4-4 Loss-of-Potential, Load Encroachment, and Directional Element Logic Date Code 990430
SEL-351P Manual Técnico
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 SECTION 4: .2.
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
0.25 - 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°)
Load-Encroachment Setting Example
Example system conditions:
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
The PTs are connected line-to-neutral.
Convert Maximum Loads to Equivalent Secondary Impedances
Start with maximum forward load:
800 MVA • (1/3) = 267 MVA per phase
230 kV • (1/√3) = 132.8 kV line-to-neutral
267 MVA • (1/132.8 kV) • (1000 kV/MV) = 2010 A primary
2010 A primary • (1/CT ratio) = 2010 A primary • (1 A seconday/400 A primary)
= 5.03 A secondary
132.8 kV • (1000 V/kV) = 132800 V primary
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