*
Curve
2 3 5 4 1 2
Fig. 3 . Typical Torque Curves o f the Operating
&
Re
straint Coils.
A core screw accessible from the top of the
switch provides the adjustable pickup range .
OP E RATION
The CA-6 relay has three restraining elements,
each with two windings which are energized from the
secondaries of current transformers connected to
the bus. The relay has one operating electromagnet
energized through an
external auxiliary current
transformers in accordance with the current flowing
in the differential connection of the current trans
formers.
Refer to the internal schematic, Fig.
1.
A cur
rent of 5 amperes in at terminal 18 and out of termi
nal
19
will produce a definite amount of restraining
(/)
(/)
<t
(J)
w
...J
u
>
u
0
<.0
(/)
w
...J
u
>
u
Curve
2 3 5496
Fig.
4.
Typical Differential Unit Time Curve.
torque as indicated in Fig. 3. Similarly, a current
of 5 amperes flowing in at termiRal 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 produc e the same torque as
though
10
amperes were flowing in one winding
alone. 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 other two re
straining units of the relay.
This relay has variable percentage character
istics which means that the operating coil current
required to close the relay contacts, expressed in
percent of the total restraint current, varies with
the magnitude of the restraint current. The relay
sensitivity is high, corresponding to a low percent
age ratio , at light currents, and its sensitivity is
3
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