Generator synchronisation
How several generators become one power plant: the three conditions that must match before a breaker closes, how load is shared, and what it means for redundancy.
What is generator synchronisation?
Generator synchronisation is the process of matching an incoming generator to a live bus in voltage, frequency and phase angle, then closing its breaker at the right instant. Once connected, the generators run in parallel as one source and share the load.
Which conditions must match before generators connect?
Three: voltage magnitude, frequency and phase angle. Phase sequence (rotation) must also be correct, which is checked once at installation.
| Condition | What is compared | If it is wrong |
|---|---|---|
| Voltage | Incoming generator voltage vs bus voltage | Reactive current flows between the machines |
| Frequency | Speed difference (slip) between generator and bus | The incoming unit is motored or suddenly loaded |
| Phase angle | Angle between the two voltage waveforms at the moment of closing | Current and torque surge; possible damage and tripping |
| Phase sequence | L1-L2-L3 rotation | Severe fault; checked at installation and after any cable change |
How does an automatic synchronising sequence run?
The controller starts the engine, brings it to speed and voltage, trims it until frequency, voltage and phase match the bus, closes the breaker, then ramps the unit up to its share of the load.
- StartEngine starts, reaches rated speed
- ExciteAlternator builds voltage
- MatchSpeed and voltage trimmed to the bus
- CloseBreaker closes inside the phase window
- ShareUnit ramps to its share of kW and kvar
How is load shared between generators on a common bus?
Real power (kW) is shared by controlling each engine's fuel; reactive power (kvar) is shared by controlling each alternator's excitation. A power management system also starts and stops modules as demand changes, keeping the running units in an efficient load range.
How does SINTAQA use synchronisation?
Every SINTAQA 1,250 kVA module has a digital controller with synchronising capability. Modules are linked through synchronising controllers and a power management system, share load automatically and run in parallel on a common bus, which is how single modules become multi-megawatt plants with N+1 redundancy.
Synchronisation FAQ
What is generator synchronisation?
Matching an incoming generator's voltage, frequency and phase angle to a live bus (or another generator) before its breaker closes, so the two sources can run in parallel without a damaging current surge.
What happens if generators are connected out of phase?
Closing a breaker with a large phase difference forces a sudden surge of current and torque between the machines. It can trip protection, damage couplings, windings and breakers, and cause a blackout. Synchronising controllers and check-synchronising relays prevent it.
How do synchronised generators share load?
The controllers adjust each engine's fuel (for real power, kW) and each alternator's excitation (for reactive power, kvar) so the units carry the load in proportion to their ratings. Identical modules therefore share load equally.
Can different generator sizes run in parallel?
Yes, with compatible controllers, but load then shares in proportion to rating. Plants built from identical modules, such as SINTAQA's 1,250 kVA units, are simpler to control, maintain and expand.
Can rental generators synchronise with the grid?
Technically yes, but paralleling with a utility network needs the utility's approval, grid protection and a specific study. Most temporary plants run as an island supply or transfer the load without paralleling.
Technical content prepared and reviewed by the SINTAQA Engineering Team, Dubai. Last updated September 2026. Configurations shown are indicative; every project is engineered to its own load, site and standards.
Plan a synchronised power plant
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