Siemens siprotec 7SA522 - Polarity Check for the Voltage Input U4

3.3 Commissioning
415
7SA522 Manual
C53000-G1176-C155-3
Q negative, if reactive power flows toward the busbar.
Figure 3-23 Apparent Load Power
The power measurement provides an initial indication as to whether the measured
values have the correct polarity. If both the active power as well as the reactive power
have the wrong sign, the polarity in address  &76WDUSRLQW must be checked
and rectified.
However, power measurement itself is not able to detect all connection errors. Accord-
ingly, the impedances of all six measuring loops are evaluated. These can also be
found as primary and secondary quantities in the operational measured values.
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.
In this case the normal situation is assumed whereby the forward direction (measuring
direction) 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 measurements must then be repeated.
Finally, switch off the protected power line.
3.3.9 Polarity Check for the Voltage Input U
4
Depending on the application of the voltage measuring input U
4
, a polarity check may
be necessary. If no measuring voltage is connected to this input, this subsection is ir-
relevant.
If the input U
4
is used for measuring a voltage for overvoltage protection (36\VWHP
'DWD Address  8WUDQVIRUPHU = 8[WUDQVIRUPHU), no polarity check is