WAGO-I/O-SYSTEM 750 XTR
Connect Devices 169
750-495/040-00x 3-Phase Power Measurement Module 690 V
Manual
Version 1.2.0
7.7.2.1.2 2-Wattmeter Method (Aron Circuit/Blondel’s Theorem)
For voltage measurement, set the topology to “3-Wire Wye/Delta” (“3-W”) in
WAGO-I/O-
Check
.
This topology is available with firmware versions 05 and above and WAGO-
I/O-
Check
versions IO-3.18.1 (CS0609) and above.
This measurement circuit is used in all 3-phase networks without a neutral
conductor, with a star point grounded on the source side, and with loads in a wye
or delta connection.
The measurement circuit uses the principle of the 2-wattmeter method.
2 electrically isolating voltage transformers (VTs) reduce the 2 line-to-line
voltages U
12
and U
23
to u
12
and u
23
with electrical isolation. Line-to-line voltages
u
12
and u
23
are measured. From the measurement results, the I/O module first
calculates line-to-line voltage u
31
and then line-to-line voltages U
12
, U
23
and U
31
.
The current measurement is performed via current transformers (CTs) or
Rogowski Coils.
Always use voltage transformers with reinforced insulation and ground the
module-side N connection
In 3-wire networks with a star point grounded on the source side, always use
voltage transformers with reinforced insulation and ground the module-side N
connection.
Otherwise, touch-proof protection from the system may no longer be given in the
event of a fault. This can cause electric shock or burns.
The voltage transformer ratio and current transformer ratio must be taken into
account for the correct calculation of all values in the process image.
The nominal input voltage is:
- u
LL
= 200 V
RMS
if a voltage ≤
120 V
RMS
is parameterized for the “Secondary
Voltage” setting
- u
LL
= 400 V
RMS
if a voltage > 120 V
RMS
is parameterized for the “Secondary
Voltage” setting
Parameter 47 is used for the setting.
