To calibrate merging units with analogue input by using the fixed time-delay method and to promote the level of test technique for intelligent substations of new generation

we put forward a calibration system independent of signals based on high-accuracy data acquisition cards. In the process of structure design

strict working timing of the merging units is utilized

and in the aspect of data processing

data synchronization method based on least-square fitting is researched. Moreover

measurement uncertainties are presented

and the designed system is employed to test the accuracy of a merging unit wish analogue input. Comparison of the results obtained through two different test methods shows that the differences of ratio errors are below 0.02%

and the maximum difference of phase errors is about 4′

which are in conformity to the existing test results. This indicates that the design scheme is feasible

and the designed calibration system meets the requirements of calibrating merging units with analogue input without using synchronization signals.