Schweitzer Engineering Laboratories SEL-351 - 50 QFP - Forward Directional Negative-Sequence Current Pickup; 50 QRP - Reverse Directional Negative-Sequence Current Pickup; Z2 F and Z2 R Set Automatically

4-30 Loss-of-Potential, Load Encroachment, and Directional Element Logic Date Code 20001006
SEL-351 Instruction Manual
-128.00 to 128.00 W secondary (300 V voltage inputs, VA, VB, VC; 5 A nominal phase
current inputs, IA, IB, IC)
-640.00 to 640.00 W secondary (300 V voltage inputs, VA, VB, VC; 1 A nominal phase
current inputs, IA, IB, IC)
Z2F and Z2R are used to calculate the Forward and Reverse Thresholds, respectively, for the
negative-sequence voltage-polarized directional elements (see Figure 4.8 and Figure 4.14).
Z2F and Z2R Set Automatically
If enable setting E32 = AUTO, settings Z2F and Z2R (negative-sequence impedance values) are
calculated automatically, using the positive-sequence line impedance magnitude setting Z1MAG as
follows:
Z2F = Z1MAG/2 (W secondary)
Z2R = Z1MAG/2 + z (W secondary; “z” listed in table below)
If enable setting E32 = Y, settings Z2F and Z2R (negative-sequence impedance values) are
calculated by the user and entered by the user, but setting Z2R must be greater in value than setting
Z2F by value “z”:
Relay Configuration z (W 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
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 4.5). 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 4.5). Ideally, the setting is
above normal load unbalance and below the lowest expected negative-sequence current magnitude
for unbalanced reverse faults.
Courtesy of NationalSwitchgear.com