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Negative sequence current appears due to unbalance in the network. This unbalance can be caused by unbalanced loads, a loss of a phase or a phase to earth fault. Unbalance protection relays are mostly applied to protect induction motors. An unbalance protection is a part of circuit breaker in Vision.

 

 

The tripping characteristic can be defined in the same manner as for the current protection. The only difference is that the unbalance protection relay operates based on the negative sequence component of the current (I2) instead of the positive sequence for the current protection.