Parallel operation of Alternators


                The operation of connecting an alternator in parallel with another alternator or with common bus-bars is known as synchronizing. Generally, alternators are used in a power system where they are parallel with many other alternators. It means that the alternator is connected to a live system of constant and constant frequency.

                  Often the electrical system to which the alternator is connected, has already so many alternators and loads connected to it that no matter what power is delivered by the incoming alternator, the voltage and frequency of the system remain the same. In that case, the alternator is said to be connected to infinite bus-bars.

                  It is never advisable to connect a stationary alternator to live bus-bars, because, stator induce being zero, a short-circuit will result. For proper synchronization of alternators, the following three conditions must be satisfied.

  1. The terminal voltage (effective) of the incoming alternator must be the same as bus-bar voltage
  2. The speed of the incoming machine must be such that its frequency (= PN/120) equals bus-bar frequency.
  3. The phase of the alternator voltage must be identical with the phase of the bus-bar Voltage. It means that the switch must be closed at (or very near) the instant the two voltages have relationship. Condition (1) is indicated by a voltmeter, conditions (2) and (3) are indicated by synchronizing lamps or a synchronoscope.


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