When 3-core distribution power cable is in service

unbalanced current in 3-phase usually occurs due to the different demands of consumers load in different phases. As a result

it is necessary to determine the cable temperature rise under unbalanced current. Only balanced conditions of 3-phase current are considered in IEC 60287 and the thermal circuit method is too difficult to calculate temperature rise. Therefore

we applied a finite element method to build a numerical model for cables’ thermal field. Using the cable thermal field model

we set different unbalanced degrees in phase-A and calculated the greatest load current of phases-B and phases-C by dichotomy. According to the results

if the further unbalanced degree deviates from 0 value

the total current of cable transmitting under 90 ℃ is less. Besides

the total loss of cable is smallest when the unbalanced degree is 0.6. Distribution administrator can make use of different unbalanced degrees to decrease the line loss rate and increase the cable utilization ratio.