The function is based on the asymmetic differential current. If the content of asymmetry of two phases
exceeds the allowed degree of asymmetry, differential protection will be blocked. In order to prevent a mal-
function under single phase earthed fault, another degree of asymmetry the max phase criterion is used to
unblock this logic.
The restraint with harmonics does not influence the stage I-DIFF>>.
See following logic diagram for the details:
[lo_cwa-7utx, 1, en_GB]
Figure 2-51 Logic Current Waveform Analysis Restraint (CWA)
NOTE
The current values Ι/Ι
NO
in the settings overview below always refer to the rated current of the main
protected object. The current values Ι/Ι
NS
always refer to the rated current of the relevant side of the main
protected object.
Settings
Addresses which have an appended “A” can only be changed with DIGSI, under “Additional Settings”.
Addr.
Parameter Setting Options Default Setting Comments
1201 DIFF. PROT. OFF
ON
Block relay
OFF Differential Protection
1205 INC.CHAR.START OFF
ON
OFF Increase of Trip Char. During Start
1206 INRUSH 2.HARM. OFF
ON
ON Inrush with 2. Harmonic Restraint
1207 RESTR. n.HARM. OFF
3. Harmonic
5. Harmonic
OFF n-th Harmonic Restraint
1208 I-DIFF> MON. OFF
ON
ON Differential Current monitoring
1210 I> CURR. GUARD 0.20 .. 2.00 I/InS; 0 0.00 I/InS I> for Current Guard
1211A DIFFw.IE1-MEAS NO
YES
NO Diff-Prot. with meas. Earth Current
S1
1212A DIFFw.IE2-MEAS NO
YES
NO Diff-Prot. with meas. Earth Current
S2
2.2.8
Functions
2.2 Differential Protection
SIPROTEC 4, 7UT6x, Manual 121
C53000-G1176-C230-5, Edition 09.2016
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