DG Synchronisation

In this post, we will discuss DG Synchronisation, this post will help you to understand the Synchronisation of DG.

when mains are healthy, both the DG ’s remain in the standby mode.

When mains fails, it is sensed by Line Voltage Monitor (L.V.M.). Starting pulses are given to the Master D.G. Set. After satisfactory starting of the D.G.Set 1, Generator Voltage Monitor (G.V.M.) senses the voltage. If the voltage is healthy, then the closing signal is given to D.G.1 breaker and it is closed.

synchronizing Panel gives corresponding pulses to start load automatically. The load is then sensed by KW (Kilo Watt)transducer in the panel & continuously monitored by PLC (Programmable Logic Controller).

Engine & Alternator parameters are also continuously monitored by a Programmable Logic Controller (P.L.C.) in the Panel. In the case of any fault (e.g. High Cooling Water Temperature, Low Lube Oil Pressure etc), the breaker is tripped & the engine is stopped.

If the load reaches & crosses Approximately 75 % of the rated capacity of the D.G. 1, then starting pulses are given to the second D.G.set by Programmable Logic Controller.

G.V.M. checks the voltage again When D.G.2 starts, the breaker 2 is closed if the voltage is healthy.

Autoload sharing function starts sharing the load between the two D.G.Sets, after closing of the second breaker

The percentage of sharing is directly proportional to their individual capacities.

Since sharing is proportional to their respective capacities, even D.G.sets of different capacities can be synchronized successfully.

DG Synchronisation
DG Synchronisation

D.G.sets continue to run in Synchronization until the load is above 75 % of any one set of D.G.

When the load comes below 75 % of anyone D.G. set, then the automatic signal is given to that D.G. & then it starts taking the full load.

After transferring the total load to one D.G. (on which 75 % load is to be connected), the breaker of the second D.G.is opened. Now one D.G.will take the load.

The second D.G. is then stopped after its cooling period.

When mains are resumed, then the load is transferred to the mains & both the D.G. sets are stopped after their cooling period.

DG Synchronisation
DG Synchronisation

The total Automatic operation has a manual override. In manual mode, the total operation can be performed manually.

Autoload shedding facility can be incorporated by suitable programming of PLC. With this facility, various loads can be brought in or switched off at a particular time or for various intervals.

The function of system protection loop:

A: Protection of machine failure

B: Reverse power protection

C: Protection of over-current and short-circuit D: Protection of over-voltage and low-voltage

E: Protection of over-frequency and low-frequency

F: Protection of emergency shut down

G: Protection of positive power monitoring


Changing of logic is very easy because of the changes are made through software only. There is no changing of wires, adding of components like contractors, relays which is very time consuming, cumbersome & requiring additional space.

For any type of load addition or reduction, manual intervention as regards D.G.set operation is not required. However, in case of emergency manual override is possible.

Because of KW dependent load sharing, optimum utilization of D.G. sets are possible. This increases D.G. sets efficiency & saves a lot of fuel.

Use of PLC reduces no. of relays, wiring, contractors, etc. This reduces fault points & increases the MTBF of the system.


     Advantages of the parallel operation system

  1. Two or more sets of generators in parallel operation are equal to one set of large power generator to supply the power the load and can balance the load over various circuits and supplement the peak to valley mutually, and can decide how many sets should be started according to the load level (when the sets are in the operating condition by 75% of the rated load, the fuel consumption is minimum) so as to save the diesel and reduce the generating.
  2. The uninterrupted power supply (UPS), the operation exchange among the generator sets can be actualized to ensure the normal production of the plants; when the sets are converting, the standby generator sets can be merged into the operation system; after all the load can be transferred to the standby sets that are already running, the former operating sets can stop, during which it no need to cut off the power.
  3. When two or more sets are in parallel operation and the load increases all of a sudden, the two or more sets can share the current impact evenly, therefore, the mutual aid and mutual supplement of the load and the among each set have higher shock resistance to reduce the impact of each set; under the situation of larger load impact, two or more sets in parallel operation can bear larger impact than that on the single set, at the same time, two sets in parallel operation can stabilize the voltage and the frequency and prolong the service life of the generator.
  4. Whether the single set operation or the dual sets in parallel operation can be decided according to the different amount of electricity utilization so as to avoid the waste caused by the load operation of two or more sets and the risk of the single set operating under overloading.

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