Siemens 3AH3 Instruction Manual page 12

1
2
4
3
5
6
7
8
9
Item Description
Fixed contact-current
1
connection
2 Ceramic insulator
3 Arc shield
4 Fixed contact
5 Moving contact
6 Ceramic insulator
7 Metal bellows
8 Guide
Moving contact-
9
current connection
Figure 3: Vacuum interrupter cut-
away view
12
3AH vacuum circuit breaker operator
3AHc vacuum circuit breaker operator
Figure 4: Vacuum circuit breaker operator module
The circuit breaker includes three vacuum
interrupters, a stored-energy operating
mechanism, necessary electrical controls
and interlock devices, disconnect devices to
connect the circuit breaker to both primary
and control power (for drawout
applications) and an operator housing.
In a typical installation in a drawout truck,
insulating barriers may be located between
the vacuum interrupters and along the
sides.
This section describes the operation of each
major subassembly as an aid in the
operation, installation, maintenance and
repair of the circuit breaker.
Vacuum interrupters
The operating principle of the vacuum
interrupter is simple. Figure 3 is a section
view of a typical vacuum interrupter. The
entire assembly is sealed after a vacuum is
established.
3AH3 operator mechanism
The vacuum interrupter stationary contact is
connected to the upper pole head of the
circuit breaker. The vacuum interrupter
movable contact is connected to the pole
bottom and driving mechanism of the circuit
breaker.
3AHc operator mechanism
The vacuum interrupter stationary contact is
connected to the lower pole head of the
circuit breaker. The vacuum interrupter
movable contact is connected to the upper
pole head (pole bottom) and drive
mechanism of the circuit breaker.
The metal bellows provide a secure seal
around the movable contact, preventing loss
of vacuum while permitting vertical motion
of the movable contact.
When the two contacts separate, an arc is
initiated that continues conduction up to
the following current zero. At current zero,
the arc extinguishes and any conductive
metal vapor that has been created by and
supported the arc condenses on the
contacts and on the surrounding arc shield.
Contact materials and configuration are
optimized to achieve arc motion and to
minimize switching disturbances.
Primary connections (refer to Figure 2)
Figure 2 illustrates the pad provision to
accept the primary connections. Each circuit
breaker has three upper and three lower
primary disconnect pad provisions, to allow
connection to the switchgear.
For stationary circuit breaker applications,
bus conductors connect directly to these
pads. Bolting hardware is M12 x 1.75 grade
8. Torque M12 bolts to 52 ft-lb (70 Nm).