SF6 Circuit Breaker Design

Are these homework questions or are you really an industrial power and/or protection engineer asking project-related questions.

Please explain why you are asking questions such as the one above (and your previous questions) in posts here on CR4. This is obvious stuff that a professional WOULD know (hell, even our power transmission salesmen can answer these), and the questions you are asking appear to be outside your level of experience and qualifications (hence you should NOT be asking them).

Please indicate WHY you are asking these questions:

Is this homework?

Are you working on some sort of electrical projects, if so what is your role/position?

What are your qualifications?

Why are you asking these question?

You should NOT make any further posts here on CR4 until you answer the above questions. Knowledge is very dangerous in the wrong hands, and the industry professionals here will not stand by and hand it out to people who are not qualified and experienced enough to use it safely without killing themselves or others thru its misapplication or misuse.

Jack - A power engineer suitably experienced and qualified to make the above comments.

jack of all trades, while I understand your position on this and I agree in principle with most of what you are saying, I don't believe that you have the right to try and stop someone from posting questions on this forum - who made you judge and jury ?

This is somewhat of a chicken and egg situation : What you are saying is that if you don't have the knowledge then don't ask - well how do you get the knowledge ? It is better to ask a question 10 times until you (the person asking) understands.

"Knowledge is very dangerous in the wrong hands" - actually no. It is the lack of understanding of that knowledge that is very dangerous, for example most people know how to drive a car, however some people do not seem to understand that if they drive a car at 150Km/hr on a busy motorway/street that there is a higer risk that they may be involved/cause an accident. Therefore it is not the knowledge about being able to drive the car that is dangerous, it is the actual understanding - I hope you see what I am trying to say.

Regards

Mr. W.A Snow

Thanks Hole, for your decisive concise reply, there is some man who always try to be a judge. I believe if you ask a silly question, you will be fool for few minutes but if you don't ask you will be fool for ever!!

Thank you Mr.MArirul, and Mr. Hole,

I strictly believe this, if you ask a silly question, you will be fool for few minutes but if you don't ask you will be fool for ever!!.

Because, I am a junior engineer, just now started my career. So I couldn't able understand the practical things. So, i am asking these type of questions which are existing in my plant and so I want to understand the design. Anyhave, thank you for your support. With CR 4, lot of engineers like me, understand the basic concepts of engineering through your answers and guidence.

Thank you Very much.

Regards,

kailash

manirul and kailasamvv, some of what jack of all trades was saying should be taken onboard. I have read a number of his (I am assuming male based on the name so please forgive me if I have gotten this wrong) reponses and althought I do not know him, I believe that he is a very experienced engineer and his heart is in the right place. It is very dangerous to both yourself and other persons if a system is not installed correctly (regarless of the type of system). Hopefully you are lucky enough to have an experienced engineer like jack of all trades working with you.

You should continue to ask questions until you have gained an understanding and never be put off by anyones remarks. Your understanding of your chosen subject will increase with projects and the years.

I wish you all the best.

Kind Regards

Mr. W.A Snow

(I am assuming male based on the name so please forgive me if I have gotten this wrong)

Correct (I am the one on the left of my Avatar (not the tank on the right)).

Hello kailasamvv

Given the large increase in the type of questions similar to yours (and others) it was time that someone started to make a little noise. I am glad that this has caused some controversy as hopefully it will attract people's attention to some of the issues at hand when asking questions on CR4 (or any other on-line forum), namely

"Please provide more information when asking a question"

As you and others here on CR4 can imagine it is very difficult to guess by the limited amount of information that gets included in a new post, what the poster's level of experience is. It really is necessary for people who post questions to include a little more background information on why they are asking the question so the right people get the right answers. In your case all you need to indicate is what you said above, that you are a junior engineer just starting your career and after a little insight into what you are seeing around you in new line of work.

This clearly indicates that you

a) Are not asking a homework question. This happens often here on CR4 and some people are quite sneaky in how they ask, making it look like an industrial problem. CR4 is not a homework answer site.

b) Are not some poorly educated contractor, etc trying to do a job he/she is not qualified to do. This is actually more common than people realise and is one of the main reasons I am cautious about giving out information that could result in destruction of property and/or loss of life. Commonly this involves unqualified people trying to do electrical wiring or sizing jobs illegally when they really need to get a professional electrician, contractor, protection engineer, etc to do the job properly.

c) Are not looking to use the information in some non-constructive/illegal way. Less common than b) above, but we still need to be careful (the CR4 moderators are usually very quick to block these threads). Such posts as bomb making and cell phone scramblers fall into this category.

As for comments above regarding myself acting as "Judge", as engineers it is up to us in-part to ensure that information is used and given out responsibly, because in a way we are all Judges. Like doctors we to have a professional responsibility to the public.

Now that all the crap is finished, I will try to answer your question. The FLA expected will be 140MVA/(230Kv X square root 3) Sometimes you reduce the voltage by 10% to account for the possibility of reduced line voltage. By the way are you protecting a transformer or a line? If the line you need to size the breaker for the line and not the transformer. Another probably more important question is what interrupting current do you have to design for. Most companies have design standards for such equipment as it is rather expensive. You should refer to those standards to fine tune your design. If your company has none, you can bet that the utility feeding your substation does and can help you size the breaker.

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