Inspection - GE CEY51A Instructions Manual

GEK-1275
Figure 7 should be checked to determine that the test current to be used is
high enough to produce a characteristic at the calculated value.
If the ohmic pickup of the mho unit checks correctly according to the above,
the chances are that the angle of the characteristic is correct. The angle may,
however, be very easily checked by using the calibrated test resistor in combination
with various reactor taps. The calibrated test-resistor taps are pre-set in such a
manner that when used with the 12- and 6-ohm taps of the specified test reactor,
impedances at 600 and 300 respectively will be available for checking the mho-unit
reach at the 600 and 300 positions. The mho-unit ohmic reach at the zero-degree
(0
0 )
position may be checked by using the calibrated test resistor alone as the line
impedance. The calibrated test resistor is supplied with a data sheet that gives
the exact impedance and angle for each of the combinations available. The test-box
auto-transformer percent tap for pickup at a particular angle is given by:
% Tap
200 Z MIN cos
(0 -
81- (100)
ZL (Tap Setting
%)
where 8 is the angle of maximum torque of the unit, 0 is the angle of the test
impedance (ZL), Z is the 60 0 , 300 or 00 impedance value taken from the calibrated
resistor data sheet. As in the case of the previous tests, the load box that serves
as the source impedance should be adjusted to allow approximately 10 amperes to flow
in the fault circuit when the fault switch is closed.
When checki ng the mho unit at angl es of more than 300 off the maximum reach
position, the error becomes relatively large with phase-angle error. This is
apparent from Figure 11 where it is seen, for example at the zero-degree position,
that a 20 or 3 0 error in phase angle will cause a considerable apparent error in
reach.
OVERALL TESTS
An overall check of current transformer polarities, and connections to the
relay, can be made on the complete installation by means of the test connections and
tabulation in Figure 13. A check of the phase angle meter readings in the table for
power factor angle and phase sequence involved will indicate whether the relay is
receiving the correct voltage and currents for the conventional connections shown in
Figure 3.
INSPECTION
Before placing a relay into service, the following mechanical adjustments
should be checked, and faulty conditions corrected according to instructions in the
ADJUSTMENTS subsection of this section or under the MAINTENANCE section.
TARGET AND SEAL-IN UNITS
The armature and contacts of the target and seal-in units should operate freely
by hand.
There should be a screw in only one of the taps on the right-hand contact of
the target and seal-in unit.
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