Melb Airport Trigen plant

8MW Trigeneration Project

AIEglobal was contracted by TSF Engineering to design and install the PLC/Scada Automation System, and also to Nilsen for the HV/LV Electrical Design for the Trigeneration Energy Plant at the Melbourne Airport. The system comprises 4 x 2MW Natural Gas driven generators with heat exchangers on the Engine Exhaust Gases to provide hot water for general consumption, and as a source of heat for one of the two Chillers. Engine Jacket Water heat exchangers also provide source heat energy for the second Chiller.

Beckhoff PLC’s with Ethercat I/O.

AIEglobal used Beckhoff CX2020 PLC’s for the automation of each Genset, Hot Water Reticulation, and overall plant control including HV substation circuit breaker switching.



Each Generator has a separate heat exchanger system for the Engine Turbo and Jacket Water, with high temperature hot water being generated by the Exhaust Gas Boiler. The two pictures above show the Ethercat distributed I/O for each Genset. Having local I/O on each Generator considerably reduced the amount of electrical wiring having to go to the central control room, and reduced the central PLC cabinet size to one 800mm tier. The cost savings of this approach are substantial, and by using Ethercat there is no performance degradation as there is with many other field bus types. The I/O scan time for the four Gensets and central PLC I/O was less than 1 msec. 

Modbus RTU control of VSD’s


There were over thirty variable speed drives on pumps and fans all controlled by ten Modbus RTU serial communication networks. Each Modbus network used an Ethercat EL6021 Modbus master terminal and connected to approximately four VSD’s. This approach kept the RS485 cable runs short, enabled connections based on functionality and consequently achieved the high performance necessary for PID control from the relevant PLC.

Woodward EasyGen and LS5 controllers.


Each Genset’s speed and load sharing control including synchronization on the LV MCC uses a Woodward EasyGen and LS5 controller, with overall control coming from a CX2020 PLC via Modbus/TCP and the Esenet/CAN gateway. Additional LS5’s were used on specific HV circuit breakers when a synchronization point was necessary.


The automation of the Trigeneration project required the use of many different types of communication protocols, the Beckhoff CX2020 PLC with Ethercat I/O proved very powerful in this respect. Listed below are the protocols used and their communication functions.

  • OPCuA – PLC to PLC, and Scada to PLC.
  • TCP/IP – SCADA and PLC remote access.
  • Modbus RTU – PLC to VSD’s, Circuit Breakers, and Energy Meters (Elec and Gas).
  • Modbus TCP – PLC to Gensets, Esenet Gateways, Modbus RTU Gateway, and Sepam Controllers.
  • Mbus – PLC to Gas Energy Meters.
  • DNP3 – PLC to external Rapid Load Shedding controller.
  • BacNet  – Scada to external BMS.


The SCADA system built using InduSoft/Webstudio provided plant operational status, Alarms, trending graphs, and remote Web access for up to 16 users.

Local HMI panels on each PLC provided sectional operational status along with any relevant active alarms.

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