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SUMMARYThe partial discharge (PD) activity during propagation of electrical treeing in epoxy resin is described. The electrical trees grew in needle-plane samples without and with an internal barrier up to the final breakdown. The simultaneous tree growth and discharge activity show a correlation between the propagation state of the tree and the thereby measured PD. Especially, the changes in the tree structure can clearly be detected. Based on these characteristics a new model describing tree growth is presented. It appears that measurements from machine insulation can be interpreted in terms of the PD pattern.

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The use of high voltage cables is today recommended and sometimes mandatory in order to avoid environmental concerns of the public, especially when the power system is crossing areas of dense population. The reunion of the former GDR with the Federal Republic of Germany has stimulated the interest in this settlement especially for the city of Berlin, where the increase of energy demand requires the use of innovative solutions. The paper reports the activities that BEWAG, the electrical utility of Berlin, performs in order to investigate the feasibility of setting up an urban bulk power connection using 400 kV XLPE cables During a first accelerated voltage endurance test (at CESI in Miladtaly) on cables and accessories of six major European manufacturers several failures in joints and SF6 terminations were encountered [l]. testing period were additionally equipped with partial discharge sensors for an insulation monitoring system. Sensors of this type will in the future be integrated into the cable accessories to improve after laying quality control. It is thought that this partial discharge test will replace high voltage DC-tests which were found unsuitable for the 400 kV XLPE cable technology.

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For reliable verification of the quality of both, new and aged insulating systems, not only the correct measurement of significant internal partial discharges (PD) but also an exact localization and physical interpretation of the detected PD-signals is needed. A step forward towards the interpretation of conventionally measured PD-signals is realized by a digital data processing. This paper describes PD-measurements performed on different highvoltage apparatus using a computer controlled phase resolving partial discharge analyzer (PRPDA). The PRPDA-system records partial discharge (PD) activity of a test object during a given number of cycles of the applied ac voltage, or during a fixed time. Some typical results obtained in SFg-insulated systems (GIs), power transformers and power generators in off-line and in on-line condition are presented and discussed.

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