4.5
Date Code 20080213
Instruction Manual
SEL-351A Relay
Loss-of-Potential, Load Encroachment, and Directional Element Logic
Load-Encroachment Logic (Not in SEL-351A-1)
Note that a positive-sequence impedance calculation (Z
1
) is made in the load-
encroachment logic in
. Load is largely a balanced condition, so
apparent positive-sequence impedance is a good load measure. The load-
encroachment logic only operates if the positive-sequence current (I
1
) is
greater than the Positive-Sequence Threshold defined in
. For a
balanced load condition, I
1
= phase current magnitude.
Forward load (load flowing out) lies within the hatched region labeled
ZLOUT. Relay Word bit ZLOUT asserts to logical 1 when the load lies within
this hatched region.
Reverse load (load flowing in) lies within the hatched region labeled ZLIN.
Relay Word bit ZLIN asserts to logical 1 when the load lies within this
hatched region.
Relay Word bit ZLOAD is the OR-combination of ZLOUT and ZLIN:
ZLOAD = ZLOUT + ZLIN
Settings Ranges
.
Load-Encroachment
Setting Example
Example system conditions:
The PTs are connected line-to-neutral.
Convert Maximum Loads to Equivalent Secondary Impedances
Start with maximum forward load:
Equation 4.1
Setting
Description and Range
ZLF
Forward Minimum Load Impedance—corresponding to maximum load
flowing out
ZLR
Reverse Minimum Load Impedance—corresponding to maximum load
flowing in
0.10–128.00
Ω
secondary (5 A nominal phase current inputs,
IA
,
IB
,
IC
)
0.50–640.00
Ω
secondary (1 A nominal phase current inputs,
IA
,
IB
,
IC
)
PLAF
Maximum Positive Load Angle Forward (–90° to +90°)
NLAF
Maximum Negative Load Angle Forward (–90° to +90°)
PLAR
Maximum Positive Load Angle Reverse (+90° to +270°)
NLAR
Maximum Negative Load Angle Reverse (+90° to +270°)
Nominal Line-Line Voltage:
230 kV
Maximum Forward Load:
800 MVA
Maximum Reverse Load:
500 MVA
Power Factor (Forward Load):
0.90 lag to 0.95 lead
Power Factor (Reverse Load):
0.80 lag to 0.95 lead
CT ratio:
2000/5 = 400
PT ratio:
134000/67 = 2000
800 MVA
1
3
---
⎝ ⎠
⎛ ⎞
•
267 MVA per phase
=
Содержание SEL-351A
Страница 10: ...This page intentionally left blank Courtesy of NationalSwitchgear com ...
Страница 16: ...This page intentionally left blank Courtesy of NationalSwitchgear com ...
Страница 34: ...This page intentionally left blank Courtesy of NationalSwitchgear com ...
Страница 126: ...This page intentionally left blank Courtesy of NationalSwitchgear com ...
Страница 184: ...This page intentionally left blank Courtesy of NationalSwitchgear com ...
Страница 198: ...This page intentionally left blank Courtesy of NationalSwitchgear com ...
Страница 228: ...This page intentionally left blank Courtesy of NationalSwitchgear com ...
Страница 278: ...This page intentionally left blank Courtesy of NationalSwitchgear com ...
Страница 384: ...This page intentionally left blank Courtesy of NationalSwitchgear com ...
Страница 410: ...This page intentionally left blank Courtesy of NationalSwitchgear com ...
Страница 450: ...This page intentionally left blank Courtesy of NationalSwitchgear com ...
Страница 454: ...This page intentionally left blank Courtesy of NationalSwitchgear com ...
Страница 472: ...This page intentionally left blank Courtesy of NationalSwitchgear com ...
Страница 504: ...This page intentionally left blank Courtesy of NationalSwitchgear com ...
Страница 558: ...This page intentionally left blank Courtesy of NationalSwitchgear com ...
Страница 562: ...This page intentionally left blank Courtesy of NationalSwitchgear com ...
Страница 586: ...This page intentionally left blank Courtesy of NationalSwitchgear com ...
Страница 608: ...This page intentionally left blank Courtesy of NationalSwitchgear com ...
Страница 666: ...This page intentionally left blank Courtesy of NationalSwitchgear com ...