Online error detection for primary equipment of power system

which can reduce the operation cost and equipment failure rate

is the inevitable trend of power grid development. A great number of voltage transformers have been used in the power system

so it is difficult to take off-line detection for all of them. The capacitive volt-age transformer（CVT）has open structure

hence its voltage division ratio is affected by the electromagnetic envi-ronment in substation. This effect is ultimately reflected in the deviation between off-line and on-line error data. In order to investigate the influence degree of the magnetic interference on the error of CVT

the finite element meth-od is used to analyze the change of initial voltage unit in the CVT under the electromagnetic environments of off-line and on-line error detections. Considering practical engineering

the electromagnetic voltage transformer which meets the requirements of error detection is taken as the reference standard to conduct CVT on-line error detec-tion. The on-line error data in the error detection of CVT

which have deducted the additional error induced by tem-perature and power frequency are compared with the off-line error data

and the result shows that the stray capaci-tance distribution due to the change of the angle between conducting rod and CVT has significant effect on the er-ror data of CVT

proving that the electromagnetic field in substation induces the deviation between off-line and on-line error detection data. This work may provide a theoretical support for promoting CVT on-line error detection.