Explain negative phase sequence protection of alternator.

Explain negative phase sequence protection of alternator.
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Negative phase sequence protection of alternator: Unbalanced loading on alternator mainly causes the negative sequence currents which generate the negative sequence components of magnetic fields. These fields rotate in opposite direction of the main field and induce emfs of double frequency in rotor winding causing overheating. Figure shows a scheme for protection against negative phase sequence currents. Three CT’s are connected in star and the secondaries are connected to negative sequence filter. The relay is connected to sequence filter. The negative sequence filters consists of number of inductors and resistors. This negative sequence filter detects the presence of negative sequence components due to unbalance and operates the relay which further operates CB.

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