MI 2883 Energy Master
Recording Practice and Instrument Connection
107
N
L2
L1
high
voltage
power plant
measuring instruments
A
A
A
L3
xA / 5A
xA / 5A
xA / 5A
Transformer
Type:
Figure 4.14: Connecting instrument to the existing current transformers in medium
voltage system
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.
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 A1227 and iron clamps A1281. Also
other Metrel clamp models A1033 (1000 A), A1069 (100 A), A1120 (3000 A), A1099
(3000 A), etc. can be used.
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.
