Siemens 38-3AH3 38 kV instruction manual Racking interlocks Closed circuit breaker interlock

The two plates are mounted in alignment and must pass through each other in order for the circuit-breaker vehicle to enter the drawout compartment. The interlock is coded to test rated voltage, as well as interrupting and continuous current ratings. The circuit breaker must equal or exceed all of the cubicle ratings in order to enter the compartment.

2.Racking interlocks

A.CLOSED circuit breaker interlock

Figure 32: Circuit-breaker interlocks and ground disconnect on page 33 shows the location of the CLOSED circuit-breaker interlock-plunger on the circuit-breaker frame.

The purpose of this interlock is to positively block circuit-breaker racking-operations whenever the circuit breaker is CLOSED. The plunger is coupled to the jack shaft as seen in Figure 15: Stored-energy operating mechanism, item 63 on page 20. When the jack shaft rotates to close, the interlock plunger is driven straight downward beneath the frame of the circuit breaker. The downward projecting plunger blocks racking operation when the circuit breaker is CLOSED.

Figure 33: Circuit-breaker compartment (MOC/TOC switch cover plate removed for photo) on page 34 shows the racking mechanism located on the floor in the center of the circuit breaker compartment. Note the two "wing- like" elements that project from the left side of the racking mechanism. The CLOSED circuit breaker interlock plunger, when down (circuit breaker CLOSED), falls behind the front wing in the TEST position and behind the rear wing in the CONNECT position.

Vacuum interrupter/ operator

Figure 34: Interlock mechanisms on the type 38-3AH3 vacuum circuit breaker

The wings are coupled to the element of the racking mechanism that shrouds the racking screw. This shroud must be moved rearward to insert the racking-crank socket in order to engage the racking shaft. With the plunger down (circuit breaker CLOSED), the wings and shroud cannot be moved and thus racking is blocked.

B. Trip-free interlock

Figure 32: Circuit-breaker interlocks and ground disconnect on page 33 shows the trip-free interlock. This interlock is a plunger with a roller on the lower end. The plunger roller tracks the shape of the cam profiles on the racking mechanism in the switchgear (refer to Figure 33: Circuit-breaker compartment (MOC/ TOC switch cover plate removed for photo) on page 34).