41-337.3L
4
gap fluxes cause a contact closing torque.
2.3.
Sensitive Fault Detector Circuit
– when used
The sensitive fault detector circuit consists of an
auto-transformer and a contactor switch. The contac-
tor switch is connected across the secondary (tapped
section) of the auto-transformer winding.
The contactor switch is a small solenoid type ele-
ment. A cylindrical plunger rides up and down on a
vertical guide rod in the center of the solenoid coil.
The guide rod is fastened to the stationary core. The
guide rod is fastened to the stationary core, which in
turn screws into the unit frame. A silver disc is fas-
tened to the moving plunger through a helical spring.
When the coil is energized, the plunger moves
upward carrying the silver disc which bridges three
conical-shaped stationary contacts. In this position,
the helical spring is compressed and the plunger is
free to move while the contact remains stationary.
Thus, ac vibrations of the plunger are prevented from
causing contact bouncing. A Micarta disc is fastened
to the bottom of the guide rod by two small nuts. Its
position determines the pick up current of the ele-
ment.
The auto-transformer is designed to saturate at high
values of current to limit the amount of current to the
contactor switch.
2.4.
Indicating Contactor Switch Unit (ICS)
The dc indicating contactor switch is a small clapper
type device. A magnetic armature, to which leaf-
spring mounted contacts are attached, is attracted to
the magnetic core upon energization of the switch.
When the switch closes, the moving contacts bridge
two stationary contacts, completing the trip circuit.
Also during this operation two fingers on the arma-
ture deflect a spring located on the front of the
switch, which allows the operation indicator target to
drop. The target is reset from the outside of the case
by a push rod located at the bottom of the cover.
The front spring, in addition to holding the target, pro-
vides restraint for the armature and thus controls the
pick-up value of the switch.
Sub 2
187A434
Figure 5: Internal Schematic of the Type CA-16 Bus
Relay with a Sensitive Fault Detector.
Curve 537956
Figure 6: Typical Time Curves of the CA-16 and CA-26
differential Relays.
