P.3.329
Date Code 20151029 Protection Manual SEL-411L Relay
Protection Functions
Protection Application Examples
Load Encroachment
The minimum load impedance is as follows:
Equation 3.122
This impedance is much larger than the Zone 2 characteristic, so load
encroachment is not necessary.
We would have the following at both terminals:
ELOAD := N Load Encroachment (Y, N)
Switch-Onto-Fault Scheme
Because the PTs are located on the line side of the disconnect, the SOTF
function is necessary for the case in which the current differential element and
the distance element are unavailable. Apply typical settings for this function.
We would have the following at both terminals:
ESPSTF := Y Single-Pole Switch-Onto-Fault (Y, N)
EVRST := Y Switch-Onto-Fault Voltage Reset (Y, N)
VRSTPU := 0.8 Switch-Onto-Fault Reset Voltage (0.60–1.00 pu)
52AEND := 10 52A Pole Open Time Delay (OFF, 0.000–16000 cycles)
CLOEND := OFF CLSMON or 1 Pole Open Delay
(OFF, 0.000–16000 cycles)
SOTFD := 10 Switch-Onto-Fault Enable Duration (0.500–16000 cycles)
CLSMON := NA Close Signal Monitor (SEL
OGIC control equation)
The Zone 2 distance element or the instantaneous overcurrent element will
initiate an SOTF trip. Set overcurrent pickup values at 50 percent of the fault
current for a close-in internal fault.
We would have the following at Relay S:
Pickup: 1/2 • (V
LN
/ [Z1S • CTRS])
= 1/2 • 288.67 kV / [50 • 320])
= 9.02 A
50P1P := 9.02 Level 1 Pickup (OFF, 0.25–100 A, sec)
We would have the following at Relay R:
Pickup: 1/2 • (V
LN
/ [Z1R • CTRR])
= 1/2 • 288.67 kV / [20 • 400])
= 18.04 A
50P1P := 18.04 Level 1 Pickup (OFF, 0.25–100 A, sec)
Pole-Open Detection
Configure open pole detection to use the breaker position, because this
detection is wired to the relay. Set the undervoltage open pole threshold at
60 percent of the nominal line-neutral voltage. Set the dropout delays to allow
voltage transients to disappear following a reclose.
ZL
Min
V
LN
IL
Max
---------------
CTRS
PTR
----------------•
500 kV
3 1500 A•
--------------------------------
320
4500
------------• 13.69 == =
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