Schweitzer Engineering Laboratories SEL-700G Series, Инструкция по эксплуатации

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4.92
SEL-700G Relay Instruction Manual Date Code 20170814
Protection and Logic Functions
Group Settings (SET Command)
n = 1 or 2.
Torque Control switch position = Closed when corresponding control bit is asserted (e.g., 50N1TC = 1);
open when it is deasserted.
Not shown in the figure, Relay Word bit ORED50T is asserted if any of the 50Pm3AT, 50Pm3BT, 50Pm3CT,
50PmnT, 67PYnT, 50QmnT, 50GmnT, 67GmnT, 50NnT, or 67NnT Relay Word bits are asserted.
Figure 4.56 SEL-700G0, SEL-700G1, SEL-700GGT Instantaneous Neutral-Ground Overcurrent Element Logic
(Generator Protection)
When a core-balance CT is connected to the relay
IN
input, as in Figure 4.56,
use the neutral overcurrent element to detect the ground faults. Calculate the
trip level settings based on the available ground fault current and the core-
balance CT ratio.
EXAMPLE 4.3 Ground Fault Core-Balance CT Application
A resistance-grounded power system limits the ground fault currents.
The resistor is sized to limit the current to 10 A primary. The three
feeder leads are passed through the window of a 10:1 core-balance CT.
The CT secondary is connected to the SEL-700G
IN current input
(terminals Z07, Z08), as shown in Figure 4.57. Setting the Neutral OC
CT Ratio (CTRN) equal to 10 and Neutral Trip Lvl (50N1P) equal to 0.5 A
or lower with 0.10-second time delay ensures that the element quickly
detects and trips for feeder ground faults.
Figure 4.57 Ground Fault Protection Using Core-Balance CT
q
From Figure 4.53
w
From Figure 4.84
e
Only applicable to SEL-700GT
r
Applicable to SEL-700G0, SEL-700G0+, SEL-700G1, SEL-700G1+, SEL-700GT+
Relay
Word
Bits
50NnP
50NnD
0
50NnP
50NnT
50NnD
0
50NnP
|IN|
50NnTC
50NnTC
NXnDIR
|IN|
67NnT
67NnP
1
2
1
3
4
Z07 Z08
10 A
C-Ground Fault
10 A
A B C
1 A
10:1
Window CT
Feeder 52
IN
NOTE:
Phase CT ratios are typically
higher than core-balance (CB) CT
ratios. For this reason, the relay
sensitivity to ground faults is less
when the residual overcurrent
element is used instead of the CB
element. A separate ground fault
detection method should be used if a
CB CT is not available in applications
where resistance grounding reduces
the available ground fault current.