MI 2893 / MI 2892 / MI 2885
Connection setup
150
4.2.3
Current clamp selection and transformation ratio setting
Clamp selection can be explained by two typical use cases: direct current measurement and indirect
current measurement. In next section recommended practice for both cases is shown.
Auto range current clamp operation
Most of Metrel current clamps are developed as Smart clamps. They are automatically recognised by the
instrument. Most of clamps support more different current ranges, for example 30/300/3000 A (Current
clamps A 1501/A 1502/A 1227/A 1445/A 1582). Power Quality Instrument could operate in so called
“Auto” range, where instrument automatically select the most optimal current clamp range. In this case,
the most accurate current measurements are guaranteed.
Note 1: In case of “auto range” selection, Inrush measurements are not reliable.
Note 2: In case of “auto range” selection, synchronisation could not be selected to current.
Note 3: Current clamps with external current range (range selection on the clamps itself) selection does
not support “auto range”.
Note 4: Current clamp needs specific time during current range changing to stabilize the readings
(stabilization time is bigger for flex than for iron clamps). During stabilization time, current values are
not presented (for the registration periods, shorter than 1 minute).
Figure 127: Smart current clamps auto range selection
Direct current measurement with clamp-on current transformer
In this type of measurement load/generator current is measured directly with one of clap-on current
transformer. Current to voltage conversion is performed directly by the clamps.
Direct current measurement can be performed by any clamp-on current transformer. We particularly
recommend Smart clamps: flex clamps A 1502, A1227 and iron clamps A1281, A 1588 for example. Also,
other Metrel clamp models A1033 (1000 A), A1069 (100 A), etc. can be used. For more details about the
current clamps, please check the Metrel‘s General catalogue.
In the case of large loads there can be few parallel feeders which can’t be embraced by single clamps. In
this case we can measure current only through one feeder as shown on figure below.
