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Equipment Description
01.4IB.77020
PowlVac-ND
®
and PowlVac-NDA
™
Series 4
Vacuum Circuit Breakers
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
, 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
. 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
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
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
. Crank pins
are assembled to the crank
arms, which point outward. The crank arms
engage the bottom ends of the connecting
rods
. 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
and the motor cutoff switch is
operated.
The motor cutoff switch
located at the right of the mechanism, is
operated by the spring charge indicator
and motor cutoff cam
. The
spring charge indicator
will
display that the mechanism is charged.