Data Formats

Author: Alexander Apostolov, USA

To better understand the effects of different parameters of the power supplied to sensitive customers it is necessary to provide engineers with the right tools to allow them to establish the correlation between the combination of certain attributes of the power and the failure of equipment (Figure 1).

The integration of multifunctional intelligent electronic devices (IEDs) from different manufacturers in substation protection, automation and control systems requires a significant effort due to the different formats of the data available from these devices. Measurements, status, event, disturbance, maintenance or configuration data is used at different times by different applications. The article discusses the requirements for common data formats for all these different types of data in order to allow the development of tools that will simplify the engineering and analysis process in electric utilities and will ultimately support its automation. This will meet one of the key characteristics of the Smart Grid - improved quality and efficiency.

One common format that can be used for analysis of event data is IEC 61850, but it covers only a couple of the requirements listed above and is also used only by devices that support the standard. There are ongoing activities in the IEEE PES Power Systems Relaying Committee working on the establishment of common data formats not only for IEC 61850 based devices and systems, but also for any IED with communications capabilities.

The article introduces the completed and ongoing work on the following common data formats that can help with the development of tools for automatic event and disturbance analysis:

  • IED configuration data
  • IED event reports
  • Sampled values based records
  • Substation configuration description
  • File naming convention
  • IED naming convention

The use of all these standard data formats for analysis is also described in the article.

Analysis of Events and Disturbances
The analysis of protective relays operation that are typically part of the event or disturbance analysis today is based on the different reporting functions in these IEDs. They include:
Event reports
Fault records
Waveform records

In many cases the fault records are included in the event report. At the same time in order to determine if the relay operated as expected, it is necessary to know what exactly the relay settings at the time of operation were. The distribution of the fault currents and their magnitude at the time of a short circuit fault also has an impact on the operation of protection devices. That is why the analysis needs also to consider the electric power system and substation topology at the time of the event (Figure 2).

The experience from the analysis of many relay operations and system disturbances demonstrates that one of the main problems (other than IEDs that are not time-synchronized) is the fact that all the data available from different devices and tools is in proprietary formats that requires significant effort to convert to a common format in order to perform the analysis. Usually this processing of records and data is done manually, which slows down the process and can also lead to errors that may affect the results from the analysis. It also requires a significant number of people with high level of knowledge and experience to perform the work.

In order to improve the analysis process and create an environment supporting the development of automatic fault and relay operation analysis tools, the industry has been working for years on the standardization of reporting, recording and configuration data.

IED Configuration Data Standardization
The description of the functionality of protection devices for many years has been based on the IEEE C37.2 standard that assigns function numbers to substation devices. The problem with this standard is that it has been designed in the twentieth century with electromechanical devices in mind and focused primarily on the representation of substation (including protection) functions on a drawing.

The complexity of the protection functions in modern IEDs and their different possible states that need to be understood during the process of relay analysis cannot be modeled in sufficient detail using IEEE C37.2.
IEC 61850 has made a significant progress in the definition of standard description of the functionality of protection IEDs. The fact that any protection function element is represented by a logical node (see an example of an overcurrent protection element represented by logical node PTOC in Table 1) that can have a Started and Operated state, as well as different modes, associated measurements, settings, etc. allows the detailed description of the behavior of a multifunctional protection IED under abnormal system conditions.

The IEEE PES Power System Relaying Committee understood the need for standardization of the modeling of IED configuration data and started a working group – H5a - in the Relay Communications subcommittee with the task to define a common data format for relay configuration.

The idea was to get a consensus in the industry that the function that can be implemented in many different ways by different relay manufacturers, can be represented using a common model and file format. Once this report is published (it is going through committee balloting now), a new working group will be formed with the goal to complete the models of all remaining protection functions and develop the standard file format to exchange the settings between relay configuration software and different tools used by protection engineers in event and disturbance analysis (Figure 3).

The file format will be based on XML and the substation configuration language as defined in IEC 61850 Part 6. This will allow the import and export of the settings for any multifunctional protection IED (they do not need to be IEC 61850 compliant in that case) in a common format that can be imported into an event analysis tool for the automatic analysis of a protection or other system operation.

IED Event Reports
Event reports are available from any multifunctional protection IED and have been used for more than twenty years. They are typically in the form of a record available in the memory of the relay that can be viewed from the front panel, or can be extracted locally or remotely using the IED communications capabilities.
The format of the event reports are different for the different manufacturers, which makes it difficult to process in automatic fault analysis tools.

IEC 61850 made the first significant step in the development of data models and services (Figure 4) that define standard reporting that can be used in automatic event analysis. Event reports in IEC 61850 are based on Report Control Blocks. They control the procedures required for reporting values of event data from one or more logical nodes to a client. Instances of report control are configured in the IED at configuration time.

IEC 61850 defines two classes of report control:

  • Buffered Report Control Block (BRCB)
  • Unbuffered Report Control Block (URCB)

Buffered Report Control Blocks are used for sequence of event purposes. They define internal events (caused by trigger options data-change, quality-change, and data-update) that issue immediate sending of reports or buffer the events for transmission. This prevents from data being lost in case of loss of connection.

Unbuffered Report Control Blocks are quite similar to the BCRB. However they don’t buffer the data, so event information may be lost in the case of communication problems. Obviously the unbuffered report control block does not support sequence of events reporting in case of loss of communications.

The only problem with the use of the reports described above is the fact that they are available only from IEDs that support IEC 61850. That is why the IEEE PES Power System Relaying Committee understood the need for standardization of the event reporting and started a working group - H5b - in the Relay Communications subcommittee with the task to prepare a Report on a Common Data Format for IED Event Data (Figure 5).

The report defined a common XML-based file format for describing and exchanging event data records collected from devices in the power system. It addressed the fact that protection relays and other IEDs store in their memory historical event data. The main categories of event data considered in this report were:

  • Sequence of events (SOE)
  • Fault reports
  • Summary reports
  • IED Status
  • Other

The content and the format of the data recorded are vendor specific and therefore cannot be easily integrated in a power network post analysis tool.
The main purpose of this file format is to facilitate power systems event data integration and analysis by enabling event data exchange between multiple data sources from different vendor devices and vendor-independent analysis tools.
The report was completed and published in 2008. A new working group (H16) was started with the task to define a new standard. The development and balloting of the standard has been completed and now it is available as C37.239-2010 IEEE Standard for Common Format for Event Data Exchange (COMFEDE) for Power Systems.

Relion advanced protection & control.
BeijingSifang June 2016