IEEE Power & Energy Magazine - May/June 2016 - 90
time for an
ON-LINE MASTER'S PROGRAM
In Electric Power Engineering
University of Waterloo | Department of
Electrical & Computer Engineering
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The current will be interrupted at a
current zero following contact part. If
the contact gap and gas pressure conditions are not sufficient at the first
current zero, the arc reignites and the
breaker then waits for the next current
zero. This process is continued until either the arc is interrupted or a failure
occurs. The 230- and 138-kV breakers
had a rated interrupting time of three
cycles (50 ms). The maximum arcing
time allowed for the first SF6 design
was therefore approximately 1.25 cycles (20 ms) since the contact part occurred at approximately 1.75 cycles
(30 ms). Asymmetrical currents alter
the current zero locations, further complicating the decision point times.
The original 230-kV SF6 interrupter
design used a mechanically operated
pilot valve that, in turn, opened the
blast valve, which then provided the
flow of gas to interrupt the arc. Initial
tests indicated that the pilot-operated
blast-valve system was too slow because of the low velocity of SF6 gas,
and the three-cycle interrupting time
could not be met if the pilot valve design was used. The linkage was redesigned to mechanically operate the
blast valve directly when the contacts
started to move.
The design of the interrupting nozzle
and contacts was based on the successful testing of the earlier research with
the 138-kV puffer prototype, backed
up by data provided by the subsequent
two-pressure, porcelain-clad prototype.
The use of the charged spring to provide the energy for the opening of the
breaker provided a slower contact travel
curve than that experienced with the
hydraulically operated puffer design.
The result was a device with a different
contact travel curve and a different gas
pressure profile from those used to provide the basic interrupter design data.
The current interrupting tests on the
230-kV pole unit in the High Power
Laboratory immediately ran into trouble. The laboratory provided 40 kA
at 44 kV, so we started with a "unit"
test by electrically shunting two of
the breaks. We started testing break 3
(furthest from the high-pressure reservoir), but it failed to interrupt currents
above 28 kA. The gas was venting out
of breaks 1 and 2 (which had no arcing), and we then tried tests using only
break 1. The results were discouraging,
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» Master of Engineering (MEng)
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» Graduate Diploma (GDip) in
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Awarded on completion of 6 courses
» Certificate of Completion: Awarded
on completion of a single course.
The MEng and GDip Programs are
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figure 3. The original 3 February 1959 patent disclosure sketch prepared by the
authors for Westinghouse.