Sel 751A - Table 4.3 Voltage Configuration Settings

4.4
SEL-751A Relay Instruction Manual Date Code 20100129
Protection and Logic Functions
Group Settings (SET Command)
Table 4.3 shows voltage settings for relay models with optional voltage inputs.
These settings configure the optional relay voltage inputs to correctly measure
and scale the voltage signals. Set the phase PT ratio (PTR) setting equal to the
VT ratio. The synchronism-check voltage input VS is an optional single phase-
neutral or phase-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 14400:120 V rated
voltage transformers (connected in open delta) are used.
Set PTR := 14400/120 := 120 and DELTA_Y := DELTA.
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 2.17, the single voltage must be connected to the
A-phase input, but it may 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 performance changes in the
following ways:
➤ Voltage Elements. When you use one phase-to-phase voltage,
the relay overvoltage and undervoltage elements use the
applied phase-to-phase voltage only. When you use one phase-
to-neutral voltage, the relay voltage elements use the applied
phase-to-neutral voltage only.
➤ Power Elements. When you use one voltage, the relay assumes
that the system voltages are balanced in both magnitude and
phase angle to calculate apparent, real, and reactive power and
power factor.
➤ Metering. When you use one voltage, the relay displays that
magnitude and phase angle. The relay displays zero for the
magnitudes of the unmeasured voltages. Balanced voltages are
assumed for power, power factor, VG, and 3V2 metering.
Relays that are not equipped with phase voltage inputs hide these settings and
disable voltage-based protection and metering functions.
Table 4.3 Voltage Configuration Settings
Setting Prompt Setting Range
Setting Name :=
Facto ry Defau lt
PHASE PT RATIO 1.00–10000.00 PTR := 180
SYNCV PT RATIO 1.00–10000.00 PTRS :=180
XFMR CONNECTION WYE, DELTA DELTA_Y := DELTA
LINE VOLTAGE 100–250 V
a
a
The line voltage setting range is 100–440 if DELTA_Y := WYE.
VNOM := 120
SINGLE V INPUT Y, N SINGLEV := N