Siemens siprotec 7SD5 User Manual page 102

2 Functions
With more than two line ends the parameter of address 1114 Tot.Line Length is
to be considered. If the unit of length in address 236 is changed for the total line length
in address1114, the line data have to be set anew for the unit of length which has been
changed. It is possible to enter here unrealistic data (very long line with extremely high
capacitance). The charging current compensation is in that case ineffective and pro-
vides restraint with a very high restraint current. This can also be seen from the mea-
sured restraint values and from the output of an „effective-OFF" indication.
In address 1221 Ic-comp. you can determine whether the charging current compen-
sation is to be switched ON or OFF. Please note that the parameter I-DIFF> in
address 1210 must absolutely be increased to a value of 2 to 3 times I
compensation is switched OFF, because otherwise a spurious trip might be the result.
Note
If the protected line section includes transformers or compensation reactors, the
charging current compensation must not be switched on.
In the following cases, an active protection device is not able to assess the charging
current (charging current compensation is ineffective):
• No voltage measurement (depends on configuration),
• Fuse Failure, or
• Detection of a ΣU measuring error.
In all these cases the protection device remains active for its assigned line section, but
must return to its "classic" restraint strategy, i.e. with I
calculated charging current is set to zero. The charging current tolerance, however,
should be set to 2.5 · I
tion. Address 1224 IcSTAB/IcN allows you to determine the charging current re-
straint factor. Since in the latter descriptions the charging current was already consid-
ered using setting 1210 I-DIFF> = 1 · I
is calculated as follows: (IcSTAB/IcN – 1) · I-DIFF> divided by the number of de-
vices. This value is added to the normal restraint in case of a failure of the the protec-
tive device voltage to be measured.
Inrush Restraint The inrush restraint of the differential protection is only necessary when the devices
are operated on a transformer or on lines which end on transformers. The transformer
is inside the differential protection zone. At address 2301 INRUSH REST. it can be
switched ON or OFF.
It is based on the evaluation of the second harmonic which exists in the inrush current.
Ex-works a ratio of 15 % of the 2nd HARMONIC I
which can normally be taken over. However the component required for restraint can
be parameterized. In order to be able to achieve a higher degree of restraint in case
of exceptionally unfavourable inrush conditions, you may also set a smaller value.
However, if the local measured current exceeds a value set in address 2305 MAX
INRUSH PEAK, there will be no inrush restraint. The peak value is decisive. The set
value should be higher than the maximum inrush current peak value that can be ex-
pected. For transformers set the value above √2·I
transformer, a smaller value may be selected, considering the damping of the current
by the line impedance.
The crossblock function can be activated (YES or deactivated (NO) in address 2303
CROSS BLOCK. The time after exceeding of the current threshold for which this cross-
102
· line section portion to avoid spurious tripping of the protec-
cN
, the additional restraint value of the device
cN
before the
cN
being 2 to 3 times I
cRest
is set under address 2302,
/I
2fN fN
/u . If a line ends on a
NTransf. kTransf.
C53000-G1176-C169-1
. The
cN
7SD5 Manual