MI 2892 Power Master
Recording Practice and Instrument Connection
121
N
L2
L1
high
voltage
power plant
measuring instruments
A
A
A
L3
xA / 5A
xA / 5A
xA / 5A
Y
Δ
:
Measurement Settings
Connection setup
Nominal Voltage
3
Figure 4.18: Connecting instrument to the existing current transformers in medium voltage system (star
– delta)
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.
