Details
| Original language | English |
|---|---|
| Title of host publication | 2020 IEEE Electrical Insulation Conference, EIC 2020 |
| Publisher | Institute of Electrical and Electronics Engineers Inc. |
| Pages | 298-301 |
| Number of pages | 4 |
| ISBN (electronic) | 9781728154855 |
| ISBN (print) | 978-1-7281-5486-2 |
| Publication status | Published - 2020 |
| Event | 2020 IEEE Electrical Insulation Conference, EIC 2020 - Knoxville, United States Duration: 22 Jun 2020 → 3 Jul 2020 |
Abstract
Wax-formation in electrical equipment is usually associated with oil impregnated cables and capacitors. Its formation is generally attributed to high field strength and partial discharges. In context with power transformers x-wax only appeared in the bushings. In recent years, however, there was an increasing number of failures in hermetically sealed power transformers with wax formation in the high voltage windings. Wax formation in transformers may block the cooling ducts and lead to overheating. Especially compact power transformers with synthetic ester and silicone fluid seem to be affected. This investigation sought the necessary conditions under which x-wax is formed in power transformers and how these conditions differ for different types of insulation liquids. A laboratory model of the high voltage insulation of a distribution transformer is used to investigate the influence of temperature, partial discharges (PD) and pressure on the x-wax formation. In hermetically sealed transformers the internal pressure can change depending on the load and ambient conditions. Previous investigations have shown that small reduction of the internal pressure can significantly reduce PD inception voltage and increase the apparent charge of the PDs. This is a transient situation that may happen in wind turbine transformers when the transformer cools down during a calm phase. For this study, different insulation fluids, such as synthetic and natural esters, silicone fluid and mineral oil are stressed with partial discharges for 200 hours at various temperatures both at ambient pressure and at a reduced pressure of approx. 800 mbar. The partial discharges are monitored to allow a comparison between the PD energy and the amount of wax formed during the experiment. The overall behavior of the PD was quite different with the different liquids, requiring an increasing voltage to keep igniting in the case of natural ester. Dissipation factor, permittivity, DC resistance and breakdown voltage of the fluids are measured before and after the PD stress to see if these can be used as indicators for wax generation. The investigation shows, that, when stressed with partial discharges over extended periods of time, all insulation fluids form some sort of solid ageing product, which are being investigated and may or may not be classified as x-wax. The amount of solid and the conditions under which they are formed differs greatly according to type of the fluid.
Keywords
- insulation liquid, mineral oil, natural ester, power transformer, solid ageing products, synthetic ester, x-wax
ASJC Scopus subject areas
- Energy(all)
- Energy Engineering and Power Technology
- Engineering(all)
- Electrical and Electronic Engineering
- Engineering(all)
- Safety, Risk, Reliability and Quality
- Materials Science(all)
- Electronic, Optical and Magnetic Materials
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2020 IEEE Electrical Insulation Conference, EIC 2020. Institute of Electrical and Electronics Engineers Inc., 2020. p. 298-301 9158704.
