Schweitzer Engineering Laboratories SEL-751 - Table 4.5 Main Relay Functions that Change with VNOM:= off; Figure 4.1 Low-Energy Analog Voltage Sensor (Capacitive Voltage Divider)

4.7
Date Code 20170927 Instruction Manual SEL-751 Relay
Protection and Logic Functions
Group Settings (SET Command)
EXAMPLE 4.5 VNOM Setting Calculation for LEA Voltage Inputs
Consider a 10 kV (phase-to-phase) system with a wye-connected LEA sensor
with a ratio of 2500:1 (LEA_R := 2500).
The setting for VNOM would be VNOM := 10000/2500 • 37.5 := 150.0
Low-Energy Analog
(LEA) Voltage Inputs
The SEL-751 can be ordered with different secondary ac input voltage config-
urations—standard voltage inputs rated for 300 V and LEA voltage inputs
rated for 8 V. The LEA voltage inputs are suitable for C37.92 compliant high-
impedance sensors, such as capacitive voltage dividers and resistive voltage
dividers (see Figure 4.1).
Figure 4.1 Low-Energy Analog Voltage Sensor (Capacitive Voltage Divider)
Derived LEA Scale for 8 Vac LEA Voltage Inputs and Voltage-Related
Settings
Irrespective of the voltage input option, standard (300 Vac) or LEA (8 Vac),
all the voltage related settings are based at 300 V. For example, the 59 element
pickup range for standard voltage inputs is 2.0–300.0 V and this range will
remain the same for LEA inputs as well. To maintain the same 300 V base
across different voltage options, such as LEA inputs, the relay scales up the
input signal by a factor of 37.5 (300 V/8 V). Likewise, you can scale the volt-
Table 4.5 Main Relay Functions That Change With VNOM := OFF
Relay Function
When VNOM :=
Numeric Value
When VNOM := OFF
Load-encroachment logic
(enable setting ELOAD)
Available Not available
Negative-sequence and posi-
tive-sequence voltage polar-
ized directional elements
Available DIRQE is disabled, FDIRP/ RDIRP
disabled, ground directional ele-
ment ORDER setting choice “Q”
not selectable
Phase and negative-sequence
element directional control
Available Not available (defaults to “nondirec-
tional” in levels DIR1–DIR4)
Loss-of-potential logic Available Not available
Voltage unbalance logic Available Not available
Vector shift element Available Not available
Voltage Divider
Voltage Input
(8 Vac LEA Input)
C
1
C
2
V
pri
V
sec
SEL-751