Mounting and Commissioning
3.3 Commissioning
SIPROTEC, 7SD80, Manual
E50417-G1140-C474-A1, Release date 09.2011
274
Polarity Check
If the device is connected to voltage transformers, the local measured values already allow a polarity check.
A load current of at least 5% of the rated operational current is still required. Any direction is possible but must
be known.
• With closed circuit breakers, the power values are viewed as primary and secondary values on the front
display panel or via the operator or service interface with a personal computer.
• The measured power values on the actual device or in DIGSI enable you to verify that they correspond to
the load direction (Figure 3-30):
P positive, if active power flows into the protected object,
P negative, if active power flows towards the busbar,
Q positive, if (inductive) reactive power flows into the protected object,
Q negative, if reactive power flows toward the busbar.
Therefore, the power results and their components must have opposite signs at both ends.
It must be taken into consideration that high charging currents, which might occur with long overhead lines
or with cables, are capacitive, i.e. correspond to a negative reactive power into the line. In spite of a resistive-
inductive load, this may lead to a slightly negative reactive power at the feeding end whereas the other end
shows an increased negative reactive power. The lower the load current for the test, the higher the signifi-
cance of this influence. In order to get unambiguous results, you should increase the load current if neces-
sary.
Figure 3-30 Apparent load power
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