Siemens 38-3AH3 38 kV Primary disconnects, Phase barriers, Stored-energy operating mechanism

Figure 10: Upper and lower primary disconnects (outer-phase barrier removed)

Primary disconnects

Figure 10: Upper and lower primary disconnects (outer-phase barrier removed) is a side view of the circuit breaker with the outer-insulating phase barrier removed to show details of the primary disconnects. Each circuit breaker has three upper- and three lower-primary disconnects. Upper- primary disconnects are connected to the stationary contacts of the vacuum interrupters, and the lower-primary disconnects are connected to the movable contacts. Each disconnect arm has a set of multiple spring-loaded fingers that mate with bus bars in the metal-clad switchgear. The number of fingers in the disconnect assembly varies with the continuous and/ or interrupting rating of the circuit breaker.

There are three insulating push rods. Each push rod connects the movable contact of one of the vacuum interrupters to the jack shaft driven by the closing and tripping mechanism. Flexible connectors provide secure electrical connections between the movable contacts of each vacuum interrupter and its bottom-primary disconnect.

Phase barriers

Figure 11: Type 38-3AH3 vacuum circuit breaker with inter-phase and outer-phase barriers installed on page 17 is a rear view of a type 38-3AH3 vacuum circuit breaker that shows the outer- (phase-to-ground) and interphase-insulating barriers. These glass-polyester insulating barriers are attached to the circuit-breaker frame and provide suitable electrical insulation between the vacuum-interrupter primary circuits and the housing.

Stored-energy operating mechanism

The stored-energy operating mechanism of the type 38-3AH3 vacuum circuit breaker is an integrated arrangement of springs, solenoids and mechanical devices designed to provide a number of critical functions. The energy necessary to close and open (trip) the contacts of the vacuum interrupters is stored in powerful tripping 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. The operation of the stored-energy mechanism will be discussed later in this section.