
Z <
ZL
Z <
E
SA
U
A
U
B
A
B
E
SB
I
A
I
B
R
f
p*ZL
(1-p)*ZL
Z
SA
Z
SB
IEC09000247-1-en.vsd
IEC09000247 V1 EN-US
Figure 138: Influence of fault current infeed from remote end.
The effect of fault current infeed from remote end is one of the most driving factors for justify
complementary protection to distance protection.
7.4.2.4
Load encroachment
SEMOD154453-97 v4
In some cases the load impedance might enter the zone characteristic without any fault on the
protected line. The phenomenon is called load encroachment and it might occur when an
external fault is cleared and high emergency load is transferred on the protected line. The
effect of load encroachment for the mho circle is illustrated to the left in figure
entrance of the load impedance inside the characteristic is of course not allowed and the way
to handle this with conventional distance protection is to consider this with the settings, that
is, to have a security margin between the distance zone and the minimum load impedance.
This has the drawback that it will reduce the sensitivity of the protection, that is, the ability to
detect resistive faults.
jX
R
Load
Load
Load
Load
jX
R
Load
Load
Load
Load
No
operation
en06000403.vsd
IEC06000403 V1 EN-US
Figure 139: Load encroachment phenomena and shaped load encroachment
characteristic
The Faulty phase identification with load encroachment for mho (FMPSPDIS) function shapes
the characteristic according to the diagram on the right in figure
. The load encroachment
algorithm will increase the possibility to detect high fault resistances, especially for phase-to-
earth faults at remote line end. For example, for a given setting of the load angle
ArgLd (see
) for the Faulty phase identification with load encroachment for mho function
(FMPSPDIS), the zone reach can be expanded according to the diagram on the right in
given higher fault resistance coverage without risk for unwanted operation due to
load encroachment. The part of the load encroachment sector that comes inside the mho
circle will not cause a trip if FMPSPDIS is activated for the zone measurement. This is valid in
both directions.
1MRK 505 343-UEN B
Section 7
Impedance protection
223
Application manual
Содержание Relion 670 series
Страница 1: ...RELION 670 SERIES Line differential protection RED670 Version 2 1 IEC Application manual...
Страница 2: ......
Страница 40: ...34...
Страница 64: ...58...
Страница 150: ...144...
Страница 406: ...400...
Страница 472: ...466...
Страница 494: ...488...
Страница 512: ...506...
Страница 524: ...518...
Страница 604: ...598...
Страница 686: ...680...
Страница 718: ...712...
Страница 722: ...716...
Страница 758: ...752...
Страница 759: ...753...