Parallel Operation Procedure for Marine Diesel Generators

 In order to operate two generator in parallel we need to synchronize the alternators. The following conditions must be fulfilled to make the generator synchronized.
> Incoming generator voltage is almost equal to the bus bar voltage.
> The incoming generator frequency is equal to or slightly higher than the bus bar frequency
> The generator voltage is in phase in opposition to the bus bar voltage

Paralleling of alternators can be done in three method
> Synchroscope Method 
> Three Lamp Method
> Voltmeter method

Synchroscope: A synchroscope is a device that indicates the degree to which two systems are synchronized with each other.
> Synchroscopes measure and display the frequency difference and phase angle between two power systems
> 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

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Three Lamp Method or Emergency synchronizing (synchroscope is out of order)
   This method is used when there is a failure of the synchroscope. 
> Three lamps should be connected between three phases of the bus bar
> The two lamps will be bright and one lamp will be dark when incoming machine is coming in phase with the bus bar
> The movement of these bright and dark lamps indicates whether the incoming machine is running faster or slower
> For e.g. there is a moment when lamp A will be dark and lamp B & C will be bright, similarly there will be instances 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
> Clockwise movement indicates fast and  anti clockwise direction indicates slow running of incoming generator.

Voltmeter method
> Connect voltmeter as shown in fig.
> Check circuit diagram before such testing
> Adjust generator speed until voltmeter very slowly move from zero to maximum and close the breakup when the voltmeter indication passes through zero

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