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Type PM Line of Relays For Pilot Wire Monitoring
And Transferred Tripping
the monitoring current. The resistors can be checked
with an ohmmeter, and the diode can be checked
either with an ohmmeter, or as explained in the sec-
tion entitled "Rectifier Check" under "Routine Mainte-
nance". If an ohmmeter is used, the difference in
forward and reverse resistance readings obtained
will be dependent on the current flowing through the
diode.
7.1.6
PM-5 Relay
Apply 5 volts dc in series with a 0-1 dc milliammeter
and a 20,000 ohm variable resistor to terminals 6 and
7 with positive on terminal 6. The left-hand contact
should close at approximately 0.3 mA. Now apply the
same circuit to terminals 8 and 9 with positive on ter-
minal 9. The right-hand contact should close at
approximately 0.3 mA.
7.1.7
PM-13 Relays – ac and dc
Alarm Unit (1)
Connect a variable 20,000 ohm resistor (10,000
ohms for a 3-terminal line relay) in series with a dc
milliammeter across terminals 8 and 9 with the instru-
ment positive on terminal 9. For the ac relay, set the
primary tap on 120 volts. Now apply the rated supply
voltage to terminals 4 and 5. This will be 48, 125, or
250 volts dc, or 120 volts ac as indicated on the relay
nameplate. Adjust the variable resistor to obtain a
current of one mA for a 2-terminal line relay, or 2 mA
for a 3-terminal relay. At this value, the moving con-
tacts of the alarm or monitoring (1) relay unit (the
upper polar unit) should float between the two sets of
stationary contacts. Increase and decrease the one
or 2 mA monitoring current to check the calibration
values listed in Tables 4 and 5.
Tripping Unit (3)
To check the operation of the tripping unit 3 (the
lower polar unit), apply a dc potential across termi-
nals 16 (positive) and 20 (negative). The tripping
polar unit should pick up at 14 volts. The resistance
of the series dropping resistors for transferred trip-
ping (listed in Table 3A and Table 3B) can be
checked with an ohmmeter. The circuit location of
these resistors can readily be seen from the external
schematic, figure 27.
7.1.8
PMG-13 Relays – ac and dc
Alarm and Tripping Units
Follow the procedure given in the previous section
for the ac and dc PM-13 relays.
Ground Unit (5)
Connect the 20,000 ohm (or 10,000 ohm) resistor
and milliammeter across terminals 8 and 9. With
rated voltage applied and one mA (or 2 mA) flowing,
successively short circuit terminals 3 and 8, then 3
and 9. The ground alarm unit 5 (lower polar unit)
should move first to the left, then to the right. To
check the pickup current of the ground detector, first
remove the 20,000 ohm resistor from terminals 8 and
9. Connect a 0-1 dc milliammeter in series with a
variable resistor of about 50,000 ohms between ter-
minals 3 and 8. The left-hand contact should close at
approximately 0.3 mA dc. With the milliammeter
resistor connected between terminals 3 and 9, the
right-hand contact should close at 0.3 mA dc. The
external schematic diagrams for these relays are
shown in figures 27 and 29.
8.0 ROUTINE MAINTENANCE
!
DO NOT make any performance check, calibra-
tion tests, or adjustments while the PM relays are
energized or connected to the pilot-wires, to pre-
vent the possibility of inadvertently causing a
break operation. The PM relays may be removed
from service for testing, without jeopardizing
HCB relay protection, providing that the connec-
tions between the 10 mfd capacitor and the HCB
insulating transformer are not disturbed.
8.1
CONTACTS
All contacts should be periodically cleaned. A contact
burnisher Style number 182A836H01 is recom-
mended for this purpose. The use of abrasive mate-
rial 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.
8.2
OPERATIONAL CHECK
In addition to cleaning contacts, it is recommended
that an operational check be performed periodically
by opening and short circuited the pilot-wires, as well
as grounding term at the relay terminals.
NOTE: These pilot-wire faults should not be applied
directly to the pilot-wires when the HCB relays
are in service. It is recommended that the trip
circuits of the PM relays be opened (where trip-
41-973.5R
CAUTION
9
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