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Equipment Description
PowlVac® DHP 15kV Replacement Circuit Breaker
01.4IB.50032C
e. Control Circuit
The typical electrical control scheme is
shown in Figure 8. The control scheme
of any particular circuit breaker may
differ from these typical schemes
depending on the user’s requirements,
operating solenoids, and the control
devices furnished with that circuit
breaker.
The sequence of operation for all
control schemes is shown in
Figure 7. Circuit breaker mounted
auxiliary contacts not used in the
control circuit are brought out for
control and indication functions. The
metal-clad switchgear equipment
may provide a circuit breaker MOC
(Mechanism Operated Cell Switch) for
additional contacts.
c. r
AckInG
M
echAnISM
1) General Description
The racking mechanism is the mechanical
assembly that facilitates moving the
circuit breaker between the breaker
test/disconnected and the connected
positions in the circuit breaker
compartment. This consists of components
which are installed as part of the circuit
breaker chassis assembly. The
racking shaft (Figure 1, k) is securely
fastened to the guide tube and is loosely
retained in a housing fastened to the rear
of the chassis. The operation consists
of engaging the rotatable racking shaft
on the circuit breaker with the racking
screw mounted on the rear wall of the
compartment.
By traversing the racking nut along the
racking screw, the circuit breaker is moved
between test and connected positions
within the switchgear compartment.
The guide tube (Figure 9, c) is slotted
lengthwise for a distance about equal to
the travel distance of the circuit breaker.
The racking shaft has two rectangular
hardened keys welded to it, which slide in
the guide tube slot. Thus, as the racking
shaft is rotated, the guide tube and nut are
also rotated.
As the circuit breaker is racked in by
clockwise rotation, the keys on the
racking shaft move toward the end of the
guide tube slot. As the rear key comes out
of the slot, the racking shaft turns freely and
the circuit breaker can be moved no further.
The end of the guide tube is shaped like
a steep-pitch one-turn screw thread so
that when the racking shaft is rotated
counterclockwise, the rear key will catch
and enter the slot and rotate the guide
tube and nut and the circuit breaker will be
withdrawn.
At the end of travel, the nut will disengage
from the screw and spin freely. The main
components of the racking device are
shown in Figure 9.
