Abstract
The aim of this study is to create references to mineral oil and recommendations for design rules for ester oil applications. Interest in the application of natural and synthetic ester-based fluids in different types of high voltage power equipment has increased over the last years. Most of the parameters relevant to insulation and cooling of high voltage equipment are studied at room or normal operating temperatures. Nevertheless, this equipment has to keep its functionality over the range of various uncommon conditions. For regions with cold climates, an important issue is the behaviour at low temperature. The objective of this work was to determine the insulation strength of mineral- and ester-based oil under a homogenous field at low temperatures for different oil states (moisture content between 5 and 25%). At low temperature (-25°C), the tested ester-based oil is not solidified but in a very thick aggregate state. At this temperature its insulation strength is still very high, even higher than at room temperature. As soon as the ester-based oil becomes solidified (-35°C), its insulation strength drops dramatically. The insulation strength of the tested ester-based oil at a low temperature, when the oil changes its aggregate state, is not dependent on water content.
Highlights
ester-based fluids in different types of high voltage power equipment has increased over the last years
relevant to insulation and cooling of high voltage equipment are studied at room
this equipment has to keep its functionality over the range of various uncommon conditions
Summary
Napon se podiže 2 kV/s sve do proboja. Ova vrednost je maksimalni izlazni napon korišćenog AC 60 Hz testera ulja (Baur DTA 100 E – slika 1). Korišćene su merne ćelije od pleksiglasa zapremine 1.5 l (slika 1), prvenstveno zbog male potrošnje i jednostavnosti. Ukoliko su merenja vršena na sobnoj temperaturi, merne ćelije se jednostavno postavljaju na tester ulja i zatim se testiraju. Ukoliko su merenja vršena na niskim temperaturama, merne ćelije sa uljem bi najpre bile ostavljene unutar rashladne komore Vötsch VT 7010. Na temperaturi od -35 °C, odnosno -25 °C, viskoznost Lyra X ulja raste, ali je ulje i dalje u izrazito tečnom stanju (slika 2 i slika 3). Na temperaturi od -35 °C FR3 ulje je u potpunosti zaleđeno, dok je na -25 °C u čvrstom agregatnom stanju (slika 2 i slika 3). Merna ćelija sa Lyra X uljem (levo) i FR3 uljem (desno) na temperaturi od -35 °C
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