Ratings - GE CEY51A Instructions Manual

GEl-1275
Since system swings are not usually a problem on short lines, but arc resistance
is, and since arc resistance may not be a problem on long lines but system swings
might be, it is a good general practice to use the lower maximum-torque angle
universally except where system swings may be a problem.
Since this is a short line, the normal 600 angle of maximum torque will be
used. Thus, 9
=
600.
Percent Tap Setting
=
100(1.5) Cos (80.5-60)
2.19
T
=
64%
=
64%
A check with the table in the
APPLICATION
section will indicate that the
mi nimum faul t current of 8 amperes is suffi ci ent to operate the rel ay for the
settings selected.
A plot of this characteristic on the R-X diagram will show that the unit will
accommodate approximately 1.15 secondary ohms of arc res i stance for a faul t at the
origin.
A rough estimate of the arc resistance that a relay will see for a mul ti-phase
fault is given by
RA
=
3
~
where
130
=
three-phase fault current flowing in the relay.
Since the minimum three-phase fault current in the relay for a close-in fault
was given as 11 amperes, the maximum arc resistance is
RA
=
3
=
0.27 secondary ohms
11
The 60
0
relay setting will accommodate this very easily and so would a 750 setting.
However, the 600 setting will accommodate more arc resistance near the balance
point, and since the line is short, and
if
system sVJings are not apt to be a
problem, the 600 setting is desirable.
RATINGS
The type-CEY51A relay covered by these instructions is available for 120 volts,
5 amperes, 60 cycle rating. The one-second rating of the current circuits is 225
amperes. The basic minimum reach and adjustment ranges of the mho units are given
in Table II.
6