The principle of electronic current transformer was described in this paper.For shunt and connecting conductor

thermal effect was analyzed.Theoretical analysis shows that shunt and connecting conductor have thermal effect in direct current

and skin effect in harmonic current would produce addition thermal.They may influence measurement result.Experiments proof that cage structure shunt can restrain the thermal effects of harmonic current effectively.Thermal stability test of electronic current transformer is inappropriate to use the frequency equivalent exchange.When the transformer works in direct current

its thermal stability is trued.