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Anonymous Poster #1

Transformer Distribution Panel

07/16/2017 1:43 PM

Hello,

A three phase 25 kVA transformer will have 40 Amps of TPN MCCB.

But a statement reads it shall have one outdoor distribution panelboard with 40 Amps, TP-1 , 20A, TP-2.with copper busbar and hardware complete set.

How we get 40 A TP-1 and 20 A, TP-2?

Regards,

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#1

Re: tranformer distribution panel.

07/16/2017 2:39 PM

That depends on what the 1 and 2 designation means...

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#7
In reply to #1

Re: tranformer distribution panel.

07/17/2017 11:55 AM

...which abbreviations the Document Author needed to have listed in part of the document.

The document and the name of the author cannot be seen from here and this is the best source of information:

will yield the solution.

Every time.

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#8
In reply to #1

Re: tranformer distribution panel.

07/17/2017 12:03 PM

TPN is a nutritional measure?

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#9
In reply to #8

Re: tranformer distribution panel.

07/17/2017 12:25 PM

Unless it means "three phases and neutral", then probably.

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#11
In reply to #9

Re: tranformer distribution panel.

07/17/2017 1:30 PM

Thomas Paul Newton would disagree.

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#2

Re: tranformer distribution panel.

07/16/2017 4:45 PM

You did not state the ingoing voltage and rated output voltage, so the rated current is guesswork for us, but if you meant the secondary is 380/220V that is 38 amps/phase.

Since transformers are rated at 40 Celsius, but breakers often 30 Celsius, the tranfo may be correctly protected against overload by 40 amp MCCB as incomer protection/isolator, particularly since MCCBs are often adjustable for overcurrent.

If the TP-1 and TP-2 are panelboard MCBs with Three Poles (TP) they are possibly for motors which will have overloads in their starters but need to supply 6-8 times full load starting current for many seconds without tripping.

If the sum of the running loads is less than 40 amp an overload is not likely to arise.

In the case of short-circuit, the 40A MCCB probably has a longer trip time than the 40A TP-2 MCB, so the desirable tripping of sub-circuit first can be got.

So it is expected that the basic rules for protection against overload and short circuit for transformer, cables and motors (or other load) are met.

There is no rule that the sum of outgoing breaker ratings must be less than the incoming breaker or fuse rating - if you look at typical house distribution a 100 amp incomer may have 10 or more MCBs which could be 6 to 40 amps with same physical size.

Electrical regulations allow that, in practice, every circuit will not be fully loaded simultaneously (many circuits will never be fully loaded) - applying rules for "diversity". The most obvious case is circuits for house power sockets, where it is well known that most sockets will only have a small load so there can be as many sockets as convenient, despite the circuit rating exceeding that of a single socket. In many countries, there is no regulation to have fuse/breaker in socket, plug or appliance.

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#3
In reply to #2

Re: tranformer distribution panel.

07/16/2017 8:17 PM

it is 11/0.4 kV transformer.

Regards,

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#4

Re: tranformer distribution panel.

07/16/2017 11:17 PM

I Guess , It is Distribution board with One incomer of 40 Amps and two outgoing 20 Amps each.

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#5

Re: tranformer distribution panel.

07/16/2017 11:48 PM

Do we really know yet if this a fully 3-phase transformer/panel, versus two phases with either a star or center neutral tap?

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#10
In reply to #5

Re: tranformer distribution panel.

07/17/2017 12:27 PM

<...two phases with either a star or center neutral tap...> is not used in more developed countries.

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#14
In reply to #10

Re: tranformer distribution panel.

07/18/2017 6:35 PM

Ya sure, ya betcha. Give us poor colonies another 241 years, and maybe we'll catch up--and save your sorry asses out of another war or two.

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#6

Re: tranformer distribution panel.

07/17/2017 5:12 AM

You already have the 40 A TPN MCCB. Now you need to acquire a 20 A TPN MCCB.

Connect the Output of 40A MMCB to TP-1 and the output of 20A MCCB to TP-2.

That should do the job.

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#12

Re: Transformer Distribution Panel

07/17/2017 1:48 PM

TP-1 and 2 are NEMA energy efficiency ratings for transformers based on Dept of Energy 10 C.F.R. Part 431specifications. "TP" just stands for "Test Procedure" involved in determining the efficiency, performed by the transformer mfr. So you "get" that rating by buying a transformer that has it, you can't afford to get it after the fact

Most stand-alone transformers between 15 and 150 kVA installed in any government funded projects must meet TP-1 from a chart based on size. It basically says that a 25kVA transformer must be 98.6% efficient at rated load. Forget needing to meet TP-2, because if you meet TP-1 you will meet TP-2 even at 1/2 load.

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#13
In reply to #12

Re: Transformer Distribution Panel

07/18/2017 2:16 AM
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#15

Re: Transformer Distribution Panel

07/19/2017 11:20 PM

What is your voltage ?

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