Schweitzer Engineering Laboratories SEL-351-7 - 50 QFP and 50 QRP Set Automatically; 50 QFP-Forward Directional Negative-Sequence Current Pickup; 50 QRP-Reverse Directional Negative-Sequence Current Pickup

Date Code 20020426 Loss-of-Potential, Load Encroachment, and Directional Element Logic 4-43
SEL-351-5, -6, -7 Instruction Manual
Relay Configuration
z (Ω
ΩΩ
Ω secondary)
5 A nominal current, 150 V voltage inputs 0.1
5 A nominal current, 300 V voltage inputs 0.2
1 A nominal current, 150 V voltage inputs 0.5
1 A nominal current, 300 V voltage inputs 1.0
Figure 4.25 and Figure 4.26 and supporting text concern the zero-sequence impedance network,
relay polarity, and the derivation of settings Z0F and Z0R. The same general approach outlined
for deriving settings Z0F and Z0R can also be applied to deriving settings Z2F and Z2R in the
negative-sequence impedance network, though the preceding method of automatically making
settings Z2F and Z2R usually suffices.
50QFP—Forward Directional Negative-Sequence Current Pickup
50QRP—Reverse Directional Negative-Sequence Current Pickup
Setting Range:
0.25–5.00 A secondary (5 A nominal phase current inputs, IA, IB, IC)
0.05–1.00 A secondary (1 A nominal phase current inputs, IA, IB, IC)
The 50QFP setting (3I
2
current value) is the pickup for the forward fault detector 50QF of the
negative-sequence voltage-polarized directional elements (see Figure 4.6). Ideally, the setting is
above normal load unbalance and below the lowest expected negative-sequence current
magnitude for unbalanced forward faults.
The 50QRP setting (3I
2
current value) is the pickup for the reverse fault detector 50QR of the
negative-sequence voltage-polarized directional elements (see Figure 4.6). Ideally, the setting is
above normal load unbalance and below the lowest expected negative-sequence current
magnitude for unbalanced reverse faults.
50QFP and 50QRP Set Automatically
If enable setting E32 = AUTO, settings 50QFP and 50QRP are set automatically at:
50QFP = 0.50 A secondary (5 A nominal phase current inputs, IA, IB, IC)
50QRP = 0.25 A secondary (5 A nominal phase current inputs, IA, IB, IC)
50QFP = 0.10 A secondary (1 A nominal phase current inputs, IA, IB, IC)
50QRP = 0.05 A secondary (1 A nominal phase current inputs, IA, IB, IC)