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Equipment Description
01.4IB.77000B
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, g), located
on the bottom right of the mechanism
compartment, is assembled to the circuit
breaker by a cover plate which is bolted to
the circuit breaker right frame side sheet.
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, n). 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
wheel, 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, aa) located at 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, q) 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, ab). Crank pins
(Figure 2, ac) are assembled to the crank
arms, which point outward. The crank arms
engage the bottom ends of the connecting
rods (Figure 2, c). 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 will drive 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 plate
(Figure 2, r) and the motor cutoff switch is
operated.
The motor cutoff switch (Figure 2, k),
located at the right of the mechanism, is
operated by the spring charge indicator
and motor cutoff cam (Figure 2, h). The
spring charge indicator (Figure 1, m) will
display that the mechanism is charged.
