3.15
Date Code 20110408 Instruction Manual SEL-551 Relay
Relay Elements and Logic
Time-Overcurrent Elements
Figure 3.10 Neutral Ground Time-Overcurrent Element 51N1T
To understand the operation of Figure 3.10 for the neutral ground time-
overcurrent element (51N1T), follow the explanation given for Figure 3.9 for
the first phase time-overcurrent element (51P1T), substituting I
N
for I
P
and
like settings and Relay Word bits.
Residual Ground
Time-Overcurrent
Element
One residual ground time-overcurrent element (51G1T) is available (see
Figure 3.11). Its pickup setting (51G1P) is compared to the magnitude of the
residual ground current (I
G
= 3I
0
, derived from I
A
, I
B
, and I
C
).
Figure 3.11 Residual Ground Time-Overcurrent Element 51G1T
To understand the operation of Figure 3.11 for the residual ground time-
overcurrent element (51G1T), follow the explanation given for Figure 3.9 for
the first phase time-overcurrent element (51P1T), substituting I
G
for I
P
and
like settings and Relay Word bits.
51N1P
I
N
Setting
51N1TC
Torque Control Switch
51N1T Neutral Ground
Time-Overcurrent Element
Curve Timing and Reset Timing
Settings
51N1P Pickup
51N1C Curve Type
51N1TD Time Dial
51N1RS Electromechanical
Reset? (Y/N)
Pickup
Curve
Timeout
Reset
51N1
51N1R
51N1T
Torque Control
51N1TC State Switch Position
Logical 1 Closed
Logical 0 Open
SEL
OGIC Setting 51N1TC Controls the Torque Control Switch
Setting
51N1RS = Reset Timing
Y Electromechanical
N 1 Cycle
Relay
Word
Bits
SELOGIC
Setting
51G1P
I
G
Setting
51G1TC
Torque Control Switch
51G1T Residual Ground
Time-Overcurrent Element
Curve Timing and Reset Timing
Settings
51G1P Pickup
51G1C Curve Type
51G1TD Time Dial
51G1RS Electromechanical
Reset? (Y/N)
Pickup
Curve
Timeout
Reset
51G1
51G1R
51G1T
Torque Control
51G1TC State Switch Position
Logical 1 Closed
Logical 0 Open
SEL
OGIC Setting 51G1TC Controls the Torque Control Switch
Setting
51G1RS = Reset Timing
Y Electromechanical
N 1 Cycle
Relay
Word
Bits
SELOGIC
Setting
(residual)
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