Differential Protection For Shunt Reactors - Siemens SIPROTEC 4 7UT6 Series Manual

[diff-generator-querdiff-020926-rei, 1, en_GB]
Figure 2-37
The currents flow into the protected object even in case of healthy operation, in contrast to all other applica-
tions. For this reason, the polarity of one current transformer set must be reversed, i.e. you must set a "wrong"
polarity, as described in Subsection
Measuring Locations".
Starpoint Conditioning
If the differential protection is used as generator or motor protection, the starpoint condition need not be
considered even if the starpoint of the machine is earthed (high- or low-resistant). The phase currents are
always equal at both measuring points in case of an external fault. With internal faults, each fault current is
completely included in the formation of the differential current.
If the machine starpoint (high- or low-ohmic) is earthed, increased earth fault sensitivity in the protected zone
can be achieved by "restricted earth fault protection" (see Section
the "high-impedance differential protection" (see Section

Differential Protection for Shunt Reactors

2.2.4
If current transformers are available for each phase at both sides of a shunt reactor, the same considerations
apply for series reactors.
In most cases, current transformers are installed in the lead phases and in the starpoint connection (see
Figure 2-38). In this case, comparison of the zero sequence currents is reasonable. The "Restricted Earth Fault
Protection" is most suitable for this application (see Section
If current transformers are installed in the line at both sides of the connection point of the reactor (see
Figure 2-38), the same conditions as for auto-transformers apply. Such an arrangement is therefore treated
like an auto-transformer.
A neutral earthing reactor (starpoint former) outside the protected zone of a power transformer can be treated
as a separate protected object provided it is equipped with current transformers like a shunt reactor. The
difference is that the starpoint former has a low impedance for zero sequence currents.
[diff-querdrossel-stromdefinition-020926-rei, 1, en_GB]
Figure 2-38
SIPROTEC 4, 7UT6x, Manual
C53000-G1176-C230-5, Edition 09.2016
Definition of current direction with transverse differential protection
2.1.4 Power System Data 1
Definition of current direction on a shunt reactor
under "Current Transformer Data for 3-Phase
2.3 Restricted Earth Fault
2.7 Single-Phase Time Overcurrent
2.3 Restricted Earth Fault
Functions
2.2 Differential Protection
Protection) or by
Protection.
Protection.
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