Siemens 3AH3 Instruction Manual page 14

14
During closing, the opening spring (64.0)
(refer to Figure 6) and the contact pressure
springs (49.0) are charged and latched by
pawl (64.2) (refer to Figure 6). The closing
spring (62.0) (refer to Figure 5) of the
motor-operated circuit breaker is recharged
immediately after closing.
In the closed state, the necessary contact
pressure is maintained by the contact
pressure springs (49.0) and the atmospheric
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 (49.0) is released by pawl
(64.2) (refer to Figure 6).
The opening sequence is similar to the
closing sequence. The residual force of the
opening spring maintains the moving
contacts in the open position.
Operating mechanism
The operating mechanism is comprised of
the mechanical and electrical components
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 the three vacuum
interrupters.
4. Operate all these functions
automatically through an electrical
charging motor, cutout switches, an
anti-pump relay, a close coil, an open
coil and an auxiliary switch.
5. Provide indication of the circuit breaker
status (OPEN/CLOSED), spring condition
(CHARGED/DISCHARGED) and number of
operations.
Construction
The essential parts of the operating
mechanism are shown in Figures 5 and 6.
The control and sequence of operation of
the mechanism is described in Figure 7.
Motor-operating mechanism (refer to
Figure 5)
The spring-charging motor (50.4) is bolted
to the charging mechanism (50.2) gear box
installed in the operator housing. Neither
the charging mechanism nor the motor
require any maintenance.
Mode of operation
The operating mechanism is of the stored-
energy trip-free type. For example, the
charging of the closing spring is not
automatically followed by the contacts
changing position, and tripping function
prevails over the closing function.
When the stored-energy mechanism has
been charged, the mechanism is ready for a
closing operation at any time.
The mechanical energy for carrying out an
"Open-Close-Open" sequence for auto-
reclosing duty is stored in the closing and
opening springs.
Charging
The details of the closing spring charging
mechanism are shown in Figure 5. The
charging shaft is supported in the charging
mechanism gear box (50.2), but is not
coupled mechanically with the charging
mechanism. Fitted to it are the crank (62.2)
at one end, and the cam (62.3), together
with lever (62.5), at the other.