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5.100
SEL-421 Relay
Instruction Manual
Date Code 20171021
Protection Functions
Inverse-Time Overcurrent Elements
NOTE:
In the SEL-421, the time-
overcurrent elements are not
directionally controlled in the internal
logic. Directional control may be
achieved through the use of torque
control settings, as shown in
Section 6: Protection Applications
Examples
. Also refer to
Each time-overcurrent element has a torque control SEL
OGIC
equation 51S
k
TC
(
k
= 1–3) that enables the element when the equation evaluates to logical 1, and
disables the element when the equation evaluates to logical 0. See
for
a logic diagram of the time-overcurrent elements, including the torque control input.
The enable setting (E51S) controls how many time-overcurrent elements are
available. For example, if E51S := 1, only 51S1 is processed. The remaining
time-overcurrent elements 51S
k
(
k
= 2–3) are defeated, and the output Relay
Word bits are forced to logical 0.
Table 5.61
Selectable Current Quantities
Quantity
a
a
Parameter
n
is L for Line, 1 for BK 1, and 2 for BK 2.
Description
Analog Quantities
IA
n
A-Phase
LIAFIM, B1IAFIM, B2IAFIM
IB
n
B-Phase
LIBFIM, B1IBFIM, B2IBFIM
IC
n
C-Phase
LICFIM, B1ICFIM, B2ICFIM
IMAX
n
Maximum Phase
N/A
I1L
Line positive-sequence current
LI1FIM
3I2L
Line negative-sequence current
L3I2FIM
3I0
n
Zero-sequence current
LIGFIM, B1IGFIM, B2IGFIM
Table 5.62
Selectable Inverse-Time Overcurrent Settings
Setting
a
a
Parameter
n
is L for Line, 1 for BK1, and 2 for BK2.
Prompt
Range
Default (5 A)
E51S
Selectable Inverse-Time Overcurrent Element
N, 1–3
1
51S1O
Operating Quantity Element 1
IA
n
, IB
n
, IC
n
, IMAX
n
, I1L, 3I2L, 3I0
n
3I0L
51S1P
51S1 O/C Pickup Element 1 (A)
(0.05–3.2) • I
NOM
0.75
51S1C
51S1 Inverse-Time O/C Curve Element 1
U1–U5, C1–C5
U3
51S1TD
51S1 Inverse-Time O/C Time-Dial Element 1
0.50–15.00 (U
x
)
b
0.05–1.00 (C
x
)
b
Parameter
x
is a number from 1—5 indicating the operating curve (see
through
1.0
51S1RS
51S1 Inverse-Time O/C Electromechanical Reset Element 1
Y, N
N
51S1TC
51S1 Inverse-Time O/C Torque Control Element 1
SEL
OGIC
Equation
32GF
51S2O
Operating Quantity Element 2
IA
n
, IB
n
, IC
n
, IMAX
n
, I1L, 3I2L, 3I0
n
3I2L
51S2P
51S2 O/C Pickup Element 2 (A)
(0.05–3.2) • I
NOM
5.00
51S2C
51S2 Inverse-Time O/C Curve Element 2
U1–U5, C1–C5
U3
51S2TD
51S2 Inverse-Time O/C Time-Dial Element 2
0.50–15.00 (U
x
)
0.05–1.00 (C
x
)
1
51S2RS
51S2 Inverse-Time O/C Electromechanical Reset Element 2
Y, N
N
51S2TC
51S2 Inverse-Time O/C Torque Control Element 2
SEL
OGIC
Equation
32QF
51S3O
Operating Quantity Element 3
IA
n
, IB
n
, IC
n
, IMAX
n
, I1L, 3I2L, 3I0
n
IMAXL
51S3P
51S3 O/C Pickup Element 3 (A)
OFF, (0.05–3.2) • I
NOM
5.00
51S3C
51S3 Inverse-Time O/C Curve Element 3
U1–U5, C1–C5
U3
51S3TD
51S3 Inverse-Time O/C Time-Dial Element 3
0.50–15.00 (U
x
)
0.05–1.00 (C
x
)
1
51S3RS
51S3 Inverse-Time O/C Electromechanical Reset Element 3
Y, N
N
51S3TC
51S3 Inverse-Time O/C Torque Control Element 3
SEL
OGIC
Equation
Z2P
Summary of Contents for SEL-421-4
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