IEEE Power & Energy Magazine - May/June 2018 - 92

figure 9. A trip-free mechanism schematic. (From Westinghouse Descriptive Data 33-123, Sept. 1938.)

figure 10. The Westinghouse pneumatic mechanism types AA-7 and AA-14.
(From Westinghouse Descriptive Bulletin 33-350, June 1959.)
92

ieee power & energy magazine

mechanisms were capable of providing five-cyle interrupting times. this
is one of the first mechanisms providing the trip-free feature. trip free
is now a standard requirement that
permits a breaker to be opened immediately, even if the closing operation is in progress, thus resulting in a
close-open operation. Figure 9 is a schematic of a trip-free operation of the
solenoid mechanism.
the shorter interrupting times and
higher currents required increased energy, resulting in mechanisms using
high pressure air, and hydraulic mechanisms were subsequently developed.
the trigger systems for faster release
required complete redesigns. Figure 10
shows a family of pneumatic mechanisms with air cylinder diameters of 7
and 14 in with operation at air pressure
up to 270 psig. the largest single mechanism with a 14-in diameter operated
all three phases of a 345-kV OCB in
may/june 2018



Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - May/June 2018

Contents
IEEE Power & Energy Magazine - May/June 2018 - Cover1
IEEE Power & Energy Magazine - May/June 2018 - Cover2
IEEE Power & Energy Magazine - May/June 2018 - Contents
IEEE Power & Energy Magazine - May/June 2018 - 2
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IEEE Power & Energy Magazine - May/June 2018 - Cover3
IEEE Power & Energy Magazine - May/June 2018 - Cover4
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