41-337.31B
3
2.1.
Restraint Elements
Each restraint element consists of an “E” laminated
electromagnet with two primary coils and a second-
ary coil on its center leg. Two identical coils on the
outer legs of the laminated structure are connected
to the secondary winding in a manner so that the
combination of all fluxes produced by the electro-
magnet results in out-of-phase fluxes in the air gap.
The out-of-phase fluxes cause a contact opening
torque.
2.2.
Operating Circuit
The operating circuit consists of an autotransformer
and an operating element. The primary of the auto-
transformer, which is the whole winding, is connected
to receive the differential or unbalanced current from
the various transformers connected to the bus. The
secondary winding of the autotransformer, which is a
tapped section of the winding, is connected to the
operating element of the relay.
The operating element consists of an “E” type lami-
nated electromagnet with an autotransformer winding
on its center leg. Two identical coils on the outer legs
of the laminated structure are connected to the sec-
ondary (tapped section) of the autotransformer wind-
ing in a manner so that the combination of all fluxes
produced by the electromagnet results in out-of-
phase fluxes in the air gap. The out-of-phase air gap
fluxes cause a contact closing torque.
2.3.
Sensitive Fault Detector Circuit
The sensitive fault detector circuit consists of an
autotransformer 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,
which in turn screws into the unit frame. A silver disc
is fastened 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 sta-
tionary. Thus, ac vibrations of the plunger are pre-
vented 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 element.
The auto-transformer is designed to saturate at high
values of current to limit the amount of current to the
contactor switch.
2.3.1. 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 a restraint for the armature and thus controls
the pick-up value of the switch.
3.0
OPERATION
The type CA-16 relay is an induction disc relay with
four electromagnets mounted on two discs that are
fastened on a common shaft. One of the electromag-
nets is the operating element while the other three
are restraint elements. The restraint elements are
energized from the secondaries of current transform-
ers connected to the bus, and the operating circuit is
energized in accordance with the current flowing in
the differential connection of the current transform-
ers.
A current of 5 amperes in at terminal 18 and out of
terminal 19 will produce a definite amount of restrain-
ing torque
(see Figure 3.)
Similarly, a current of 5
amperes flowing in at terminal 16 and out of terminal
17 will produce an equal amount of torque. If both of
these currents flow at the same time with the polarity
as indicated above, their effect will be additive and
they will produce the same torque as though 10
amperes are flowing in terminal 16 and out of termi-
nal 17. Conversely, if equal currents flow in these two
coils, but in opposite directions, their ampere turns
will cancel and no torque will be produced. The same
relationship applies for the paired coils of the other
two restraining units of the relay. The restraint effect
will always be additive if currents flow in the coils
which belong to different restraint elements.
4.0
CHARACTERISTICS
4.1.
CA-16 Bus Relay
This relay has variable percentage characteristics
which means that the operating coil current
