The distance protection function in the IED is designed to meet basic requirements for
application on transmission and sub-transmission lines although it also can be used on
distribution levels.
7.9.2.1
System earthing
GUID-AA9E698B-D0B5-45FC-ABA5-6A2CD988E16D v1
The type of system earthing plays an important role when designing the protection system.
Some hints with respect to distance protection are highlighted below.
Solid earthed networks
GUID-02632014-090D-4D95-B678-6DFC7DE998A7 v1
In solidly earthed systems, the transformer neutrals are connected solidly to earth without any
impedance between the transformer neutral and earth.
IEC05000215 V2 EN-US
Figure 162: Solidly earthed network.
The earth-fault current is as high or even higher than the short-circuit current. The series
impedances determine the magnitude of the fault current. The shunt admittance has very
limited influence on the earth-fault current. The shunt admittance may, however, have some
marginal influence on the earth-fault current in networks with long transmission lines.
The earth-fault current at single phase-to- earth in phase L1 can be calculated as equation :
L1
L1
0
1
2
0
f
1
N
f
3 U
U
3I
Z
Z
Z
3Z
Z
Z
Z
×
=
=
+
+
+
+
+
EQUATION1267 V3 EN-US
(Equation 251)
Where:
U
L1
is the phase-to- earth voltage (kV) in the faulty phase before
fault
Z
1
is the positive sequence impedance (Ω/phase)
Z
2
is the negative sequence impedance (Ω/phase)
Z
0
is the zero sequence impedance (Ω/phase)
Z
f
is the fault impedance (Ω), often resistive
Z
N
is the earth return impedance defined as (Z
0
-Z
1
)/3
The voltage on the healthy phases is generally lower than 140% of the nominal phase-to-earth
voltage. This corresponds to about 80% of the nominal phase-to-phase voltage.
The high zero sequence current in solid earthed networks makes it possible to use impedance
measuring technique to detect earth-fault. However, distance protection has limited
possibilities to detect high resistance faults and should therefore always be complemented
with other protection function(s) that can carry out the fault clearance in those cases.
1MRK 505 343-UEN B
Section 7
Impedance protection
267
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...