IEEE Power & Energy Magazine - May/June 2016 - 93

may/june 2016

current and the travel curve of the piccolo moving contact.
In this new design, known as the
"swiss cheese" (see Figure 4), the moving contact was made larger in diameter, 2.5 in (6.4 cm) outside and 2.0 in
(5.1 cm) inside, and the number of sidewall holes was increased. The Teflon
chamber was enlarged and reshaped to

form the chamber walls. The interrupting tests with the "swiss cheese" design
were successful up to 38 kA, leading to
the next modification.
The overall dimensions were retained, and the sidewall holes were replaced by longitudinal slots. This new
design revision, shown in Figure 5, the
"slot," was able to interrupt 48 kA within

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1.5 in (3.8 cm) diameter moving contact.
The center hole was vented through the
side wall and was intended to assist in
centering the arc and to prevent the arc
terminal from running down the outside of the contact. The net effect was
to provide a closed cavity until the contact cleared the nozzle throat except for
the center hole configuration, which
allowed for a minimal flow of highpressure SF6. Could this observation
lead to an answer? We made the hole
in the center deeper, added additional
holes through the sidewall, and the
"piccolo" interrupter was born. Still using only break 1 with maximum flow
conditions, the revised design was able
to interrupt 32 kA within the allowed
1.25 cycles of arcing but failed to interrupt at higher currents.
Based on the results to date, a different interrupter design was needed.
A meeting to discuss the problem was
held with engineering management
and engineers Yeckley and Colclaser.
At this point, because of time constraints, a new concept would, of necessity, be limited to a configuration
that used as much of the surrounding
structure and gas delivery system as
possible. After considerable discussion, we proposed a new design based
on the piccolo data but with increased
dimensions. The managers, in an effort to show their own upper management some progress and to buy some
time, agreed to let us make a prototype
of our idea while they would "go ahead
and solve the problem."
A copy of the original patent disclosure sketch for a new interrupter concept, dated 3 February 1959, is shown
in Figure 3. The contacts would be enlarged in diameter; several discharge
holes would be added; and the Teflon
nozzle would become a chamber surrounding the moving contact, forcing
the gas flow into the arc and discharging only through the center of the contact. The metal orifice interrupter was
"born." Note that the proposed design
was not based on advanced engineering calculations but, instead, was the
result of observations of the test data
as related to the interruption of high

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Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - May/June 2016