The measurement and diagnosis of partial discharge（PD）is accepted as one of the most valuable means for assessing the quality of high voltage（HV）power apparatus and their running status. However

the current partial discharge monitoring is mainly based on single equipment

which needs multi-process test equipment

high cost

and large maintenance engineering. This paper introduces the use of four antennas array to receive ultrahigh fre-quency（UHF）signal

and to define 3-D coordinate system

then PD source in the field of the substation is located. Furthermore

the principle of the location algorithm based on time difference is discussed and the origin of its loca-tion error is analyzed. Then the connection of location error and the placement of UHF sensors array and the error of time difference has been discussed theoretically. Finally

the optimal placement of the radio frequency antenna ar-ray is provided.