In stations with automation systems according to IEC 61850, network technologies are used for different types of information exchange. Binary information like switch positions or switching commands can be transmitted via the substation network. Analog voltage and current values can also be transmitted. From instrument transformers or sensors, the merging unit collects the measured values, merges these sampled values into a data stream belonging to one feeder, and publishes them to the substation network. The CPC 100 can test the ratio and polarity of instrument transformers in IEC 61850 applications.