IEEE Power & Energy Magazine - May/June 2018 - 87

in arc extinction. In spite of the flammability of both oil and the gases produced by arcing, safe operation is obtained by submerging the contacts in
an oxygen-free environment deep in
the oil and allowing gases to cool as
they rise to the surface.

Advancements
in the 1920s
In the early 1920s, engineers began
investigating interruption with the intent to provide breakers with higher
interrupting capabilities and shorter
interrupting times. at Westinghouse,
this investigation was led by research
scientist dr. Joseph Slepian. his work
resulted in a detailed scientific explanation of arc behavior based on the ionization of gases both from theoretical
and practical standpoints. during arcing, the current is conducted through
the ionization of the interrupting medium, and at current zero, interruption of
the current is the result of deionization
of the arc space. One of the basic truths
developed in Slepian's studies was that
the extinction of an arc depended on
two factors: 1) the rate of recovery of
dielectric strength of the arc space after current zero and 2) the rate at which
voltage tending to reignite the arc is applied by the external circuit.
In the late 1920s, this investigation
resulted in the development of a deionizing interrupter originally applied to
69-kV breakers, and eventually various
versions of deionizing grids (discussed
later) were applied to OCBs up to voltages of 345 kV and 63-ka interrupting
currents. the interrupter development
controlled the arc and enhanced the deionization process, resulting in a shorter
arcing time and increased interrupting
current capability. a deionizing interrupter assembly for 69 kV is shown in
Figure 4. It consists of a grid composed
of fiber plates, each of which was cut
to a specific flat geometric configuration so that, when assembled one on top
of each other, the plates allowed space
for the contacts, flow passages for venting gases, segregation of the arc, and
oil pockets to provide fresh oil to cool
the arc and promote deionization. the
may/june 2018

fiber plates are unique for this application since the material is clean burning,
meaning that the high temperatures of
the arc did not result in carbonization
but maintained its insulating characteristics. the decomposition of the fiber
also produced gases to enhance the deionization. the use of arc-resistant (sil-

ver tungsten) arcing contacts reduced
the contamination of the arc space with
ionized gases.

A Push to Higher Voltages
and Currents
at higher voltages and interrupter currents, the single break interrupter was

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