Siemens siprotec 7SD5 User Manual page 497

• With closed circuit breaker, the power values can be viewed as primary and sec-
• With the aid of the measured power values you are able to verify that they correlate
Figure 3-28
7SD5 Manual
C53000-G1176-C169-1
ondary measured values in the front display panel or via the operator or service in-
terface with a personal computer.
Here, again, the „WEB-Monitor" is a comfortable help as the vector diagrams also
show the correlation between the currents and voltages (Figure 3-27). Cyclically
and acyclically swapped phases can easily be detected.
to the load direction, reading either at the device itself or in DIGSI
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 (inductive) 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 significance of this influence. In order to get unambiguous results, you
should increase the load current if necessary.
Apparent load power
3.3 Commissioning
®
(Figure 3-28).
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