4.5
Date Code 20170927 Instruction Manual SEL-751 Relay
Protection and Logic Functions
Group Settings (SET Command)
available for setting as explained in Low-Energy Analog (LEA) Voltage Inputs.
The DELTA_Y, VSCONN, VNOM, and SINGLEV settings are applicable to
either of the voltage input options.
Set the phase PT ratio (PTR) setting equal to the VT ratio. The synchronism-
check voltage input VS is an optional single phase-to-neutral or phase-to-
phase voltage input. Set the synchronism-check voltage input PT ratio (PTRS)
setting equal to the VT ratio of the VS input.
EXAMPLE 4.2 Phase VT Ratio Setting Calculations
Consider a 13.8 kV feeder application where you use 14400:120 V rated
voltage transformers (connected in open delta).
Set PTR := 14400/120 := 120 and DELTA_Y := DELTA.
Set the phase LEA ratio (LEA_R) setting equal to the marked LEA sensor
ratio. The synchronism-check voltage input VS is an optional single phase-to-
neutral or phase-to-phase voltage input. Set the synchronism-check voltage
input LEA ratio (LEA_S_R) setting equal to the marked LEA sensor ratio of
the VS input.
EXAMPLE 4.3 Phase LEA Ratio Setting Calculations
Consider a 13.8 kV feeder application where you have a 2500:1 ratio LEA
sensor (connected in wye).
Set LEA_R := 2500/1 := 2500 and DELTA_Y := WYE.
When phase-to-phase potentials are connected to the relay, set DELTA_Y to
DELTA. When phase-to-neutral potentials are connected to the relay, set
DELTA_Y to WYE.
In applications where only a single voltage is available, set SINGLEV equal
to Y. As shown in Figure 2.20, the single voltage must be connected to the
A-phase input, but it can be an A-N or an A-B voltage. Be sure to set
DELTA_Y equal to WYE for an A-N input or DELTA_Y equal to DELTA for
an A-B input voltage. When you set SINGLEV equal to Y, the relay perfor-
mance changes in the following ways:
➤ Power and Voltage Elements. When you use one voltage, the
relay assumes that the system voltages are balanced in both
magnitude and phase angle. Power, power factor, and positive-
sequence impedance are calculated assuming balanced
voltages.
➤ Metering. When you use one voltage, the relay displays
magnitude and phase angle for the measured PT. The relay
displays zero for the magnitudes of the unmeasured voltages.
Balanced voltages are assumed for power, power factor, VG,
and 3V2 metering.
Table 4.4 Effect on Group Settings When SINGLEV := Y (Sheet 1 of 2)
Identifier Settings
Group Setting Change Reason
VNOM Forced to OFF and hidden Loss-of-Potential logic
requires three-phase voltage.
Line Parameter Settings
Z1MAG, Z1ANG,
Z0MAG, Z0ANG,
Z0SMAG, Z0SANG
Hidden Impedance calculations
require three-phase voltage.
To Next Page
Loading...
