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The system of the parallel operation of diesel gensets (synchronization)

Parallel operation of diesel gensets - electric generation by two or more (up to 32) gensets to the shared load, which is distributed proportionally to their rated power. For a high-voltage diesel genset a control panel, which supports the parallel operation mode is required, and for a diesel genset with a voltage of 0,4 kV – a motor-driven generator circuit breaker is required too.

The advantages of the parallel operation of diesel gensets:

  • Guaranteed start in case of emergency even if one of the gensets will not start;
  • Possibility of expanding capacities by putting new gensets into operation;
  • Optimizing the load dump/rise cycles for every genset by using pre-set rules for loading/ unloading.

Example of a project with the organization of the parallel of three DGs for Rostelekom:

Diesel gensets designed for parallel operation are equipped with a ComAp - InteliCompact NT MINT controller with iAVR unit, which ensures the operation of up to 32 generator units in parallel and implements the load division and optimization of the number of running gensets in parallel operation mode: Download the ComAp operator’s manual

  • Automatic synchronization when connected in parallel and automatic load acceptance during parallel operation of the diesel gensets;
  • Automatic, proportional distribution of the active load between the diesel gensets of different power with an accuracy of 10% of the rated power of the smaller unit;
  • Automatic maintenance of the rated speed and output voltage of generators throughout the load range;
  • Smooth DG unloading when quitting from the parallel operation.

Download quotation for 3 DG Cummins 800 kW in parallel>>>

Options for organizing the parallel system of generators:

Backup source: short-term parallel with the mains. When the mains fails, a DG auto-starts. The automatic circuit breaker turns off. The DG automatic switch turns on. The load is powered by the running DG. After the restoration of the mains, the DG control panel checks the parameters of the mains voltage for compliance with the norm.

Long-term parallel with the mains. A single DG with auto-start operates in parallel with the mains and is used at a limited power of the mains. When the power consumed by the network is exceeded, the DG automatically starts. When the load power decreases (mains power is sufficient for a normal load operation, DG is not needed), the output current of DG gradually decreases to 0.

Backup source without parallel with the mains. In case of mains failure, the automatic circuit breaker of the mains in the ATS turns off and all DGs automatically start. As the DGs synchronize with each other, the circuit breakers AVG1, AVG2 switch on. If the power consumption of the load can be provided by a smaller number of DGs, then the DG is automatically unloaded, its automatic circuit breaker is turned off, cooled down, and stopped. When the power consumed by the load increases, the DG automatically starts, synchronizes with the group, closes its circuit breaker, and connects to the load. When the mains is restored in the ATS, the automatic switch is turned off and the automatic switch of the mains is turned on, the load is switched to mains power.

Expanding capacities, long parallel with the mains. DG with automatic start work on standby with the mains as an additional or main electricity source (power export). If the mains fails or there is a lack of power from the mains control unit, all DGs auto-start and they work in parallel with the mains.

DG as the main electrical power source (no mains). All gensets start in manual mode (from the control panel). When necessary, one or more DGs turn off. All DGs are stopped by the cancel of the START/STOP command, in doing so, the general generator circuit breaker turns off the load.

The examples of backup power supply systems based on parallelly operating diesel gensets:

  • DGs synchronized with the mains;
  • DGs with power control depending on load;
  • Mobile diesel generators;
  • Back-up parallel system for the uninterruptible power supply of consumers of the 1st reliability category.

Request the calculation for DG parallel operation project budget - write a request to

Video: starting up the DG in parallel

Diesel generator sets: