Siemens SIPROTEC 7UT613 series Manual page 415

Angle Error
Correction
7UT613/63x Manual
C53000-G1176-C160-2
Figure 3-41 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 Sub-
section 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 lo-
cation, currents may flow through the measuring locations without entering the protec-
tive 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.
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 reactive 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 ϕ),
a very low active power must be calculated from a large apparent power. In case of
7UT613/63x 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, devia-
tions are determined taking three measuring points into consideration, if possible, from
which the correction value ϕ
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 com-
pensated in the factory.
• Start up generator and synchronize with network. During exact synchronous work-
ing, active and reactive power are theoretically zero.
• Reduce driving power to zero by closing the regulating valves. The generator now
takes motoring energy from the network.
is derived. It is not important in which dimensions the
corr
3.3 Commissioning
415