Siemens SIPROTEC 4 7UT6 Series, Руководство пользователя

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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
2.22.9.1 Web-Monitor ).
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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.
[7ut613-lastscheinleistung-030324-rei, 1, en_GB]
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 Section 2.1.6.1 Setting Notes 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.
Angle Error Correction
During power calculations errors may occur due to angle errors in the current and voltage transformers. In
most cases, these errors are of minor importance, i.e. when referring mainly to the power direction in network
applications, e.g. during network coupling or load shedding.
Errors may not be ignored during the determination of active and reactive power or electrical active and reac-
tive energy. Especially where reverse power protection with highly accurate active power measurement is
used, a correction of the angle error of the involved current and voltage transformer is inevitable. Here (in
case of low cos

), a very low active power must be calculated from a large apparent power. In case of 7UT6x
the angle errors are corrected in the voltage paths.
In case of generators, a precise determination of the angle errors is carried out during primary commissioning
of the engine by means of the motoring power. Hence, deviations are determined taking three measuring
points into consideration, if possible, from which the correction value φ
corr
is derived. It is not important in
which dimensions the following measured values are read, as reference or as absolute values, primary or
secondary. All measured values must of course be converted into one dimension. The angle errors caused by
the device internal input transformers have already been compensated in the factory.
Mounting and Commissioning
3.3 Commissioning
388 SIPROTEC 4, 7UT6x, Manual
C53000-G1176-C230-5, Edition 09.2016