EXPERIMENTAL INVESTIGATION OF SURFACE TRACKING FORMATION AND BREAKDOWN BEHAVIOR OF SOLID PRESSBOARD INSULATION IN TRANSFORMERS
III. Baskent International Conference on Multidisciplinary Studies, Ankara, Türkiye, 23 - 25 Eylül 2022, ss.397-412, (Tam Metin Bildiri)
- Yayın Türü: Bildiri / Tam Metin Bildiri
- Basıldığı Şehir: Ankara
- Basıldığı Ülke: Türkiye
- Sayfa Sayıları: ss.397-412
- İstanbul Üniversitesi-Cerrahpaşa Adresli: Hayır
Özet
The main source of heat generation in transformers is copper loss. Although hysteresis and
eddy currents cause heating in the transformer, the copper loss is very high compared to these
losses. If the heat generated in the transformer is not distributed correctly, the temperature of
the transformer will increase continuously, thus causing damage to the paper and liquid
insulation environment of the transformer. In electrical power transformers, external cooling
system is used to increase the rate of dissipation of transformer heat. Faults that may occur in
these systems affect the entire transformer system and may cause the windings to burn.
In oil-type transformers, pressboards are used together with oil for insulation. The pressboards
are found in the transformer submerged in oil. While the pressboards provide insulation up to
a certain voltage level, they can be pierced after a certain value. The breakdown situation in
solids is unidirectional, in other words, after breakdown, the distorted part in solid insulators
becomes completely conductive. Among the areas where solid insulators are widely used
today are underground high voltage cables with polymeric insulation and oil-impregnated
pressboards used in transformers.
It is known that some of the 400kV transformer boards used in the electricity transmission
network have unexpected surface and internal structure deterioration under normal conditions.
It is thought that these deteriorations observed in pressboard are caused by electrical
discharges that occur both on the surface and under the surface. These surface deteriorations
usually show themselves as surface tracking.
In this study, breakdown beaviour and surface tracking of pressboards used as solid insulator
in transformer were investigated. During the experimental studies, a non-uniform electric field was created on the pressboard thanks to the rod-plane electrode system. The distance
between the tip point of the rod electrode and the starting point of the plane electrode used as
the ground was adjusted to be 2 cm, 3 cm and 4 cm, respectively, and the experiments were
carried out. Experiments were carried out at only 5.4 kV and 10.8 kV high voltage levels,
with the voltage level being constant. Honeywell brand SS49E coded linear Hall Effect
Sensor was placed under the pressboard insulator and magnetic field values were read. In
addition, leakage currents over a 10 kΩ resistor were recorded with the help of an
oscilloscope. Harmonic values up to 1 kHz frequency value were examined. In addition, the
temperature differences on the surface were examined with the help of a thermal camera.