Polarity Testing For Ground Fault Protection - Siemens SIPROTEC 7SJ62 Instruction Manual

8.3.3

Polarity Testing for Ground Fault Protection

7SJ62 Manual
C53000-G1140-C121-1
direction of the normal network current flow or the load current flow for this test. For all
three phases, the corresponding power flow directional messages must be reported
properly. If all directions are incorrect, then there is conflict between the polarity of the
current transformers and the polarity set under Address  &7 6WDUSRLQW, in
36\VWHP 'DWD. The polarity of the current transformers must be determined and
properly set in the 7SJ62 according to Sub-section 6.1.1. If the directional data are di-
verse, then individual phases in the current or voltage connections are interchanged,
or the phase sequence is not correct. The connections must be checked and correct-
ed.
Capacitive currents, which can be caused, for example, by under-excited generators,
can occasionally produce limit conditions with respect to the directional characteristic
of 67-TOC. The result can be undefined or diverse directional data in this test. In such
a case, use the indications of real power P, reactive power Q, and the power factor
cosϕ in the metering of the device to determine the position of the complex (apparent)
power phasor in the complex P-Q diagram. See Figure 8-10.
Note! Set the pickup values that have been changed for testing back to the valid set-
tings!
Directional
Characteristic
Q
Negative Reactive Power
Figure 8-10 Apparent Power
With standard current transformer connections to the device, current input 3I
connected to the starpoint of the current transformers. See Figure A-6 in the Appendix.
The polarity of the ground current is generally correct; however, if the current I
from another summation current transformer, an additional directional test is needed
for this current.
Testing is done with primary load current. The trip contacts of the 7SJ62 must be dis-
connected. Proper backup protection should be present. The threshold of 50Ns must
be set so that the element picks up for the load current. Note that all simulations do
not correspond exactly with the situation in practice because of asymmetry in the mea-
Installation and Commissioning
P
Positive Real Power in
the Direction of the Line
S = Apparent Power
Load
Phasor
Positive Reactive Power
(I ) is
0 4
is
Ns
8-21