SF6 and vacum breakers 2

[ahmadnece]

what is the differnce in costs ,operation and maintenance ?

 

[RalphChristie]

If you do a search on this site, you'll find a lot of info regarding SF6 vs vacuum. Both have advantages and disadvantages, however it will be difficult to answer your question in full, because it will depend on the voltage level, the kind of load and the age of the equipment you are going to feed.

advantages of SF6:
Softer switching than vacuum breakers, meaning that less pronounced voltage peaks are caused when interrupting large currents.
Suitable for voltages up to 66kV for metal-clad switchgear and 800kV for GIS
SF6 gas pressure can be easily monitored
Insulating medium present no fire/explosion hazard.
disadvantages of SF6
Depositories formed during switching limit the number of achievable operations before maintenance/refurbishment is required
More expensive than other types of switchgear.
Not environment friendly
May pose a health risk to human beings in that it may cause suffocation to unaware workers (if it leaks)

advantages of vacuum:
Due to virtually no depositories being formed during the breaking operation, vacuum support a large number of operations
More compact than other breakers
Vacuum bottles are relatively inexpensive and easy to replace.
disadvantages of vacuum:
Tendency to cause voltage spikes when interrupting large currents.
No practical method available at this stage to monitor the vacuum inside the bottle
Generally limited to voltages of up to 36kV.

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[cuky2000]

For MV application, VCB is preferred over SF6 because cost, reliability, comparable performance with SF6 and not potential risk of contamination.

In HV application above 38 kV, SF6 virtually dominating the interrupting technology today.

Here is more about comparison between SF6 and vacuum interrupters.

http://www.panickker.net/article6.htm

 

[khadisa]

RalphCristie have mentioned most of the differences, but in my place, where the breakers are operated quite often, we find the Sf6 breakers more suitable. We always have a gas density monitor and alarm. It can easily be refilled.

 

[cuky2000]

Khadisa,

How often the breaker is operated?

Based on several CB performance reports, the number of Closed-Open operations favors the VCB over the SF6 counterpart.

Probably the concern of vacuum monitor referred in your post is magnified from previous reports in old VCB designed in early 60’s. Appears this is not longer a problem since the failure rate of today's VCB is so low that loss of vacuum made difficult to justify its development.

 

[khadisa]

Sometimes it is operated 4 to 5 times in a day due to fault or load shedding.

 

[cuky2000]

Switching 4 to 5 times in a day appear to be an excessive operation duty.

Did you check with the manufacturer to verify this operation mode?