We have a GE 7H2 generator and have been changing out brushes every 6 months during our seasonal outages. The electricians does not feel comfortable changing brushes online and are a baseload unit. Is your site brave enough to change brushes out online or do you wait for a shutdown? Also what is the frequency? We run at high lagging MVARS, near the OEL limit which really shortens the life of the brushes.

These brushes were designed to be replaced online. There is a clear indicator that the spring is no longer seating the brush, replace prior to this on a daily basis whenever noted.

Also brush changes should be an operation dept task, incorporated into daily rounds.

we have the same Model and doing online ofcause. nearly the same frequency ofr every brushes, but some are even faster. we have replaced old model brushes that are with plastic roller by new design, since they easily hang up when over heated. still the new design give some problems, specially over heating of prussure springs that leads less performance and dis engage the brush from operation/ hang up.

atleast once in every month we open the comparment cover for online maintenance, operation routine check it visually every day each shift, since its so critical and recently we have a bad experience of flash over in another plant of us. changing brushes online is practical and require more experience to feel comfortable. during shutdown a good maintenance is possible.

razeen
KSA

There have been some explosion issues with carbon dust buildup in the compartment as well. While changing brushes on line is pretty standard, I would clean the compartment of dust at least annually to prevent this.

another question to add, how often do you change the shaft grounding brush? does anyone even inspect it on a regular basis?

Hi

we inspect the grounding and excitation brushes once weekly, we change it according to its thickness, and we change the excitation brushes at base load (up to 250 MW) but with one brush at time, if we removed two brushes at the same time the generator will trip.

siemens generator (50 Hz - 16.5 KV)
Excitation voltage = 255 VDC

we normally go for inspection for grounding brushes every 3 months during offline water wash shutdown, further more if there will be any alarm for shaft voltage, its attended imediately. some times only cleaning of the shaft by cleaner spray after removal of brushes when rotating also has given good results.