4-22
Protection and Control
BE1-951
Example: Read the SG-LINE settings
1.
>SG-LINE
8.00,80.0,24.0,80.0, 100
Only the angle parameters are used in determining the fault direction. The other parameters are used for
fault location as described in section 6,
Reporting and Alarm Functions, Fault Reporting. An entry for Z2
negative sequence impedance is not required since Z2 and Z1 are considered to be equal. These angles
represent the line angle present between the sequence voltage and current if a fault has occurred on the
power line.
A fault current is considered to be in a forward direction when the current, after being offset by the line angle,
is in phase with the voltage. The forward direction zone extends for approxi/- 90° from the nominal
line angle. A similar argument applies for the reverse direction with the current 180° out of phase from the
voltage. Z1’s angle is used during positive and negative sequence directional test. Likewise, Z0’s angle is
used during the zero sequence directional test. Angle compensation is not required for current polarization
since the polarizing quantity IG is inherently compensated.
Internally, the BE1-951 also uses several constant limits to determine if the system levels are adequate to
perform reliable directional tests and set directional bits. See Table 4-15
Table 4-15. Internal Constants
Internal Constant
Purpose
Value
I1_Minimum
Min 3I1 current threshold for Positive Sequence test
0.50A
Iz_Minimum
Min 3I0 current threshold for Current Polarization test
0.25A
Ig_Minimum
Min Gnd current threshold for Current Polarization test
0.50A
V2_Minimum
Min V2 voltage threshold for Negative Sequence test
3.33% of V
nominal
V0_Minimum
Min V0 voltage threshold for Zero Sequence test
3.33% of V
nominal
VX_Minimum
Min external V0 voltage threshold for Zero Sequence
test
10% of V
nominal
Seq_Ratio
Min Ratio between I1 and I2 for Positive Sequence test
9%
Note: Min Ratio between I1 and I0 for Zero Sequence test is 9%
If the minimum levels are not met for a particular directional test, then the test is not run, and the directional
bits are clear for that test. For instance, if 3I1 is less than I1_Minimum level, the positive sequence test is
skipped and the positive sequence directional bits are cleared.
The Seq_Ratio refers to the minimum ratio required between the positive sequence current and either the
negative or zero sequence current. A negative sequence directional test would be allowed if the negative
current is greater than 9% of the positive sequence current. The same applies for the zero sequence
directional test.
The directional tests are also supervised by the loss of potential function 60FL. If the 60FL bit is TRUE, then
voltage sensing was lost or is unreliable. Under this condition positive, negative, and zero sequence
directional tests are disabled and their bits are cleared. Current polarization is not effected by the 60FL
since it does not rely on voltage sensing.
Negative Sequence Overcurrent Protection
For years, protection engineers have enjoyed increased sensitivity to phase-to-ground unbalances with the
application of ground relays. Ground relays can be set more sensitively than phase relays because a
balanced load has no ground (3
I0
) current component. The negative sequence elements can provide similar
increased sensitivity to phase-to-phase faults because a balanced load has no negative sequence (I
2
)
current component.
Содержание BE1-951
Страница 157: ...BESTlogic Programmable Logic BE1 951 7 2 Figure 7 1 BESTlogic Function Blocks Courtesy of NationalSwitchgear com...
Страница 238: ...BE1 951 Human Machine Interface 10 5 Figure 10 5 Metering Menu Branch Structure Courtesy of NationalSwitchgear com...
Страница 239: ...10 6 Human Machine Interface BE1 951 Figure 10 6 Reports Menu Branch Structure Courtesy of NationalSwitchgear com...
Страница 270: ...12 2 Installation BE1 951 Figure 12 1 BE1 951 S1 Case Dimensions Courtesy of NationalSwitchgear com...
Страница 274: ...12 6 Installation BE1 951 Figure 12 5 BE1 951 H1 Case Dimensions Courtesy of NationalSwitchgear com...
Страница 283: ...BE1 951 Installation 12 15 Figure 12 16 Typical AC Connections Courtesy of NationalSwitchgear com...
Страница 394: ...A 18 Appendix BE1 951 Figure A 14 Time Characteristic Curve B Very Inverse 99 1376 Courtesy of NationalSwitchgear com...
Страница 396: ...A 20 Appendix BE1 951 Figure A 16 Time Characteristic Curve G Long Inverse 99 1622 Courtesy of NationalSwitchgear com...
Страница 397: ...BE1 951 Appendix A 21 Figure A 17 46 Time Characteristic Curve Courtesy of NationalSwitchgear com...