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Participant

Join Date: Jul 2012
Posts: 4

### Transformer Calculation

07/20/2012 4:49 AM

Hi,

I am living in Lahore, Pakistan. We have 40 houses in our lane and are using following appliances

No. of Air conditioners (18000 BTU)= 2/house

No. of refrigerators (16 Cubic Ft) =2/house

No of Ceiling Fans (150W) =4/house

No. of lights (40W) =6/house

No. of TV =2/house

No of Computers =2/house

No. of Washing Machines =1/house

No. of Microwaves =1/house

No.of Water pumps =1/house

Question is how many KVA transformer would be enough for 40 Houses ?

Thanks with regards

TIRMIZI

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Active Contributor

Join Date: Feb 2012
Posts: 24
#1

### Re: Transformer calculation

07/20/2012 5:34 AM

kw=pf*kva(t/f rating)... each house 350KW/HOUSE,350*40=14MW.IF YOU HAVE MANY MOTORS USED TO PF IS VERY LOW.APPROXIMATLY PF 0.8,

KW=14000.

PF=0.8,

KVA=17500KVA. YOU HAVE 17.5MVA RATING TRANSFORMER SUITABLE FOR YOUR HOUSES. THIS IS APROXIMATLY NOT EXACTLY....

Off Topic (Score 8)
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#2

### Re: Transformer calculation

07/20/2012 5:34 AM

The local utility company will have ready-reckoners for this sort of thing that are based upon local experience, so these people would be the best ones to approach.

• In the UK, for instance, each home will usually have a 100A rated and fused single-phase feeder at 230V. However, no home draws 100A all the time, and a measure of diversity will be used to size the transformer; locally the average current drawn over a quarter-year is 2A or so for a home that uses electric cooking and if the cooking is otherwise then the average draw will be somewhat less. Larger homes might run to a three-phase supply at a higher tariff, though the single-phase loads will be split across the three phases; there is little of a domestic nature that requires a three-phase supply in itself.
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#13

### Re: Transformer calculation

07/24/2012 12:14 PM

Off Topic (Score 5)
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#3

### Re: Transformer Calculation

07/20/2012 7:29 AM

Without knowing what diversity factors you are allowed (or required?) to use, my estimate is 250 KVA, which at 0.8 PF would equate to 200 KW.

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#4

### Re: Transformer Calculation

07/20/2012 11:17 PM

In a Ms excel sheet enter the loads,diversity factor,load factor etc and calculate. If not sure show it to an experienced engineer and verify.

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pnaban
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#5

### Re: Transformer Calculation

07/21/2012 1:38 AM

Trimzi sb, would u take 11KV feeder from LESCO? which area is that in Lahore? Transformer is the property of LESCO in Lahore and they provide it according to your load.

Participant

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Posts: 4
#7

### Re: Transformer Calculation

07/21/2012 2:12 AM

Zaman Sb Assalam O Allaikum,

We all are layman, Let me brief you, As I told you that we have 40 houses in our lane. there are 5 lanes that are running on 1 transformer of 250 KVA. Every day that transformer turns out of order and we spend our whole night in the street. We have requested LESCO several times but they did not agree that its overloaded. After several years of efforts they agreed to provide one more transformer of 100 KVA that will share the load of previous one of 250 KVA for the same 5 lanes (each contains 40 house). When I do calculate our one lane need approximately 200 KVA load, so how come they dont agree in providing at the rate of 200 KVA for each lane.

I am living in Nizam block, Allama Iqbal town Lahore.

How can we ask them to provide 11 KV feeder from them? or even we dont know which feeder supplies here.

This was the reason I wanted to know from experts that what should be the capacity of that transformer for 1 lane ?

regards

TIRMIZI

Participant

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Posts: 4
#6

### Re: Transformer Calculation

07/21/2012 2:00 AM

The total KW will come around 200KW and if the power factor will be taken =0.8

then the total KVA required will be around 250KVA

but the above calculations based on total connected load without diversity factor consideration.

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#8

### Re: Transformer Calculation

07/21/2012 2:26 AM

I don't know what LESCO's thinking would be, unless they are trying to size the transformer on average load rather than near peak load. Wouldn't it be more profitable for them to provide adequate transformer(s) and thus sell more electricity?

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Participant

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#9

### Re: Transformer Calculation

07/21/2012 4:10 AM

Yes Tornado, you are absolutely right, but the problem is we have load shedding of 12 hours a day, they don't have electricity (according to them).

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#10

### Re: Transformer Calculation

07/23/2012 9:49 AM

If the supplier simply doesn't have the electricity to sell, then it explains why the supplier is reluctant to replace the transformer with a larger one, and it also explains the power outages. Demand has simply outstripped supply.

However, this would point to a significant investment opportunity for the supplier. Point it out to them.

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#11

### Re: Transformer Calculation

07/23/2012 10:04 AM

The Client should submit to the Utility a technical report prepared by an experienced engineer(C.Eng/P.E) showing calculations or readings taken by a power analyser to convince them the actual demand.

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#12

### Re: Transformer Calculation

07/24/2012 4:25 AM

They have monopoly, no other party has right to enter as a power supplier directly. If in case someone wants to produce electricity, new entrant will supply to LESCO who has the only distribution rights all over the city LAHORE. ITS A BIG WHITE ELEPHANT working under our beloved MINISTERS

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#14

### Re: Transformer Calculation

07/24/2012 11:25 PM

Approach a good lawyer or consumer protection authority.

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