Functions
2.3 Differential Protection
SIPROTEC, 7SD610, Manual
C53000-G1176-C145-6, Release date 02.2011
75
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 overfunction 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 trans-
former 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 com-
ponent 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 expected. For transformers, you can set the value above √2·I
NTransf
/u
kTransfo
by
rule of thumb. 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 crossblock 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 Additional Settings.
The table indicates region-specific presettings. Column C (configuration) indicates the corresponding second-
ary 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
1218 T3I0 1PHAS 0.00 .. 0.50 sec; ∞ 0.04 sec Delay 1ph-faults
(comp/isol. star-point)
1219A I> RELEASE DIFF 1A 0.10 .. 20.00 A; 0 0.00 A Min. local current to
release DIFF-Trip
5A 0.50 .. 100.00 A; 0 0.00 A
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