Siemens 3AH Installation Operation & Maintenance - Page 10
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Vacuum Interrupter/Operator Description
Construction (Figures 1, 2, 5, 6a and 6b)
Each of the circuit breaker poles are fixed to the rear of the
operating mechanism housing by two cast-resin insulators.
The insulators also connect to the upper and lower pole
supports which in turn support the ends of the vacuum inter-
rupter. The pole supports are aluminum castings (1200A and
2000A) or copper castings (3000A). Primary stud extensions
may be attached directly to the upper and lower pole sup-
ports.
The energy-storing mechanism and all the control and
actuating devices are installed in the mechanism housing.
The mechanism is of the spring stored energy type and is
mechanically and electrically trip free.
The close-open indicator, closing spring charge indicator,
and the operation counter are located on the front of the
mechanism housing.
The control connector for the control and signalling cables is
a multi contact plug.
Figure 5. Pole Assembly
Circuit Breaker Pole (Figure 5)
The vacuum interrupter is rigidly connected to the pole head
by its post insulator. The lower part of the vacuum interrupt-
er is stabilized against lateral forces by a centering ring on
the pole bottom. The external forces due to switching opera-
tions and the contact pressure are absorbed by the struts.
Current-Path Assembly (Figure 5)
The current-path assembly consists of the pole head, the
stationary contact, and the moving contact, which is con-
nected to the pole bottom by a terminal clamp and a flexible
connector.
Vacuum Interrupter (Figure 5)
The moving contact motion is aligned and stabilized by a
guide bushing. The metal bellows follows the travel of the
contact and seals the vacuum interrupter against the sur-
rounding atmosphere.
Switching Operation (Figures 5 and 6a)
When a closing command is initiated, the closing spring
(62), which was previously charged by hand or by the mo-
tor, actuates the moving contact through the jack shaft (63),
lever, contact pressure spring (49), insulating coupler (48),
and angled lever.
The forces that occur when the action of the insulating cou-
pler (48) is converted into the vertical action of the moving
contact are absorbed by the guide link, which pivots on the
pole bottom and the eye bolt.
During closing, the opening spring (64) (Figure 6a) and the
contact pressure springs (49) are charged and latched by
pawl (64.2) (Figure 6b). The closing spring (62) (Figure 6a) of
the motor-operated circuit breaker is recharged immediately
after closing.
In the closed state, the necessary contact pressure is main-
tained by the contact pressure spring (49) and the atmo-
spheric pressure. The contact pressure spring automatically
compensates for arc erosion, which is very small.
When a opening command is given, the energy stored in
the opening and contact pressure springs (49) is released
by pawl (64.2) (Figure 6b). The opening sequence is similar
to the closing sequence. The residual force of the opening
spring arrests the moving contact in the open position.
Operating Mechanism
The operating mecha-
nism is comprised of the mechanical and electrical compo-
nents required to:
1. Charge the closing spring with sufficient potential energy
to close the circuit breaker and to store opening energy
in the opening and contact pressure springs.
2. Mechanisms to release closing and opening actions.
3. Means of transmitting force and motion to each of three
pole positions.
4. Operate all these functions automatically through electri-
cal charging motor, cutout switches, antipump relay,
close coil, open coil, and auxiliary switch.
5. Provide indication of the circuit breaker status (open/
closed), spring condition (charged/discharged), and
number of operations.
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