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Participant

Join Date: Jan 2014
Posts: 4

# Question about Vacuum Circuit Breakers

01/30/2014 3:49 AM

Recently i've been asked if there is a method,technique, formula or any means necessary to calculate or to determined the amount of force that a vcb particulary siemens sion generates at the moment of tripping. This info is so important so that the designer will able to determined what size or dimensions the cradle or casing of the vcb will be. Thank you in advance , please bear in mind that i'm a young engineer and i am new to CR4 so welcome for me.

Pathfinder Tags: force VCB
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Join Date: May 2009
Location: Richland, WA, USA
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#1

### Re: Question about Vacuum Circuit Breakers

01/30/2014 3:56 AM

I'm almost sure you would have to ask Siemens. If you knew the spring rate, how far stretched/compressed it is, and the weight of components it moves; you might be able to calculate. But most likely only Siemens has that information, unless you buy one and take it apart.

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Participant

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#2

### Re: Question about Vacuum Circuit Breakers

01/30/2014 4:08 AM

OK so it ends in determining the size of the spring itself. Since we have a method on determining the force and stresses of a spring. Yes we have access and can thinker the said breaker. Thank you

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#5

### Re: Question about Vacuum Circuit Breakers

01/30/2014 6:52 AM

Force exerted by the VCB is dependant on the current being broken.

The resilience of the buffering to prevent bounce is the thing to look for.

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#3

### Re: Question about Vacuum Circuit Breakers

01/30/2014 4:23 AM

Maybe put it on a scale that retains the maximum reading, and then cause it to trip....

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#4

### Re: Question about Vacuum Circuit Breakers

01/30/2014 6:07 AM

Do talk to Siemens in the first instance. That's what the telephone is for.

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#6

### Re: Question about Vacuum Circuit Breakers

01/30/2014 10:57 AM
 Re: Question about Vacuum Circuit Breakers I shall make a bit of historical comparison. In classical solutions the electrodes were in a volume filled with a gas. The gas could become ionized so that the build up arch had to extinguished as fast as possible. This lead to the design of a blowing system - a kind of compressor blowing a strong gas flow in the arc region to cool the zone and reduce the arc effects. All tis system was based on the energy in a mechanical accumulator many time a hydraulic accumulator with rather high pressure. Of course this required a lot of energy. Siemens idea was to take off the stuff which could generate the ionized "gas" by the design of a switching in vacuum. No gas no ionized particles thus shorter arc and less wear. However during the process of contact opening current grows per surface unit and a local high warm up occurs. This leads to vaporization of contact metal. The solution is to increase the acceleration of moving parts in order to reduce this period and reduce the possible surface wear. In the Siemens design there is a further interesting feature. The current generates a magnetic field which leads to a helical movement of electric charges and increases the path length over the geometrical distance thus increasing apparently the distance between electrodes over its actual value. In such a way the arc is stopped even faster. The switching times are in the range of a few milliseconds and the average velocity around 1...1.5 m/s, the distances between electrodes can be small even at high voltages since the breaking voltage for vacuum is high (V/m). Thus forces have not to be so high, the energy is a lot smaller than in the case of classical solution and overall volume can be reduced. The force magnitude at stroke start can be estimated assuming following parameters: stroke 3E-3 [m] travel time t= 6 E-3 [s] (is indicated as switching time in the Siemens leaflet) with those values the Fo [N/kg] ≈ 3 E-3*1/36 E-6= 83.3 [N/kg]. It is for 1 [kg] moved mass. If the moved mass is higher then it has to be multiplied. GE gives a switching time of 2 ms which leads to 750 N/kg . Those values are only valid as a rough estimation based on the movement dynamic differential equation but not considering for instance the below's stiffness or mass. I hope to bring the required information.
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#11

### Re: Question about Vacuum Circuit Breakers

01/30/2014 3:43 PM

Thanks a lot! I really appreciate your response

Guru

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#7

### Re: Question about Vacuum Circuit Breakers

01/30/2014 11:44 AM

I believe our young engineer is trying to reverse engineer the housing for the breaker mechanism, which normally comes as a complete assembly. The fact that he seems satisfied with determining the force of the spring speaks to his naivete, as illustrated by his statement "...OK so it ends in determining the size of the spring itself..."

No it does not end there, you are totally ignoring all the dynamic forces that act on a piece of switchgear during a short circuit, those forces far exceed the opening force of the spring.

Of course you are going to test the entire assembly under all of its emergency ratings, just make sure you have a ballistic shield between you and the test bed.

Why so many of us are eager to assist in violating intellectual property laws is beyond comprehension, especially when all the dangers of this particular piece of equipment are considered.

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#8

### Re: Question about Vacuum Circuit Breakers

01/30/2014 1:17 PM

I take it as direct reproach.

I may say that even if he knows the force it is not simple to copy such a device. One of the best examples is the CONCORDOWSKY, it was the total copy, by the soviets, of the Concorde developed by French and British engineers. They arranged to have ALL drawings stolen with ALL specs and the result was a big big failure although as you know the Russians were able to make quite good planes. But they did not have a lot of the technologies involved and tried to use substitutes thus the result.

Reverse engineering is not only compute the stuff but also build it and make it work for this the copier should have same skills as the original designer since many details are not to be understood simply by a even very complete drawing.

According to your comment the moderator should introduce in the procedure the text : " Do not help those who try to understand how it works, this can be considered as stolen intellectual property". I wrote it this way since you never know how the knowledge will be used.

If this will be introduced then the whole support an OP could get is how to repair their cars or appliances. Or may be have a discussion about Curiosity.

I doubt this is the scope of CR4.

