IEEE Power & Energy Magazine - May/June 2016 - 94

figure 6. Short-line fault reactors in the Westinghouse
High Power Laboratory. (Photo courtesy of the authors.)

the three-cycle limit, and we were ready
to proceed with a complete test program.
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94
ieee power
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23/03/13 10:38 AM

figure 7. Voltage injection circuit components in the
Westinghouse High Power Laboratory. (Photo courtesy of
the authors.)

line of Westinghouse two-pressure SF6
circuit breakers.
Because of High Power Laboratory
limitations, some form of unit testing was
required on a single break. The lack of
arcing in the shunted breaks and its effect
on gas flow from the common reservoir
still had to be addressed. Unit tests with
the new interrupter design were tried
with the flow partially blocked to shunted
breaks, but the tests were not satisfactory.
Arcing in all of the breaks was required
to provide gas flow conditions expected
during an actual current interruption. A
test circuit was devised that had high-current arcing in all three breaks but stressed
only the test break with the transient recovery voltage.
One of the critical design criteria,
based on oil breaker designs, was the
"no opening resistor" requirement. Airblast breakers required resistors to control the severe transient recovery voltages associated with transmission line
faults a short distance from the breaker.
The new SF6 breaker was subjected to
simulated short-line fault tests using
air-core reactors specifically designed
for these tests (see Figure 6). Currents
associated with short-line faults were
successfully interrupted over a range of
70-95% of the full rated bus fault value.
Voltage-current constraints of the
High Power Laboratory prevented
tests at rated bus fault current and the

corresponding required transient recovery voltage. A series of tests at
rated bus fault current were made with
a voltage injection synthetic circuit using the specially designed components
shown in Figure 7.
Historically, oil breaker contacts
met the standard of five operations at
full rated interrupting current. It quickly became apparent that the SF6 breaker contact structure was capable of at
least twice that number of operations,
and the new SF6 breaker was rated for
ten 40-kA fault current interruptions
before maintenance would be required.
In fact, the breaker under test was often subjected to as many as 20 40-kA
interruptions before the contacts had to
be replaced.

Early Installations
The first actual order for an SF6 breaker
was from PP&L for a 230-kV breaker,
which was installed at the Brunner Island substation (see Figure 8) in September 1960. The first two installed
SF6 power circuit breakers, with a rating of 138 kV, 10,000 MVA, were at the
Con Edison Hellgate substation in May
1960. At Con Edison, a failure occurred
in February 1961. Previous experience
by Con Edison with oil or compressed
air breaker failures indicated that total,
or near total, destruction usually occurred. The SF6 breaker was repaired
may/june 2016

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