GE Multilin 850, Instruction Manual

Page: 295 / 664

CHAPTER 6: PROTECTION SETPOINTS CURRENT ELEMENTS
850 FEEDER PROTECTION SYSTEM – INSTRUCTION MANUAL 6–27
FWD LA = 80° (forward limit angle = the ± angular limit with the ECA for operation
REV LA = 80° (reverse limit angle = the ± angular limit with the ECA for operation).
The element incorporates a current reversal logic: if the reverse direction is indicated for at
least 1.25 of a power system cycle, the prospective forward indication will be delayed by
1.5 of a power system cycle. The element is designed to emulate an electromechanical
directional device. Larger operating and polarizing signals will result in faster directional
discrimination bringing more security to element operation.
The forward-looking function is designed to be more secure as compared to the reverse-
looking function, and should therefore be used for the tripping direction. The reverse-
looking function is designed to be faster as 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 Neutral Directional
Overcurrent element to directionalize other protection elements.
Figure 6-9: Neutral Directional Voltage-polarized Characteristics
827805A1.CDR
VAG
(reference)
VBG
VCG
-3I_0 line
3I_0 line
ECA line
-ECA line
LA
LA
LA
LA
ECA
FWD LA
line
FWD Operating
Region
REV Operating
Region
FWD LA
line
REV LA
line
REV LA
line
-3V_0 line
3V_0 line