41-116.1A
5
tor target should drop freely.
Repeat above except pass 85% of ICS
nameplate rating current. Contacts
should not pickup and target should
not drop.
6.1.3. Indicating Instantaneous Trip
Unit (IIT)
The core screw which is adjustable
from the top of the trip unit and the tap
located on the top of the IIT deter-
mines the pickup value. The trip unit
has a nominal ratio of adjustment of 1
to 24.
Apply sufficient current to operate the
IIT. the operation indicator target
should drop freely.
Table 1:
TIME CURVE CALIBRATION DATA -50-60 HERTZ FOR
OVERCURRENT UNIT
Permanent
Magnet Adjustment
Electromagnet
Plug Adjustment
Relay
Type
Time
Dial
Position
Current
(Multiples of
Tap Value)
Operating
Time
(Seconds)
Current
(Multiples of
Tap Value)
Operating
Time
(Seconds)
6
6
2
2.46
20
1.19
7
6
2
4.27
20
1.11
8
6
2
13.35
20
1.11
9
6
2
8.87
20
0.65
11
6
2
11.27
20
0.24*
* For 50 hertz COV-11 relay, 20 times operating time limits are 0.24 + 10%, -5%
contacts until they deflect the stationary con-
tact to a position where the stationary contact
is resting against its backstop. The index
mark located on the movement frame should
coincide with the “O” mark on the time dial.
For double trip relays, the follow on the sta-
tionary contacts should be approximately
1/64”.
2) For relays identified with a “T”, located at
lower left of stationary contact block, the
index mark on the movement frame will coin-
cide with the “O” mark on the time dial when
the stationary contact has moved through
approximately one-half of its normal deflec-
tion. Therefore, with the stationary contact
resting against the backstop, the index mark
is offset to the right of the “O” mark by
approximately .020”. The placement of the
various time dial positions in line with the
index mark will give operating times as shown
on the respective time-current curves. For
double trip relays, the follow on the stationary
contacts should be approximately 1/32”.
B. Minimum Trip Current – Set the time dial to posi-
tion 6. Alternately apply tap value current plus
3% and tap value current minus 3%. The moving
contact should leave the backstop at tap value
current plus 3% and should return to the back-
stop at tap value current minus 3%.
C. Time Curve –
Table 1
shows the time curves cal-
ibration points for the various types of relays.
With the time dial set to the indicated position,
apply the currents specified by Table 1 (e.g., for
the COV-8, 2 and 20 times tap value current) and
measure the operating time of the relay. The
operating times should equal those of Table 1
plus or minus 5%.
For type COV-11 relay only, the 1.30 times tap
value operating time from the number 6 time dial
position is 54.8
±
5% seconds and should be
checked first. It is important that the 1.30 times
tap value current be maintained accurately. The
maintaining of this current accurately is neces-
sary because of the steepness of the slope of the
time-current characteristic (Figure 8). A slight
variation,
±
1%, in the 1.3 times tap value current
(including measuring instrument deviation) will
change the timing tolerance to
±
10% and the
effects of different taps can make the total varia-
tions appear to be
±
15%.
6.1.2. Indicating Contactor Switch (ICS)
Close the main relay contacts and pass sufficient dc
current through the trip circuit to close the contacts of
the ICS. This value of current should not be greater
than the particular ICS nameplate rating. The indica-
