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Fig. 10. External Schematic Diagram of the Type CA-S Relay In the Type FT21 Case for Protection of a
Wye-Delta Transformer Bank.
straint current, the relay should operate with
following operating current.
a) Transfonner Relay
b) Generator Relay
B.
Indicating Contactor Switch (ICS)
Close the main relay contacts and pass suf
ficient d-e current through the trip circuit to close
the contacts of the ICS. This value of current
should be not greater than the particular ICS tap
setting being used. The operation indicator target
should drop freely.
The contact gap should be approximately .047
inch between the bridging moving contact and the
adjustable
stationary
contacts.
10.5± 7% amperes
6.7± 7% amperes
Routine Maintenance
year or at such other time intervals as may be die-
The
bridging
D.C. TRIP BUS
POS.
2
87
PH. PH.
a
2
,,.
DE�ICE NUMBER CHART
87 -- TRANSFORMER PERCENTAGE
DIFFERENTIAL RELAY,TYPE CA-S
87R - RESTRAINING COIL OF TYPE CA-S
RELAY
870P- OPERATING COIL OF TYPE CA-S
RELAY
86
- AUXILIARY TRIPPING RELAY,
S2
TYPE WL
-
-
POWER CIRCUIT BREAKER
a
-- BREAKER AUXILIARY CONTACT
TC -- BREAKER TRIP COIL
ICS - INDICATING CONTACTOR SWITCH
moving contact should tJouch both stationary con
tacts simultaneously.
c.
Indicating
Instantaneous
(When Supplied)
The core screw which is adjustable from the
top of the trip unit detennines the pickup value.
The trip unit has a nominal ratio of adjustment
of 1 to 4 and an accuracy within the limits of
Pickup current should be measured with the
tenninals of the external transfonner shorted.
All relays should be checked at least once every
3
ALARM
Trip
Unit
(ITT)
lOo/c.
10
7
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