Siemens siprotec SJ62 User Manual page 432

SIPROTEC 4, 7SJ62/63/64 Handbuch
C53000-G1140-C147-A, Edition 07.2015
lagging the voltage (resistive or resistive-inductive load). The direction of the load
current must be known. If there is a doubt, network or ring loops should be opened.
The line remains energized during the 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
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.
Figure 3-36 Apparent Load Power
All signs of powers may be inverted deliberately. Check whether polarity is inverted in
address 1108 P,Q sign in the P.System Data 2. In that case the signs for active
and reactive power are inverse as well.
The power measurement provides an initial indication as to whether the measured
values have the correct polarity. If both the active power and the reactive power have
the wrong sign and 1108 P,Q sign is set to not reversed, the polarity according
to address 201 CT Starpoint must be checked and corrected.
However, power measurement itself is not able to detect all connection errors. For this
reason, directional messages should be generated by means of the directional over-
current protection. Therefore, pickup thresholds must be reduced so that the available
load current causes a continuous pickup of the element. The direction reported in the
messages, such as „Phase A forward" or „Phase A reverse" must correspond
to the actual power flow. Be careful that the „Forward" direction of the protective
element is in the direction of the line (or object to be protected). This is not necessarily
identical with the direction of the normal the power flow. For all three phases, the di-
rectional messages to the power flow must be reported properly.
If all directions differ from each other, individual phases in current or voltage transform-
er connections are interchanged, not connected properly or phase assignment is in-
correct. After isolation of the line and short-circuiting of the current transformers the
connections must be checked and corrected. The measurements must then be re-
peated.
Finally, switch off the protected power line.
3.3 Commissioning
430