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Join Date: Feb 2011
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# How Do I Calculate Max Load on my 1000 KVA Transformer?

02/18/2011 2:38 AM

I have a 1000kva transformer. It has dol start type motors of various capacities and adds upto 1555KW. Can I add more equipments from this 1000KVA transformer?

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Guru

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#1

### Re: How Do I Calculate Max Load on my 1000 KVA Transformer?

02/18/2011 3:10 AM

I'm surprised it hasn't blown up already; 1555 kw is about 1800 kva, which would be way overloaded.

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#2

### Re: How Do I Calculate Max Load on my 1000 KVA Transformer?

02/18/2011 3:55 AM

There always is an element of diversity, clearly not all the motors would not be running simultaneously.

Standard practice is that the diversity factor of mixed light and power feeders is considered to be 1.5 to 2 (or even more per the designer's detailed assessment).

For a power transformer, condition for maximum efficacy is about 80% of its rating accordingly the average working load except for the peak periods is approximately in the range 800 Kva.

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#3

### Re: How Do I Calculate Max Load on my 1000 KVA Transformer?

02/18/2011 4:34 AM

As Tornado said it's a wonder the transformer has blown up already! Never mind increasing the load you should be looking at either reducing the load or an additional transformer.

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#5

### Re: How Do I Calculate Max Load on my 1000 KVA Transformer?

02/18/2011 5:18 AM

As KW=KVA*p.f.

The transformers do have a p.f of 0.8 normally,

so max running load, above mentioned t/f can bear is 800KW.

So, Both (tornado & mountK2) ANS are true in their context.

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#4

### Re: How Do I Calculate Max Load on my 1000 KVA Transformer?

02/18/2011 5:07 AM

<....add more equipments from this 1000KVA transformer?....>

Up to the point where the correctly-set transformer overload and downstream circuit protection devices operate, yes.

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#6

### Re: How Do I Calculate Max Load on my 1000 KVA Transformer?

02/18/2011 7:17 AM

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#7

### Re: How Do I Calculate Max Load on my 1000 KVA Transformer?

02/19/2011 12:53 AM

I am amazed at such question based solely on equipment plate values. I have a surely novel proposal: MEASURE IT, in many detail, you just might learn plenty.

For a starter, motors at starting may draw 2,5 times of the running max. current. At the same time in normal usage they may run at a fraction of their nominal current draw. Can you make it sure, only one load is started up at any given time? I do doubt it. So you playing a game now, flying blind, so to speak. Not healthy.

And there is the Electric Code. Unless you know for sure, you may be violating a couple. Fire departments and insurance companies take very dim view of that.

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#8

### Re: How Do I Calculate Max Load on my 1000 KVA Transformer?

02/19/2011 11:48 AM

I wonder there is no ACB installed

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#9

### Re: How Do I Calculate Max Load on my 1000 KVA Transformer?

02/19/2011 4:32 PM

The following is just food for thought:

Under specific circumstances you may be well below your capacity. As an example, on a paper machine the total installed motor HP may far exceed the supply KVA. BUT, the running load of many sections may be only 20% of NP. So while running the total utilized KVA is only 50%. Adding another load depends on its service factor and total rated. This distinguishes between the normal running load and the section NP power. The sections that are "over sized" are to accelerate large inertia loads. Acceleration loads may be 150% of rated for 1 minute, or even longer. Once up to speed it will run weeks at a much reduced load. In this situation the sections are programmed to start one after the other to ensure the transformer does not overload. Within power distribution it is common to find the total connected load exceeds the supply KVA, but it assumes not all the load is connected at one time. Obviously you need to ensure the distribution transformer has adequate O/L and O/C protection.

Load shedding techniques can also be used to protect the system.

If you are installing new equipment it is often only a marginal increase in cost to upgrade one size. (Unless you run into short circuit capacity issues, which can significantly increase the cost of downstream protection to achieve the interrupting capacity.)

I suggest you enlist the help of an engineering firm familiar with your process and power distribution.

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Join Date: Feb 2011
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#10

### Re: How Do I Calculate Max Load on my 1000 KVA Transformer?

02/19/2011 8:58 PM

Hello sirs.. Thanks evry1 4 ur replies and valuable comments.! im sorry i missd out on sum facts..! the name plate rating of all these motors add up2 1555..! but as you all said not evrythng is going 2 load or peak at d same time..! my question was actually vague ..! was in a hurry .n thts hw i missd 2 mention a few more stuff.! i did a detailed study n found tht i have 850 KVA (taking into account what all motors load at a given point) on this 1000kva transformer . is it advisable to add equipment/s requiring 300A to this transformer..? or vil i have 2 increase d capacity of my transformer..? or have a separate transformer for this equipmnt exclusively.? pls comment..

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#11

### Re: How Do I Calculate Max Load on my 1000 KVA Transformer?

02/19/2011 9:08 PM

Assume it is 600V system, you will be overloaded.

However, check the NP of the transformer, you may be able to fan cool and get your rating up another 20%.

Anonymous Poster
#12

### Re: How Do I Calculate Max Load on my 1000 KVA Transformer?

02/19/2011 9:31 PM

Please rewrite that; the texting crap is offensively unprofessional.

--Editor Crankshaft

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