Schweitzer Engineering Laboratories SEL-351-5, Instruction Manual

Page: 104 / 706

3.24
SEL-351-5, -6, -7 Relay Instruction Manual
Date Code 20070117
Overcurrent, Voltage, Synchronism Check, Frequency, and Power Elements
Time-Overcurrent Elements
To understand the operation of Figure 3.20 , follow the explanation given for
Figure 3.14 in Phase Time-Overcurrent Elements on page 3.15 , 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
P
and like settings and Relay Word bits.
Settings Ranges
See Section 9: Setting the Relay for additional time-overcurrent element
setting information.
Accuracy
Pickup:
±0.05 A secondary and ±3% of setting
(5 A nominal phase current inputs,
IA
,
IB
,
IC
)
±0.01 A secondary and ±3% of setting
(1 A nominal phase current inputs,
IA , IB , IC )
Curve Timing:
±1.50 cycles and ±4% of curve time for currents between (and including)
2 and 30 multiples of pickup
Table 3.6 Negative-Sequence Time-Overcurrent Element Settings
Setting Definition Range
51QP pickup 0.25–16.00 A secondary
(5 A nominal phase current inputs,
IA , IB , IC )
0.05–3.20 A secondary
(1 A nominal phase current inputs,
IA , IB , IC )
51QC curve type U1–U5 (US curves) see Figure 9.1 – Figure 9.10
C1–C5 (IEC curves)
51QTD time dial 0.50–15.00 (US curves) see Figure 9.1 – Figure 9.10
0.05–1.00 (IEC curves)
51QRS electromechanical
reset timing Y, N
51QTC SEL
OGIC
control
equation torque
control setting
Relay Word bits referenced in Table 9.5 or set directly
to logical 1 (= 1)—see note
NOTE:
SEL
OGIC
control equation
torque control setting (e.g., 51QTC)
cannot be set directly to logical 0.