(/)
a
z
0
(.)
w
(/)
..J
..J
�
z
w
�
5 0
4 0
30
2 0
1 0
0
0
2
4
T Y P I C A L T I M E C U R V E S
C Y L I N D E R
I N STA N TA N EO U S OVE R C U R RE N T U N I T
6
8
1 0
1 2
1 4
1 6
M U LT I P L E S O F TAP VA L U E C U R RE N T
184A946
Fig.
1 1 .
Typical Time Curve
of
the Instantaneous Overcurrent Unit.
S E T T I N G S
T i m e O verc urrent U n i t ( C O )
The time overcurrent unit settings can b e defined
either by tap setting, and time dial position or by tap
setting and a specific time of operation at some cur
rent multiple of the tap setting ( e . g.
4
tap setting,
2
time dial position
or
4
tap setting,
0 . 6
seconds
at
6
times
tap value current).
To provide selective circuit breaker operation, a
minimum coordinating time of
0.
3
seconds plus circuit
breaker time is recommended between the rei ay being
set and the relays with which coordination is to be
effected.
The connector screws on the tap plate above the
time dial makes connections to various turns on the
operating coil . By placing this screw in the various
terminal plate holes, the relay will respond to multi
ples of tap value currents in accordance with the
various typical time-current curves.
C A U T I O N
Since the tap block connector screw car
ries operating current, be sure that the screw is turned
tight. In order to avoid opening the current transformer
circuits when changing taps under load, connect the
spare connector screw in the desired position before
16
removing the other tap screw from the original tap
position.
I n stantaneous R e c l o s i n g
The factory adjustment o f the C O unit contacts
provides a contact follow. Where circuit breaker re
closing will be initiated immediately after a trip
by
the
CO
contact, the time
of the
opening of the contacts
should be
a
minimum. This condition is obtained
by
loosening the stationary contact mounting screw,
removing the contact plate and then replacing the
plate with the bent end resting against the contact
spring.
I n stantaneous O v erc urrent U n i t ( I )
The only setting required is the pickup current
setting which is made by means of the connector
screw located on the tap plate. By placing the con
nector screw in the desired tap, the relay will just
close its contacts at the tap value current.
C A U T I O N
Since the tap block connector screw car
ries operating current, be sure that the screw is
turned tight.
In order to avoid opening the current transformer
circuits when changing taps under load, connect the
spare tap screw in the desired tap position before re-
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