In short. A plant master controller coordinates several generator sets as one power plant. It manages start and stop, sharing, breakers and auxiliaries, but each set keeps its own protection and basic control. The plant should stay safe and share load if the master is lost.
What the master coordinates
- Which sets are available, running, loaded or on standby.
- Start and stop sequences. See sequencing and dispatch.
- Synchronising and breaker closing. See synchronising.
- kW and kVAr sharing.
- Plant auxiliaries: fuel transfer, cooling, ventilation, battery chargers, room dampers.
- Plant alarms and summary status to SCADA.
Architecture options
| Option | Description | Trade-off |
|---|---|---|
| Central master | One controller commands all sets | Simple, but a single point of failure |
| Peer-to-peer | Set controllers communicate and agree | No single master; more tuning |
| Hybrid | Peer sharing with a master for dispatch and reporting | Common in practice |
Plant states
Define states such as Stopped, Standby ready, Starting, Synchronising, Running on load, Shedding, Restoring, Fault and Maintenance. Each has entry conditions and permitted actions. See state machines.
Auxiliary readiness
A set that is mechanically ready but has no fuel transfer, no cooling air or a flat starting battery is not available. Include auxiliary status in availability logic. Starting battery state in particular should be monitored, because a failed start system means zero capacity.
Alarms and events
Group alarms into plant-level and set-level. Provide a clear first-out indication so operators see the initial cause. See alarm rationalisation.
Illustrative example
A four-set plant has a master controller. A fuel-transfer pump fault leaves one set’s day tank low. The master marks that set unavailable for the next dispatch, raises a plant alarm with the cause, and dispatches another set instead, so a failed start is avoided.
The plant master as conductor
A generator plant master control coordinates individual set controllers so the plant behaves as one system: it receives a plant-level demand and decides which sets run, at what load.
| Level | Function |
|---|---|
| Set controller | Engine and alternator protection, governor and AVR interface, synchronising |
| Plant master | Dispatch, sequencing, bus and breaker coordination, load shedding |
| Supervisory | Operator interface, alarms, history |
Core plant master responsibilities
- Establish the bus on a mains failure: the first set to reach healthy voltage closes to the dead bus; others synchronise.
- Pick the lead and standby sequence, rotating to balance run hours.
- Ramp load onto the plant in steps that match engine capability.
- Manage the tie to the utility.
Failure handling
If the plant master fails, each set controller must hold its last state or fall back to droop sharing. The plant should not black out because a supervisory device failed.
Parameters to document
| Parameter | Example |
|---|---|
| Start-up delay per set | Seconds from start to breaker closure |
| Step size | Percent of rating per load step |
| Minimum run time | Minutes before auto-stop |
| Fail-to-start timeout | Seconds before the next set is called |
See multi-DG sequencing and PMS architecture.
The master engineering question
Does the master know which sets can truly carry load right now, including their auxiliaries, and what does each set do on its own if the master stops?
What to send us
Send the plant layout, set data and auxiliary list. Send your application details.
Questions engineers ask
Do identical sets simplify control?
Yes. Mixed sets are possible but need more careful sharing and dispatch rules.
Should the master also control fuel?
It should at least monitor fuel and auxiliary availability.
What about remote operation?
Allow with authority rules. See control philosophy.
Can the master be replaced later?
If interfaces are standard, yes.
This guide gives general principles. Confirm with a project design.