1 2 3 4 A - SIPROTEC

Mounting and Commissioning
3.3 Commissioning
448
• In a first step, check whether power measurement is carried out at the desired measuring location, i.e. that
the assignment of the 3-phase voltage transformer set is made correct. The powers are always calculated
from the connected voltages and the currents of that measuring location to which the voltages are assigned.
If the voltage inputs are assigned to a side of the protected object with more than one measuring location,
the sum of the currents flowing into the protected object is decisive.
Address is relevant 261 VT SET. Refer to Subsection 2.1.4 under margin heading „Assignment of Voltage
Measuring Inputs“.
• With closed circuit breaker, the power values can be viewed as primary and secondary measured values in
the front display panel or via the operator or service interface 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. Cyclically and acyclically swapped phases can easily be detected
(see figure ).
• With the aid of the measured power values you are able to verify that they correlate 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 leaves the protected object,
Q positive, if (inductive) reactive power flows into the protected object,
Q negative, if (inductive) reactive power leaves the protected object.
Figure 3-47 Apparent power
If all signs are inverted this may be intentional. Check in the setting of address 1107 P,Q sign in the power
system data 2 whether the polarity is inverted (see also Subsection 2.1.6.1 under „Sign of Power“). In that case
the signs for active and reactive power are inverse as well.
Otherwise, swapped polarities of the voltage connections may be the cause. If wrong sign is indicated in spite
of correct VT connections, all CT polarities must be wrong!
If the voltage inputs are assigned to a side with more than one current measuring location, currents may flow
through the measuring locations without entering the protective object because they cancel each other out.
Power measurement is not possible in this case. Make sure that the currents for power measurement flow really
through the protected object. Preferably use only one measuring location for the power test.
Finally, disconnect the power plant.
SIPROTEC, 7UT6x, Manual
C53000-G1176-C230-2, Release date 06.2012