Transformer Model Design

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gmanojkumar301 Participant Join Date: Oct 2010 Posts: 2	Transformer Model Design 10/08/2010 11:14 AM
	1)I am designing a 230/15V transformer.I need an LV current of 2 Amps.Then it will be 30 VA.But if load draws more than 2 Amps,LV gets damaged.So,how to get rid of this? 2) (i)In actual power transformers,say 100MVA with a given voltage(V) and current rating(I) installed in a given area.Then will it be designed with VA rating=V*I or (ii)However,the power transformers will have upto 50-80% overload capability(as per my knowledge). Then how to decide the VA rating? Either method (i) or (ii) please clear my doubt
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TonyS Guru Join Date: Aug 2010 Location: Resting under the Major Oak Posts: 4347 Good Answers: 181	#1 Re: Transformer Model Design 10/08/2010 11:36 AM
	Homework question? Search transformer design. __________________ The reports of my death are greatly exaggerated.
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mountk2 Power-User Join Date: Jun 2010 Posts: 348 Good Answers: 10	#2 Re: Transformer Model Design 10/08/2010 12:48 PM
	1) Install a fuse or a CB to limit the current. 2) Rating is V*I or kVA A commercial power transformer can be safely overloaded 110% for half hour every 24 hours __________________ Knowledge sharing is a WIN-WIN situation
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Anonymous Poster	#3 Re: Transformer Model Design 10/09/2010 12:23 AM
	check the utility factors and as well as Z value for transformer then you will know how to calaulate load and fix the capacity required....
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MOURADIG Associate Join Date: Nov 2007 Location: Beirut Posts: 33 Good Answers: 2	#4 Re: Transformer Model Design 10/09/2010 6:57 AM
	I think I figured out what you want. you are trying to design a step down transformer 230v/15v and you need to draw 2 amps at 15v. so you have 15x2=30va right? this is the 15v side . what concerns the 230v side it must also support 30va. 30va divided by 230v is equal to 0.130 amps which is 130mA . usually stepdown transformers are protected on the primary side which is 230v so you need a fuse of 130mA .when your load is more than 2 amps on the secondary voltage side then the fuse in the primary side will be blown. Plus it will protect the primary coil from overvoltages, which will cause excessive draw of current. ofcourse you can also protect the secondary coil with a 2 A fuse. In this way you will have double protection. __________________ A man wants to know everything about everything, a woman wants to know everything about everybody
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Tornado Guru Join Date: May 2009 Location: Richland, WA, USA Posts: 21017 Good Answers: 795	#5 In reply to #4 Re: Transformer Model Design 10/09/2010 1:04 PM
	This is mostly the right idea, except that on the primary side the high inrush current requires a higher rated fuse/CB. (There is a graduated set of multipliers depending on the VA of the transformer.) On the secondary the fuse can be up to 1.25 x FLC. Local codes should have this information. [By "design" does the OP mean to select a suitable transformer, as from a catalog; or actually to compute core size, laminations, ampere-turns, etc.?] __________________ In vino veritas; in cervisia carmen; in aqua E. coli.
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Anonymous Poster	#6 In reply to #5 Re: Transformer Model Design 10/09/2010 1:17 PM
	Well, could you please explain why the primary has high inrush current and not the secondary ? What is CB ?
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Tornado Guru Join Date: May 2009 Location: Richland, WA, USA Posts: 21017 Good Answers: 795	#7 In reply to #6 Re: Transformer Model Design 10/09/2010 2:31 PM
	For inductive devices such as transformers and motors, the initial impedance is very low until the magnetic field builds up. This magnetizing current is several times higher than the running current. CB = circuit breaker. __________________ In vino veritas; in cervisia carmen; in aqua E. coli.
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gmanojkumar301 Participant Join Date: Oct 2010 Posts: 2	#8 In reply to #5 Re: Transformer Model Design 10/10/2010 12:31 PM
	Design means i have a core with net crosssection area of 3 sq.cm made of Si-Steel laminations assembled to form shell type transformer. I was pleased with your answer but I wanted to know how the commercially available 230/15V transformers are made without any fuses or CB.
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Anonymous Poster (2); gmanojkumar301 (1); mountk2 (1); MOURADIG (1); TonyS (1); Tornado (2)

You might be interested in: Transformers, Electronic Transformers, Instrument Transformers

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