Functions
6-170 7SA6 Manual
C53000-G1176-C156-2
Calculation example:
110kVoverheadline150mm
2
as used in the example in Subsubsection 6.2.4.2:
s(length)= 60km
R
1
/s = 0,19 Ω/km
X
1
/s = 0,42 Ω/km
Short circuit power at the beginning of the line:
S
k
'=2,5GVA
current transformers600 A/5 A
ThelineimpedanceZ
L
and source impedance Z
S
are calculated with these values as
follows:
Z
1
/s = √0.19
2
+0.42
2
Ω/km = 0.46 Ω/km
Z
L
=0.46Ω/km · 60 km = 27.66 Ω
The three phase short circuit current at the end of the line is I
F end
:
With a safety margin of 10 % the resultant primary setting value is:
SetvalueI>>=1.1·2150A=2365A
or the secondary setting value:
i.e. if the fault current is greater than 2365 A (primary) or 19.7 A (secondary) the fault
is definitely on the protected feeder. This fault may be cleared immediately by the
overcurrent protection.
Comment: The calculation was carried out with scalar quantities which is sufficient for
overhead lines. If there is a large difference in the angle of the source and line imped-
ance, the calculation must be done with complex values.
An analogous calculation can be done for earth faults, whereby the maximum earth
fault current that flows during an earth fault at the end of the line is decisive.
The set time delays are pure additional delays, which do not include the operating time
(measuring time).
The parameter
I>> Telep/BI (address 2614) determines whether the delay times
T Iph>> (address 2611)andT 3I0>> (address 2613) may be bypassed via the bi-
nary input “
>O/C InstTRIP”(F.No.7110) or via the automatic reclose ready state.
The binary input (if assigned) is common to all stages of the overcurrent protection.
With the parameter
I>> Telep/BI = Yes it is determined that the I>>–stages trip
without delay following pick up if there is an operating signal present at the binary in-
put; if the setting is
I>> Telep/BI = No the set delay times always come into effect.
IftheI>>-stageistotripwhenswitchingthelineontoafaultwithorwithoutashort
delay,
SOTF Time DELAY (address 2680, see above and refer to Sub-section “Gen-
eral”), the parameter
I>> SOTF (address 2615)mustbesettoYes. For this fast
switch on to a fault protection any other stage may also be selected.
Z
S
110
2
kV
2
2500 MVA
------------------------------
4.84 Ω
==
I
Fend
1.1 U
N
⋅
3Z
S
( Z
L
)+⋅
--------------------------------------
1.1 110 kV⋅
34.84Ω( 27.66 Ω)+⋅
----------------------------------------------------------------
2150 A
== =
Setting value I>> 1.1=
2150 A
600 A
-------------------
5A⋅⋅19.7 A=
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