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Real-Time Automation Controller (RTAC)

Unmatched performance for all your automation and control needs

  • Multicore processing handles automation and integration for small and large projects.
  • Powerful real-time operating system ensures deterministic and uninterrupted automation for all critical applications.
  • Integrated web human-machine interface (HMI) with local display port eliminates the need for an additional computer.
  • Robust cybersecurity is engineered throughout the system architecture.
  • Now supports 100,000 tags!

Discover why made in the U.S.A. is important.

RTAC Family Comparison Chart

acSELerator Diagram Builder Software

Starting At

$7,560 USD

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Network Security Device—Make the SEL-3555 Real-Time Automation Controller (RTAC) the secure access point into your substation or plant. Implement Lightweight Directory Access Protocol (LDAP) central authentication and role-based user authentication, project passwords, web upload features, access logs, and secure engineering access via Secure Shell (SSH). Map security tags into SCADA reports for industry-leading integration of security technologies.

SCADA Remote Terminal Unit (RTU)—Quickly design an integrated substation RTU system that includes protocol conversion, SCADA communications, synchrophasors, time synchronization, data management, and custom logic.

Data Concentration—Communicate with any device through built-in client and server protocols. Exchange data through DNP3, Modbus, IEC 60870-5-101/104, LG 8979, SES-92, SEL Fast Messaging, Mirrored Bits communications, and IEEE C37.118 for synchrophasors. Convert data between protocols, perform math and logic functions, and execute output logic for real-time control.

Substation Controller—Create your logic solutions in the embedded IEC 61131 logic engine, which comes standard with every RTAC. Build custom user logic. Access all system tags, including diagnostics, contact I/O, protocol data, and communications statistics, to provide unparalleled control flexibility.

IEC 61850 Integration—Integrate modern intelligent electronic devices (IEDs) into control and automation schemes with IEC 61850 GOOSE and the manufacturing message specification (MMS) client and server.

Operation Supporter/Regulator—Meet or exceed IEEE 1613 and protective relay specifications for harsh environments with the RTAC, which is designed to withstand vibration, electrical surges, fast transients, and extreme temperatures.

Event Collection—Detect, filter, and collect event data automatically from connected SEL relays. Fault location, fault current, and other data are populated into tags for easy retrieval through SCADA protocols. Automatically collect and archive events through the RTAC with acSELerator Team SEL-5045 Software.

Integrate Power Management With Industrial Control—Provide a powerful gateway between the substation and the factory using EtherNet/IP. This popular industrial protocol facilitates reliable communication between electronic devices in industrial automation systems. Use the RTAC EtherNet/IP adapter to exchange critical data for real-time monitoring, process control, and power system integration.

Substation Human-Machine Interface (HMI)—Provide cost-effective local and remote monitoring, control, and annunciation for substations and other processes by installing the optional web-based HMI, available for the RTAC and SEL-2240 Axion. acSELerator Diagram Builder SEL-5035 Software easily maps the RTAC tag database to reduce screen development time.


    1. 1

      Lamp test button

    2. 2

      Ethernet activity LEDs

    3. 3

      Serial port activity LEDs

    4. 4

      SSD activity LED

    5. 5

      Programmable bicolor LEDs

    6. 6

      2 front-panel USB 3.1 ports

    7. 7

      SSD with storage capacity up to 480 GB

    1. 1

      DVI-D ports

    2. 2

      2 high-speed Gigabit Ethernet ports

    3. 3

      4 USB 3.1 ports

    4. 4

      2 built-in EIA-232 ports

    5. 5


    6. 6

      Form C alarm contact output

    7. 7

      PCIe expansion slots

    8. 8

      6 EIA-232/422/485 ports

    9. 9

      Dual hot-swappable power supplies



Note: Beginning with RTAC R144-V2 firmware released on February 18, 2019, the BIOS upgrade is included and managed with the firmware. If you own an SEL-3555 with firmware older than R144-V2, you can upgrade the BIOS by downloading the “SEL-3355 BIOS Update” package on the SEL-3355 webpage. Installation instructions for the SEL-3555 are available in the README.txt file included in the download.


Fast, Deterministic Processing
A quad-core Intel Xeon processor provides powerful and deterministic processing rates as low as 1 millisecond.

Integrated Human-Machine Interface (HMI)
Connect Digital Visual Interface (DVI) or DisplayPort interfaces for high-definition viewing or control of local HMI diagrams. HTML5 graphics provide support for additional browsers and enhanced graphics.

Cybersecure Using Exe-GUARD Technology
Exe-GUARD whitelist anti-malware technology provides increased security, making the SEL-3555 the first product in the market to include a whitelist antivirus solution that does not require end-user patch updates.

Renowned SEL Reliability
The RTAC is designed and tested to meet or exceed IEEE 1613 and protective relay specifications for harsh environments and to withstand vibration, electrical surges, fast transients, and extreme temperatures. The SEL RTAC operates reliably, even in challenging environments.

