GE D30 Instruction Manual page 342

GROUPED ELEMENTS
The negative-sequence voltage must be greater than the
 DISPLAY PROPERTIES
forward nor reverse indication is given. The following figure explains the usage of the voltage polarized directional unit of
the element. It shows the phase angle comparator characteristics for a phase A to ground fault, with settings of
ECA = 75° (element characteristic angle = centerline of operating characteristic)
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 is delayed by 1.5 of a power system cycle. The element emulates an
electromechanical directional device. Larger operating and polarizing signals result in faster directional discrimination,
bringing more security to the element operation.
5
The forward-looking function is designed to be more secure compared to the reverse-looking function, so use the forward-
looking function for the tripping direction. The reverse-looking function is faster compared to the forward-looking function,
so use the reverse-looking function for the blocking direction. This allows for better protection coordination. Take this bias
into account when using the negative-sequence directional overcurrent element to directionalize other protection
elements. The negative-sequence directional pickup must be greater than the
 CURRENT CUT-OFF LEVEL
Settings
NEG SEQ DIR OC1 OFFSET
impedance is to guarantee correct identification of fault direction on series compensated lines (see the Application of
Settings chapter for information on how to calculate this setting). In regular applications, the offset impedance ensures
proper operation even if the negative-sequence voltage at the relaying point is very small. If this is the intent, the offset
impedance shall not be larger than the negative-sequence impedance of the protected circuit. Practically, it is several
times smaller. Enter the offset impedance in secondary ohms.
NEG SEQ DIR OC1 TYPE
Sequence" and "Zero Sequence." In some applications it is advantageous to use a directional negative-sequence
overcurrent function instead of a directional zero-sequence overcurrent function as inter-circuit mutual effects are
minimized.
5-210
menu to be validated for use as a polarizing signal. If the polarizing signal is not validated, neither
Figure 5-115: Negative-sequence directional characteristic
REV
LA
REV Operating
Region
LA
–I_2 line
–ECA line
LA
VCG
setting value.
— Specifies the offset impedance used by this protection. The primary application for the offset
— Selects the operating mode for the overcurrent unit of the element. The choices are "Neg
setting specified in the
VOLTAGE CUTOFF LEVEL
–V_2 line
FWD
VAG (reference)
LA
LA
ECA
LA
REV FWD
LA LA
V_2 line
PRODUCT SETUP  DISPLAY PROPERTIES
D30 LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 5: SETTINGS
PRODUCT SETUP
ECA line
I_2 line
FWD Operating
Region
VBG
827806A2.CDR