Schweitzer Engineering Laboratories SEL-751 - Table 4.6 Line Parameter Settings

4.10
SEL-751 Relay Instruction Manual Date Code 20170927
Protection and Logic Functions
Group Settings (SET Command)
Consider what is happening in Example 4.7. First, assume the primary voltage
(V
pri
) is the same magnitude for each phase. When this primary voltage is run
through the respective true ratios, the secondary voltage outputs vary widely.
Presuming a primary voltage of 12.47 kV (7.2kV line-to-neutral), the resultant
secondary voltages are listed below:
7200 V / 10780 = 0.67 V (true secondary voltage to voltage input VA)
7200 V / 8830 = 0.82 V (true secondary voltage to voltage input VB)
7200 V / 11120 = 0.65 V (true secondary voltage to voltage input VC)
Note that the true secondary voltages to voltage inputs VA and VC are running
low (below the normalized secondary voltage 0.72 V = 7200 V / 10000), while
the voltage to voltage input VB is running high (above the normalized second-
ary voltage 0.72 V). But the RCF values adjust these true secondary voltages
to normalized secondary voltage:
0.67 V • 1.078 = 0.72 V (normalized voltage from voltage input VA)
0.82 V • 0.883 = 0.72 V (normalized voltage from voltage input VB)
0.65 V • 1.112 = 0.72 V (normalized voltage from voltage input VC)
Again, the normalized secondary voltage (0.72 V) is the same for all three
phases in this example, because the primary voltage is assumed to be the same
magnitude for each phase (7200 V). The relay uses these normalized second-
ary voltages for all the voltage-based protection elements and metering. The
true secondary voltages cannot be seen (via the SEL-751) unless the RCF val-
ues are set to unity (RCF := 1.000).
Phase Angle Compensation (PAC) for Voltage Inputs
Use the VAPAC, VBPAC, VCPAC, and VSPAC voltage phase-angle correc-
tion Global settings for the voltage inputs VA, VB, VC, and VS, respectively.
These settings compensate for the phase error caused by the voltage divider
and the cable connected to the relay. Use a positive phase angle correction set-
ting if the resulting phase error is negative and vice versa. For example, if the
resulting phase error on the VA input is –1.00 degree, then set VAPAC := 1.00
degrees.
Line Parameter
Settings
Table 4.6 Line Parameter Settings
Setting Prompt Setting Range
Setting Name :=
Factory De fault
POS SQ LN Z MAG 0.10–510.00 ohms
a
a
Settings ranges and default ohm values shown are for 5 A nominal CT rating. Multiply by 5 for
1A CTs.
Z1MAG := 2.14
a
POS SQ LN Z ANG 5.00–90.00 deg Z1ANG := 68.86
ZERO SQ LN Z MAG 0.10–510.00 ohms
a
Z0MAG := 6.38
a
ZERO SQ LN Z ANG 5.00–90.00 deg Z0ANG := 72.47
ZERO SQ SR Z MAG 0.10–510.00 ohms
a
Z0SMAG := .36
a
ZERO SQ SR Z ANG 0.00–90.00 deg Z0SANG := 84.61
LINE LENGTH 0.10–999.00 LL := 0.10–999