What does the SEL RTAC do?

The RTAC collects data from relays via SEL protocol, DNP3, Modbus, and IEC 61850, concentrates it into a unified tag database, presents it to SCADA typically via DNP3, runs IEC 61131-3 automation logic, and can serve an optional web-based HMI. ICCP/TASE.2 is not an RTAC protocol.

Is the SEL RTAC a PLC?

Not a conventional PLC — it is purpose-built for power systems with native protection protocol support, pre-built power system function blocks, and multi-protocol gateway capability alongside IEC 61131-3 programmability.

What is the difference between SEL-3530 and SEL-3555?

The full-rack SEL-3530 is legacy (SEL-3530-4 remains the compact midrange option; SEL often recommends SEL-3350 as the successor path). SEL-3555 is a high-performance RTAC with exe-GUARD allowlisting and stronger compute — preferred for large or high-security deployments.

Complete Guide to the SEL Real Time Automation Controller (RTAC)

Quick Answer

The SEL Real Time Automation Controller (RTAC) is a substation automation controller and multi-protocol gateway manufactured by Schweitzer Engineering Laboratories. It collects data from SEL and third-party relays using SEL protocol, DNP3, Modbus, and IEC 61850, and presents aggregated data to utility SCADA masters typically via DNP3 (other supported servers include Modbus, IEC 60870-5-104, and IEC 61850 MMS). ICCP/TASE.2 is not an RTAC protocol — control-center ICCP links (e.g., QSE to ERCOT) sit upstream of the substation RTAC. The RTAC also runs IEC 61131-3 control logic for substation automation and supports an optional web-based HMI (configured with acSELerator Diagram Builder SEL-5035) for operator displays.

What Is the SEL RTAC?

The RTAC serves four roles in substation automation: protocol gateway (translating between SEL protocol, DNP3, Modbus, and IEC 61850), data concentrator (aggregating multiple relay data to a single SCADA point), automation controller (executing IEC 61131-3 logic), and optional substation HMI (serving web-based operator displays). See What Is the SEL RTAC? for details.

RTAC Hardware Platforms

SEL-3530-4 — Compact midrange RTAC; the full-rack SEL-3530 is no longer in production (SEL recommends SEL-3350 for many replacements)
SEL-3350 — Current midrange computing platform configurable as an RTAC (successor path for many SEL-3530 installs)
SEL-3555 / SEL-3560S / SEL-3560E — High-performance RTACs with exe-GUARD allowlisting; TPM on current 3555-class hardware
SEL-3505 / SEL-3505-3 — Compact lower-voltage RTACs for smaller gateways
SEL-2240 Axion — Modular I/O RTAC platform with EtherCAT I/O modules

Legacy note: the SEL-3354 Embedded Automation Computing Platform is not an RTAC by itself — it required the discontinued SEL-3532 conversion kit. For new work, select a current RTAC model rather than a converted 3354.

ACSELERATOR RTAC Software (SEL-5033)

acSELerator RTAC (SEL-5033) is the integrated development environment for configuring tag databases, protocol drivers, and IEC 61131-3 programs. Optional HMI screens are built with acSELerator Diagram Builder (SEL-5035). See the interface overview for navigation details.

RTAC as Protocol Gateway

The RTAC simultaneously runs multiple protocol clients and servers:

SEL Protocol Client — Polls SEL relays for relay word bits, metering, and events
DNP3 Master — Polls third-party RTUs (SCADAPack, Bristol FB300, ABB Totalflow)
DNP3 Outstation — Serves aggregated data to Geo SCADA and Ignition
Modbus Client/Server — Polls meters and drives, serves data to legacy SCADA
IEC 61850 MMS Client — Reads MMS data from modern IEDs; GOOSE is peer-to-peer (subscriber/publisher), not an MMS client function

RTAC as IEC 61131-3 Automation Controller

The RTAC runs IEC 61131-3 programs in Ladder Diagram, Structured Text, and Continuous Function Chart (CFC) — SEL's FBD-style editor. Sequential Function Chart (SFC) is not a listed RTAC editor. SEL provides a power system function block library with pre-built protection and automation logic.

RTAC Tag Database

The tag database is the central data hub — all protocol drivers read and write tags, all programs access tags, and all HMI elements bind to tags.

RTAC HMI and Operator Displays

Most RTAC models support an optional web-based HMI for operator display pages — one-line diagrams, metering, alarm lists, and trends accessible from a browser on the substation LAN. Screens are developed with acSELerator Diagram Builder (SEL-5035), not as a built-in free feature on every SKU.

Cybersecurity and NERC CIP

RTAC cybersecurity hardening covers password management, port hardening, audit logging, DNP3 Secure Authentication, exe-GUARD allowlisting on modern platforms, and NERC CIP compliance for BES cyber systems.