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Mätning av krafttransformatorers nollföljdsimpedans

Selimovic, Jasmin (2012) In CODEN:LUTEDX/TEIE EIE920 20121
Industrial Electrical Engineering and Automation
Abstract
In the E. ON sponsored research project, Distibution LABoratory, at the Department
of Industrial Electrical Engineering and Automation at LTH the impact
of the increased move towards use of cables in the Swedish distribution
grid is examined. The project also built a model of a small distribution grid.
The model was used to simulate a Petersen coil earthed grid system. Petersen
coil earthing lowers the fault current by compensating the capacitive currents.
Since the share of cables in the medium-voltage networks have increased so have
the capacitive currents. In order to minimize the fault current the inductive
compensation currents need to be increased. When calculating the compensation
current an uncertainty is found as an... (More)
In the E. ON sponsored research project, Distibution LABoratory, at the Department
of Industrial Electrical Engineering and Automation at LTH the impact
of the increased move towards use of cables in the Swedish distribution
grid is examined. The project also built a model of a small distribution grid.
The model was used to simulate a Petersen coil earthed grid system. Petersen
coil earthing lowers the fault current by compensating the capacitive currents.
Since the share of cables in the medium-voltage networks have increased so have
the capacitive currents. In order to minimize the fault current the inductive
compensation currents need to be increased. When calculating the compensation
current an uncertainty is found as an unknown zero sequence impedance in
the Yyn-connected transformers.
The purpose of this master thesis is to measure the zero sequence impedance
of the power transformers, investigate the transformer tank's impact on it, and
to develop a method that can be used for measurement on the full-scale transformers.
The work shows that the zero sequence impedance in Yyn-connected transformers
is not infinite as many textbooks show. For phase-to-ground faults the zero
sequence magnetic flux is forced to flow into the air and the transformer tank
which greatly affects the size of the zero sequence impedance. As a consequence,
the zero sequence impedance should be measured on site and after installation
to obtain an more accurate result.
The measurements of the zero sequence impedance in transformers gives some
uncertainty that makes it difficult to draw definite conclusions. Measurements
made on full-scale transformers where raw data is saved would increase the
possibility to process the information and to exclude the influence of the Petersen
coil earthing used in the distribution model. (Less)
Please use this url to cite or link to this publication:
author
Selimovic, Jasmin
supervisor
organization
course
EIE920 20121
year
type
H3 - Professional qualifications (4 Years - )
subject
publication/series
CODEN:LUTEDX/TEIE
report number
5293
language
Swedish
id
3731788
date added to LUP
2013-05-21 15:00:17
date last changed
2014-09-04 08:29:54
@misc{3731788,
  abstract     = {In the E. ON sponsored research project, Distibution LABoratory, at the Department
of Industrial Electrical Engineering and Automation at LTH the impact
of the increased move towards use of cables in the Swedish distribution
grid is examined. The project also built a model of a small distribution grid.
The model was used to simulate a Petersen coil earthed grid system. Petersen
coil earthing lowers the fault current by compensating the capacitive currents.
Since the share of cables in the medium-voltage networks have increased so have
the capacitive currents. In order to minimize the fault current the inductive
compensation currents need to be increased. When calculating the compensation
current an uncertainty is found as an unknown zero sequence impedance in
the Yyn-connected transformers.
The purpose of this master thesis is to measure the zero sequence impedance
of the power transformers, investigate the transformer tank's impact on it, and
to develop a method that can be used for measurement on the full-scale transformers.
The work shows that the zero sequence impedance in Yyn-connected transformers
is not infinite as many textbooks show. For phase-to-ground faults the zero
sequence magnetic flux is forced to flow into the air and the transformer tank
which greatly affects the size of the zero sequence impedance. As a consequence,
the zero sequence impedance should be measured on site and after installation
to obtain an more accurate result.
The measurements of the zero sequence impedance in transformers gives some
uncertainty that makes it difficult to draw definite conclusions. Measurements
made on full-scale transformers where raw data is saved would increase the
possibility to process the information and to exclude the influence of the Petersen
coil earthing used in the distribution model.},
  author       = {Selimovic, Jasmin},
  language     = {swe},
  note         = {Student Paper},
  series       = {CODEN:LUTEDX/TEIE},
  title        = {Mätning av krafttransformatorers nollföljdsimpedans},
  year         = {2012},
}