Siemens SIPROTEC 7SD610 Manual page 313

Figure 3-25
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.
Here, again, the „WEB-Monitor" is a convenient help since the vector diagrams also show the allocation
between the currents and voltages (Figure 3-25). Cyclically and acyclically swapped phases can easily be
detected.
• The measured power values on the actual device or in DIGSI enable you to verify that they correspond to
the load direction (Figure 3-26):
P positive if active power flows into the protected object,
P negative if active power flows toward the busbar,
Q positive if reactive power flows into the protected object,
Q negative if reactive power flows toward the busbar.
Consequently, the powers and their components must have opposite signs at both ends.
Consider also that high load currents, which can occur on long overhead lines or cables, are capacitive,
which means that they correspond to a negative reactive power. In spite of a resistive-inductive load, this
may lead to a slightly negative reactive power at the feeding end, whereas the other end features an in-
creased negative reactive power. The lower the load current for the test, the higher the significance of this
influence. In order to get unambiguous results, you should increase the load current if necessary.
SIPROTEC, 7SD610, Manual
C53000-G1176-C145-6, Release date 02.2011
Remote measured values in the WEB-Monitor - Examples of plausible measured values
Mounting and Commissioning
3.3 Commissioning
313