The electronic transformer

merging unit

switches and other digital processing equipment introduced by digital substation will inevitably generate definite signal transmission delay. The delay may even reach several power frequency cycles

causing relay protection device maloperation. Currently

it is impossible for testing methods and equipment of time delay based on the steady-state waveform to reflect a delay with a difference greater than a power frequency cycle (whole cycle time delay). The mechanism of signal transmission delay in a digital substation is analyzed in principle and the current detection method is summarized. A test method of signal absolute transmission delay for digital substation is proposed based on coding test waveforms

the detectable whole cycle time delay and freedom from pulse synchronizing signals. Accordingly equipment is developed and the effectiveness of the proposed method is verified.