GE Industrial Solutions PowerVac with ML-18 or ML-18H Mechanism - Manual (Page 8)

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SECTION 5—Operation
5.1—General
The PowerVac ® vacuum circuit breaker uses sealed vacuum
power interrupters to establish and interrupt a primary circuit.
Primary connections to the associated metalclad switchgear are
made by horizontal bars and disconnect fingers, electrically and
mechanically connected to the vacuum interrupters. Molded
interrupter supports, one per phase on a three-phase circuit
breaker, provide mountings for the primary bars, interrupters,
current transfer fingers, and heat dissipation fins (where used).
The operating mechanism provides direct motion at each phase
location in order to move the lower contact of the vacuum
interrupters from an open position to a spring-loaded closed
position and then back to the open position on command.
The ML-18/18H mechanism (Figure 17) is of the stored-energy
type and uses a gearmotor to charge a closing spring. During a
closing operation, the energy stored in the closing spring is used
to close the vacuum interrupter contacts, compress the wipe
springs which load the contacts, charge the opening spring, and
overcome bearing and other friction forces, The energy then
stored in the wipe springs and opening spring will open the
contacts during an opening operation.
Closing and opening operations are controlled electrically by the
metalclad switchgear or remote relaying. Mechanical control is
provided by manual close and trip buttons on the circuit breaker.
The closing spring may be manually charged, and a method for
slow-closing the primary contacts is available. The mechanism
will operate at the ac or dc voltage indicated on the circuit
breaker nameplate.
5.2—Close Spring Charging
Figure 17 shows a front view of the ML-18 in a schematic form.
The primary contacts are open and the closing spring is charged.
The closing spring charging system consists of a closing spring
(item 1, view B) mounted on the left side of the breaker and the
electrical charging system mounted on the right side of the
breaker. Both components are fastened to the cam shaft (item
2, view B). A manual charging system (item 3, view A) is
provided so that the mechanism can be slow closed and the
closing spring can be charged if there is a loss of electrical
control power.
Spring charging is accomplished electrically by a rotating
eccentric on the output shaft of the gear motor driving pivoted
charging arms (item 4, view C) which oscillate about the
centerline of a ratchet wheel (item 5, view C). A driving pawl
(item 6, view C), mounted within the charging arms, oscillates
with the charging arms. Starting from its rear-most position, as
the charging arms rotate forward, a spring forces engagement
of the driving pawl with a tooth of the ratchet wheel. The
ratchet wheel is advanced by the rotating charging arms and
pawl assembly. Advancement of one tooth spacing is provided
for each oscillation of the system. The ratchet motion is
restricted to one direction by a spring-loaded holding pawl that
prevents the ratchet wheel from going backwards as the
charging arms oscillate back to pick up the next tooth. Thirteen
complete cycles of the charging arms are needed for a full
charge of the closing spring. The efficient, compact gear motor
accomplishes this action in about two seconds. When the
charging cycle is complete, the ratchet wheel is positioned so
that a missing tooth is adjacent to the driving pawl and any
motor over spin will not drive the ratchet wheel, thus preventing
damage to the system.
When the spring is completely charged, the assembly is
retained in that position by the close latch, until it is desired
to close the circuit breaker.
The closing coil cannot be electrically energized unless the
closing spring is completely charged. This action is prevented by
the 52/CHG switch in the closing circuit.
The manual charging system (item 3, view A) works directly on
the cam shaft where a one-way clutch (item 7, view A), driven
by a manual handle, provides rotation of the ratchet wheel.
Manual pumping of the handle advances the ratchet wheel and
the holding pawl prevents counter-rotation while the handle is
returning for another stroke. Approximately eight complete
strokes of the manual handle are required for one complete
spring-charging operation. When the spring charge indicator
(item 9, Figure 3) shows “CHARGED”, MANUAL CHARGING
MUST BE DISCONTINUED TO AVOID MECHANISM DAMAGE.
Figure 3 Front view of PowerVac breaker
without front cover
1. Upper interrupt connection 8. Counter
2. Interrupter support
9. Spring charge indication
3. Operating rod 10. Manual charge lever
4. Racking arm 11. Manual close button
5. Compartment track rollers 12. Secondary disconnect
6. Manual trip button
handle
7. Open/Close indicator 13. Closing spring gag access
5.3—Closing Operation (Refer to Figure 17)
By either energizing the close solenoid or depressing the
manual close button, the close latch (item 8, view C) is rotated,
releasing the closing spring (item 1, view B). This
action releases the energy in the closing spring and transmits it
to the closing cam (item 9, view D) and closing roller (item 10,
view D) and causes the linkage to rise until the prop (item 11,
view D) can slip under the close roller (item 10, view D) and
hold the linkage in place. As the linkage moves, the output crank
(item 12, view D) rotates the cross shaft (item 13, view D)
which in turn rotates the phase bell cranks and compresses the
two opening springs (item 15, view E) on poles 1 and 3, this
closes the vacuum interrupters, and compresses the wipe
springs (item 16, view E) on each pole.
The rotation of the cross shaft (item 13, view D) also changes
the auxiliary switch (item 7, view D) position. The position flag
on the front panel will then indicate “CLOSED”. After the breaker
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