Construction
> The synchroscope consists of a small motor with coils on the two poles connected across two phases.
> Suppose it is connected in red and yellow phases of the incoming machine and armature windings supplied from red and yellow phases from the switchboard busbars.
> The bus bar circuit consists of an inductance and resistance connected in parallel.
> The inductor circuit has the delaying current effect by 90 degrees relative to current in resistance.
Working
> These dual currents are fed into the synchroscope with the help of slip rings to the armature windings which produces a rotating magnetic field.
> The polarity of the poles will change alternatively in north/south direction with changes in red and yellow phases of the incoming machine.
> The rotating field will react with the poles by turning the rotor either in clockwise or anticlockwise direction.
> 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.
> Generally, it is preferred to adjust the alternator speed slightly higher, which will move the pointer on the synchroscope in clockwise direction.
> 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