A New Standard for Digital Interface

Today’s IEC 61850 9-2 implementations of merging units and multifunctional IEDs are based on the Implementation Guideline for Digital Interface to Instrument Transformers using IEC 61850-9-2 published by the UCA International Users Group. The scope of IEC Technical Committee 38 is Standardization in the field of AC and/or DC current and/or voltage instrument transformers, including their subparts like (but not limited to) sensing devices, signal treatment, data conversion and analog or digital interfacing. IEC TC 38 has published the CDV (Committee Draft for Voting) of IEC 61869-9 - a product family standard for instrument transformers.

To reduce the engineering amount required to achieve interoperability for the digital interface between instrument transformers and equipment that uses the digital signal (like protective relays, meters or bay level controllers), this standard specifies additional constraints on implementing a digital communication interface. The IEC 61869-9 standard:

  • Replaces IEC 60044-8 digital solution
  • Provides a product standard for instrument transformers with a digital interface according to 61850
  • Includes backward compatibility for the UCA International Users Group Implementation Guideline for Digital Interface to Instrument Transformers Using IEC 61850-9-2
  • Uses IEC 61588 for time synchronization, with an option for 1PPS

A merging unit is modelled as one or more logical devices that contain multiple logical nodes, data sets and sampling rates as shown above. The FDIS (Final Draft International Standard) is expected to be published later this year.  

Let?s start with organization in protection testing