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3.38
SEL-311C Relay
Instruction Manual
Date Code 20060320
Distance, Out-of-Step, Overcurrent, Voltage, Synchronism Check, and Frequency Elements
Time-Overcurrent Elements
Negative-Sequence
Time-Overcurrent
Element
To understand the operation of
, follow the explanation given for
, substituting negative-sequence current 3I
2
[3I
2
= I
A
+ a
2
• I
B
+ a •
I
C
(ABC rotation), 3I
2
= I
A
+ a
2
• I
C
+ a • I
B
(ACB rotation), where a = 1
∠
120° and a
2
= 1
∠
–120°] for maximum phase current I
ABC
and like settings
and Relay Word bits.
Figure 3.26
Negative-Sequence Time-Overcurrent Element 51QT
Settings Ranges
for additional time-overcurrent element
setting information.
IMPORTANT
Setting Negative-Sequence
Overcurrent Elements
for information
on setting negative-sequence
overcurrent elements.
51QP
3I
2
Setting
51QTC
Torque Control Switch
SEL
OGIC
Torque Control
51QT Negative-Sequence
Time-Overcurrent Element
Curve Timing and Reset Timing
Settings
51QP
Pickup
51QC
Curve
Type
51QTD
Time
Dial
51QRS
Electromechanical
Reset? (Y/N)
Pickup
Curve
Timeout
Reset
51Q
51QR
51QT
Torque
Control
51QTC State Switch Position
Logical 1
Closed
Logical 0
Open
Logic Point 51QTC Controls the Torque Control Switch
Setting
51QRS =
Reset Timing
Y
Electromechanical
N
1
Cycle
Relay
Word
Bits
SEL
OGIC
Setting
Table 3.12
Negative-Sequence Time-Overcurrent Element Settings
Setting
Definition
Range
51QP
pickup
OFF, 0.25–16.00 A secondary
(5 A nominal phase current inputs,
IA
,
IB
,
IC
)
OFF, 0.05–3.20 A secondary
(1 A nominal phase current inputs,
IA
,
IB
,
IC
)
51QC
curve type
U1–U5 (U.S. curves) see
–
C1–C5 (I.E.C. curves)
51QTD
time dial
0.50–15.00 (U.S. curves) see
–
0.05–1.00 (I.E.C. curves)
51QRS
electromechanical
reset timing
Y = Enable electromechanical reset timing
N = 1-cycle reset delay
51QTC
SEL
OGIC
control
equation torque
control setting
Relay Word bits referenced in
and
a
a
SEL
OGIC
control equation torque control settings (e.g., 51QTC) cannot be set directly to
logical 0.
Summary of Contents for SEL-311C
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