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8.3.9
Polarity check for the voltage input U
Only for Synchro-
nism Check
7SA6 Manual
C53000-G1176-C156-2
All six measured loops must have the same impedance components (R and X). Small
variations may result due to the non-symmetry of the measured values. In addition the
following applies for all impedances when the load is in the first quadrant:
R, X both positive, when power flows into the line,
R, X both negative, when power flows towards the busbar.
The general case is assumed here, whereby the forward direction (measuring direc-
tion) extends from the busbar towards the line. In the case of capacitive load, caused
by e.g. underexcited generators or charging currents, the X-components may all have
the opposite sign.
If significant differences in the values of the various loops are present, or if the individ-
ual signs are different, then individual phases in the current or voltage transformer cir-
cuits are swapped, not connected correctly, or the phase allocation is incorrect. After
isolation of the line and short-circuiting of the current transformers the connections
must be checked and corrected. The measurement must then be repeated.
Finally the power line is again isolated.
Depending on the application of the voltage measuring input U
be necessary. If no measuring voltage is connected to this input, this subsection is ir-
relevant.
If the input U
is used for measuring a voltage for overvoltage protection (Power
4
System Data 1 address 210 U4 transformer = Ux transformer ), no polarity
check is necessary because the polarity is irrelevant here. The voltage magnitude was
checked according to Subsection 8.3.7.
If the input U
is used for measuring the displacement voltage Uen (power system data
4
1 address 210 U4 transformer = Udelta transf. ), the polarity is checked to-
gether with the measured current test according to Subsection 8.3.11.
If the input U
is used for measuring a busbar voltage for synchronism check (power
4
system data 1 address 210 U4 transformer = Usync transf. ), the polarity must
be checked as follows using the synchronism check function.
The device must be equipped with the synchronism and voltage check (dead-line/
dead-bus check) function which must be configured to enabled under address 135
(see section 5.1).
The voltage Usync connected to the busbar must be specified correctly under ad-
dress 212 Usync connect. (see Subsection 6.1.1).
If there is no transformer between the two measuring points, address 214A
ϕ Usync-Uline must be set to 0° (see Subsection 6.1.1).
If the measurement is made across a transformer, this angle must correspond to the
phase rotation through which the vector group of the transformer as seen from the
feeder in the direction of the busbar rotates the voltage. An example is shown in Sub-
section 6.1.1.
If necessary different transformation ratios of the voltage transformers on the busbar
and the feeder may have to be considered under address 215 U-line / Usync .
Installation and Commissioning
4
, a polarity check may
4
8-61
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