How to Synchronize Generators on a Ship?

Synchronizing of an incoming generator or alternator is very important before paralleling it with another generator. The synchronizing of the generator is done with the help of synchroscope or with three bulb method in case of emergency. It is of utmost importance that before paralleling the generators the frequency and voltage of the generators need to be matched. In this article we will describe the method for synchronizing generators on a ship.

There are two methods to synchronize generators on a ship – one is the normal and other is the emergency method.

Synchroscope method



  1. Ÿ  The synchroscope consists of a small motor with coils on the two poles connected across two phases. Let’s say it is connected in red and yellow phases of the incoming machine and armature windings supplied from red and yellow phases from the switchboard bus bars.
  2. Ÿ   The bus bar circuit consists of an inductance and resistance connected in parallel.
  3. Ÿ  The inductor circuit has the delaying current effect by 90 degrees relative to current in resistance.
  4. Ÿ  These dual currents are fed into the synchroscope with the help of slip rings to the armature windings which produces a rotating magnetic field.
  5. Ÿ  The polarity of the poles will change alternatively in north/south direction with changes in red and yellow phases of the incoming machine.
  6. Ÿ  The rotating field will react with the poles by turning the rotor either in clockwise or anticlockwise direction.
  7. Ÿ  If the rotor is moving in clockwise direction this means that the incoming machine is running faster than the bus bar and slower when running in anticlockwise direction.
  8. Ÿ  Generally, it is preferred to adjust the alternator speed slightly higher, which will move the pointer on synchroscope is in clockwise direction.
  9. Ÿ  The breaker is closed just before the pointer reaches 12 o clock position, at which the incoming machine is in phase with the bus bar
 Emergency synchronizing lamps or three bulb method


This method is generally used when there is a failure of synchroscope. In case of failure a standby method should be available to synchronize the alternator, and thus the emergency lamp method is used.

Three lamps should be connected between three phases of the bus bar and the incoming generator should be connected as shown in the diagram:-

  1. Ÿ  The lamps are connected only in this manner because if they are connected across, the same phase lamps will go on and off together when the incoming machine is out of phase with the switchboard .
  2. Ÿ  In this method as per the diagram the two lamps will be bright and one lamp will be dark when incoming machine is coming in phase with the bus bar.
  3. Ÿ  The movement of these bright and dark lamps indicates whether the incoming machine is running faster or slower.
  4. Ÿ  For e.g. there is a moment when lamp A will be dark and lamp B & C will be bright, similarly there will be instance when B is dark and others are bright and C is dark and other two are bright. This example indicates that machine is running fast and the  movement of the lamps from dark and bright gives an clockwise movement
  5. Ÿ  Clockwise movement indicates fast and  anti clockwise direction indicates slow running of incoming generator.

You may also like to read: Green source of power-Shaft generator.

References and Image Credits: marine electrical equipment and practice by H.D Mcgeorge, generator arrangement –

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  1. raunekk says

    We update our website regularly. Just surf around and you will find loads of useful information. Also, please do let us know if there is anything specific you will like to read on and we will get it published for you.


  2. rolfox78 says

    @runekk, good stuff! nice description of synchronizing a ship’s generator..not mentioning the “auto-synchronizing”,(as i experienced) nowadays operators explicitly dependent on this auto-mode, However; when auto-mode fail they forget the BASIC, as when the vessel is underway at critically heavy traffic, channelling, etc where electrical power is very important – that may lead to catastrophic events. no offend.

  3. sudipto ghosh says

    very nice website.i’ll be grateful to this site.this is very beneficial for marine students..a lot of thanks………..

  4. Wai lin says

    Excellent website. Please supply more pictures and movies. So we can easily do it onboard.

  5. Wai Lin says

    Excellent web page.

    Actually we close the breaker before 12 o’clock (10 or 11 o’clock) for human delay. And incoming generator should also have a frequency a bit higher than running generator so that incoming generator can take load.

    For detail synchronizing procedures, please refer to videotel series generator movie.

  6. jgheisari says

    Im going up for my MCA orals exam in a couple of weeks and this site has been a big help….thanks

  7. anuaplcoral says

    relay helpful this one for our knowledge.plz can somebody explain me what will happens if we give the load for incoming generator when the synchronizer on six “o” clock position.

  8. Peter says

    I would like some info on how & why three air conditioning compressors should be stage on start up & shut down

  9. Njabulo sithole says

    thnks but i have a question….Why is it unsafe to close the breaker of an incoming generator if the voltage is not the same as in the main board??? and what would happen if you do????


  10. Sundararajan says

    Can anyone explain how to test a Paralleling Impulse Transmitter (PIG 21)


  11. Marcos says

    Hi fellows
    I’ve a question regarding governors. On board, the governors work in speed droop mode or isochronous mode?
    Isochronous mode would be my answer, controlled by a load sharing device
    Let me know if I’m wrong


  12. trutsky says

    reunekk, thanks for your useful website, make me read more about engineering electricals. kindly educate me on this isssues. differente bt insulated neutral and earthed neutral distribution system.
    2- which is used most on ship and why?

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