GE CEY51A Instructions Manual page 11

GEK-1275
be enlarged, that is, the mho-unit reach can be increased by up to 10/1 by reducing
the percentage of the terminal voltage supplied to the restraint circuit by means of
the taps on the autotransformer tap
~ocks,
and the circle can be further enlarged,
providing a total range adjustment of up to 40/1, by means of the basic-minimum-
reach tap screws. The circle will always pass through the origin and have a
diameter along the 600 impedance line equal to the ohmic reach of the unit as
expressed by the following equation:
Ohmic Reach
=
%)
where:
Zmin
=
Basic minimum phase-to-neutral ohmic reach of the unit (as set by taps).
The angl e of maximum torque of the mho uni t can be adjusted up to 750 (see
SERVICIIG)
with negligible effect on the reach of the unit.
Directional Action
The mho unit is carefully adjusted to have correct directional action under
steady-state, low-voltage and low-current conditions. For faults in the non-
tripping direction, the contacts will remain open at zero volts between 0 and 60
amperes. For faul ts in the tri ppi ng di recti on, the uni t wi 11 close its contacts
between the current limits in Table IV for the three basic-minimum-reach settings
(see Table II) at the voltage shown.
Bas i c-M in imum-
Reac h Tap
0.2
0.375
0.4
0.75
0.8
1.5
3.0
6.0
TABLE IV
Vol ts
(See
Fi~ure
10)
2.0V
2.0V
2.0V
2.0V
2.0V
2.0V
2.0V
2.0V
Current Range For
Correct Directional
Action
22.5 - 60A
12.0 - 60A
11 .25 - 60A
6.0 - 60A
5.6 - 60A
3.0 - 60A
1.5 - 60A
0.75 - 60A
The unit is set at the factory on the 1.5 ohm or 0.4 ohm tap for
correct directional action over the indicated current range. A
variation of
~
10% can be expected on the values listed.
For performance during transient low-voltage conditions, where the voltage was
normal at 120 volts prior to the fault, refer to the paragraph on MEMORY ACTION.
9