Vacuum Interrupters; Primary Disconnects (Figure 4); Phase Barriers; Stored Energy Operating Mechanism - Siemens 3AH Series Instructions Manual

Vacuum Interrupter/Operator Description
Rxed C ontact
current
Ceramic
lnsiJator --�
FIXed
Contact
Moving
Ceranic
Metal
Guide
Moving
contact
Current Connectkln ---- -- -'
Figure 3. Cutaway View of Vacu u m Interrupter

Vacuum Interrupters

The operating principle of the vacu um interrupter is simple.
Figure 3 is a cutaway view of a typical vacu u m interru pter.
The entire assembly is sea led after a vacu um is established.
The vacu um interrupter stationary contact is connected to
the pole head of the circuit breaker. The vacu u m 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 vacu um while permitting vertical motion of the
movable contact.
When th e two contacts separate, an arc is initiated which
continues conduction up to the fol lowing current zero. At
current zero, the arc extinguishes and any cond uctive 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 th e
connection to the switchg ear.
Bolting hardware is M 1 2 1.75 grade 8.Torque M 1 2 bolts to
x
52 ft/lbs (70 N m ) .

Phase Barriers

Plates of glass polyester insulating material are attached to
th e circuit breaker and provide suitable e lectrical insu lation
between the vacuum interrupter primary circu its 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 vacu um interrupters is stored in powerful open­
ing and closing springs. These springs are normally charged
a utomatically, 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 a utomatically 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 vacu u m interrupter/operator module consists of the
three poles, each with its vacuu m interrupters and primary
insulators, mounted on the common motor or manually
charged spring stored energy operating mechanism hous­
ing. This module is sh own in Figure 4.
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