We put forward a stray flux test method for the heavy current transform（HCT） in a three-phase horizontal alignment bus system

based on the magnetic field synthesis of both the eccentric bus current and the return bus current to calculate the stray flux generated from external currents in a three-phase bus system. In the proposal

based on intensive analysis of numerical simulation results

a formula is obtained for solving the HCT stray flux and the maximum interference magnetic field. Under the formula

the mathematical model of the equivalent relationship between two types of magnetic field is given. Moreover

by solving the equation

we get the locating place of the eccentric and return buses. In order to evaluate the presented method

a real HCT has been taken as an example

the calculation results show that magnetic field curve and maximum HCT stray flux curve are consistent in shape

the presented method can accurately and effectively simulate the stray flux of the HCT in a three-phase bus system.