If we divide U
A
by I
A
we get Z present to the IED at A side:
I
A
+ I
B
U
A
I
A
I
A
Z
A
= = p ·Z
L
+ ·R
f
EQUATION1274-IEC-650 V1 EN-US
(Equation 362)
The infeed factor (I
A
+I
B
)/I
A
can be very high, 10-20 depending on the differences in source
impedances at local and remote end.
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 201: Influence of fault current infeed from remote line end
The effect of fault current infeed from remote line end is one of the most driving factors for
justify complementary protection to distance protection.
When the line is heavily loaded, the distance protection at the exporting end will have a
tendency to overreach. To handle this phenomenon, the IED has an adaptive built-in algorithm,
which compensates the overreach tendency of zone 1 at the exporting end and reduces the
underreach at the importing end. No settings are required for this function.
7.13.2.3
Load encroachment
GUID-D846C3D9-4C79-40B5-9ED2-23934214AADB v5
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 is illustrated in the left part of figure
. The entrance of the load
impedance inside the characteristic is not allowed and the previous way of handling this was
to consider it with the settings, that is, with 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.
The IED has a built-in function which shapes the characteristic according to the right part of
. The load encroachment algorithm will increase the possibility to detect high fault
resistances, especially for phase-to-earth faults at the remote line end. For example, for a
given setting of the load angle
ArgLd the resistive blinder for the zone measurement can be
expanded according to the right part of the figure
, given higher fault resistance coverage
without risk for unwanted operation due to load encroachment. This is valid in both directions.
The use of the load encroachment feature is essential for long heavily loaded lines, where there
might be a conflict between the necessary emergency load transfer and necessary sensitivity
of the distance protection. The function can also preferably be used on heavy loaded medium
long lines. For short lines, the major concern is to get sufficient fault resistance coverage. Load
encroachment is not a major problem. Nevertheless, always set
RLdFw, RLdRv
[5]
and
ArgLd
[5] RLdRv=RLdRvFactor*RLdFw.
1MRK 505 343-UEN B
Section 7
Impedance protection
327
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...