Digital Interface Of Electronic Instrument Transformer

For the purpose of successfully applying electronic instrument transformers to substation automation system, the most typical problem to be solved is the interface between electronic instrument transformers and substation secondary equipment.The secondary output of electronic instrument transformers divides into digital output and analog output.Analog output is a transitional step, which makes use of substation secondary equipment with analog interface. Digital output is the final requirement requested by new-style substation.IEC make out the standard about electronic instrument transformers named IEC60044-7/8, in which involves the expatiation of interface part. Out of development of electronic instrument transformers, the standard don't rule the function of electronic instrument transformers, it only give expatiation of outside visible function and consistency requirment.The most difference between electronic instrument transformers and traditional electromagnetic transformers is that the former can provide digital signal directly, Due to this difference, it will impact on substation automation system widely and deeply. Well-designed interface between electronic instrument transformers and secondary equipment can not only simplify secondary equipment, but aslo improve veracity and reliability of the whole system.The interface standardization will urge optimization of substation automation communication-control system.Benefited from interface standardization, information sharing and system integration in substation will come true finally. Firstly, the paper introduces merging unit that realize digital output.And then, it introduces digital output communication model.Secondly, the paper makes an analysis on the function integration scheme of substation automation based on IEC61850 standard.Through the research on communication specification between process level and bay level, it puts forward the stepped improvement to substation architecture induced by electronic instrument transformers.After detailed expatiation about digital output characteristic, the paper puts forward a set of digital interface scheme. Followingly, the digital interface based on IEC61850 standard is developed.At the bottom of this paper, a calibration experiment is carried out toward the designed digital interface. The experiment result indicates that communication capability of the designed digital interface can meet stabilty and real-time requirement of substation automation system.At the same time, error is completely in conformity with precision requirement to 0.2 class electronic instrument transformers ruled by IEC60044-8 standard.Therefore, the designed digital interface is available for digital output application in 0.2 class electronic instrument transformers.