2.3 Differential Protection
73
7SD610 Manual
C53000-G1176-C145-4
The pickup thresholds are finally checked during commissioning. Further information
can be found in chapter Installation and Commissioning.
Pickup value when
switching on the
charge comparison
If bushing transformers are used for a transformer in the protected line section, stray
fluxes through the bushing transformers may occur when reclosing after an external
fault. These stray fluxes may cause a distortion of the secondary current and an over-
function of the charge comparison.
If bushing transformers are used, the setting value of parameter 1235 I-
DIF>>SWITCHON should be 2 to 3 times the setting value of I-DIFF>>. The default
setting of I-DIF>>SWITCHON corresponds to the default setting of parameter 1233
I-DIFF>>. In the default setting, this parameter is therefore ineffective.
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 located inside the differential protection zone. Inrush restraint can be turned ON or
OFF at address 2301 INRUSH REST..
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
2fN
/I
fN
is set under address 2302,
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
NTransf.
/u
kTransf.
. If a line ends on a
transformer, a smaller value may be selected, considering the damping of the current
by the line impedance.
At address 2303 CROSS BLOCK, the crossblock function can be activated (YES) or
deactivated (NO). The time after exceeding the current threshold for which this cross-
block is to be activated is set at address 2310 CROSSB 2HM. With the setting ∞ the
crossblock function is always active until the second harmonic content in all phases
has dropped below the set value.
2.3.3 Settings
Addresses which have an appended "A" can only be changed with DIGSI, under Ad-
ditional Settings.
The table indicates region-specific presettings. Column C (configuration) indicates the
corresponding secondary nominal current of the current transformer.
Addr. Parameter C Setting Options Default Setting Comments
1201 STATE OF DIFF. OFF
ON
ON State of differential protec-
tion
1210 I-DIFF> 1A 0.10 .. 20.00 A 0.30 A I-DIFF>: Pickup value
5A 0.50 .. 100.00 A 1.50 A
1213 I-DIF>SWITCH ON 1A 0.10 .. 20.00 A 0.30 A I-DIFF>: Value under
switch on condition
5A 0.50 .. 100.00 A 1.50 A
1217A T-DELAY I-DIFF> 0.00 .. 60.00 sec; ∞ 0.00 sec I-DIFF>: Trip time delay
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