We have a large >300MW hydro pump-gen unit where during start up, the EX2100 is exhibiting the following as of recent:

1. Start command given- unit reaches 95% speed - 41 exciter breaker closes - EX2100 begins to excite the field.
2. Voltage builds (gen output reaches ~16KV) - loud audible hum/buzz is heard from the SCR power cabinet (not typical) - the 41 breaker immediately trips open.
3. Attempted a re-start, similar event.
4. Final restart but using 'Exciter Auto Start', unit goes online without issue.
4. No fault codes other than De-Excitation trip on OIT screen.
5. Troubleshooting in progress, diagnostic codes are De-Excitation Trip.The codes relates to check SCR or diodes, Hall Effect transducer, or EDEX board.

Has any site experienced similar and willing to share? I have little experience and lots to learn with checking SCRs on this vintage unit.

Thanks,
Denis

 

For Exciters dont take risks from the public forum.
Will recommend to get in touch with the OEM for better support.

Recently red in news paper [did not disclose the site name ] one site had a flash over damage, when they tried a test based on public form's inputs. Pictures were scarry.
Sad part is, insurance did not cover the damages.

 

We have a large >300MW hydro pump-gen unit where during start up, the EX2100 is exhibiting the following as of recent:

1. Start command given- unit reaches 95% speed - 41 exciter breaker closes - EX2100 begins to excite the field.
2. Voltage builds (gen output reaches ~16KV) - loud audible hum/buzz is heard from the SCR power cabinet (not typical) - the 41 breaker immediately trips open.
3. Attempted a re-start, similar event.
4. Final restart but using 'Exciter Auto Start', unit goes online without issue.
4. No fault codes other than De-Excitation trip on OIT screen.
5. Troubleshooting in progress, diagnostic codes are De-Excitation Trip.The codes relates to check SCR or diodes, Hall Effect transducer, or EDEX board.

Has any site experienced similar and willing to share? I have little experience and lots to learn with checking SCRs on this vintage unit.

Thanks,
Denis

What exactly do you mean by “Exciter Auto Start”, and how does it differ from your “Normal Start”? With Hydro applications there can be many modes of start, so depending on how you start will define which circuits are in use during this initial stage of operation.

 

Denis,

A few thoughts based on what you’re seeing:

• The 41E breaker disconnects the exciter from the generator. If it’s tripping, it’s worth confirming whether you’re actually losing positive DC output at the moment of the event.
• The audible hum could point to a rectifier/SCR issue under load, but it could also be the 41E solenoid coil energizing/de‑energizing. On some units the disconnect is motor‑operated, typically on the positive DC leg.
• Check whether any additional faults are being logged in the background, even briefly.
• Review your startup trends—field voltage, field current, feedback signals, and breaker status—right at the moment the hum occurs.
• I’ve seen cases where the 41E feedback switch became unreliable due to contamination (e.g., coal dust in a thermal plant). Cleaning restored proper feedback and stopped nuisance trips.
• The loud buzz you describe could be the solenoid dropping out, which would explain the immediate breaker opening.

If you need help walking through SCR or diode checks, or interpreting the EX2100 feedback signals, feel free to reach out.

Woody