The moving electrode micro-gap is a core part of short-circuit spark discharge system of safety spark test apparatus (STA) specified by the international electrotechnical commission (IEC)

it is the key difficulty of researching on IEC-STA short circuit discharge mechanism and characteristic.In order to establish the mathematical models of capacitive circuit short-circuit discharge on the IEC-STA

its electrodes are scanned with scanning electron microscope (SEM).A physical model of the electrodes micro surface in the most dangerous case is established.Mathematical models of IEC-STA cathode surface electric field are established by improved charge simulation method (CSM)

the parameters setting

algorithm technological process and the method for ill-conditioned matrix are presented.The numerical computation for IEC-STA cathode surface electric field in different micro-protrude density being developed with CSM shows that there is one density which makes the electric field enhancement factor be the highest.The cathode surface electric field in different electrode-spacing being calculated with CSM shows that the enhancement factor decreases with the reduced electrode-spacing when the electrode-spacing is longer

while it increases with the reduced electrode-spacing when it is shorter.The results will prepare for the further research on the short-circuit discharge with IEC-STA.