Noise Reduction Techniques - Omicron CT SB2 User Manual

CT Analyzer User Manual
3.7.2

Noise reduction techniques

For proper test results it is important to consider the following:
► If possible, disconnect both primary terminals of the CT from the utility lines.
► If possible, always use the original coax measurement cables delivered by OMICRON. If it is
necessary to use loose single-wire measurement cables, twist the wires to a twisted-pair line. Avoid
open loops consisting of individual single-wire measurement cables in order to prevent interference
voltages caused by magnetic fields.
► Connect one terminal of the CT's primary side to protective earth. If it is not possible to disconnect
the utility lines from both primary terminals, connect that side of the primary circuit that is able to
receive more interferences to PE (the primary side that is still connected to the utility lines or the side
with the longer line length, respectively). The ungrounded side should be the side that receives less
interferences.
► When testing a CT in a utility, take care that one side of the CT is connected to PE and at least the
ungrounded terminal is disconnected from all utility lines.
Refer to Figure 3-20.
NOTICE
Falsification of measurement results possible
► Do not connect both primary terminals to PE. This would cause incorrect measurement results.
Connecting both primary terminals to PE has the same effect as a short-circuit in the CT.
Utility line
Connection required if secondary
side terminal cannot be disconnected
Burden
Figure 3-20: Noise reduction for CT measurement
46
Utility line
Use coax measurement cables!
OMICRON