19
For 3-phase measurement, it is advisable to connect the
N
terminal as well. This enables the high
measurement accuracy of the PQC to be achieved when measuring phase–neutral voltages and
the parameters derived from these. If no neutral conductor is present, the
N
terminal can be left
unconnected. However, this is only advisable when the phases are symmetrically loaded.
NOTE!
With instrument types designed for three-phase measuring, the voltage mea-
surement inputs not in use must be commoned with the terminal N. This is
necessary, for example, with single-or two-phase connections.
If this is not done, phantom measurement readings may be displayed for the
inputs that are not in use.
With three-phase measurement, automatic connection identification is not
possible.
5.5 Current measurement
The PQC is designed for connection to x / 1 A and x / 5 A current transformers. Only AC currents
can be measured; DC currents cannot be measured. Depending on the instrument type
[see
Section 9, Instrument versions]
, the PQC can measure one, two or three AC currents.
[See Sec-
tion 2, Technical data]
, for the measurement ranges.
DANGER!
If live current transformer circuits are interrupted, there is the danger that arcing
may occur, which would cause electric shock, burns or eye injuries. In addition,
red-hot metal particles could be spattered, which apart from the health hazard
also constitute a fire risk.
To avoid accidents, the following must be observed:
- The safety instructions in
[Section 5.1, Electrical connections]
.
- The current measurement inputs must be connected as specified.
- The retaining screws on the connectors must be tightened to prevent the
connectors accidently working loose.
- The secondary-side connections of the current transformers must be short-
circuited before the circuits to the PQC are interrupted or the connector
removed!
When work is carried out on the instrument terminals and connecting cables,
there is a risk of live components being touched inadvertently. The working
voltage may present a hazard to health or may even be life-threatening.
If the above instructions are followed, and the precautions specified in
[Section
1.2, Safety instructions]
, are taken, the risk of damaging equipment and assets or
endangering life and limb can be significantly reduced.
DANGER!
The retaining screws on the sides of the connectors for the current transformer
circuits must always be tightened before the instrument is put into service.
Tightening these retaining screws prevents the connectors from accidentally
working loose and therefore reduces the risk of arcing.
