YOKOGAWA WT1800 User Manual page 52

2.11 Wiring the Circuit under Measurement When Using Voltage and Current Transformers
Note
• The thick lines on the wiring diagrams are the parts where the current flows. Use wires that are suitable
for the current levels.
• Make sure that you have the polarities correct when you make connections. If the polarity is reversed,
the polarity of the measurement current will be reversed, and you will not be able to make correct
measurements. Be especially careful when connecting clamp-type current sensors to the circuit under
measurement, because it is easy to reverse the connection.
• Note that the frequency and phase characteristics of the VT or CT affect the measured data.
• For safety reasons, the common terminals (+/−) of the secondary side of the VT and CT are grounded in
the wiring diagrams in this section. However, the necessity of grounding and the grounding location (ground
near the VT or CT or ground near the power meter) vary depending on the item under measurement.
• To measure the apparent power and power factor more accurately on an unbalanced three-phase circuit,
we recommend that you use a three-phase, three-wire system that uses a three-voltage, three-current
method (3P3W; 3V3A).
The following wiring examples are for connecting a CT. When connecting a clamp-type current sensor
that outputs current, substitute the CT with the clamp-type current sensor.
The wiring examples shown below are examples of the following wiring systems in which the specified
input elements have been wired. To wire other input elements, substitute the numbers in the figures
with the appropriate element numbers.
• Single-phase, two-wire systems (1P2W): Input element 1
• Single-phase, three-wire system (1P3W) and three-phase, three-wire system (3P3W): Input
elements 1 and 2
• Three-phase, three wire system that uses a three-voltage, three-current method (3P3W; 3V3A) and
three-phase, four-wire system (3P4W): Input elements 1 to 3
Wiring Example of Single-Phase, Two-Wire Systems (1P2W) with
a VT and CT
SOURCE
L CT
l
Input element 1
Wiring Example of a Single-Phase, Three-Wire System (1P3W)
with VTs and CTs
SOURCE
N
L CT
l
Input element 1
IM WT1801-03EN
LOAD SOURCE
VT
V
v
U
±
I
±
VT
V
v
U
±
I
±
LOAD
VT
L CT V
l v
U
±
I
±
Input element 1
LOAD
L CT VT
V
l v
U
±
I
±
Input element 2
1
2
3
4
5
6
App
Index
2-23