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Directional Overcurrent Ground Relays
Types IRP, IRC and IRD
checked by inserting the tap screw in the desired
tap hole and applying rated tap value current.
The contact should close within 5% of tap value
current.
7.1.2 Directional Unit (D)
a. Contact Gap: The gap between the stationary
contact and moving contact with the relay in the
deenergized position should be approximately
.020".
b. Sensitivity: The respective directional units
should trip with value of energization and phase
angle relationship as indicated in Table 1 (page
10).
c.
Spurious Torque Adjustments: There should be
no spurious closing torques when the operating
circuits are energized per Table 2 (page 11) with
the polarizing circuits short circuited for the volt-
age polarized units and open-circuited for the
current polarized units.
7.1.3 Time Overcurrent Unit (CO)
Contacts
The index mark on the movement frame will coincide
with the "0" 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 "0" mark by approximately
.020". The placement of the various time dial posi-
tions in line with the index mark will give operating
times as shown on the respective time-current
curves.
Minimum Trip Current
Set the time dial to position 6 with the auxiliary switch
contacts blocked closed, 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%.
Time Curve
Table 3 (page 11) shows the time curve calibration
points for the various types of relays. With the time
dial set to the indicated position, apply the currents
specified by Table 3 (e.g. for the CO-2, 3 and 20
times tap value current) and measure the operating
time of the relay. The operating times should equal
those of Table 3 plus or minus 5 percent.
7.1.4 Indicating Contactor Switches
(ICS/I) and (ICS/T)
a. Close the contacts of the CO and pass sufficient
dc current through the trip circuit to close the
contact of (ICS/T). This value of current should
not be greater than the particular (ICS/T) tap set-
ting being used. The operation indicator target
should drop freely, bring the letter "T" into view.
b. Close the contacts of the instantaneous overcur-
rent unit (I) and the directional unit (D). Pass suf-
ficient dc current through the trip circuit to close
the contacts of (ICS/I). This value of current
should not be greater than the particular (ICS/I)
tap setting being used. The operation indicator
target should drop freely, bringing the letter "I"
into view.
7.2 ROUTINE MAINTENANCE
All relays should be inspected periodically and the
time of operation should be checked at least once
every year or at such other time intervals as may be
dictated by experience to be suitable to the particular
application. The use of phantom loads, in testing
induction-type relays, should be avoided, since the
resulting distorted current waveform will produce
error in timing.
All contacts should be periodically cleaned. A contact
burnisher #182A836H01 is recommended for this
purpose. The use of abrasive material for cleaning
contacts is not recommended, because of the danger
of embedding small particles in the face of the soft
silver and thus impairing the contact.
7.3 CALIBRATION
Use the following procedure for calibrating the relay if
the relay has been taken apart for repairs or the
adjustments have been disturbed. This procedure
should not be used unless it is apparent that the relay
is not in proper working order. (See Acceptance
Check, page 6.)
7.4 INSTANTANEOUS OVERCURRENT UNIT (I)
a. The upper pin bearing should be screwed down
until there is approximately .025 clearance
between it and the top of shaft bearing. The
upper pin bearing should then be securely
locked in position with the lock nut. The lower
bearing position is fixed and cannot be adjusted!
41-133S
7
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