Water Tree Growth In Polyethylene Research Articles

Observation of water tree growth in polyethylene in real time

The growth of water trees that lead to breakdown in polyethylene insulation of underground power cables is studied in real time, using a special observation cell for polyethylene that can be placed on the stage of a conventional microscope. The growth of the water tree was followed by time-lapse photography. Sample results are given. The water tree is shown to grow from a single streamer to a bushlike structure. This structure acts as an electrode, and the cycle repeats, with another streamer being sent out. >

Permanent Inhibition of Water Tree Growth in Polyethylene

A solid organic material desirable for use as extruded electrical insulation on underground power cables should provide?in addition to the expected good electrical, chemical, and physical properties- permanent resistance to the pre-electrical breakdown mechanism called treeing. Screening of numerous families of materials has revealed many agents which, as additives, confer temporary resistance to treeing upon polyethylene. However, the search for non-migratory, non-volatile additives has proved long and difficult. Other approaches which provide permanent resistance to water and electrochemical tree growth are reported here.

Water Tree Growth in Polyethylene under DC Voltage Stress

Water trees have been experimentally grown in high molecular weight, low density polyethylene when subjected to a constant dc stress. Two major types of trees have been observed; bushy trees (one-half of a bow tie) emanating outward from microvoids and larger water channels penciling inward from the perimeter or outward from the center conductor. The coaxial dielectric was subjected to an average stress of 22 kV/mm in 70°C sea water to yield a growth rate for the bushes of 0.04 im/hr. Careful microscopic observation has shown a correlation between the electrical stress, the size of the microvoids, and the length of the bush. The water channels grow inward from the perimeter when the center electrode is negative at the rate of 0.2 μm/hr. When the center electrode is positive however} the water trees initiate growth but reach saturation in a short time.