Siemens siprotec 7SA522, Руководство пользователя

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Functions
6-52
7SA522 Manual
C53000-G1176-C119-2
In the following example a maximum arc voltage of 6 kV is assumed for phase–phase
faults (line data as above). If the minimum primary short-circuit current is assumed to
be 1000 A this corresponds to 6
Ω
primary. This results in the following setting for the
resistance reach of the first zone:
primary:
or secondary:
Only half the arc resistance was applied in the equation, as it is added to the
loop
im-
pedance and therefore only half the arc resistance appears in the
per phase
imped-
ance.
A separate resistance margin can be set for earth faults. An arc resistance of 4
Ω
and
a tower footing resistance of 12
Ω
is assumed. This results in the following
primary:
or secondary:
In this case the least favourable condition was assumed, whereby the earth current
does not return via the measuring point. If all the earth current, or a portion of the earth
current flows via the measuring point, the measured resistance decreases. When
there is an infeed from the remote end, the measured resistance may be increased if
the fault resistance is constant. If the fault voltage is constant, e.g. during an arc fault
(approx. 2.5 kV per meter arc length), then the measured fault resistance decreases
with current infeed from the opposite end. Therefore, for the arc-resistance effective
at the relay location, calculated by means of calculation with constant arc-voltage, the
current from the opposite end does not have to be taken into account.
Independent Zones
Z1 up to Z5 By means of the setting parameter
02'(
each zone can be set
)RUZDUG
or
5HYHUVH
or
1RQ'LUHFWLRQDO
(Address
2SPRGH=
,
2SPRGH=
,
2SPRGH=
,
2SPRGH=
and
2SPRGH=
). This allows any com-
bination of forward, reverse or non-directional graded zones, for example on trans-
formers, generators or bus couplers. In the fifth zone different reach in the X direction
can be set for forward or reverse. Zones that are not required, are set
,QDFWLYH
.
The values derived from the grading coordination chart are set for each of the required
zones. The setting parameters are grouped for each zone. For the first zone, Z1, these
are the parameters
5=
(address ) for the R intersection of the polygon appli-
cable to phase-phase faults,
;=
(address ) for the X intersection of the poly-
gon (reach),
5(=
(address ) for the R intersection of the polygon applicable
to phase-earth faults as well as the relevant delay time settings.
R1
prim
R1
line
1
2
---
R
arc
⋅
+ 6.65
Ω
1
2
---
6
Ω ⋅
+ 9.65
Ω
= = =
R1
sec
N
CT
N
VT
---------- R1
prim
⋅
600 A/5 A
110 kV/0.1 kV
-------------------------------------- 9.65
Ω ⋅
1.05
Ω
= = =
R1E
prim
R1
line
R
arc
R
tower
+ + 6.65
Ω
4
Ω
12
Ω
+ + 22.65
Ω
= = =
R1E
sec
N
CT
N
VT
----------
R1
prim
⋅
600 A/5 A
110 kV/0.1 kV
--------------------------------------
22.65
Ω ⋅
2.47
Ω
= = =