Schweitzer Engineering Laboratories SEL-321 - Out-Of-Step Setting; Load-Encroachment Logic Setting

5-10 Applications Date Code 20011026
SEL-321/321-1 Instruction Manual
Out-of-Step Setting
Out-of-step tripping or blocking is not required for this application. The out-of-step elements are
disabled by setting EOOS = N.
EOOS = N
NN
N
- Relay Elements and Other Settings Affected
Relay Elements OSB, OST, X5ABC, X6ABC, and 50ABC.
Load-Encroachment Logic Setting
The relay uses a load-encroachment feature, which prevents operation of the three-phase
elements under high load conditions. This unique feature permits load to enter a predefined area
of the three-phase distance characteristic without causing a tripout.
The load-encroachment characteristic is defined by a load impedance setting in the forward and
reverse directions. Defined angle settings determine the load sector in the forward and reverse
direction.
The load-encroachment setting should be based upon maximum load flow conditions on the
protected line. The maximum short time load flow could be as high as 900 A with Line 5
removed. The maximum conductor current rating is 1200 amps. Assuming a 20% short time
overload factor, set the load impedance for 1440 A load. Nominal system voltage is 230 kV line-
to-line or 132.8 kV line-to-neutral. Assume a load angle range of ±30°. Both forward and
reverse load ranges are assumed to be the same.
Calculations: CTR = 200:1
PTR = 2000:1
Iload =
1440
200
72= .A
secondary
Vbus =
138790
2000
66 4= .volts
secondary
Zload =
Vbus
Iloa
d
==
66 4
72
922
.
.
. Ω
secondary
ELE = Y
YY
Y
ZLF = 9.
9.9.
9.22
2222
22
ZLR = 9.22
9.229.22
9.22
PLAF = 30
3030
30
NLAF = -
--
-30
3030
30
PLAR = 150
150150
150
NLAR = 210
210210
210
- Relay Elements and Other Settings Affected
Relay element ZLOAD.