4.28
SEL-700G Relay
Instruction Manual
Date Code 20170814
Protection and Logic Functions
Group Settings (SET Command)
The relay now calculates each tap current, using the formula
stated previously:
Thus, we have the following:
The relay calculates these taps automatically if MVA is given.
If MVA is set to OFF, you must calculate the taps and enter
them individually. The relay will check to see if a violation of
the maximum tap ratio has occurred, and it will notify you of
any violation.
Step 6. Set the differential element characteristic. Select the settings
according to our suggestions in the earlier setting descriptions.
For this example, we have selected a two slope, variable-
percentage differential characteristic for maximum sensitivity
at low currents and greater tolerance for CT saturation on
external high-current faults. The high security mode settings
are left at default; with HSM := 0, this mode is disabled.
The minimum error for selecting SLP1 for this application is
determined as follows:
➢
Excitation current (4%)
➢
CT accuracy (3%)
➢
No-Load Tap Changer (NLTC) (5%)
➢
Load Tap-Changer (LTC) (0%)
➢
Relay accuracy (±5% or ±0.02 • INOM, whichever is
largest) (5%)
The CTs have been evaluated for maximum through fault and
found to be unlikely to saturate severely. So, SLP2 does not
have to be set higher than normal.
The settings are as follows:
O87P = 0.3 (Operate current pickup in multiple of
tap)
SLP1 = 15 (15 percent initial slope)
SLP2 = 50 (50 percent second slope)
IRS1 = 6.0 (limit of Slope 1, Restraint current in
multiple of tap)
TAP
n
MVA
1000
3
VWDG
n
CTR
n
---------------------------------------------------------
C
=
where
C
1 for wye CTs
=
TAPX
30 MVA
1000
3
13.8 kV
400
------------------------------------------------
=
TAPX
3.14
=
TAPY
30 MVA
1000
3
138 kV
40
-------------------------------------------
=
TAPY
3.14
=
SLP1
M IN
%
17
200
17
–
-------------------------
100
9.3%
=
=
Содержание SEL-700G Series
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