41-973.5R
8
Type PM Line of Relays For Pilot Wire Monitoring
And Transferred Tripping
adjustments have been changed, the relay taken
apart for repairs, or if it is desired to check the adjust-
ments at regular maintenance periods, the instruc-
tions in the succeeding sections should be followed.
7.1
ACCEPTANCE TESTS
The following tests are recommended when the relay
is received from the factory. If the relay does not per-
form as specified below, the relay either is not prop-
erly calibrated or it contains a defect. (Relays must
be tested in the case.)
7.1.1
Indicating Contactor Switch (ICS)
Close the contact of the tripping unit and pass suffi-
cient direct current through the trip circuit to close the
contacts of the ICS unit. This value of current should
not be greater than the particular ICS tap setting
being used (0.2 or 2.0). The indicator target should
drop freely.
7.1.2
PMA and PMA-1 Relays
Alarm Unit (1)
Set the primary tap on 120 volts. Connect a variable
resistor of approximately 20,000 ohms in series with
a low-range dc milliammeter across terminals 6 and
7 with the instrument positive connected to terminal
7. Apply 120 volts at rated frequency to terminals 4
and 5. Adjust the 20,000 ohm resistor to obtain a cur-
rent of one mA dc. For a three-terminal line relay, use
a 10,000 ohm resistor and set the current to 2 mA dc.
At this value, the moving contact of the alarm or mon-
itoring relay unit (1) should float between the two sets
of stationary contacts. In the PMA relay, the ground
alarm unit (5) contact should also float. (This contact
will also float when the relay is deenergized.)
Increase and decrease the one or two milliampere
monitoring current to check the calibration values
listed in Tables 4 and 5.
Ground Unit (5)
Reconnect the 20,000 ohm resistor. For the PMA
relay only, short terminals 7 and 3. The contact of the
ground alarm unit (5) should close to the right when
the relay is energized. Remove the short, and con-
nect it between terminals 6 and 3. The ground alarm
unit (5) should close to the left. The action of the
monitoring unit (1) contact is of no significance in this
simulated pilot-wire ground test. To check the pickup
current of the ground detector, first remove to the
20,000 ohm resistor from terminals 6 and 7. Connect
a 0-1 dc milliammeter in series with a variable resis-
tor of about 50,000 ohms between terminals 3 and 6.
The ground unit should close its left-hand contact at
approximately 0.3 mA dc. With the milliammeter and
resistor connected between terminals 3 and 7, the
right-hand contact should close at 0.3 mA dc.
7.1.3
PMD and PMD-1 Relays
Alarm and Ground Units
Connect an adjustable 20,000 ohm resistor (or
10,000 ohms for a 3-terminal relay) in series with a
dc milliammeter across terminals 6 and 7 with the
instrument positive connected to terminal 7. Apply
rated dc voltage to terminals 8 and 9 with positive on
terminal 9. Now check the PMD and PMD-1 relays,
following the procedure given in the previous section
for the PMA and PMA-1 relays, respectively. Note,
however, that terminal 5 of the PMD relay corre-
sponds to terminal 3 of the PMA relay.
7.1.4
PM-2, PM-3, and PM-23 Relays
Alarm Unit (2)
Apply a variable dc voltage of approximately 20 volts
to relay terminals 8 and 9 (terminal 9 positive) of the
PM-2 or PM-23 relay. Adjust the voltage to obtain a
reading of one mA on the relay milliammeter. The
monitoring polar unit (2) contacts should float.
Reduce the current gradually. The monitoring alarm
contacts should close at 0.65 mA dc. The tripping
unit (3) of the PM-23 relay should not move during
this test. The milliammeter has been adjusted to read
1 mA
±
5%. As a result the pointer may not read zero
for a zero current condition.
Tripping Unit (3)
to check the PM-3 relay or the tripping unit of the PM-
23 relay, apply the variable dc voltage in series with
an external milliammeter to relay terminals 8 and 9
with terminal 8 positive for the PM-23 relay, or termi-
nal 9 positive for the PM-3 relay. When checking the
pickup of the PM-23 trip unit block open the alarm
unit contacts (2) so as to remove the shunt resistor
from around the trip coil (3).
The tripping relay unit (3) should pickup with positive
action at 14 volts dc and should drop out at approxi-
mately 10 volts. The alarm unit of the PM-23 relay
will not operate during this test.
7.1.5
PM-4 Relay
This device is simply a set of resistors and a diode to
connect into the pilot-wire circuit to provide a path for
