Please help with this. I have a generator which I loaded in parallel with other generators. I noticed that the power factor became exactly one and after a while leading.

The other two generators had a power factor of 0.5 about. Can there be a damage to the windings of the generators if I make more attempts to synchronise the leading generator in order to adjust the AVR?

It is a 6.7 KV power grid. Please don't mind the naive question I am an engineer and not an electrician ( In a ship in pacific ocean)

  • 3
    \$\begingroup\$ 0.5 pf is too low for your other generators. Odds are third generator is attempting to compensate for that. \$\endgroup\$ Nov 21, 2021 at 7:00
  • \$\begingroup\$ I am nowhere around the power grid, my weak point. :) For me to learn, and to help you getting any useful advice; you can share the setup information, like any drawings, model numbers, referencing webpages, manufacturer, etc. \$\endgroup\$
    – jay
    Nov 24, 2021 at 14:54
  • \$\begingroup\$ What is the size of your 3 generators? 6.6kV bus? What is the kW, kVAR load the generators are driving. Before and after 3rd is brought online. What is the type of load being driven? Propulsion? Has there been any recent maintenance on generators/large loads? \$\endgroup\$ Nov 26, 2021 at 20:19
  • 2
    \$\begingroup\$ To get any answer you are going to have to provide a lot more information than you have up to now. And at 6.6kV, if you do not know what you are doing, you could cause a lot of damage and injury. \$\endgroup\$ Nov 26, 2021 at 20:31

3 Answers 3


If the generators are connected in parallel but have differing power factors, this is ultimately due to uneven load-sharing between them. The overall power factor depends on the load of course, but generators in parallel won't necessarily share equal parts of the complex/apparent power.

In your case, one generator sounds like it is driving almost none of the reactive component of the load, while the other two generators are splitting the reactive component of the load between just the two of them.

This causes more or less slip of the rotor, so this is likely the cause of the slight leading.

I do not think this is a synchronization problem. Rather, you need to adjust the excitation current for the generators, as this is what determines the proportion of VARs each generator is driving. This will also eliminate the lead/lag between the generators as a result.

  • \$\begingroup\$ Thank you. I guess that this slip of the rotor will cause mechanical stress to the rotor and the prime mover? \$\endgroup\$ Nov 27, 2021 at 21:31

There's alot of information missing... it would be great if you add specifics to your question: setup schematic, model numbers, etc.

However, there may be some value in some general information wrt this type of question...

If we're talking three-phase power generation, connected to a bus bar; then a key aspect of operation is to ensure proper synchronization of the generators as you add them to the power grid:

  • for generators to share equal loads they must be identical in most aspects ... note: once synchronized they must share the total load according to their individual capacity and will not be equal otherwise (so in regards to your specific question, are the two other generators twice the size of the first?, if not I agree with @StainlessSteelRat)
  • ensure both the running generator (i.e. the first one) & incoming generator are operating with the incoming generator connected to the bus bar, but not yet being electrically connected (usu via a breaker/switch) so that the incoming generator is warmed up and operating at the same frequency & voltage as the bus bar
  • Use one of two methods to ensure proper synchronization: a Synchroscope or the Lamp Method
  • After synchronization is achieved, then make the incoming generator connection to the live circuit

Power-sharing relative to power capacity depends on voltage/current = Z matching and operating frequency. The source impedance of each generator can be lowest at Po.max/V^2=Zs=R+jX.

  • you can share equal loads or choose to share equal % capacity by controlling current.

  • Load regulation error is the ratio of Zs/Zload which can affect voltage and pf if each gen. sharing same loads has a different Zs.

  • tuning is a matter of choice of specs for VA/(|VAR|+VA) = pf and load regulation error. VAR can be + or - j

  • Define how much thermal margin you want and the power-factor correction you need if any and how to do that.

  • Avoid excess reactive currents in winding losses.


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