arc quenching&ups synchronisation

[saltukhan]

hello, i have two question:
1-How a sf6 circuit breaker can catch the zero current to extinguish an arc ? is there a sensing device or this is a natural consequence of a mechanism designed?
2- is there any application such as parallel operation of ups with utility? i just ask due to curiosity , a think-tank perhaps, is it possible that a ups will take an a.c wave and after ac-dc-ac conversion its output will be the same with the original wave and both of them will supply a load and when the utility is gone ups will take over all the load without interruption? if there is no such an application is it possible ? might it be any obstacle that ups and utility have largely different internal impedances concerning the load sharing ?

 

[GenSwgrEng]

With regards to question 2, it is possible to parallel a UPS output with the utility. UPSs very often stay in sync with the utility anyway, so that they can do a perform an overlapping maintenance- or emergency-bypass. And UPS outputs can be controlled to allow for sharing load with another source.

That said, it is not advisible or desirable to run in parallel with the utility, and I doubt any UPS manufacturer would allow it. The reason you have a UPS is that you want to isolate your loads from any problems on the utility. If the utility experiences glitch while you're in parallel, the glitch can affect your load before you can isolate. If your load is strictly on the inverter, it will never see the glitch.

Finally, you have no reason to operate in a parallel-to-utility state. If your UPS can carry your critical load, there is no reason to parallel to the utility. If the UPS is not big enough for your load, a loss of utility would overload the UPS.

 

[raithrovers1]

I can't see why anyone would want to run the output of a UPS and the utility supply in parallel.
The sole purpose of most UPS systems is to provide power to critical loads that will not tolerate any form of power interruption (brown outs, sags, total loss of utility etc).
There is no advantage whatsoever of running an inverter in parallel with the utility. As the inverter is a synthetic electronically generated sine wave there will always be points in time where the inverter will be slightly out of phase with the utility causing large unwanted circulating current. This will either damage the UPS or take out upstream breakers.

UPS engineer

http://www.calibrepower.co.uk

 

[raithrovers1]

I have just read your thread again and maybe didn't pick up on exactly what you are asking.
In most situations a UPS has AC-DC-AC conversion as you have stated. It also synchronises its output to the utility supply which is usually called the reserve or bypass supply.
In normal operation the load output is fed from the UPS via the inverter with battery back up to protect the load from any interruption. This inverter supply is always in synch with the bypass supply (utility). If the inverter fails within the UPS then a static switch will transfer the load to the bypass supply without any interruption.
Hope this helps.

UPS engineer

http://www.calibrepower.co.uk

 

[Zogzog]

An SF6 breaker does not "catch zero current", the SF6 gas quenches the arc that ocurs when current interuption occurs.

 

[ruggedscot]

Running a UPS in parallel with the supply is not a good move as this can cause issues with the UPS when there is a power failure the back feed can confuse the UPS as it sees a healthy supply which is being created from the UPS output. This can lead to a destabilised output that would wreck havoc with the protected load before the UPS was able to do its protection.

 

[Boof87]

It can be done but for it to happen the unit would have to run in static bypass with the inverter acting as an active filter, there are a few manufacturers that do this. It wouldn't be advisable to run the inverter online and in parallel with mains supply as the units have programmable outputs and there would be a P.D between the inverter output and mains and you would end up blowing the power module.

 

[m3ntosan]

saltukhan,

1 - there are switching control devices also known as Controlled point-on-wave switching devices used for independent pole operated CB.

Please find below some details for ABB SCS


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