Capacitor voltage transformer（CVT） contains capacitors and nonlinear inductances

so primary-side isolator operation may cause abnormal secondary voltage to influences normal operation of relay devices in substation

or even to lead misoperations of over-excitation protection for main transformers.This paper establishes equivalent circuits models of CVT and the substation via ATP

and simulates CVT secondary voltage as primary-side isolator operates for determining the main factors which impact the amplitude of secondary voltage

and determining the reasons for misoperating over-excitation protection of main transformers.The result shows that misoperation of over-excitation protection for main transformers will not happen in normal operation.