GE 889 Instruction Manual page 342

PROTECTION
REV Operating
Region
-I_2 line
-ECA line
VCG
4–212
Figure 4-77: Negative Sequence Directional Characteristic
-V_2 line
REV FWD
LA LA
LA
LA
V_2 line
The forward-looking function is designed to be more secure compared to the reverse-
looking function, and should therefore be used for the tripping direction. The reverse-
looking function is designed to be faster compared to the forward-looking function and
should be used for the blocking direction. This allows better protection coordination. The
above bias should be taken into account when using the Negative Sequence Directional
Overcurrent element to directionalize other protection elements.
Path: Setpoints > Protection > Group 1(6) > Current > Negative Sequence Dir OC 1(X)
FUNCTION
Range: Disabled, Enabled
Default: Disabled
POS-SEQ RESTRAINT
Range: 0.000 to 0.500 in steps of 0.001
Default: 0.063
The setting controls the positive-sequence restraint. Set to 0.125. Set to zero to remove
the restraint. Set higher if large system unbalances or poor CT performance are
expected.
VAG (reference)
LA
ECA
LA
REV FWD
LA LA
889 GENERATOR PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 4: SETPOINTS
ECA line
I_2 line
FWD Operating
Region
VBG
827806A2.CDR