An alternator is being synchronised to the power station bus bars whose frequency is 50 Hz. If the bulb of the synchroscope glows with maximum brightness, the frequency of the alternator is:

An alternator is being synchronised to the power station bus bars whose frequency is 50 Hz. If the bulb of the synchroscope glows with maximum brightness, the frequency of the alternator is: Correct Answer 50 Hz

Synchronosope method:

• It is similar to two bright dark lamp method and indicates whether the alternator frequency is higher or lower than two bar frequency
• A synchroscope is used for better accruing of synchronization and it consists of two points of terminals.
• One pair of terminal marked as ‘existing’ has to be connected cross two bars terminal or to the existing alternator and other pair of terminal marked as incoming has to be connected across the terminals of an incoming alternator.
• The synchronoscope has circular dial over which a pointer is hinged that is capable of rotating in clockwise and anti-clockwise directions.
• After the voltage condition is checked, the operator has to check the synchronoscope.
• The rate at which the pointer rotates indicator the difference of frequency between the incoming alternator and the two bar.
• The direction to which the pointer rotates (to either fast or slow) gives the information, whether the incoming alternator frequency is higher or lower than the two bar frequency and hence the pointer moves either fast or slow.
• The appropriate correction has to be made to control the speed of the alternator to bring the rate of rotation of pointer as small as possible.

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• The alternator provides the two-phase supply to the synchronoscope.
• If any of the two phases of the machine are synchronized, then the third phase was automatically being synchronized.
• When the difference in frequencies is maximum then the bulb will glow minimum (minimum brightness)
• Similarly when the difference in frequencies is minimum then the bulb of synchronoscope will glow with maximum brightness.
• Therefore according to the question, if an alternator is being synchronized to the power station has bars whose frequency is 50 Hz, and if the bulb of synchronoscope glows with maximum brightness, the frequency of the alternator will be 50 Hz (or ≈ 50 Hz)