Siemens 3AH3 Instruction Manual page 13

Phase barriers (if applicable)
Plates of glass-polyester insulating material
are attached to the circuit breaker and
provide suitable electrical insulation
between the vacuum interrupter and
primary conductors and the cubicle.
Stored-energy operating mechanism
The stored-energy operating mechanism of
the circuit breaker is an integrated
arrangement of springs, coils and
mechanical devices designed to provide a
number of critical functions. The energy
necessary to close and open the contacts of
the vacuum interrupters is stored in
powerful opening and closing springs. The
closing springs are normally charged
automatically, but there are provisions for
manual charging. The operating mechanism
that controls charging, closing and tripping
functions is fully trip-free. "Trip-free"
requires that the tripping function prevail
over the closing function as specified in
ANSI/IEEE C37.04-1999, clause 6.9.
Vacuum interrupter/operator module
The vacuum interrupter/operator module
consists of the three poles, each with its
vacuum interrupters and primary insulators,
mounted on the common operating
mechanism housing. This module is shown
in Figure 4.
Construction (Refer to Figures 1, 2, 5 and
6) (3AH only)
This description covers the type 3AH
operator. The type 3AHc differs in
arrangement but the fundamental
discussion of operation applies.
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 that in turn support the
ends of the vacuum interrupter.
The pole supports are aluminum castings
(most 1,200 A, all 2,000 A and some
3,000 A), copper castings (some 3,000 A) or
sheet steel (some 1,200 A). For type 3AH
operators, primary disconnect stud
extensions may be attached directly to the
upper and lower pole connection pads.
The energy-storing mechanism and all the
control and actuating devices are installed
in the operator 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 operator
housing.
The control connector for the control and
signalling cables is a multi-contact plug in
most designs, although direct connection to
the switchgear is used for certain products.
Circuit breaker pole (refer to Figure 2)
The vacuum interrupter is bolted to the
upper pole head and the upper pole head is
rigidly connected to the operator housing by
the post insulator. The moving contact end
of the vacuum interrupter is stabilized
against lateral forces by a centering ring on
the pole bottom. The external forces due to
switching operations and the contact
pressure are absorbed by the struts.
Current-path assembly (refer to Figure 2)
The current-path assembly consists of the
pole head, the stationary contact and the
moving contact, that is connected to the
pole bottom by a terminal clamp and a
flexible connector.
Vacuum interrupter (refer to Figure 2)
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
surrounding atmosphere.
Switching operation (refer to Figures 2
and 5)
When a closing command is initiated, the
closing spring (62.0), that was previously
charged by hand or by the motor, actuates
the moving contact through the jack shaft
(63.0), lever, contact pressure spring (49.0),
insulating coupler (48.0) and angled lever.
The forces that occur when the action of the
insulating coupler (48.0) is converted into
the vertical action of the moving contact are
absorbed by the guide link, that pivots on
the pole bottom and the eye bolt.
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