![Schweitzer Engineering Laboratories SEL-421-4 Instruction Manual Download Page 356](http://html.mh-extra.com/html/schweitzer-engineering-laboratories/sel-421-4/sel-421-4_instruction-manual_1216726356.webp)
6.20
SEL-421 Relay
Instruction Manual
Date Code 20171021
Protection Applications Examples
500 kV Parallel Transmission Lines With Mutual Coupling Example
Convert the power system impedances from primary to secondary so you can
later calculate protection settings.
lists the corresponding secondary
impedances. Convert the impedances to secondary ohms as follows:
Equation 6.6
Equation 6.7
The maximum load current is 1302 A primary and occurs when the parallel line
is out of service.
Application Summary
This application is for two circuit breakers, single-pole tripping application with
the following functions:
➤
POTT (permissive overreaching transfer tripping) scheme
➤
Three zones of phase (mho) and ground (mho and quadrilateral)
distance protection
➢
Zone 1, forward-looking, instantaneous underreaching
protection
➢
Zone 2, forward-looking, communications-assisted and time-
delayed tripping
➢
Zone 3, reverse-looking, prevents unwanted tripping during
current reversals
➤
Inverse-time directional zero-sequence overcurrent backup
protection
➤
SOTF protection, fast tripping when the circuit breaker closes
Relay settings that are not mentioned in this example do not apply to this applica-
tion example.
Table 6.8
Secondary Impedances
Parameter
Value
Line impedances:
Z
1L1
= Z
1L2
Z
0L1
= Z
0L2
3.98
87.6° secondary
14.48
82.1° secondary
Zero-sequence mutual coupling:
Z
0M
7.86
76.6° secondary
Source S impedances:
Z
1S
= Z
0S
4.45
88° secondary
Source R impedances:
Z
1R
= Z
0R
1.78
88° secondary
k
CTR
PTR
------------
400
4500
------------
0.089
=
=
=
Z
1L1
ondary
sec
k Z
•
1L1 primary
=
0.089 • (44.78
87.6
=
3.98
87.6
=
Summary of Contents for SEL-421-4
Page 6: ...This page intentionally left blank ...
Page 14: ...This page intentionally left blank ...
Page 30: ...This page intentionally left blank ...
Page 104: ...This page intentionally left blank ...
Page 128: ...This page intentionally left blank ...
Page 536: ...This page intentionally left blank ...
Page 584: ...This page intentionally left blank ...
Page 616: ...This page intentionally left blank ...
Page 696: ...This page intentionally left blank ...
Page 750: ...This page intentionally left blank ...
Page 755: ...Instruction Manual PM400 01 NB SEL 400 Series Relays Instruction Manual 20171006 ...
Page 776: ...This page intentionally left blank ...
Page 932: ...This page intentionally left blank ...
Page 976: ...This page intentionally left blank ...
Page 1024: ...This page intentionally left blank ...
Page 1038: ...This page intentionally left blank ...
Page 1064: ...This page intentionally left blank ...
Page 1128: ...This page intentionally left blank ...
Page 1206: ...This page intentionally left blank ...
Page 1316: ...This page intentionally left blank ...
Page 1350: ...This page intentionally left blank ...
Page 1464: ...This page intentionally left blank ...
Page 1468: ...This page intentionally left blank ...
Page 1492: ...This page intentionally left blank ...
Page 1518: ...This page intentionally left blank ...