Siemens SIPROTEC 7UT613 series Manual page 134

2 Functions
134
mentioned address. The restraint with harmonics does not influence the stage I-
DIFF>>.
The inrush restraint can be extended by the so-called "crossblock" function. This
means that on harmonic content overshoot in only one phase all three phases of the
differential stage I
DIFF>
tion is active can be limited at address 1272 CROSSB. 2. HARM. Setting is in multiple
of the AC-cycle. This parameter can only be set with DIGSI at Additional Settings. If
set to 0 (pre-setting is 3) the protection can trip when the transformer is switched on
a single-phase fault even while the other phases carry inrush current. If set to ∞ the
crossblock function remains effective for as long as high-order harmonics are detected
in any phase.
Apart from the second harmonic, the 7UT613/63x can provide restraint with a further
harmonic. Address 1207 RESTR. n.HARM. is used to disable this harmonics re-
straint, or to select the harmonic for it. Available for selection are the 3. Harmonic
and the 5. Harmonic.
Steady-state overexcitation of transformers is characterised by odd harmonic content.
The 3rd or 5th harmonic is suitable to detect overexcitation. As the third harmonic is
often eliminated in transformers (e.g. in a delta winding), the fifth harmonic is more
commonly used.
Converter transformers also produce odd harmonics which are practically absent in
the case of an internal short-circuit.
The harmonic content intended for blocking the differential protection is set at address
1276 n. HARMONIC. For example, if the 5th harmonic restraint is used to avoid trip
during overexcitation, 30 % (default setting) are convenient.
Harmonic restraint with the n-th harmonic operates individually per phase. However,
it is also possible – as it is for the inrush restraint – to set the protection in such manner
that not only the phase with harmonic content overshoot but also the other phases of
the differential stage I-DIFF> are blocked (so-called "crossblock" function). The du-
ration for which the crossblock function is active can be limited at address 1277
CROSSB. n.HARM. Setting is in multiple of the AC-cycle. This parameter can only be
set with DIGSI at Additional Settings. If set to 0 the crossblock function remains ef-
fective for as long as high-order harmonics are detected in any phase. When set to ∞,
the crossblock function is always active. .
If the differential current exceeds the magnitude set at address 1278 IDIFFmax
n.HM no n-th harmonic restraint takes place. This parameter can only be altered in
DIGSI at Display Additional Settings.
Note
The current values I/I
NO
current of the main protected object. The current values I/I
current of the relevant side of the main protected object.
stage are blocked. The duration for which the crossblock func-
in the settings overview below always refer to the rated
always refer to the rated
NS
7UT613/63x Manual
C53000-G1176-C160-2