Schweitzer Engineering Laboratories SEL-351A - Figure 3.17 C-Phase Time-Overcurrent Element 51 CT (with Directional Control Option in SEL-351 A); Figure 3.18 Neutral-Ground Time-Overcurrent Element 51 NT (with Directional Control Option in SEL-351 A)

3.22
SEL-351A Relay Instruction Manual Date Code 20080213
Overcurrent, Voltage, Synchronism Check, and Frequency Elements
Time-Overcurrent Elements
q From Figure 4.24. Directional Control logic input is constantly asserted to
logical 1 in SEL-351A-1.
Figure 3.17 C-Phase Time-Overcurrent Element 51CT (With Directional
Control Option in SEL-351A)
Neutral-Ground Time-
Overcurrent Element
To understand the operation of Figure 3.18, follow the explanation given for
Figure 3.14 in Phase Time-Overcurrent Elements on page 3.16, substituting
current I
N
(channel IN current) for maximum phase current I
P
and substituting
like settings and Relay Word bits.
See Tab le 4.1 and the accompanying note for a list of the directional features
available with each neutral channel (IN) rating.
q From Figure 4.18. Directional Control logic input is constantly asserted to logical
1 in SEL-351A-1.
Figure 3.18 Neutral-Ground Time-Overcurrent Element 51NT (With
Directional Control Option in SEL-351A)
51CP
I
C
Setting
51CTC
Torque Control Switch
Directional Control
(asserted to logical 1
continuously if E32 = N)
q
(Level 1)
SEL
OGIC
Torque Control
51CT C-Phase
Time-Overcurrent Element
Curve Timing and Reset Timing
Settings
51CP Pickup
51CC Curve Type
51CTD Time Dial
51CRS Electromechanical
Reset? (Y/N)
Pickup
Curve
Timeout
Reset
51C
51CR
51CT
Torque Control
TCC State Switch Position
Logical 1 Closed
Logical 0 Open
Logic Point TCC Controls the Torque Control Switch
Setting
51CRS = Reset Timing
Y Electromechanical
N 1 Cycle
TCC
Relay
Word
Bits
SELOGIC
Setting
51NP
I
N
Setting
51NTC
Torque Control Switch
Directional Control
(asserted to logical 1
continuously if E32 = N)
q
(Level 1)
SEL
OGIC
Torque Control
51NT Neutral Ground
Time-Overcurrent Element
Curve Timing and Reset Timing
Settings
51NP Pickup
51NC Curve Type
51NTD Time Dial
51NRS Electromechanical
Reset? (Y/N)
Pickup
Curve
Timeout
Reset
51N
51NR
51NT
Torque Control
TCN State Switch Position
Logical 1 Closed
Logical 0 Open
Logic Point TCN Controls the Torque Control Switch
Setting
51NRS = Reset Timing
Y Electromechanical
N 1 Cycle
TCN
Relay
Word
Bits
SELOGIC
Setting
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