Guru

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#10

### Re: Question about Vacuum Circuit Breakers

01/30/2014 3:23 PM

..Just like I don't believe it's within our scope to put potentially lethal or dangerous information into the hands of those who are clueless as to how to properly use it.

OP did not say "...I'm trying to understand what the forces are...", instead he said "...that the designer will able to determined(sic) what size...", implying that they were trying to fit a subassembly into a housing of their own design.

More than likely his company has their hands on a vacuum bottle subassembly (possibly as a maintenance part) and is wise enough to know that they can't duplicate that, but a housing for it, "...hey, that's just a piece of sheetmetal that we can fabricate...", and sell for less.

Thank you for using the word "understand" in your comment. Helping someone understand how an atomic bomb works is totally different then providing detailed information on how to build one.

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#16

### Re: Question about Vacuum Circuit Breakers

01/31/2014 5:29 AM

In his comment the OP mentioned a program to design springs. This shows the level since design a spring depends on several factors which are NOT in usual programs.

He is not aware of it, even if he "designs" a spring with his program there are many chances it will not work properly. Only to reduce your fears I shall not list all factors to be considered for a spring in a device as this I let him discover them. It will take many tests before a positive result.

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#9

### Re: Question about Vacuum Circuit Breakers

01/30/2014 1:21 PM

I have to agree given the available information, this sounds rather dodgy. The VCB and cradle are custom designed by Siemens as a complete and tested package. You buy them together not try and build your own.

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#12

### Re: Question about Vacuum Circuit Breakers

01/30/2014 3:59 PM

Ok so to reply in general to what all of you have said. First thank you for your warm responses about my 1st query here in our dear forum. Secondly i will make it clear that it is not in my purest intention to stole or copy the design. I just want to know how or is there a way, method or any means necessary to get the output that i want so that as an engineer i can integrate that in my future works and designs without necessary copying the whole siemens sion. I'm sorry if i may sound naive but it is also not my intention to put hazard and danger to the people around me by just simply ignoring the different parameters of the force generated by the moment a vcb trips.

What my intentions are similar to the concept of sizing wires and circuit breakers in a circuit. We know the methods of sizing wires/cables and cb. Similar to my question i want to know the method if there is any, so lets say if i have a vcb which is obviously a different brand, if we know the method on how to determine such forces then I, as an engineer can customize the cradle size which will not only limit to a certain brand but will apply to others as well.

I really appreciate your responses and i really love engineering, i love knowledge and willing to learn and to explore more and more about electrical engineering.

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#13

### Re: Question about Vacuum Circuit Breakers

01/30/2014 4:26 PM

First, thanks for your response, many times posters don't respond when they don't hear what they want. Unfortunately the class of breaker that you originally referred to is a much more highly engineered piece of equipment than wires and smaller circuit breakers.

As your research should have shown you, VCBs vary widely in design across manufacturers and within ratings. It is unlikely that you will find two different manufacturers whose parts are interchangeable unless the OEM has licensed his product to other manufacturers, in which case the proprietary information is shared by both parties, and the third party has to show the OEM that the secondary product is at least as good as the original.

About the only thing that may be in common is the size of the enclosure, the arrangement of terminals, and the symbol on a circuit diagram; the internals, mechanisms, and mounting points will probably be non-interchangeable.

ps- this is more of a mechanical engineering problem than an electrical one.

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#14

### Re: Question about Vacuum Circuit Breakers

01/30/2014 11:09 PM

The force exerted by operating mechanism of VCB on support structure of a Circuit Breaker is fraction of force exerted by reaction of fault currents. To calculate reaction of fault current one can use following rule:

Assume fault current path through frame around VCB.

Distance of fault current parallel to VCB column and double the clearance between VCB column and housing of switchgear panel in indoor application (and at right angle for outdoor applications).

Calculate electromagnetic force exerted by VCB on structure (and structure on VCB). Verify design by Type test.

Members can also draw inference from the reason that in Type Tests of Circuit Breakers, distortion in support structure or housing of switchgear is measured during short circuit test (not normal operation).

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#15

### Re: Question about Vacuum Circuit Breakers

01/30/2014 11:43 PM

Quite a good response all told.

My two cents worth : The basic VCB from anyone is usually a 3-phase device, with the appropriate mechanism and 3 vacuum bottles already well mounted on a strong, well-designed frame. This frame will have been designed to take all the maximum shocks that the highest short circuit current can generate. There will certainly be a factor of safety on the max computed values, and actual type tests to validate the design. For the panel maker, there is usually no work left except to ensure that the CB is strongly mounted and connections are not under strain.

The vacuum bottle itsslf is totally sealed so that nothing comes out of it. The contacts, if left to themselves, will be closed due to atmospheric pressure on the contact rod ends, so the mechanism keeps them pried apart in the open position of the CB. It actually 'lets go' the contacts when the closing command comes !

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#17

### Re: Question about Vacuum Circuit Breakers

01/31/2014 5:30 PM

What you are asking for is technical information that is only available from the vendor.

You can calculate (WAG) all you want but the odds of you getting it right are slim-to-none.

The opening speed of any/all breakers is dependent of the current interruption rating and voltage rating.

The pressure required to make the correct contact opening speed occur at the correct, safe interruption speed is dictated by breaker design and that is most likely proprietary information.

All said; Call Siemens and they may be willing to share the info with you.

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#18

### Re: Question about Vacuum Circuit Breakers

02/04/2014 7:34 PM

Recently, I attended a seminar on emerging trends in HV/LV Switchgear at CPRI, Bhopal, India. The conference included some papers on forces & spring design, etc. Kindly get in touch with CPRI & get a copy of the conference proceedings.

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