Research output: Chapter in book/report/conference proceeding › Conference contribution › Research › peer review
}
TY - GEN
T1 - Investigation of X- Wax Formation in Power Transformers under Operating Conditions
AU - Kuhnke, Moritz
AU - Werle, Peter
AU - Sbravati, Alan
AU - Rapp, Kevin
PY - 2020
Y1 - 2020
N2 - Wax-formation in electrical equipment is usually associated with oil impregnated cables and capacitors. Its formation is generally attributed to high field strength and partial discharges. In context with power transformers x-wax only appeared in the bushings. In recent years, however, there was an increasing number of failures in hermetically sealed power transformers with wax formation in the high voltage windings. Wax formation in transformers may block the cooling ducts and lead to overheating. Especially compact power transformers with synthetic ester and silicone fluid seem to be affected. This investigation sought the necessary conditions under which x-wax is formed in power transformers and how these conditions differ for different types of insulation liquids. A laboratory model of the high voltage insulation of a distribution transformer is used to investigate the influence of temperature, partial discharges (PD) and pressure on the x-wax formation. In hermetically sealed transformers the internal pressure can change depending on the load and ambient conditions. Previous investigations have shown that small reduction of the internal pressure can significantly reduce PD inception voltage and increase the apparent charge of the PDs. This is a transient situation that may happen in wind turbine transformers when the transformer cools down during a calm phase. For this study, different insulation fluids, such as synthetic and natural esters, silicone fluid and mineral oil are stressed with partial discharges for 200 hours at various temperatures both at ambient pressure and at a reduced pressure of approx. 800 mbar. The partial discharges are monitored to allow a comparison between the PD energy and the amount of wax formed during the experiment. The overall behavior of the PD was quite different with the different liquids, requiring an increasing voltage to keep igniting in the case of natural ester. Dissipation factor, permittivity, DC resistance and breakdown voltage of the fluids are measured before and after the PD stress to see if these can be used as indicators for wax generation. The investigation shows, that, when stressed with partial discharges over extended periods of time, all insulation fluids form some sort of solid ageing product, which are being investigated and may or may not be classified as x-wax. The amount of solid and the conditions under which they are formed differs greatly according to type of the fluid.
AB - Wax-formation in electrical equipment is usually associated with oil impregnated cables and capacitors. Its formation is generally attributed to high field strength and partial discharges. In context with power transformers x-wax only appeared in the bushings. In recent years, however, there was an increasing number of failures in hermetically sealed power transformers with wax formation in the high voltage windings. Wax formation in transformers may block the cooling ducts and lead to overheating. Especially compact power transformers with synthetic ester and silicone fluid seem to be affected. This investigation sought the necessary conditions under which x-wax is formed in power transformers and how these conditions differ for different types of insulation liquids. A laboratory model of the high voltage insulation of a distribution transformer is used to investigate the influence of temperature, partial discharges (PD) and pressure on the x-wax formation. In hermetically sealed transformers the internal pressure can change depending on the load and ambient conditions. Previous investigations have shown that small reduction of the internal pressure can significantly reduce PD inception voltage and increase the apparent charge of the PDs. This is a transient situation that may happen in wind turbine transformers when the transformer cools down during a calm phase. For this study, different insulation fluids, such as synthetic and natural esters, silicone fluid and mineral oil are stressed with partial discharges for 200 hours at various temperatures both at ambient pressure and at a reduced pressure of approx. 800 mbar. The partial discharges are monitored to allow a comparison between the PD energy and the amount of wax formed during the experiment. The overall behavior of the PD was quite different with the different liquids, requiring an increasing voltage to keep igniting in the case of natural ester. Dissipation factor, permittivity, DC resistance and breakdown voltage of the fluids are measured before and after the PD stress to see if these can be used as indicators for wax generation. The investigation shows, that, when stressed with partial discharges over extended periods of time, all insulation fluids form some sort of solid ageing product, which are being investigated and may or may not be classified as x-wax. The amount of solid and the conditions under which they are formed differs greatly according to type of the fluid.
KW - insulation liquid
KW - mineral oil
KW - natural ester
KW - power transformer
KW - solid ageing products
KW - synthetic ester
KW - x-wax
UR - http://www.scopus.com/inward/record.url?scp=85092176447&partnerID=8YFLogxK
U2 - 10.1109/eic47619.2020.9158704
DO - 10.1109/eic47619.2020.9158704
M3 - Conference contribution
AN - SCOPUS:85092176447
SN - 978-1-7281-5486-2
SP - 298
EP - 301
BT - 2020 IEEE Electrical Insulation Conference, EIC 2020
PB - Institute of Electrical and Electronics Engineers Inc.
T2 - 2020 IEEE Electrical Insulation Conference, EIC 2020
Y2 - 22 June 2020 through 3 July 2020
ER -