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Automatic Generator Changeover Controller

6KW Back-Up Generator  for essential services.


Our Zelio PLC generic generator automation program provided the basis for the automation project. We added additional Modbus RTU programming for communication over the network to an HMI, which was networked to enable remote monitoring and control over the ethernet.  Fuel and enclosure temperatures can be monitored locally and remotely. Safety features include a high temperature alarm will stop the  generator and auto restart when the temperature is within operating ranges. A failed generator start, low fuel or low oil alarms will also stop the generator and ensures the generator doesn't incur  mechanical damage and prevents the batteries from running  flat.

We used two mechanically interlocking   mains pole contactors that prohibited the energization of both supplies simultaneously. The Zelio generator logic programming also prohibits this as an added safety feature. A local generator mechanical E-Stop button was installed and wired into both the PLC logic input and generator run circuit. An additional HMI E-Stop was programmed into the Zelio logic.

Off the grid solar panels provide the required charging of the batteries during daylight hours. Two ventilation fans are ducted into the enclosure and run continuously off the generator supply. An "On-Line" UPS was installed to provide uninterrupted power to the server.


A compressed air purge of the enclosure is performed prior to the generator starting to purge any fuel vapour that may be present.

Generator HMI contol and communication HMI panel

HMI panel control

Generator  fuel and temperature trending on our HMI panel

HMI panel fuel + temperature trends


LOCATION: Lake Tarawera - Rotorua 
PROJECT: Generator Remote Changeover


Provide automation and remote access to a back-up generator system providing essential services. The criteria included:

1) Uninterrupted power to the server. 

2) Automatic monitoring and change over between mains and generator power supplies (should the need arise to perform a remote change over  and start/stop).

3) Independent charging for the generator battery packs.

Testing the generator  PLCprogramming logic on our test rig  prior to installation.

End product  in operation - generator HMI 

Generator  first test run


Schneider Zelio SR3B101BD PLC controller with Modbus and an analog card are used for generator automation.

PT100 temperature probe is used for the enclosure temperature control.

IFM fuel level sender is used in the fuel tank.


AEG AC1030S air compressor provides the air purge.

2 x 150mm In-Line ducted fans provide the enclosure cooling.


Schneider HMI-STU855 HMI provides the end user interaction and remote access capability.


Powershield 3KW UPS provides the uninterrupted changeover of power for the server.

Generator Control and Remote Monitoring

HMI panel operational trends

Generator Automatic Automation and start-up HMI control Panel

AEG 6KW Generator Enclosure

Generator UPS Server for Uninterupted Power Supply during changeover

UPS Server Panel

Generator Backup

AEG 6KW Single Phase Generator

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