ABB 41-101U, Instruction Leaflet, Page: 18 / 24

41-101U Type CO Overcurrent Relay
18
3% and should return to the backstop at tap value
current minus 3%.
6.1.3 Time Curve
For type CO-11 relay only, the 1.30 times tap value
operating time from the number 6 time dial position
is 53.5
±
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 cur-
rent accurately is necessary because of the steep-
ness of the slope of the time-current characteristic
(Figure 13). 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
variations appear to be
±
15%.
Table 2 shows the time curve calibration points for
the various types of relays. With the time dial set to
the indicated position and the relay set on the lowest
tap setting, apply the currents specified by Table 2,
(e.g., for the CO-2, 3 and 20 times tap value current)
and measure the operating time of the relay. The op-
erating times should equal those of Table 2 plus or
minus 5% (Use .5 tap for .1 to .5 range).
6.1.4 Indicating Instantaneous Trip Unit (IIT)
The core screw which is adjustable from the top of
the trip unit determines the pickup value. The trip unit
has a nominal ratio of adjustment of 1 to 4 and an ac-
curacy within the limits of 10%.
The making of the contacts and target indication
should occur at approximately the same instant. Po-
sition the stationary contact for a minimum of 1/32
”
wipe. The bridging moving contact should touch both
stationary contacts simultaneously.
Apply sufficient current to operate the IIT. The oper-
ation indicator target should drop freely.
6.1.5 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 be not great-
er than the particular ICS tap setting being used. The
operation indicator target should drop freely.
For proper contact adjustment, insert a .030" feeler
gauge between the core pin and the armature. Hold
the armature closed against the core pin and gauge
and adjust the stationary contacts such that they just
make with the moving contact. Both stationary con-
tacts should make at approximately the same time.
The contact follow will be approximately 1/64
” to
3/64 ” .
6.2 CALIBRATION
Use the following procedure for calibrating the relay
if the relay has been taken apart for repairs or the ad-
justments disturbed. This procedure should not be
used until it is apparent that the relay is not in proper
working order. (See Section 6.1, Performance
Check.)
6.2.1 Contact
a. By turning the time dial, move the moving con-
tacts until they deflect the stationary contact 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 stationary contacts should be ap-
proximately 1/64
” .
b. For relays identified with a “ T ” , located at lower
left of stationary contact block, the index mark on
the movement frame will coincide with the
“ O ”
mark on the time dial when the stationary contact
has moved through approximately one-half of its
normal deflection. 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 vari-
ous time dial positions in line with the index mark
will give operating times as shown on the respec-
tive time-current curves. For double trip relays,
the follow on the stationary contacts should be ap-
proximately 1/32
” .
6.2.2 Minimum Trip Current
The adjustment of the spring tension in setting the
minimum trip current value of the relay is most con-
veniently made with the damping magnet removed.
With the time dial set at “ O ” , wind up the spiral spring
by means of the spring adjuster until approximately
6 3/4 convolutions show.
Set the relay on the minimum tap setting, the time
dial to position 6.
Adjust the control spring tension so that the moving
contact will leave the backstop at tap value current
+1.0% and will return to the backstop at tap value
current -1.0%.
6.2.3 Time Curve Calibration
Install the permanent magnet. Apply the indicated
current per Table 2 for permanent magnet adjust-
ment (e.g., CO-8, 2 times tap value) and measure