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During a succeed automatic reclose on 400 kV line, one of our unit tripped on excitation fail. The other similar unit with GE EX2000 excitation didn't tripped with no alarms on the generator. After we analyzed the alarms on the excitation HMI and generator/transformers protections, we found that the excitation tripped as a consequence of generator and gsu transformers protection trip signal. Now the big problem is that neither of the generator and gsu transformers protections started off/tripped (all protection are latched). We had only one alarm,generator negative sequence, but without achieving the trip threshold. We tested all the generator/transformer protection and they worked properly staying latched after a trip. The problem is that about 6 months ago the excitation was replaced with GE EX2100e so we suspect that is something wrong with it. With the old excitation system we've seen worse grid disturbance (failed reclose) without unit tripping. The trip loop is galvanic separated (optocoupler) so we ruled out induced current theory. Our main concern is that we don't have an explanation on what happened there and in case of a grid disturbance the unit will trip again.
Have you ever encountered something similar?
Best regards.
Have you ever encountered something similar?
Best regards.
