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3.3.8
Checking the Instrument Transformer Connections of Two Line Ends
Current Test
The connections of the current transformers are tested with primary values. A load
current of at least 5% of the rated operational current is required. Any direction is pos-
sible.
This test cannot replace the visual inspection of the correct current transformer con-
nections. Therefore, the inspection according to Section „Checking the System Con-
nections" is a prerequisite.
• The current transformer connections are tested at each end of the protected object.
• After closing the circuit breakers, none of the measured value monitoring functions
• The current amplitudes must be approximately the same. All three angles ϕ (I
• The measurements are to be repeated after correcting the connections.
• The above described tests of the measured quantities also have to be performed at
In the „WEB-Monitor" the local and remote measured values can be displayed graph-
ically. The following figures show an example.
7SD610 Manual
C53000-G1176-C145-4
The current flows through the protected object.
in the 7SD610 must respond. If there was a fault indication, however, the Event Log
or spontaneous indications can be checked to investigate the reason for it.
– If current summation errors occur, check the matching factors (see Section 2.1.2
under margin heading „Connection of the currents").
– Indications from the symmetry monitoring could occur because there actually are
asymmetrical conditions in the primary system. If they are part of normal opera-
tion, the corresponding monitoring function is set less sensitive (see Section
2.15.1 under margin heading „Symmetry Monitoring").
The currents can be read as primary and secondary values on the display at the
front, or called up in the PC via the operator or service interface, and compared with
the actual measured quantities. The phase differences of the currents are indicated
in addition to the absolute values so that the correct phase sequence and polarity
of individual transformers can also be seen.
The „WEB-Monitor" allows convenient readout of all measured values with visual-
ization by means of phasor diagrams (Figure 3-24).
must be approximately 120°.
– If the measured values are not plausible, the connections must be checked and
corrected after switching off the protected object and short-circuiting the current
transformers. If, for example, the phase difference between two currents is 60°
instead of 120°, one of the currents must have a reversed polarity. The same
applies if a substantial earth current 3 I
3 I0 ≈ phase current → one or two phase currents are missing;
3 I0 ≈ twice the phase current → one or two phase currents have a reversed po-
larity.
the other end of the tested current path. The current value of the other end can also
be read out locally as percentage values as well as the phase angles.
3.3 Commissioning
occurs:
0
–I
)
Lx
Ly
309
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