Generator protection using differential protection schemes

                                 Figure : Stator biased differential protection for generator

To protect the generator against the failure of winding insulation and the failure of the field circuit as well as the primemover failures, differential protection is used with biased circulating current scheme. The theory of circulating current differential protection is discussed fully in part 7. The protection scheme is shown in Fig.1.Normally differential protection is used for generators larger than or equal to 20MW.

                                                              

                                                         Figure 2 

shows a biased percentage differential relay applied for the protection of synchronous generator windings. The relay has 0.1A minimum pick up current and a 10 %.

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