Demagnetization - Omicron CPC 100 Reference Manual

Figure 12:
CTExcitation test card -
using the crosshair
cursor
The final step of the test is the test assessment.
To learn more about test assessment, refer to "Test Assessment" on page 9-2.

Demagnetization

Both direct currents (DC) or unsymmetrical AC currents (for example,
asymmetries when the CT is switched off) can cause a residual induction in CT
cores. Residual induction can result in an high increase of the ratio error.
To reduce the residual induction to zero, the CT cores should be demagnetized
after all CT tests with DC, for example, after a measurement of the CT winding
resistance, or the measurement of the contact resistances of the primary circuit.
Also demagnetize the core before carrying out ratio measurements.
If the limit values for current and voltage (Imax and Vmax) at the CTExcitation
test card are high enough to bring the core into saturation during the recording
of an excitation curve, slowly decreasing the testing voltage demagnetizes the
CT automatically.
Demagnetization can also be done without recording an excitation curve by
pressing the Demag. button.
Current Transformer
4 - 19