Circuit breakers withstand S.C current & no. of operations?

[safy2004]

We intend to use switchgears with vacuum circuit breakers to supply power to new project but in some sites in this project there is need to cut and supply the power for many times in one day, the operating voltage is 11 kV. My question is what is the relation between the withstand short circuit current and the number of operations?
For how many times of operations can the vacuum circuit breakers work without any troubles? And what is the withstand short circuit current after 5000 operations if it is at the beginning 31.5 kA for example!
Regards,

 

[waross]

Will you be making and breaking normal load current or short circuit current several times a day?
respectfully

 

[safy2004]

Thanks, waross for your attention!
At one day for several times(about 10) the same circuit breaker will be closed and opened, some times at the normal load, and others at short circuit current, we expect 1/20 of the operations will be at short circuit current.

 

[jghrist]

The circuit breaker manufacturer can provide breaker maintenance information that lists the number of operations permitted for a given current interruption level. Many numerical relays can use this data to monitor the breaker condition and alarm when maintenance is required.

 

[waross]

My experience is with older mechanical breakers.
Typically the mean time between failures for normal currents is/was quite high. The breakers were in some instances used for motor starting with no problems.
However, the number of operations at short circuit current for some breakers was quite limited. The number of allowable interruptions of short circuit current for some breakers was less than 10. Some breakers were only rated for one interruption of short circuit current and inspection and possible rebuild was required after any interruption of short circuit current.
I know that this is not applicable to vacuum breakers, but it illustrates the difference between interrupting normal current and interrupting short circuit current.
Check your literature to determine if there is any limit for the number of short circuit operations.
Hopefully someone with current experience with vacuum breakers will add some contrasting information.
respectfully

 

[dpc]

The ANSI C37 standards give required operations and required fault clearing operations, I believe. I'm sure IEC standards have something similar.

You might want to re-think your operating practice to reduce the number of operations. And if normal load current and interrupting requirements are not too severe, you might be better of with vacuum contactors or even reclosers instead of circuit breakers.

 

[swn1]

Modern breakers are not built like the old ones. The vacuum bottles will take many operations but the mechanisms will wear out.

For this kind of duty choose a contactor, not a breaker, and back it up with fuses if necessary.

 

[JBinCA]

Swn1,

I would not have expected someone to say that the mechanisms on Vac circuit breakers would be the weak leak in the chain for the duty being discussed here.

Is this your personal experience, or do you happen to know of a referenced study or manufacturers instruction that explains this? Do you know why it is the case?

Thanks and Regards,

JB

 

[moreause]

yep breaker are always breaker, so not to much operation is prefered

contactor are good for operation but don't open any short circuit

i think your way will be the new ABB breaker Amvac serie if i remember correcly

there is in fact almost no mechanical part...

i think they are good for 100 000 operation and 100 short circuit something like that maybe less but it was more than some standard breaker that for sur

 

[swn1]

Experience in a breaker shop, we had a number of older power plants and pipeline stations as customers. The ones who had modernized old lineups, replacing old breaker-as-starter units with new vacuum-breaker-as-starter units had much sorrow and woe.

The mechs are made of stamped sheet metal and their dimensional stability is not great. And once they've been peened out of tollerance there is usually no provision for adjustment. We end up welding-and-grinding in some cases, scrapping in others.

A magnetically-held starter is just a whole lot more tollerant of high-cycle operation.

 

[Sideswiper]

Hmm. I'm pretty new in the field but the first project I got was swapping out vacuum breakers that protected a cap bank with SF6 breakers. It seems they were having problems with the vacuum variety, I'd have to ask around to get the specifics there.

 

[sslobodan]

Circuit breakers are something like the last hope that should save the rest of the system from failure in that part of a circuit. LAST OPTION. That means if nothing before turns of faulty circuit before it should. They are expensive so you don't play them as contactor and that is what you need. Generally when you need to switch on and off big systems you should break them in smaller systems for instance:
Power In > Main circuit Breaker >(multiple lines) > Cubicle for process (lets say power supply to a ventilation)> Circuit breaker with better selectivity time (smaller than on Main one)>> One process I.E. one engine in engine cooling system that can be on and off several times a day (lets say 8 fan box 2kW each that is turned on and off to have temperature at certain level) = Motor protection + contractor = System that turns on and off that engine several times in regular and iregular use.
You don't use different configuration because it costs money. And your job as a technical project manager is to save money to your company and make maintenance of gear less painfully for your company. So if you switch contractor every 5 years and spend 40 $ for it its ok. But if you spend 5000 $ in same time for switching vacuum breaker that is very bad ( You would get fired on my job ).
One thing you also mentioned 1/20 faults. That is wrong in your calculations. If you are building a system that should have 1/20 short circuits you should go over your calculations again. It is normal in power distribution system but in technical processes it is not allowed. If you have power distribution facility to project than it switches off few times a year usually for overconsumption and short circuits. there vacuum switch is useful because of his speed and reability, he has much more breaking cycles( and many more...) so its the best known option. In technical processes you don't make system that is faulty and has let's say 1 short circuit per day! System should be reliable and fault comes only due to a machine failure. You haven't gave us a lot of data about your problem, but principles you are using in your calculation are wrong from the start as I can see from this point!