Degradation Mechanism of Power Transformer's Insulation System in PLN Indonesia

Insulation system of power transformers consists of solid insulation and liquid insulation. Insulation system has a function to insulate among active parts or between active parts to ground. Insulation system, especially insulation paper could lose its ability to insulate due to ageing which consist of several mechanism i.e. hydrolysis and pyrolysis. Those two mechanisms can be detected by observing its symptoms. Hydrolysis which led by insulating oil oxidation will shows the changing of insulating oil physical properties. While pyrolysis which led by local overheat will generate combustible gases. Both hydrolysis and pyrolysis will generate CO and CO2 gases and generate 2-Furfural compound. But in hydrolysis mechanism, the generation of 2-Furfural compound will be massive due to general area of insulation paper are involved. Ageing rate of PLN's power transformers will be depends on several parameters i.e. ambient temperature, humidity, loading and preservation system. This paper explains dominant failure mode that happened in PLN's power transformers due to climate, design and operational factors.