Design and Implementation of a Modular AGC System Based on OPC UA and RX3i PLC for TM2500 Gas Turbines at PLTG Suppa 2×25 MW

In accordance with the Indonesian Grid Code (Permen ESDM No. 20/2020) and PT PLN (Persero) Directive No. 4536/TRS.00.01/C01090300/2022 requiring AGC activation across generating units, PLTG Suppa 2 × 25MW is mandated to implement Automatic Generation Control (AGC) as part of the national anti-blackout program. This paper presents the design and implementation of a modular AGC system for GE TM2500 gas turbines at PLTG Suppa 2 × 25 MW. Unlike centralized AGC at the system operator level, the proposed system operates as a plant-side dispatch-following supervisory layer that receives MW dispatch commands from the master SCADA and executes them through the existing RX3i PLC without modifying the protected OEM core logic. The architecture integrates OPC UA, Modbus communication, KEPServerEX, and a Node-RED-based HMI to enable vendorindependent dispatch execution, real-time monitoring, and AGC permissive control. Field testing confirmed reliable read/write communication and load-setpoint execution, with an average ramp-up response of 3 min at 0.8 MW/min and an average ramp-down response of 1.4 min at 1.52 MW/min. Frequency reductions to 49.76-49.80 Hz were followed by active-power increases of 1.8-2.04 MW, whereas frequency increases to 50.20-50.24 Hz resulted in power reductions of 1.78-2.64 MW. The estimated implementation cost decreased from IDR 1.6 billion under the OEM scheme to IDR 109 million using the modular system, corresponding to a cost reduction of approximately 93.19%. Overall, the proposed system provides a practical, cost-effective, and scalable solution for AGC deployment in distributed mobile power plants.