Answer / aditya

over frequency occurs when the RPM of prime mover goes above the rated speed. This protection is basically for prime mover and gives a trip signal to the prime mover in case of overspeed so that the centrifugal forces dont damage the prime mover and alternator rotor. This is generally a result of faulty speed governor or sudden throw off or throw in of large magnitude. In addition overspeeding will also result in increase of supply frequency. certian electronic equipments are very sensitive to freq and get damaged hence over freq protection is given.

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