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3.2.3 Excitation Test
IEEE defines the saturation as “the point where the tangent is at 45 degrees to the secondary exciting
amperes”. Also known as “knee” point.
This test verifies that the CT is of correct accuracy rating, has no shorted turns in the CT and no short
circuits are present in the primary or secondary windings of the CT under test.
A typical excitation curve for C class current transformer is shown in figure below.
An AC voltage is applied to the secondary winding of the CT. The voltage applied to the secondary
winding of the CT is increased slowly automatically by the test set. Voltage and current readings for the
secondary winding of CT are stored in the internal memory. At 300V AC the MVCT will switch to DC
voltage to finish saturating the CT. Test set automatically convert the DC voltage readings, generate an
AC excitation curve and determines the “Knee” point as per selected standard by observing a small
voltage increase causing a large increase in current. The excitation curve around the points where
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