LT SWITCHBOARD

[vinothkumar asaithambi]

Hi Guys! i have the basic knowledge about LT Switch Boards & Control Panels. But i want to know about KA rating in selecting the Breakers & Panel Sizing, Can you provide me a piece of idea on this???

[vinothkumar asaithambi]

Hi Megha!
Can u send me some reference materials for LT switch borad design?
vinotbe@gmail.com dis s my mail id.

Thx n advance

[AWESOMEFLINT]

@vinothkumar asaithambi said:

Hi Guys! i have the basic knowledge about LT Switch Boards & Control Panels. But i want to know about KA rating in selecting the Breakers & Panel Sizing, Can you provide me a piece of idea on this???

Hey bro,

So here is the deal, Breaking capacity is totally decided by the type of usage/type of industry . Suppose u came up wid load list….may be , lets say 800 Amps for all the feeders for an industry…..so u select an ACB of 1000 A or may be 1250 A , for safety purpose. Done…… now where does “Breaking capacity” come from?? From here ….
1. Humidity
2. Fault tolerance parameter
3 load impedance
4 load voltage.

so from some ground rules we compile them all and find out the breaking capacity.

It’s is denoted by kA….so when the fault occurs the amperage of a system can go up to 100 kA=100,000 A , this is huge trust me !!….sometimes 250,000.

so as to safeguard your motors ( from smallest 0.37kW to 150 kW bigger…or may be biggest) this 100kA has to be stopped from killing the motors……..we have to kill this huge current. We do it this way, selection of ACB/MCCB accordingly and also…. we gotta select the time for which the system shall cud quench fault

Generally its 50kA or 65 kA

Lot more to tell….keep askin

[vinothkumar asaithambi]

Thanks for ur reply my frnd..
But i gotta too many questions..you gonna answer them pls..
consider the case i am having 10 DB`s each having 100A incomer MCB..and these DB`S ll be fed from SDP(Sub distribution Panel). where this SDP and the some other SDP`s (consider same size, say 10 each) connected to the MDB ( Main Distribution Board.).
Consider this is a Domestic load and load voltage 230/400V, 50Hz.

Here is my Questions…

1. What Kind of Breakers we have to choose for each level(from DB- SDP – to MDB)??

2. What ll be the KA ratings for all these breakers (Incomer and Branches) ???

3. Is there any calculation behind this, choosing breakers and its KA ratings???

4.is there any Space Factors we have have to consider, when we are making all these panels???

5.Give me list of Busbar Sizes to carry all these for each level…

ThX n Advance,

[AWESOMEFLINT]

@vinothkumar asaithambi said:

Thanks for ur reply my frnd..
But i gotta too many questions..you gonna answer them pls..
consider the case i am having 10 DB`s each having 100A incomer MCB..and these DB`S ll be fed from SDP(Sub distribution Panel). where this SDP and the some other SDP`s (consider same size, say 10 each) connected to the MDB ( Main Distribution Board.).
Consider this is a Domestic load and load voltage 230/400V, 50Hz.

Here is my Questions…

1. What Kind of Breakers we have to choose for each level(from DB- SDP – to MDB)??

2. What ll be the KA ratings for all these breakers (Incomer and Branches) ???

3. Is there any calculation behind this, choosing breakers and its KA ratings???

4.is there any Space Factors we have have to consider, when we are making all these panels???

5.Give me list of Busbar Sizes to carry all these for each level…

ThX n Advance,

So here is the deal,

First off, I see a big flaw in ur system consideration……..i will explain it you in steps……read carefully and understand in steps.
U have domestic loads, perhaps not exceeding than 63 A or may be 100 A or may be more, well we gotta select a perfect discrimination so that we are able to safeguard the whole system. Pls read and try to understand below system from BOTTOM (read dbs…..then sdps….and finally mdbs )

