This thesis first outlines the testing undertaken on a partial core superconducting
transformer under open circuit, short circuit, full load and endurance test conditions.
During the endurance test, a failure occurred after 1 minute and 35 seconds. During the
failure, voltage dipping and rapid liquid nitrogen boil off was observed. This prompted
a failure investigation which concluded that the lack of cooling in the windings was the
most probable cause to the failure.
Full core transformer and superconductor theories are then introduced. A copper
winding transformer model, based on a Steinmetz equivalent circuit and a reverse
design method, is described. A superconductor loss model which outlines the different
types of losses experienced under AC conditions is used to determine the resistance
of the windings in the Steinmetz equivalent circuit. This resistance changes with the
magnitude of current and the strength of the magnetic field that is present in the gaps
between each layer of the windings. An alternative leakage flux model is then presented,
where the flux is modelled based on the combination of the reluctance of the core and
the air surrounding the windings. Based on these theories, an iterative algorithm to
calculate the resistance of the superconductor is developed.
A new design of a 15kVA single phase full core superconducting transformer, operating
in liquid nitrogen, is presented. The issues with building the superconducting
transformer are outlined. First, a copper mockup of the superconducting transformer
was designed where the mockup would have the same tape and winding dimensions
as the superconducting transformer, which means the same core can be used for two
different sets of windings. This led to designing a core that could be easily taken apart
as well as reassembled. Construction of the core, the copper windings and the superconductor
windings ensued. The process of cutting the core laminations, insulating the
copper and superconductor tapes, and making the steel fasteners and terminations are
described.
The copper mockup and superconducting transformers was then tested under open
circuit, short circuit, different load and endurance conditions at both liquid nitrogen
and room temperatures. These test results were then compared with the those from
two models. The comparison showed a significant inaccuracy in the reactances in
the models. This introduced a correction factor into the superconductor model which
ii
made it more accurate. However, further work is required to explain and quantify the
correction factors for the copper transformer model under different load conditions.
| Identifer | oai:union.ndltd.org:canterbury.ac.nz/oai:ir.canterbury.ac.nz:10092/4977 |
| Date | January 2010 |
| Creators | Chew, En Phin |
| Publisher | University of Canterbury. Electrical and Computer Engineering |
| Source Sets | University of Canterbury |
| Language | English |
| Detected Language | English |
| Type | Electronic thesis or dissertation, Text |
| Rights | Copyright En Phin Chew, http://library.canterbury.ac.nz/thesis/etheses_copyright.shtml |
| Relation | NZCU |
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