Schweitzer Engineering Laboratories SEL-351A, Manual

Page: 85 / 666

3.13
Date Code 20080213
Instruction Manual SEL-351A Relay
Overcurrent, Voltage, Synchronism Check, and Frequency Elements
Instantaneous/Definite-Time Overcurrent Elements
To understand the operation of Figure 3.10 and Figure 3.11 , follow the
explanation given for Figure 3.1 , Figure 3.2 , and Figure 3.3 in Phase
Instantaneous/Definite-Time Overcurrent Elements on page 3.1 , substituting
residual-ground current I
G
(I
G
= 3I
0
= I
A
+ I
B
+ I
C
) for phase currents, and
substituting like settings and Relay Word bits.
Settings Ranges
Setting range for pickup settings 50G1P–50G6P:
0.050–100.000 A secondary in 0.010 A steps
(5 A nominal phase current inputs,
IA
,
IB
,
IC
)
0.010–20.000 A secondary in 0.002 A steps
(1 A nominal phase current inputs,
IA , IB , IC )
Setting range for definite-time settings 67G1D–67G4D:
0.00–16000.00 cycles, in 0.25-cycle steps
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
)
Timer:
±0.25 cycles and ±0.1% of setting
Transient Overreach:
±5% of setting
Pickup and Reset Time Curves
See Figure 3.5 and Figure 3.6 .
Negative-Sequence
Instantaneous/
Definite-Time
Overcurrent Elements
IMPORTANT: See Appendix F: Setting Negative-Sequence
Overcurrent Elements for information on setting negative-sequence
overcurrent elements.
Four levels of negative-sequence instantaneous/definite-time overcurrent
elements are available. Two additional levels of negative-sequence
instantaneous overcurrent elements (Levels 5 and 6) are also available. The
different levels are enabled with the E50Q enable setting, as shown in
Figure 3.12 and Figure 3.13 .
NOTE:
For pickup settings below:
0.25 A secondary (5 A nominal)
0.05 A secondary (1 A nominal)
an additional 2-cycle time delay is
added on all residual-ground
instantaneous (50G1–50G6, 67G1–
67G6) and definite-time (67G1T–
67G6T) overcurrent elements. Any
time delay provided by the definite-
time settings (67G1D–67G4D) is in
addition to this 2-cycle time delay.
NOTE:
The definite-time elements
are not supported in the SEL-351A-1.
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