Power rating - mixed star/delta/single on one board

[Inteificio]

Hi,

I am required to put data labels on the equipment I manufacture (if anyone knows the reg number of it that would be helpful).

One one box on the data label I am required to put the 'KW' rating.

Only problem is a few devices I build contain distribution boards and sockets.

The maths is all quite simple if it was either a pure 3p star or delta or single; problem is there is a combination. I am not quite sure how to rate a device with a combination.


Say I have a board with a 64A main switch with a 32a star breaker, 32a delta breaker and 3 single 32A breakers.

What the hell do I put on the power label.

Also if I put in a 4-pole breaker, how do I know if it will be star wired or delta wired?

This is how I would do it, but am getting confused as I get a few answers and not sure which to use:

64 amp main switch. 3 phase.

64x400x1.7= 27.2 = 43.5KW - I used 400 as that is the highest voltage in use. But there is no way that this would be giving all 64A at 400v as only a 32A delta, so only part is 400v part 230v.

32A(de) = 400x1.7x32= 21.76KW

32A(st) = 230x1.7x32= 12.5KW - but how do I know whether a star or a delta wired device is plugged in to the sockets?

32A(si x 3) = 230 x 3 x 32= 22KW

So basically I am confused, this should be simple, but I am not sure what I am supposed to be calculating. Thinking about it, even if the 3 pole breaker I am using as the delta breaker, it could still be wired star..... dammit I am more confused.

 

[Knobhead]

The motor should have just one MCB not one for each star and delta, maybe I misunderstood something. But anyway the motor rating is it’s FLC as on the rating plate.Sorry but you’re going to have to explain the situation better.

 

[malcoa]

i'm guessing its not a star/delta circuit but a distribution board which may have a star and/or delta connected motors connected to it, I would put the max rated power (SQRT3 x V x I), thats the best you can do,whoever connects to it would have to factor in the power factor
Does it sound reasonable?

 

[Inteificio]

Hi,

Sorry I guess I did not explain this clearly.

I am making a counter that contains sockets and a distribution board.

I have to add a rating plate to this, and am not sure what to print on the rating plate as their are sockets.


So to be clear, I need to put a rating plate on my distribution board.
There are a mixture of circuits, so not sure how to proportion the load to know total power.

 

[Knobhead]

As I said did I misunderstand something, I did. 3Ph 32A at 400V is the same if it’s star or delta connected.Delta: (((400/√3)*32)*3)/1000=22.17KW.Star: ((230.94*32)*3)/1000=22.17KWIt’s phase to phase voltage you need to work on.So for your rating plate:400V63A43.64KW Max

 

[trong]

I think your problem is to find a 4 pole circuit breaker, a delta circuit breaker, and the hardest one is delta circuit breaker. you sound like an engineer that missing formula with delta, wye or buck and boost trans.

 

[Knobhead]

I think your problem is to find a 4 pole circuit breaker, a delta circuit breaker, and the hardest one is delta circuit breaker. you sound like an engineer that missing formula with delta, wye or buck and boost trans.

A/ Where does a Buck and Boost transformer come in to the equation? B/ What is a delta circuit breaker, a breaker operates on line current no matter what it’s supplying! Star or Delta! You’re the one that’s lost his way!

 

[Inteificio]

I must admit I am lost where the buck/boost come in too =-)

I was classifying a 3 pole breaker as delta as I (formerly) thought you needed a neutral for star, so it had to be delta. Now I know that is not necessarily true, so no way of knowing what the load wiring will be whether 3 or 4 pole =-(

I think you might be slightly off on the delta/star calc though Tony. Then again, you probably have more experience in one of your fingers than in all of me... so not sure what to think.

This is my calc, please point out if/where it is wrong for 3 phase power.

W=1.73xVxIxPf

Voltage is line to line for delta so 400, and line to N for star so 230.

The current is fixed at 32A
Power factor is assumed the same.

Therefore power output of delta in this circumstance will be 1.73 (~root3) higher than star.

Is that right or am I missing something?

p.s. just found this page, it's Americana but seems interesting

http://www.3phasepower.org/

 

[malcoa]

the 3 phase power formula is correct peter, i cant understand what your after, your installing a distribution board for equipment to be connected to it, a 63A or 32A breaker protects at those currents regardless of how the motor is connected, your right to say a delta connected motor pulls a little more current as it would show on its rating plate, the breaker needs to be matched to it although a motor usually as some kind of control with inline protection such as an overload. do you need to worry what the motor connections are?

 

[netblindpaul]

Peter,
Where does the 1.3 come from please?

 

[Knobhead]

That’s got me intrigued. √3 = 1.732 as I recall.

 

[Inteificio]

Maloca - Hi, I have no control over what gets plugged in; this is the crux of the issue.

If I knew what was plugged in, then the sums are easy. I have to rate a device taking in to account available options.

 

[Inteificio]

Dammit, think I got mixed up between 1.3 and 1.73....

 

[Knobhead]

Maloca - Hi, I have no control over what gets plugged in; this is the crux of the issue.If I knew what was plugged in, then the sums are easy. I have to rate a device taking in to account available options.

If you can’t control what’s to be plugged in to the unit all you ca n do is put a “Maximum loading” label on it. After that it’s out of your hands.

 

[malcoa]

If you can’t control what’s to be plugged in to the unit all you ca n do is put a “Maximum loading” label on it. After that it’s out of your hands.

Tony is right, as a guess, you've been asked to rate and install a board to supply equipment you don't have info about.