Comparative Study on Impact of Cellulose Particles on Electrical Conductivity of Mineral Oil and Natural Ester

Conference: VDE-Hochspannungstechnik 2016 - ETG-Fachtagung
11/14/2016 - 11/16/2016 at Berlin, Deutschland

Proceedings: VDE-Hochspannungstechnik 2016

Pages: 6Language: englishTyp: PDF

Personal VDE Members are entitled to a 10% discount on this title

Authors:
Vahidi, Farzaneh; Tenbohlen, Stefan (Institut für Energieübertragung und Hochspannungstechnik der Universität Stuttgart, Deutschland)
Rapp, Kevin; Luksich, John (Cargill Inc. Plymouth, MN, USA)

Abstract:
The demand for new facilities to transmit electrical power is increasing. The energy between power plants and substations is carried using two techniques: AC technique offers transmission with high efficiency and low power losses because it can simply be transformed to higher voltage levels, and DC technique, which uses direct current for the bulk transmission of electrical power that is normally used for transmission of energy over long distances. The power transformers are the most valuable component in these systems and they impact all the networks with their operation. The design of feasible insulation for AC and converter transformers requires the understanding of field distributions in insulating materials, which are normally a combination of oil and cellulose. The AC field distributions in transformers depend on the permittivity. Contrary to AC field distribution, DC field stresses are determined by the conductivity of the insulating materials. Therefore knowledge about the conductivity of the oil is of tremendous importance for design and safe operation in the DC technique. The conductivity of insulating liquids is dependent on several parameters, e.g. time, temperature, particle content, and electrical field strength. In this contribution, a measurement set-up for analysis of oil conductivity is presented. The time behavior of electrical conductivity is investigated using Envirotemp(TM) FR3(TM) natural ester and Nytro Lyra X mineral oil. The aim of this comparative study is to illustrate the electrical conductivity behavior of natural ester and its applicability as HVDC insulation. Natural ester liquids as insulation material in power transformers offer many advantages compared to conventional mineral oils. Higher thermal capability, higher flash/fire points and better environmental sustainability are some of the advantages of using natural ester. Furthermore, the impact of cellulose particles on electrical conductivity is studied. Different amounts of cellulose particles are added into dried oil specimens and the time behavior of electrical conductivity is measured after applying different DC stresses. The results indicate an increase of conductivity with an increased amount of cellulose particles for the two mentioned insulating liquids.