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10
Equipment Description
PowlVac
®
STD Vacuum Circuit Breaker
IB-60201
The mechanism employed in the circuit
breaker is a stored energy system which
uses a charging motor to compress the
main closing spring. During the closing
operation the energy stored in the main
closing spring is released. This allows the
mechanism to close the vacuum interrupter
contacts, compress the contact loading
springs, charge the opening springs, and
overcome frictional forces. When the circuit
breaker is opened, the energy stored in
the opening and contact loading springs
is released, and the vacuum interrupter
contacts are opened.
The charging motor (figure 2, o), located
on the bottom right of the base pan, is
assembled to the circuit breaker by a
bracket that is bolted to the base pan. The
charging motor drive shaft inserts into the
eccentric drive shaft. The eccentric drive
shaft is supported by needle roller bearings
in the mechanism frame side sheets and
transmits the motor torque to the left side
of the mechanism.
When the charging motor is energized, the
eccentric drive shaft rotates and causes
the pawl support arms to pivot about the
camshaft (Figure 2, l). The drive pawl, which
is supported by the arms, engages with the
ratchet wheel and drives the ratchet wheel
one tooth at a time. To prevent backwards
motion of the ratchet, a spring-loaded
holding pawl is used to latch the ratchet
wheel after each advance from the drive
pawl.
To ensure correct synchronization of the
drive and holding pawl, the position of the
holding pawl support arms are adjustable
by the holding pawl adjusting eccentric
(Figure 2, u) located to the left front of
the mechanism. When the mechanism is
operated manually, the top pawl becomes
the drive pawl and the bottom pawl
becomes the holding pawl.
The ratchet wheel (Figure 2, w) has
projections from its side faces which
engage the drive plates as it rotates. These
drive plates are attached to the camshaft,
thus causing the camshaft to rotate.
Attached to the ends of the camshaft are
crank arms (Figure 2, v). The crank pins
(Figure 2, t) on the crank arms point
outward. The crank arms engage the
bottom ends of the connecting rods
(Figure 2, d). The pins that project from
the spring yoke, which straddles the main
closing spring, engage the top ends of the
connecting rods. As the camshaft rotates
the connecting rods will pull the spring
yoke downward, compressing the main
closing spring.
The ratchet wheel drives the camshaft so
that the connecting rods go down to their
lowest position, and then start to move
upward. At a certain point, the spring force
will overcome friction and resistance and
start to rotate the camshaft. At the same
time, the pawls are uncoupled from the
ratchet wheel by the pawl lift drive plate
(Figure 2, x) and the motor cutoff switch is
operated. The motor cutoff switch
(Figure 2, ag), located to the right of the
mechanism, is operated by the spring
charge indicator and motor cutoff cam
(Figure 2, ad). The spring charge indicator
(Figure 1, q) will display that the mechanism
is charged. The camshaft would continue
to rotate, except that it is restrained by
the close latch arm (Figure 2, y) engaging
against the close latch shaft (Figure 2, aa).
The main closing cam, located between the
mechanism side sheets, is now in a position
where the fundamental linkage can move
to the reset position.
