Using a Real-Time Automation Controller (SEL RTAC) as a Utility-Scale Plant Controller

Using a Real-Time Automation Controller (SEL RTAC) as a Utility-Scale Plant Controller

By: Adam Baker

SEL RTAC is no longer just a data concentrator.

Schweitzer Engineering Lab’s (SEL) RTAC. It originally was used in utility-scale solar and other utility applications as a data concentrator, but it can do so much more. This is one powerful little device.

SEL RTAC is essentially a PLC with some capabilities that go beyond what a normal PLC does. As an industrially-hardened piece of equipment, it’s already suitable for substation environments, which makes it great for solar power applications. 

SEL RTAC: More Than Just a Data Concentrator

Early in my solar career, the SEL RTAC was used in substations primarily as a data concentrator. It would retrieve critical information from various devices around the solar site and aggregate it in one place. The monitoring system or offsite telemetry system could go to the RTAC and extract the data it needed for logging or monitoring purposes.

But using it as a PV data concentrator only skims the surface of its potential. 

Plant Controller Capabilities

The SEL RTAC can act as the overarching PV plant controller. It’s got a sophisticated execution engine. It does relay ladder logic, function charts, and state diagram-type control. It’s good at connecting to other substation devices, pulling data in, executing logic, and sending commands out to devices in the field.

Want an example of its capabilities?

I’ve used SEL RTAC in the field for inverter ramp rate control, active power curtailment, and power factor control.

HMI Capabilities

It’s very flexible in what it can do, very fast at what it can do, and also has capabilities built into it to act as a human machine interface (HMI). Don’t get me wrong, it’s not as sophisticated as a traditional rich environment like Wonderware, VTScada, Cimplicity, or FactoryTalk View. However, if you’re simply trying to design a substation single line diagram and the feeders going in and out of a solar power plant, it’s excellent.

It also has interfaces like GPS clocks and relay control.

Communications Capabilities

It’s got a lot of communications capabilities. Not only does it support popular protocols like Modbus, it also supports DNP3, IEC 61850, GOOSE, IRIG-B. Basically, it supports a ton of different protocols that substations and utilities use for real time information.

SEL RTAC has a ton of serial communications interfaces. If you’re trying to reach out into devices inside a substation that are Modbus RTU, for example, it can handle dozens of serial ports for communications in and out.

SEL RTAC Provides All Functionality Required for Solar

SEL RTAC is pretty inexpensive, widely used in substation equipment (as is all Schweitzer equipment) so it’s very well-accepted in the marketplace, and provides all the functionality required in most of the solar power projects we work on. Overall, it’s got some great solar power controller capabilities at a very reasonable price.


Adam Baker - Affinity EnergyAdam Baker is Senior Sales Executive at Affinity Energy with responsibility for providing subject matter expertise in utility-scale solar plant controls, instrumentation, and data acquisition. With 23 years of experience in automation and control, Adam’s previous companies include Rockwell Automation (Allen-Bradley), First Solar, DEPCOM Power, and GE Fanuc Automation.

Adam was instrumental in the development and deployment of three of the largest PV solar power plants in the United States, including 550 MW Topaz Solar in California, 290 MW Agua Caliente Solar in Arizona, and 550 MW Desert Sunlight in the Mojave Desert.

After a 6-year stint in controls design and architecture for the PV solar market, Adam joined Affinity Energy in 2016 and returned to sales leadership, where he has spent most of his career. Adam has a B.S. in Electrical Engineering from the University of Massachusetts, and has been active in environmental and good food movements for several years.