6-20
IM CW240E
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VT Ratio and CT Ratio
A VT ratio and CT ratio are set up when you use a VT (voltage transformer) and/
or CT (current transformer) to measure the circuit under test on the secondary
winding of the VT and/or CT.
Setting up the VT and/or CT ratio allows voltage and current values to be
applied to the primary winding.
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Indication Provided if VT and CT Are Used
If VT and CT are used (VT and CT ratios set up to conduct measurements), the
measured values are indicated as follows:
Voltage range: voltage range
⫻
VT ratio
Current range: current range
⫻
CT ratio
Power: rated power
⫻
VT ratio
⫻
CT ratio
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Examples of Calculating the VT and CT Ratios
VT ratio:
If VT of 2200 V on the primary winding and 110 V on the secondary winding are
used, the VT ratio becomes 20:1. (Set the VT ratio to 20.00.)
CT ratio:
If CT of 100 A on the primary winding and 5 A on the secondary winding are
used, the CT ratio becomes 20:1. (Set the CT ratio to 20.00.)
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For Setting Up Different CT Ratios
• If LOAD is set to multiple loads (LOAD2, LOAD3, or LOAD4), a CT ratio can
be set for each load.
• If WIRING is set to 1P3W3I or 3P4W4I, a CT ratio for I4 can be separately set.
• If WIRING is set to Scott connection (3P3W+1P3W), a CT ratio can be
separately set for the three-phase (3P3W) and single-phase (1P3W) sides.
NOTE
• The setting range of the VT and CT ratios is from 0.01 to 9999.99 (default: 1.00).
• Settings cannot be under the following conditions:
The product of “rated power
⫻
VT ratio
⫻
CT ratio
⫻
1.3” exceeds 999.9 TW.
SEE ALSO
For connection of VT and/or CT, see Section 4.6, Wiring the Measurement Circuit
Using External VT/CT.
6.2 General Settings 1/2