What is a COMTRADE file?

Pro­tec­tion relays are con­tin­u­ous­ly mon­i­tor­ing volt­age and cur­rent wave­forms, fre­quen­cy and pow­er for the pur­pose of detect­ing faults and clear­ing them to pro­tect the infra­struc­ture. This is usu­al­ly done by tak­ing oscil­log­ra­phy sam­ples at a giv­en sam­pling fre­quen­cy and per­form­ing math­e­mat­i­cal oper­a­tions in the dig­i­tal domain, for exam­ple the Clarke Trans­form to detect homopo­lar com­po­nents in three-phase systems.

When a fault is detect­ed these oscil­log­ra­phy sam­ples tak­en before and after the fault can also be used to ana­lyze the behav­ior of the sys­tem in order to improve it. Com­mon analy­sis are, for example;

  • Eval­u­at­ing the degree of suc­cess of the pro­tec­tion sys­tem in clear­ing the fault, for exam­ple how long it has tak­en the pro­tec­tion relays to detect and clear the fault
  • Gain­ing under­stand­ing into the behav­ior of the dif­fer­ent ele­ments; for exam­ple, know­ing the fault cur­rent flow­ing through a trans­former and the dura­tion of the fault may help ana­lyze its pos­si­ble degra­da­tion, esti­mate its life­time and trig­ger a deci­sion on pre­ven­tive maintenance
  • Col­lect­ing sta­tis­ti­cal data about the most com­mon faults in a giv­en line, for exam­ple phase-to-earth faults because of veg­e­ta­tion or phase-to-phase faults because of the wind
  • In large black­outs affect­ing large geo­graph­i­cal areas foren­sic analy­sis may help under­stand how the fault was orig­i­nat­ed and how it prop­a­gat­ed through the grid

These sam­ples are stored in files often cre­at­ed by the pro­tec­tion relays or oth­er IEDs and ana­lyzed with the aid of com­put­er tools. To facil­i­tate the analy­sis and ensure com­pat­i­bil­i­ty between pro­tec­tion relay man­u­fac­tur­ers and soft­ware tools it was clear from the begin­ning that these sam­ples should be stored in a stan­dard­ized for­mat. For this pur­pose, the Insti­tute for Elec­tri­cal and Elec­tron­ics Engi­neers approved IEEE Stan­dard C37.111 in 1991, defin­ing the so-called COMTRADE file for­mat (Common For­mat for Transient Data Exchange). Two revi­sions of the stan­dard were made in 1999 and 2013 to keep pace with the evo­lu­tion of the tech­nol­o­gy and improve the accu­ra­cy of the results; for exam­ple, 16-bit, 32-bit or float­ing-point for­mats were introduced.

IEEE C37.111‑1999 is the most wide­ly used ver­sion of the COMTRADE for­mat and was lat­er adopt­ed by the Inter­na­tion­al Elec­trotech­ni­cal Com­mis­sion as IEC 60255–24. As a stan­dard to nor­mal­ize the for­mat of the sam­ples, IEEE Std C37.111‑1999 defines the fol­low­ing files asso­ci­at­ed with the COMTRADE recording;

  • *.DAT file: data file con­tain­ing numer­i­cal val­ues of all sam­ples togeth­er with a time stamp
  • *.CFG file: a con­fig­u­ra­tion file that states how to inter­pret the *.dat file (samplig rate, fre­quen­cy of pow­er sys­tem, num­ber of chan­nels in the record­ing, bina­ry for­mat of the information, …)
  • *.HDR file; an option­al head­er file with addi­tion­al infor­ma­tion, for exam­ple test con­di­tions if the record­ing has been tak­en in a lab­o­ra­to­ry test

In a real sub­sta­tion the COMTRADE file can be gen­er­at­ed by dif­fer­ent devices, often depend­ing on the type of IED and the com­mu­ni­ca­tions pro­to­col. It can be gen­er­at­ed, for exam­ple, by the pro­tec­tion relays or the RTUs or gate­ways. The File Trans­fer capa­bil­i­ty, includ­ed for exam­ple in IEC 60870–5‑104 and DNP3.0 and present in iGrid’s port­fo­lio, becomes so a use­ful tool to han­dle COMTRADE files.

The attached dia­gram shows a typ­i­cal sub­sta­tion with pro­tec­tion relays and an iRTU (RTU device) or an iGW pro­to­col con­vert­er com­mu­ni­cat­ing to an iCon­trol SCADA sys­tem. The fol­low­ing dif­fer­ent sce­nar­ios are possible;

  • When the pro­tec­tion relays com­mu­ni­cate via IEC 60870–5‑103 pro­to­col, they send the sam­ples togeth­er with their respec­tive time stamps to the iRTU using a sin­gle pack­et. The iRTU/iGW will cre­ate the COMTRADE file with the infor­ma­tion giv­en by the relays, and store it inter­nal­ly. This file may be lat­er col­lect­ed by the con­trol cen­ter, like iCon­trol SCADA, using SFTP, DNP3.0 or IEC 60870–5‑104
  • In IEC 61850, IEDs cre­ate the COMTRADE file, which can be col­lect­ed lat­er by the iRTU/iGW or the iCon­trol SCADA using IEC 61850 file trans­fer or SFTP. The files are stored and made avail­able to the con­trol center

The File Trans­fer capa­bil­i­ty allows the iGW/iRTU to play an active role and trans­fer the COMTRADE and oth­er IEC 61850 files to the Con­trol Cen­ter, via pro­to­cols (IEC 61850, IEC 60870–5‑104 or DNP3.0) or SFTP with­out wait­ing for the SCADA to retrieve them. Of course, the File Trans­fer capa­bil­i­ty can also be used to trans­fer any oth­er type of files, such as IEC 61850 CID con­fig­u­ra­tion files or log files.