41-116.1C
5
COV Voltage Controlled Overcurrent Relay
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 accu-
rately. The maintaining of this current accu-
rately is necessary because of the steepness
of the slope of the time-current characteristic
(Figure 8, page 17). A slight variation,
±
1%, in
the 1.3 times tap value current (including mea-
suring instrument deviation) will change the
timing tolerance to
±
10% and the effects of dif-
ferent taps can make the total variations
appear to be
±
15%.
6.2
VOLTAGE UNIT (V)
1) Contact Gap – The gap between the station-
ary contact and moving contact with the relay
in a de-energized position should be
approximately .020”.
2) Sensitivity – The contacts should close when
voltage is reduced to approximately 90 volts.
6.3
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-
tor target should drop freely.
Repeat above except pass 85% of ICS nameplate
rating current. Contacts should not pickup and target
should not drop.
6.4
TELEPHONE RELAY (T)
The telephone relay has a dropout time of 250
milliseconds
±
50 milliseconds. It has a burden of
1.56 watts at 125 volts dc nominal. It should pickup
whenever the voltage unit contacts close.
7.0
ROUTINE MAINTENANCE
All relays should be inspected and checked once a
year or at other time intervals as dictated by experi-
ence to assure proper operation. Generally a visual
inspection should call attention to any noticeable
changes. A minimum suggested check on the relay
system is to close the contacts manually to assure
that the breaker trips and the target drops. Then
release the contacts and observe that the reset is
smooth and positive.
If an additional time check is desired, pass second-
ary current through the relay and check the time of
operation. It is preferable to make this at several
times pick-up current at an expected operating point
for the particular application. For the .05 to 2.5
amperes range CO-6 induction unit use the alterna-
tive test circuit in Figure 9 (page 18) as these relays
are affected by a distorted waveform. With this con-
nection the 25/5 amperes current transformers
should be worked well below the knee of the satura-
tion (i.e., use C 50 or better).
All contacts should be periodically cleaned. A contact
burnisher S#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.
8.0
CALIBRATION
Use the following procedure for calibrating the relay if
the relay has been taken apart for repairs or the
adjustments disturbed. This procedure should not be
used until it is apparent that the relay is not in proper
working order (see “ACCEPTANCE TEST”).
NOTE: A spring shield covers the reset spring of
the CO unit. Removing the spring shield
requires that the damping magnet be
removed first. The screw connection hold-
ing the lead to the moving contact should
be removed next. The second screw hold-
ing the moving contact assembly should
then be loosened, not removed. (Caution:
this screw terminates into a nut held cap-
tive beneath the molded block. If screw is
removed, difficulty will be experienced in
the re-assembly of the moving contact
assembly.) Slide the spring shield outward
and remove from relay. Tighten the screw
holding the moving contact assembly to
the molding block.
8.1
OVERCURRENT UNIT (CO)
A. Contact
1) By turning the time dial, move the moving
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 “0” mark on the time dial.
For double trip relays, the follow on the sta-
