DC transmission project is different from AC transmission project because the electric field around DC transmission equipment is synthetic electric field of DC electrostatic field and space ion flow field.However

the present safety protection of the maintenance personnel for DC transmission project in China refers to the one for AC transmission project.In fact

construction and repair with large machines and tools in the field for live-line will affect the safety protection of the maintenance personnel due to the DC synthetic electric field and space ion flow.In this paper

the DC synthetic electric field and space ion flow density in the typical construction area of a convertor station with or without machines and tools are measured according to the real arrangement of DC convertor station.The results show that:① the large machines and tools in the field lower the DC synthetic electric field and space ion flow density because of their screening effects;②in the convertor station

the DC synthetic electric field on the ground or at the height of 2 m is less than 240 kV/m

and the space ion flow-induced space ion flow density is less than1 000 nA/m2（except for the area outside the wall bushing

where the ion flow density is less than100 nA/m2）.In consequence

extra safety protection against the DC synthetic electric field and ion flow is unnecessary for the maintenance personnel in the convertor station.