪ very fast tree growth in PE or XLPE insulation

   ▪ accompanied by partial discharge

   ▪ long channel structures(visible trees)

   ▪ clear indication of an electrical breakdown

Dear Sied Mohsen,

Treeing in extruded dielectric cable insulation is the term that has been given to a type of electrical pre-breakdown deterioration that has the general appearance of a tree-like path through the wall of insulation. Trees form in insulations XLPE are considered as two distinct types:

• Water trees :

-Develop from voids, contaminants and defects which occur within the insulation or on the semiconducting screen. The phenomenon is not confined to highly stressed dielectrics. Many trees have been found in cables operating at stress levels of less than 1 kV/mm. 

-Water trees grow in the direction of the electrical field and emanate from imperfections which have the effect of increasing the electrical stress at local sites. The branches of water trees are very narrow, of the order of 0.05 um

-Water trees increase in length with time, frequency and increasing voltage.

- Water required, Fan or bush shaped, Grow for years, Microvoids connected by tracks

• Electrical trees :

-Electrical trees in extruded dielectric cables are the result of internal electrical discharges that decompose the organic materials.

- Water not required, Needle or spindle shaped, Failure shortly after formation, Microvoids connected by tracks, Carbonized regions.

- Several mechanisms have been proposed to explain the initiation of electrical trees. Each requires a very high electrical stress to attain the energy level that would be required. Below are some of the possibilities:

1. Localized heating and thermal decomposition

2. Mechanical damage due to high electrical stress

3. Fatigue cracking from polarity changes

4. Small voids

5. Air inclusions around contaminants

6. Electron injection.

Best regards.

Water trees can grow in the insulating materials which is exposed to the water and that is consist of dissolving ions or without dissolving ions in an ac electric field. In water trees they can take long time to initiate and grow and in water trees the growth rate is growth rate £ 1mm/day. Water trees can’t grow in the pure d.c field.

I think my new article can help you in this regard

please follow this DOI:

10.1007/s11664-019-07402-4

Article Comparing the Performance of γ-Alumina Nanofiller and Titani...

Sied Mohsen Hosseini