Concentrate and manage data from new and legacy relays and other IEDs using our extensive set of protocols.

Minimum QuickSet Version


Introducing SEL-3555 Real-Time Automation Controller (RTAC)

Video Playlists

Videos in this series:

  • SEL RTAC—Install
  • SEL RTAC—Basic Software
  • SEL RTAC—Building a Project
  • SEL RTAC—DNP Client
  • SEL RTAC—Tag Processor Intro
  • SEL RTAC—Tag Processor Logging
  • SEL RTAC—Tag Processor Logic
  • SEL RTAC—Engineering Access with Legacy Commands
  • SEL RTAC—Engineering Access with Automatic Connections
  • SEL RTAC—IEC 61131 Programming
  • SEL RTAC—IEC 61131 Functions
  • SEL RTAC—IEC 61131 Function Blocks

Videos in this series:

  • How to Use the RTAC HMI, Part 1: acSELerator Diagram Builder™ Overview
  • How to Use the RTAC HMI, Part 2: Building a Project
  • How to Use the RTAC HMI, Part 3: Shared Tags

Latest Firmware Versions

There are no firmware versions available for this product.

Product Revision Firmware ID Date Available Serial Number
SEL-3555 R149-V0 SEL-3555-R149-V0-Z000004-D20210915 9/22/21 ~1212650001

The Firmware IDs for older versions of the firmware can typically be found in Appendix A of the instruction manual.

Minimum QuickSet Version

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Download the acSELerator RTAC library extensions, and take advantage of the flexibility that the SEL RTAC product line provides for your automation and integration applications. These library extensions are prebuilt code components for the advanced users of the SEL RTAC. Once downloaded, the instruction manuals for each of the library extensions will be accessible via the acSELerator RTAC help menu.

You can find the instruction manuals for the general purpose and optional libraries in the Programming Reference.

General Purpose Toolbox Libraries (Complimentary)

AnalogCondProcess analog quantities and digital filtering.
CrossTaskDataShare data between Main and Automation tasks.
ChannelMonitoringProvide alerts when a channel deviates from user-defined parameters.
DictionariesCreate lookup tables for fast data retrieval.
DynamicVectorsStore an arbitrary number of items, such as an automatically resizing array.
EmailSend alerts and notifications from an RTAC to a mail server.
IPAliasRedundancyShare a single IP between two RTACs in a redundancy scheme by using an IP alias.
MathComplexPerform mathematical operations on values with real and imaginary components.
MathMatrixPerform common matrix operations.
PacketEncodingsSerialize and deserialize information to/from a socket connection.
PowerMeteringPerform energy and demand calculations.
PowerSystemAutomationDetect synchrony between two independent voltage sources.
PowerSystemProtectionIdentify fault conditions, and unlock the potential of the SEL-2245-42 AC Protection Module.
QueueKeep track of ordered lists of objects.
QuickSortSort objects.
RecordingTriggersDetect specific conditions in analog and digital signals to initiate the capture of data.
SELEthernetControllerManage both UDP and TCP raw socket connections.
SELRandGenerate random numbers.
SELServerSimulatorsSimulate an SEL-351 client.
SELStringCombine and split strings in constant time.
SnmpLiteIdentify and troubleshoot network connectivity.
SyslogCollectorReceive Syslog messages from other devices.

Optional Value-Added Automation Solutions

To select any of the following libraries, choose the library as an option in the RTAC hardware configuration.

LibraryApplication/DetailsDependency Libraries
Grid Connection ControlControl the point of common coupling (PCC) between the utility and renewable power generation sources.Dynamic Disturbance Recorder, File I/O
Horizon SVP PlusTurn the RTAC into a synchrophasor vector processor. Detect the onset of uncontrolled wide-area oscillations with SVPplus modal analysis.None
Horizon Power System ModelResolve synchrophasor data streams using a model of the power system.File I/O
Dynamic Disturbance RecorderCollect data from within the logic engine to generate Sequence of Events (SOE), time-aligned CSV, and COMTRADE files in the RTAC.File I/O
Meter Trend RecorderRecord analog data in the RTAC, and send data to acSELerator Team SEL-5045 and acSELerator Meter Reports SEL-5630 Software for analysis.File I/O
Report Generator/EmailPlus ClientGenerate custom reports from data available from the RTAC's logic engine. It is bundled with a fully featured email client that integrates into secure email systems. File I/O
FTP SyncConnect to established S/FTP server infrastructure and automatically push files from the RTAC file system to remote destinations. File I/O
File I/ORead and write files to the RTAC file system. It includes a built-in SFTP/FTP client for sending and receiving files and provides programmatic access to fault and SOE records.None

Engineering Services Libraries (Contact Engineering Services for ordering information.)

Distribution AutomationFault location, isolation, restoration, and volt-VAR control of distribution feeders
Automated System Verification and MonitoringProtection system monitoring and verification (NERC PRC-005)
Ground Fault DetectionGround fault identification for ungrounded power systems

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