My PhD project was done in the department that at the start (October 2003) was Electrotechnical Design, and at the end (September 2010) was Electromagnetic Engineering: more detail of the research group and department is here.
It went under a broad title (with variations over time)
along the lines of:
Stator Insulation Diagnostics by Combined Measurements, using
Dielectric Spectroscopy including Harmonics, and variable-frequency
Partial Discharge analysis.
From this the main differences from current industrial
practice are seen to be the following:
a varied frequency of the sinusoidal excitation
is used for the DS and PD measurements, rather than just a single
frequency such as power-frequency; the low harmonics of the DS
measurement are included, rather than just the fundamental frequency;
the two types of measurement are made simultaneously.
Although the thesis was submitted in 2010, there is plenty of work remaining that I would like to finish. Some of this is mentioned in the `future work' part of the conclusions chapter of the thesis (see below).
The objects of my attentions are the insulation systems of high-voltage rotating-machine stator windings (large motors and generators, with rated voltages of several kilovolts and higher).
Partial discharge (PD) is common in this type of insulation, and many existing diagnostic methods measure PD signals, display power-frequency phase-resolved PD patterns, or localise PD sources by simultaneous measurements, on-line or off-line.
Simple dielectric measurements -- capacitance and dissipation -- are often made with varied voltage at power frequency, with the main interest being an increased dissipation with increased voltage, due to PD activity. DC measurements of `insulation resistance' are another popular means of detecting damage.
An insulation failure depends on just one weak spot; any method of trying to predict time to failure from measurements is doomed to be unable to get the answer right every time. Users of these large machines have to get the right balance between investment in more methods, equipment and staff for more accurate diagnostic work, and likelihood and consequence of a failure.
The methods investigated here are hoped to be useful as a further source of information about the condition of stator insulation. The need for different equipment and longer measurement times than the more simple methods makes it likely that their usefulness would be limited to machines in especially important applications, or as a further type of measurement when results from conventional methods do not permit clear enough conclusions to be drawn.
Page started: 2003-10-01
Last change: 2011-08-22