How to Determine the Capacity of Transformer

NO.

1, When the load of transformer reachs to 70%-80%, the efficiency will higher.

2.Use capacitys to realize reactive power compensation to 0.95.

Assuming the diversity factor is correct, then, yes! these two transformers can very well take all the factory load (I mean, running load).

Pls, can you explain me the contrary case : when they couldn't cover the total load

Regards

Simple! The total load is 3350kVA and the combined transformer capacity is only 2632 kVA. Hence these transformers cannot cover the total load.

Hi there

1. The two Transformers does not even cover the total load....

2. If you are going to run your transformers in parallel you are going to overheat the small transformer soon because of circulating current between them

3. Why dont you run two x 2000KVA transformers

4. If you take one transformer out for maintenance you are left with 2000KVA

I would not use that consultant in my plant

Thanks friend

but the two transformers not running on parallel, each transformer feed power to some equipment and total connected load related to each one is over, but we use diversity factor can be cover

my inquiry is : can be running without issues? and for long time?

Who said the load is 3350kVA,how did they calculate?. Calculations are not always accurate,it depends on diversity,pf of loads in different sections of the factory,whether VAr compensation is done etc What is the kVA shown by the max demand meter in each section?.

Or else measure the load in different sections by power analyser or data logger when energised by a generator(hired)and add up. If you have a standby or emergency generator of sufficient capacity you may use it.

From the information you have given the total load is 3350 KVA

Because there is a diveristy factor of 0.7 assumed [Hope this figure is correct], the actual connected load at any given point of time is = 3350*0.7 = 2345 KVA only. Add a safety margin of 10% or so to it and that should be sufficient.

some of the other consideration used in transformer sizing is voltage regulation, limiting short circuit current

on principle, this what they think to do, but I want to understand how we can use this type of transformer with breakers support currents more high each time.

really I have confuse between diversity, demand & power factor for transformer choice.

Thanks & Regards

It sounds like you are confused and should consult a professional and get their opinion.

If the transformers are not paralleled, then the total 3350KVA is irrelevant. You need the total connected KVA x diversity factor for each transformer separately.

Moreover, it would be better to analyze the possible concurrent loads, rather than using some generic diversity factor.

The determination of the connected load is important, was diversity included in the calculation or was it the nameplate ratings of the machines that was used?

The two transformers, whatever their capacity, should not be run in parallel on the secondaries due to increased fault currents. The transformers should supply a double bus bar panel with bus section isolators and bus couplers to enable shifting of loads and/or transformer in-feeds.

The bus zone protection should be designed to cope with limited circulating currents whilst loads are being shifted or transformer feeders are changed; there is an acceptable risk involved during these operations.

However, care should be taken to ensure that both transformers have the same vector grouping and similar impedances and that the on line tap changers can be set to manual operation during load shifting.

Ask your consultants for details of their calculations and design in respect of the protection scheme for the installation.

Diversity factor

I was questioning the veracity of the information (3350 kVA) because of that very fact that there exists some confusion when assessing loads.

It is important to know whether or not demand factor was included in the initial assessment.

it's not taken in beginning

Hi achoor1

Why don't you send us a single line diagram showing your load distribution and I'm sure one of us can help you

If you company is likely to expand, then you'll have problems that time.

3350 kVA: Have you done a chronogramme of your loads to obtain this apparent power?

You have to couple each load with its time of delivery, put it on an horizontal diagram showing all loads during 24 hours, then, vertically, you will find the necessary true maximum load (which is probably 50 % of your installed load, 3350 kVA). Then you will choose what solution you need. If you have 2 trafos in parallel on the same LV bus, you may need a synchronous device to put the second onload, which is generally critical. Then, you need a HV breaker and a LV breaker by trafo and a LV breaker between the 2 trafos, in order to protect them correctly. More, with 2 trafos solution, you need, for each one, a trafo tank protection, in order to keep away problems of surge protection and, even, lightning protection, if the trafos have no shelters.

Good nights, BRZK.

Thanks for your answer, but my inquiry is for future installation, we have information getting from suppliers concerning consumption loads and we proposal of one consultant of installation of 2 transfo (2000+632)KVA ; but each transfo feed power to some equipment separately, I have doubt to can running 3350KVA by 2632KVA (consultant give diversity factor of 0,7)

Thanks & have a good night

3350 kVA down to 2632 kVA:

Does it include the derating factor due to high operating temperature (I understood you were in a hot country). If not, 2635 kVA seems optimistic. If yes, the trafos risks to be short in power. Generally, an operating factor of 50 % is necessary to avoid climatic over temperature and temperature due to continuous surge overvoltage in operation. A factor of 0.5 will guarantee a minimum life of ten years without tanking out the trafo. The bigger this derating operational factor, the shortest the life. This diversity factor of 0.7 seems a bit generous, in adding derating due to temperature and derating due to operation. A 0.5 factor seems to me, to be more adequate: that's give 1675 kVA instead of 2632 kVA (anyway 3350 x 0.7 = 2345 kVA !!) It seems you need a trafo of 2 MVA and a trafo of 1 MVA (not in a parallel mode, as you told me), in order to keep a good safety margin. the whole 2632 kVA seems to me too short, as par the hypothesis you gave to me (as far as i know nothing about the final loads). And what about the cooling of your trafos? Is it by air or by oil ? Which also change the final operational factor (632 kVA seems to be a dry type, but what about the 2 MVA trafo?).

Good night, BRZK.

the consultant give his new proposal with 632kVA (exist Oil type) + 2800kVA (new Dry type) to cover 3348kVA.

What you said?

Regards

17# already tell you to analyze loads. Diversity Factor means at the same time, how many loads are working.

There are different in day and night time.

The biggest loads at one time is your trafos' caculation bench mark. Now your thinking is 0.7. but you also need to split into 2 trafos.

Our talking about the diversity factor is basing on your consideration of power factor. That means before you are calculating the loads, you had already allowed for power factor.

The golden load coeffcient is 85%. Your total load is 3350KVA, you at least let your trafos reach to 3350*0.7/0.85=2758KVA. Due to your seperating load into to different Trafos, your trafos may be over 2758KVA.

IDTIEC606 IDIIEC354 EQVIEC905 may have details. I'm Chinese, so our standards let us design according 85%.

New dry type can overload, so the choosing detail will base on you load type.