Schweitzer Engineering Laboratories SEL-311C - Load-Encroachment Setting Example; Settings Ranges; Table 4.1 Load-Encroachment Logic Settings Ranges

4.6
SEL-311C Relay Instruction Manual Date Code 20060320
Loss-of-Potential, CCVT Transient Detection, Load-Encroachment, and Directional Element Logic
Load-Encroachment Logic
encroachment logic only operates if the positive-sequence current (I
1
) is
greater than the Positive-Sequence Threshold shown in Figure 4.3. For a
balanced load condition, I
1
= phase current magnitude.
Forward load (load flowing out) lies within the hatched region labeled
ZLOUT. Relay Word bit ZLOUT asserts to logical 1 when the load lies within
this hatched region.
Reverse load (load flowing in) lies within the hatched region labeled ZLIN.
Relay Word bit ZLIN asserts to logical 1 when the load lies within this
hatched region.
Relay Word bit ZLOAD is the OR combination of ZLOUT and ZLIN:
ZLOAD = ZLOUT + ZLIN
Settings Ranges
Refer to Figure 4.3.
Load-Encroachment
Setting Example
Example system conditions:
The PTs are connected line-to-neutral.
Convert Maximum Loads to Equivalent Secondary Impedances
Step 1. Start with maximum forward load:
a. 800 MVA • (1/3) = 267 MVA per phase
b. 230 kV • (1/ √3) = 132.8 kV line-to-neutral
c. 267 MVA • (1/132.8 kV) • (1000 kV/MV) = 2010 A
primary
d. 2010 A primary • (1/CT ratio)
= 2010 A primary • (1 A secondary/400 A primary)
= 5.03 A secondary
e. 132.8 kV • (1000 V/kV) = 132800 V primary
Table 4.1 Load-Encroachment Logic Settings Ranges
Setting Description and Range
ZLF Forward Minimum Load Impedance;
corresponding to maximum load flowing out
ZLR Reverse Minimum Load Impedance;
corresponding to maximum load flowing in
0.05–64.00 Ω secondary (5 A nominal phase current inputs, IA, IB, IC)
0.25–320.00 Ω secondary (1 A nominal phase current inputs, IA, IB, IC)
PLAF Maximum Positive Load Angle Forward (–90° to +90°)
NLAF Maximum Negative Load Angle Forward (–90° to +90°)
PLAR Maximum Positive Load Angle Reverse (+90° to +270°)
NLAR Maximum Negative Load Angle Reverse (+90° to +270°)
Nominal Line-Line Voltage: 230 kV
Maximum Forward Load: 800 MVA
Maximum Reverse Load: 500 MVA
Power Factor (Forward Load): 0.90 lag to 0.95 lead
Power Factor (Reverse Load): 0.80 lag to 0.95 lead
CT ratio: 2000/5 = 400
PT ratio: 134000/67 = 2000