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If it is found during the installation or periodic tests that the mho unit calibrations are out of
limits, they should be recalibrated as outlined in the following paragraphs.
calibrations be made in the laboratory.
as factory adjustments , are used in recalibrating the units. These parts may be physically located from
Fig. 1 and 2. Their locations in the relay circuit are shown in the internal connection diagrams of Fig. 10.
- 0
R
1 _ 2
unit r.hmic
11
- 0
R
1_2 unit angle
21
- 0
R
2 _ 3
unit ohmic
l2
- 0
R
unit angle
22
2-3
R
- 0
unit ohmic
3-1
l3
R
- 0
unit angle of maximum torque adjustment
23
3-1
NOTE:
Before making pickup or phase-angle adjustments on the mho units, the units s hould be allowed
to heat up for approximately 15 minutes energized with rated voltage alone and the restraint
taps lead set for 100 percent .
position so that the units are level.
Control Spring A djustment
a.
Make connections to the relay as shown in Fig. 11 and set the restraint tap leads on 100 percent .
basic reach taps should be set in the position for the basic minimum reach shown in Table XII.
Make sure that the relay is in an upright position so that the units are level.
5 amperes and the voltage V A - B at 120 volts, s et phase shifter so that the phase-angle meter reads the va 1 ue
shown in Table XII.
Now reduce the voltage to the test voltage value and set the current at the value shown in Table XII for
the unit being adjusted.
spring adjusting ring (see Fig. 1 5) and turn the ring until the contacts of the unit just close.
tacts were closing below the set point shown in Table XII, the adjusting ring should be turned to the right.
If they were closing above the set point, the adjusting ring should be turned to the left.
Ohmic Reach A djustment
b.
The basic minimum reach of the mho units can be adjusted by means of the rheostats which are accessible
from the front of the relay.
and be sure that the basic minimum reach taps are in the position shown in Table XIII. With current at
5 amperes, and voltage at 120 volts set the phase shifter so that the phase-angle meter reads the angle shown
in the table for the unit to be checked.
adjust the appropriate rheostat so tha t the unit picks up at
A ngle of Maximum Torque
c.
The angle of maximum torque of the mho units can be adjusted by means of rheostats which are accessible
from the front of the relay.
sure that the basic minimum reach taps are in the position shown in Table XI V.
The procedure used in setting angle of maximum torque is to adjust the reactor so that the pickup
amperes, at a s pecified set voltage V A B • will be the same at angles leading and lagging the maximum torque
angle by 30 degrees.
The test angles, set voltages, and the pickup amperes are shown in Table XIV.
First, the reach of the unit at its angle of maximum torque should be checked and adjusted if necessary
as described in paragraph (b) and Table XIV.
330 degrees (Note that phase-angle adjustments should be made at 120 volts and
test volts and adjust the proper reactor so that the ohm unit closes its contacts at 17.3 amperes +5 percent.
The pickup should then be checked at 270 degrees with the same set voltage and should be 17.3 amperes �5 per
cent. Refine the adjustments of rheostats until the pickup is within limits at both 270 degrees and
330 degrees.
GEK-45495
The circuit components listed below, which are normal ly considered
reach adjustment
of maximum torque adjustment
rP.ach adjustment
of maximum torque adjustment
reach adjustment
A lso it is important that the relay be mounted in an upright
Insert the blade of a thin screwdriver into one of the slots in the edge of the
Connect the relay as shown in Fig. 11; leave the restraint taps at 100 percent
Now reduce the voltage V A B to
Use the connections in Fig. 11. Leave the restraint taps to 100 percent and be
Next set the phase shifter so that the phase-angl e meter reads
SERVICING
amperes
15
15
It is suggested that these
With the current s et at
the set value shown in
percent.
�5
amperes). Then set V A B at
5
The
If the con
Table
XIII and
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