Disturbance Analysis in Brazil - Grid Procedures and Infrastructure

Authors: Marco A.M. Rodrigues, Joao C.C. Oliveira, Antonio C.R. Duarte, Sergio R.M. Alves, Jorge M. Ordacgi F, Brazil

Disturbance & Events Recording Architecture

Disturbance Recording Architecture: Digital fault recording (DFR) has been established as an essential post-event analysis source of information, particularly after the new regulatory requirements imposed strict economic and legal issues regarding system availability.

Concerning digital fault recordings, Brazilian utilities can be divided in two groups - Utilities that base their post-analysis on:

  • Stand-alone DFRs: These are, generally, transmission utilities. The reason is related to both history and regulatory enforcement. The first one is because fault recording has been used for quite a long time, before the introduction of multi-function digital devices and this technology is still in use. The other reason is that Brazilian ISO (ONS) enforces the use of dedicated fault recording devices for monitoring busbars and transmission line currents on higher voltage levels
  • Data from multi-function IEDs: These are, generally, distribution and sub-transmission utilities, where the use of dedicated hardware is not economically justifiable and the regulation is not so strict. Such companies have many new installations, where adoption of modern technology is common

The architecture used in most transmission utilities for dealing with fault recordings, with minor variations, is depicted in Figure 1, which shows dedicated DFRs connected to a Concentrator Machine (CM) and protection multifunction IEDs also connected to the CM, but through a switch that segregates the IEDs network, for security reasons. Some companies have such a good communication infra-structure, based on dedicated optical fibers, that the CM can be eliminated and DFRs are accessed as computers in the local network. Where an Ethernet backbone is not available, DFRs are connected to the central office using telephone lines, although this arrangement is rapidly disappearing.

The CM runs software from the manufacturers to retrieve fault recordings and status reports from DFRs and IEDs, as well as proprietary software to adapt and correct these files to the COMTRADE/COMNAME standards. Other pieces of software used in the CM are related to remote administration and to automated delivery of files to a central server.

The “Web Server’ in Figure 1 acts as the final recipient of fault recording files, and runs an automated fault analysis system. Automated fault analysis applications help at a great extent the specialized personnel responsible for detailed fault analysis in gathering information relevant for the complete post-event understanding of the disturbances. Its functions are:

  • Organization of DFR and other relevant files: This can be accomplished by storing in database the file location, relating it to a physical recorder and relating each measured channel to power system quantities. In some cases, the file name and contents may be modified to adapt to the naming conventions of the organization
  • Automated fault analysis: Distinct utilities use systems with different features, but the most common is the fault location algorithm. Some systems enable file classification according to the severity of the event registered, data and power system components monitored; calculate important figures, such as fault identification, fault duration, voltage and current intensity during the fault, fault location in transmission lines, faulty transmission line (by verification of current directions in each line terminal); and report system pre-fault conditions (power quality). Also, interaction with SCADA data is available, such as the correlation with sequence of events information to find out the faulty equipment
  • Visualization of fault information: Data in the files can be accessed as raw waveform graphics or as processed data, leading to reports dedicated to protection, maintenance or operation personnel. Symmetrical components and impedance plots are other very useful features available. Visualization tools are migrating to WEB based technology (Figures 2 and 3).
  • Systemic view: Utilities are now pursuing the facility of using information from fault recorders in a systemic view, so that the amplitude of the disturbance in the power system can be clearly depicted and understood (Figure 3)

Events Recording Architecture: In Brazil sequence of events (SOE) logs are used by operational, maintenance and post mortem analysis teams, but with different scopes and time requirements. The information concept is used for SOE application in Brazil, regarding the operators at each hierarchical level. Station operators shall access all events originated by SAS - devices and systems within the station, because they shall activate maintenance teams. At the GT&D control center level, the operators shall have access information on component protection and local SIPS events (data) to understand SIPS operation within the utility. At the regional control center level the operators shall also have access to the information on the component protection and local SIPS and on regional and global SIPS, to understand systemic SIPS operation.

The information on the component protection includes breaker open and close status, main 1 or main 2 protections tripping orders and blocking (ANSI 86) devices. The 86 devices nomenclature informs the kind of failure that will keep a component out of service, thus requiring maintenance people to intervene. If main 1 or 2 protection trips, the time stamp of the internal function that operates in the first place will be the info time stamp. If more than one internal function operates, the time stamp of the last internal unit to reset will be the time stamp of the reset info. Figure 4 sums up this philosophy, exemplifying for a transmission line:

Table 1depicts how SOE is dealt with in the Grid Procedures:
From 2005 to 2010, Brazil invested some US $ 30,000,000.00 in terms of SOE for nearly 100 substations in the Main Grid.

Time Synchronization: Synchronized time tag signals provided by high accuracy Global Positioning System (GPS) are presently used by electric power utilities and industries for many applications that can benefit of an absolute time reference. These coded signals can be provided through communications network and received by internal mechanism of modern IEDs such as fault recorders and protective relays that can register synchronized oscillographic data with a resolution time of milliseconds.

Multiple data-recording devices can be triggered during one fault event. Depending on the event, the specialist must handle a large number of files generated in a short period of time in order to perform a post-disturbance analysis and figure out the set and sequence of registers that belongs to the same occurrence. Without a precise time reference, due to differences between IDE’s internal clock, this task must rely only in the general characteristics of analog and event sequence signals. With the advent of time-synchronized tags the analyst can now not only put together simultaneous oscillographic registers but also capture the real events sequence. Furthermore, data correlation can be done aided by automated analysis software.

Time synchronization of fault recording events is very important for the calculation of fault location using signals from both transmission line terminals. Having a reliable time-tag it is possible to correlate precisely phase module and angle values enhancing fault location results. However, at the early stages of GPS technology, a number of incompatibilities led to huge errors in the time tag of DRF files. As some utilities in Brazil purchased and used such devices and will take some time to replace them, a solution to this problem was needed. Although such errors did not enable the use of conventional fault locating algorithm, they made the automated correlation of files related to a given event possible. This feature allowed for the development of techniques and algorithms to improve automated fault location results using data form both line terminals with excellent results.

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