Once the setting have been sent to the device, relay calculates the scaling factors and displays them
for the user. The "CT scaling factor P/S" describes the ratio between the primary current and the
secondary current. The per-unit scaling factors ("Ipu scaling") for both primary and secondary
values are also displayed (in this case they are the set primary and secondary currents of the CT).
If the protected object's nominal current is chosen to be the basis for the per-unit scaling, the option
"Object in p.u." is selected for the "Scale meas to In" setting (see the image below).
Figure. 5.2.1 - 58. Setting the phase current transformer scalings to the protected object's nominal current.
Once the measurement scaling is tied to the protected object's nominal current, the user must set the
appropriate input for the "Nominal current In" setting. One can now see the differences between
the two scaling options (CT nominal vs. object nominal). The "CT scaling factor P/S" is the direct ratio
between the set CT current values, and the "CT scaling factor NOM" is now the ratio between the set
CT primary and the nominal current. The "Ipu scaling primary" is now equal to the set nominal current,
and the "Ipu scaling secondary" is the ratio between the nominal current and the "CT scaling factor P/
S".
Residual I0 CT scaling
Next, we set the residual IO CT scalings according to how the phase current CTs and the ring core CT
are connected to the module (see the Connections image at the beginning of this chapter).
The phase current CTs are connected to the module via a Holmgren (summing) connection, which
requires the use of coarse residual current measurement settings: the "I01 CT" settings are set
according to the phase current CTs' ratings (100/5 A).
Figure. 5.2.1 - 59. Residual I01 CT scaling (coarse).
The ring core CT is connected to the CTM directly, which requires the use of sensitive residual current
measurement settings: the "I02 CT" settings are set according to the ring core CT's ratings (10/1 A).
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Q-T215
-T215
Instruction manual
Version: 2.04
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