MDB -1
And finally….(HERE IS YOUR FLAW IN SYSTEM)…SO IF YOU HAVE 10 MORE SDPs……SO IF YOU TAKE BASICS AND CONSIDER THE BREAKER RATING …THEN IT COMES AS “1250×10 = 12500 A”…..DUDE…. THIS IS FUCKING HUGE….i mean wot is the rating of your transformer….. is it super duper ultra large transformer ?? ….:p …..THAT MEANS U HAVE TO BREAK OR BIFURCATE THE SYSTEM SOMEWHERE !!…AND ALSO… I AM SURE…. U MUST NOT HAVE 10. NOS OF SDPs….AND EVEN IF U HAVE…. THEN ITS A DIFFERENT SYSTEM

SDPs-10
As we now know when in full load we have 1000A drawn by your system (system below this) …so be safe…..consider 1250 A MCCB,
Lets take a breaking capacity of 36 or 50 kA…. no less available….and higher the better , if i was you ….. i wud have considered 50kA..

DBs-10
lets say a total mcbs are 10….so 100×10=1000 A
So this gives the breaker rating for SDP. now read up.
And as its a domestic load, to safeguard u can consider 10kA (more that enough)…u can find 6kA in market too….but…as u wish !

After MDB read here !!!…

So here is a better solution…..

MDB..1 Nos
2000 A ACB / SFU wid a breaking capacity of 50kA

SDBs..1+1 = 2
800 A mccb wid 36kA or 50kA breaking capacity

DBs..5 + 5 = 10
100 A mcb for each use and 5 for 1each sdb….this way u can hook up one system of 10 dbs with 2 sdbs..

I hope i was helpful

FLINT !

P.S : PLEASE CORRECT ME IF I AM SMALLEST BIT OF WRONG !!

[vinothkumar asaithambi]

Hi flint !!!

sorry for the delayed reply.Well bck 2 topic,
Yes, U r partially right. DB main breaker is 10kA rating and its branches will be 6kA. Where SDP with MCCB, 36kA rating and MDB ll have MCCB or ACB , 50kA rating. Upto this u r rite.

consider the fact, all the loads wont be connected. pls remember concept of Demand factor. According NEC tables D.F value for SDP (10 DB`s Connected) ll be 0.4 to 0.5. hence the incoming breaker for SDP = 100A(wont be 100A at all, lets consider for the calculation) x 10( no. of DB`s) x 0.4 = 400A.

For MDB level, Demand factor ll be reduced to 0.3 to 04, rating ll be

10(No. of. SDP`s) x 10(No. of. DB`s) x 100A x 0.3 = 3000A. from this we can easily size the transformer or Generator.

Hope u can under stand this calculation.

Dear Flint, i m just looking for some proper calculation for this kA ratings. if any like that, please share with me.

ThX n Advance,

Vinoth.

if something wrong pls correct me..

[AWESOMEFLINT]

Sorry ppl,

 

   Went outta country ! life kept me busy !!

Back on !!

 

So Vinoth, here is the deal !…..I didnt understand your calculations :p !! no offense bro….. just keep it simple yaar.

Anyway !!

Bout your “breaking capacity” ….lets learn from ABC…to alpha beta….

My bro (wiki) says….: breakin capacity is the current that a fuse, circuit breaker, or other electrical apparatus is able to interrupt without being destroyed or causing an electric arc with unacceptable duration. So far so good.
 

NOW u gotta select the value of breaking capacity….which is dependent on  

1. TRANSFORMER POWER. 

2. SYSTEM VOLTAGE

thats all.

 

So, do this 

( transformer power x 1000 / 1.732 x system voltage ) = this gives your breaking capacity in kA 

 

=>  MVA x 1000/1.732 x 440 [generally the system voltage is 440 V. for LT].

 

Bam !! u have your breaking capacity of ACB/MCCB/SFU or wotever !! Enjoy

 

Regards

FLINT !

P.S : PLEASE CORRECT ME IF I AM SMALLEST BIT OF WRONG !!

[Urleandy]

@guest said:
Megha said:

send me your mail id i will send you some matareial for reference i think that is enough for the basic knowledge

---

Hi megha !

     Could you also send me the mail. Thank you so much in advance :) MEGHA

[AWESOMEFLINT]

Dear Urleandy,

 

     Kindly ask any question here itself and we will try to clarify !! Let others too share and view the discussion !!

 

Regards

[Author]

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