Electrical Checks, Mho Unit - GE CEY51A Instructions Manual

Check Points
Rotating Shaft End Play
Contact Gap
Contact Wipe
ELECTRI CAL CHEC KS - MHO UNIT
GEK-I2l5
I
TABLE V II I
MHO Uni ts
o .
010 - 0.015 i nc
~
0.030 - 0.035
inc~
0.003 - 0.005 incr
Before any electrical checks are made on the mho units, the relay should be
connected as shown in Fi gure 10 and be all owed to warm up for approximately 15
minutes with the potential circuit
alone
energized at rated voltage and the
restraint taps set as shown in Table IX. The units were warmed up prior to factory
adjustment, and i f rechecked when cold will tend to underreach by 3% or 4%.
Accurately-calibrated meters are of course essential for correct test results.
It is desirable to check the factory setting and calibrations by means of the
tests described in the following sections. The mho units were carefully adjusted at
the factory and it is not advisable to disturb these settings unless the following
checks indicate
conclusively
that the settings have been disturbed. If
readjustments are necessary, refer to the section on SERVICING for the recommended
procedures.
(a) Control-Spring Adjustment
Be sure that the relay is level in its upright position. Leave the relay
connected as sho\tln in Figure 10 and position the restraint taps according to
Table XII.
Use the following procedure in checki ng each unit. With the current set at 5
amperes and the vol tage across the rel ay vol tage studs at 120 vol ts, set the
phase shi fter so that the phase-ang1 e meter reads the val ue shown in Tab1 e I X
for the unit being tested; that is, so current lags voltage by an angle equal
to the angl e of maximum torque of the unit. Now reduce the vol tage to the low
test voltage of
2.0
volts, and reduce the current to about
2
amperes.
Gradually increase the current until the contacts of the unit just close. Thi s
should occur between 2.7 and 3.3 amperes for the 1.5 ohm setting or 10.1 and
12.4
for the
0.4
ohm setting.
(b) Clutch Adjustment
The mho un; ts i ncl ude a hi gh- set c1 utch between the cup-and- shaft assembl y and
the moving contact to prevent damage during heavy fault conditions. These
c1 utches have been set at the factory to sl i p at approximate1 y 40-60 grams
applied tangentially at the moving contact. This can best be checked in the
field in terms of volt-amperes by the following method.
Use the connections of Fi gure 10 and set the phase shifter so that the phase-
a ngl e meter reads 3000 at 120 vol ts and 5 amperes. Disconnect the No. 1
restraint tap leads from the tap block and short to stud 16, then set the
15