Directional Checks With Load Current - Siemens siprotec 7SA6 User Manual

8.3.7

Directional Checks with Load Current

Load Current
≥ 10 % I
N
7SA6 Manual
C53000-G1176-C133-1
If the VT mcb is open the message "!)$,/ %XV 97 21" appears, if it is closed the
message "!)$,/ %XV 97 2))" is displayed.
Switch off the protected power line.
The connections of the current and voltage transformers are checked using load
current on the protected line. The secondary load current must be at least 0.10 · I
The load current should be in-phase or lagging the voltage (resistive or resistive-
inductive load). The direction of the load current must be known. If there is a doubt,
network loops should be opened or other action taken to guarantee the direction of the
load current. The line remains energized during this directional test.
The direction can be derived directly from the operational measured values. Initially
the correlation of the measured load direction with the actual direction of load flow is
checked. In this case the normal situation is assumed whereby the forward direction
(measuring direction) extends from the busbar towards the line (Figure 8-23).
P positive, if active power flows into the line,
P negative, if active power flows towards the busbar,
Q positive, if reactive power flows into the line,
Q negative, if reactive power flows toward the busbar.
jQ
Positive reactive power
in
the direction of the line
Figure 8-23 Complex (apparent) 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.
The power measurement on its own is however not able to recognize all types of
incorrect connection. Accordingly, the impedances of all six measuring loops are
evaluated. These can also be found as primary and secondary quantities in the
operational measured values (Sub-section 7.1.3.1).
Installation and Commissioning
P
Positive active power in
the direction of the line
S
Load
.
N
Negative reactive power
in
the direction of the line
8-49