YOKOGAWA CW140, Руководство пользователя, Страница: 30 / 292

IM CW140-E
3-8
3.5 Wiring the Circuit under Test Using
External VT/CT
WARNING
• When using an external CT, be careful not to allow the secondary stage of the CT to become
open-circuited while the primary stage is being electrified. Otherwise, a high voltage may
develop on the secondary stage, causing extreme danger.
• The current under test flows through the bold lines shown in the figure below. For these lines,
use wire that has an adequate margin of current-carrying capacity.
If the maximum voltage or current level being measured exceeds the
maximum measurement range of the CW140, use an external VT and/or CT.
This strategy enables the measurement of voltage or current levels above the
maximum range.
If the maximum voltage level exceeds 600 V, attach an external VT. Then,
connect the secondary stage of the VT to the voltage input terminals.
If the maximum current level exceeds the following value, attach an
external CT. Then, connect the secondary stage of the CT to the current-
sensing clamp.
200 A, when clamp A (20, 50, 100 and 200 A) is used
500 A, when clamp C (50, 100, 200 and 500 A) is used
1000 A, when clamp B (200, 500 and 1000 A) is used
Example of 1 φ 2W
1
N
V1 Voltage input terminals Current input terminals N CH1
V
v
L
艎
Voltage
transfomer
CT
Current
transfomer
S
O
U
R
C
E
L
O
A
D
VT
TIP
• The CW140 can show the primarystage value even if the scaling function is applied using VT/CT.
SEE ALSO
Section 7.7, "Scaling Function," for details on how to use VT/CT.
• The lowest current range of the CW140 main unit itself is 20 A on full scale and the accuracy also
depends on this value. Note therefore that if a CT is used and its secondary output is too small when
compared with 20 A, then the error ratio will become higher.