Water trees in cables-experimental findings and theoretical explanations

Experimental results on service-aged high voltage cables and results of experiments in which full-size cables were used are reconsidered. The results are discussed in connection with the model concept of the water treeing phenomenon. It is shown that water treeing is primarily a result of dielectrophoretic forces on water molecules that lead to a local supersaturation of the water molecules and, as a consequence, to the creation and growth of water trees. The important point in this process is the formation of a liquid phase. It is concluded that the size distribution of water trees, the influence of soluble particles, or the influence of a temperature gradient across the insulation can be understood on the basis of a model concept involving dielectrophoresis and precipitation phenomena as the important points. A numerical growth simulation based on this model concept leads to a true description of the size distributions of water trees found in cables