Vacuum Interrupters; Primary Disconnects (Figure 4); Phase Barriers; Stored Energy Operating Mechanism - Siemens 3AH Installation Operation & Maintenance

Vacuum Interrupter/Operator Description
Figure 3. Cutaway View of Vacuum Interrupter

Vacuum Interrupters

The operating principle of the vacuum interrupter is simple.
Figure 3 is a cutaway view of a typical vacuum interrupter.
The entire assembly is sealed after a vacuum is established.
The vacuum interrupter stationary contact is connected to
the pole head of the circuit breaker. The vacuum interrupter
movable contact is connected to the pole bottom and driv-
ing mechanism of the circuit breaker. The metal bellows
provide a secure seal around the movable contact, prevent-
ing loss of vacuum while permitting vertical motion of the
movable contact.
When the two contacts separate, an arc is initiated which
continues conduction up to the following current zero. At
current zero, the arc extinguishes and any conductive metal
vapor which has been created by and supported the arc
condenses on the contacts and on the surrounding vapor
shield. Contact materials and configuration are optimized to
achieve arc motion and to minimize switching disturbances.

Primary Disconnects (Figure 4)

Figure 4 illustrates the pad provision to accept the primary
disconnects. Each circuit breaker has three upper and three
Figure 4.
Vacuum Interrupter/Operating Mechanism Module
lower primary disconnect pad provisions, to perform the
connection to the switchgear.
Bolting hardware is M12 x 1.75 grade 8. Torque M12 bolts to
52 ft/lbs (70 Nm).

Phase Barriers

Plates of glass polyester insulating material are attached to
the circuit breaker and provide suitable electrical insulation
between the vacuum interrupter primary circuits 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 con-
tacts of the vacuum interrupters is stored in powerful open-
ing and closing springs. These 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, i.e., spring charging
does not automatically change the position of the primary
contacts, and the closing function may be overridden by the
tripping function at any time.

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 motor or manually
charged spring stored energy operating mechanism hous-
ing. This module is shown in Figure 4.
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