Checking The Instrument Transformer Connections Of Two Line Ends - Siemens siprotec 7SD5 User Manual

3 Mounting and Commissioning
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 visual inspection of the correct current transformer connec-
tions. Therefore, the inspection according to Section „Plant Connections" is a prereq-
uisite.
• 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 setting the connections right.
• The above described tests of the measured values also have to be performed at the
In the „WEB-Monitor" the local and remote measured values can be shown graphical-
ly. The following figures show an example.
494
The current flows through the protected object. For more than two ends, one current
path (i.e. two ends) is tested first.
in the 7SD5 must respond. If there was a fault message, however, the Event Log or
spontaneous messages could be checked to investigate the reason for it.
– If current summation errors occur, check the matching factors (see Section 2.1.2
at margin heading „Connection of the Currents").
– Messages 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
2.22.1 under margin heading „Symmetry Monitoring").
Currents can be viewed as primary or secondary measured values in the front
display panel or via the operator or service interface with a personal computer, and
compared with the actually measured values. The absolute values as well as the
phase differences of the currents are indicated so that the correct phase sequence
and polarity of individual transformers can also be seen.
The „WEB-Monitor" provides comfortable read-out possibilities for all measured
values with visualization using phasor diagrams (Figure 3-26).
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 is
the case, if a substantial earth current 3I
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.
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.
occurs:
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7SD5 Manual