- The synchroscope works based on AC motor in principle.
- It has two poles connected across any two phases (say red and yellow) of the incoming machine.
- The armature windings are supplied from the similar two phases (red and yellow) in the switch board bus - bars.
- The armature consists of two parallel windings.
- A resistance is connected in series with one half winding.
- An inductance is connected in series with the other half winding as shown.
- The inductance is provided to shift the current flow through itself by 90° related to current in resistance provided.
- These currents are fed to the two armature windings.
- They produce in them rotating magnetic field in combination with the field in the pole.
- The polarity of the poles will alternate north south according to changes in red and yellow phases of the incoming machine.
- The rotating field will react with the poles and rotate the rotor clockwise or anticlockwise.
- Simultaneously synchroscope pointer rotates.
- The rotation of direction of the synchroscope pointer is determined by the speed or frequency of the incoming machine.
- If the pointer rotates in anticlockwise direction, it means that the frequency e of the incoming machine is less.
- If the point rotates in clockwise direction, it means the frequency of the incoming machine is more.
- Command to close the incoming alternator breaker is given at about 11 o'clock position, when and the pointer is rotating in the clockwise direction.
- Command to close the incoming alternator breaker is given at about 10 o'clock position, when the pointer is rotating in the anticlockwise direction.
- This will make the machine getting connected to busbars exactly when the pointer reaches the 12 o'clock position of the synchroscope.
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