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
Must Read>
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
