Power Distribution Project

Is this a test question?

no .. this is my graduation project .. we ( 12 engineer in a team) have to discuss the basics for electric power distribution .. so we have to search and find answers by ourselves .. i hope you can help me find my answer ?

Find an answer by yourself has taken on a whole new meaning.

CR4 has a no homework policy. This sounds like homework to me.

I can't help you. Others may choose to. Remember, we may not be there when you get a job and need to do the work yourself.

Good luck.

You got me wrong :) .. this is not a homework ..

This is a point of discussion in our project ..

the trainer said we can load the pillar with 100% of it's KVA

the professor said .. no we can load the pillar with only 80% of It's KVA

we have the right to choose .. only that I needed to hear a third opinion ( a right one ) according to his\her experience in that career.

I want to accomplish my project as perfect as I can.

thanks in advance.

Define what you mean by a pillar. how did you arrive at the 80% figure?

In the USA, the power distribution companies load transformers too much more than 100% of rated KVA for residential loads.

The power companies thinking is that residential loads are only on for a short period of time, the ambient temperature is rarely the maximum temperature that the transformer is rated for and it is cheaper for the power companies to occasionally replace a transformer than the cost of the larger transformer and the no load losses.

Why don't you contact a power company in Egypt and see what their policy is. Let us know what the power company's policy is in Egypt please.

hi

in engineering, any equipement which is been ment to drive desired load, means if we need to have run a load of 10 kW, the rating of generator must be at least 10 kW,

so when u draw 10 kW from generator means drawing 100 % of it, now if load is capable of drawing only 8 kW i.e. generator is at its 80 % capacity but load is at its 100 % capacity,

this will help to solve ur problem

ok bye

thanks & regards

I can't resist getting in on this one.

Try some simple logic - you have 4 pillars each loaded to 200kVA then that equals a total load of 800kVA - if the load on the Transformer is 800kVA then the load on each 200kVA pillar is 100%.

If you add in another pillar you can increase the load on the transformer to 1000kVA.

None of this of course allows for load variations in the network, temperature rise constraints on loadings, power factors & many other system constraints.

One other point - you have no spare capacity in the 4 pillars - so don't add anymore load or you will be in trouble for overloading the pillar & then you get into the world of premature aging (bit like me really).

first of all it will not be economical to load the transformer at 80%, because the loads will never be turn on at the same time. you need to study the load patterns in your country (obtain data from local power supply/distributor) and apply correct diversities.

applying the correct diversities, you should be able even to put more load on these (Tx and FP) than their rated capacity.

pls study more on the economics of power systems, diversities, maximum demand, etc to get a break through.

Have you tried asking your teachers for help or is this not "culturally" permitted (as in Thailand)? A professor says one thing...a lecturer says another thing. No wonder you are confused.

Anyway, you have overlooked one thing...the learning process is not about getting top marks. It's about "learning", which means making mistakes.

Some of the best engineers, with whom I've had the pleasure of working, didn't do all that well at university.

Have you tried some university resources, like the library?

When I was learning engineering, there was no such thing as the internet...& I'm glad there wasn't!!! I had to do it all by myself.

In the US if we know a specific load we figure 80%, but for a calculated load we figure at 100%. This is because of load diversity. The utilities figure over 100% because they know from experience how the demands will play-out. Like some said, they may replace a transformer occasionally, but save money overall. An example is a dwelling unit. Notice that the sum of the branch breakers will exceed the value of the main breaker. When we calculate the loads we use demand factors from NEC Article 220 and still calculate up to 100 of the main breaker value. This is because we know all the circuits in the house will be on at the same time for 3 or more hours. Now consider many dwelling units...

I believe you would load each pillar up to 100% of rated value, but the term pillar is not familiar to me. There are not many good reasons to limit the transformer to 80% of its rating. Utility companies do overload transfomers but not for initial loads. If I had a new load of 950 kVA, I would install a 1000 kVA transformer, but I would not replace it until the load got up around 1250 to 1300 kVA on a long term basis. Even then it depends upon the load. If that load was electric resistance space heating, then I know it is on in the winter only and the transformer will be cooler. If it is air conditioning load, then the outside heat affects the transformers ability to cool and it won't carry as much load. Transformer loading is also based upon available sizes. If my load was 800 kVA, I might put in a 1000 kVA because the only alternative is a 750 kVA and that is too small. If this was a purely residential neighborhood, a 1000 kVA would be way too large for any application. You would have so many residences connected that the low voltage circuits would be too long and the houses would suffer from voltage drops and flicker. I would have smaller transformers placed closer together. If you have commercial loads, such as stores or offices on the transformer, then that is different. Diversity of load also plays a part. If I had 50 houses with a load of 20 kW each, then I would expect my total load to be much less than 1000 kW, maybe as low as 650 to 700 kW and I would size the transformer accordingly. There might be a time over a sustained period of very hot weather when the air conditioners cause the load to be higher than normal and I might burn up a transformer, but the economics are to do that rather than waste money on excess transformer capacity. Mixing commercial load with residential load also affects diversity. Businesses may reach their peak demand in mid afternoon, but the residences won't until early evening when people are home from work, watching tv and fixing dinner. Pretty big answer for a small question, but there are so many things to consider if you are designing a distribution system.

Hi,

well pillars here has no ralation with the power rating or the ratio you are using from the original one of the transformer, as a total you are loading the transformer with 80% of it's rating even if you fully loded the pillars.

Thank you

Electrical Eng.

Wisam Fatouhi

Iraq "wisamdaheen@yahoo.com"

Thanks Alot ..

In my design I will load each pillar with 80% only even this is not economoical dispatch .. so that in case the loads increased that the value I have designed for .. there will be a safety factor & we will not need to change the transformer rating after all...

so finally .. Pillar will be loaded with 80%

& Transformer will be loaded with 80%

Egypt-cairo

whats your calculated load?

Have you consiedered utilization factor of connected eqpts,simeltanuity factor etc.