Application Example; Power Measurement At A Machine - Beckhoff SCT6 Series Manual

Application example

5 Application example
5.1

Power measurement at a machine

WARNING: Risk of electric shock!
Bring the Bus Terminal system into a safe, voltage-free state before starting mounting, disassembly or
wiring of the Bus Terminals!
Attention! Risk of device damage!
Avoid confusing the current and voltage circuit during connection, since the direct connection of mains volt-
age to the terminal points for the current transformers (typical input resistance 100 mΩ) would destroy the
power measurement terminal!
EL3443
• The voltage is measured via connections L1, L2, L3 and N.
• The current is measured via three current transformers (e.g. from the Beckhoff SCT series) and the
connections I , I , I
L1 L2
Fig. 30: EL3443, power measurement at a machine
Fuse protection of the terminal
The voltage measurement inputs L1 - L3 are high-impedance; a minimum measurement current
flows. The fuses to the connection points L1 - L3 are therefore only to be designed according to the
connection cross-section.
For the current measurement inputs I
device to be measured.
The secondary currents of the transformers are not fused, see figure.
**) PE as star point for 3-phase systems without neutral line
Depending on the current transformers used, PE must be connected as star point in 3-phase sys-
tems without neutral line as shown in Fig. "EL3443, power measurement at a machine ".
Observe the regulations of the manufacturer of the current transformers!
48
WARNING
and I (star point of the current transformers).
L3 N
– I
L1
Version: 1.3
NOTE
, the fuse protection must be adapted according to the
L2
SCT6xxx