Pole Lights Calculation

[Sahib]

200-300 amps can be large enough current. Big wire can get expensive real quick..

Here only ampacity of wire is concerned and not the voltage drop and no need to maintain the voltage within limits at the ballast input and so the wire size will not be too big.

Easy enough to do if the economics are right.

In that building which availed LV supply? It is difficult to agree with you.

 

[mivey]

Here only ampacity of wire is concerned and not the voltage drop and no need to maintain the voltage within limits at the ballast input and so the wire size will not be too big.

Believe whatever you want. Compare the costs over distance and you will reach an economic crossing point between LV and MV as the distance increases.

Easy enough to do if the economics are right.

In that building which availed LV supply? It is difficult to agree with you.

Economics are economics. Many complexes have more than one supply transformer. Many add an additional supply transformer when the load gets big enough. Everything is not always served off of one supply at the far end of the complex. That's just the way it is whether you choose to agree or not.

 

[mivey]

But consider a situation where two different bean counters are in charge of installation and operation costs. You can deliver quite a bit of power using only 12 AWG wire at 480V, and if you are willing to tolerate losing 25% of that power to heating the wire, you can go for quite a distance. Compare the price of 4000 feet of 12AWG with 1000 feet of single phase MV and a transformer......

OK, I looked. You can deliver around 3 kW at somewhere around 4.5 amps. MV would not make sense at these power levels.

The scenario for this thread is in the neighborhood of hundreds of kW and amps.

 

[mivey]

I disagree with your final calculation. Assuming a constant power load, transformer loading will increase by 1/(fraction voltage remaining). So if you have a voltage drop of 10% with a constant power load, I would expect transformer loading to increase by 11%.

I agree. The other was probably the more like the I^2*R loss I estimated.

I looked at my scratching and see I forgot to take my per-phase loss times three. Oh well.

Even so, for the loads being discussed, it still makes more economic sense to extend the MV line long before we reach a 25% volt drop. Not only because of the energy losses but the higher LV installation costs for the big wire over that long distance.

I do agree with the long LV run making sense for smaller loads (assuming the vdrop is acceptable) as you mentioned in your other post.

 

[Sahib]

mivey:
Our discussion is not about whether the OP requires MV supply or not but about the industrial practice i.e the statement

80% loading of transformer is an industrial practice. This may be adopted in the OP's case.

is applicable or not.

 

[mivey]

mivey:
Our discussion is not about whether the OP requires MV supply or not but about the industrial practice i.e the statement

To conclude:
80% loading of transformer is an industrial practice. This may be adopted in the OP's case.

is applicable or not.

Really? So we come full circle?

The load calculations include safety margins for things like power factor estimates, parasitic loads, etc. This is the reason Laszlo said he would not load a transformer to 100% because there was not room for safety margins given the sketchy information from the OP. That went completely over your head.

As part of our load estimate, we often include known near-term growth in the load calculations as well. We also include things like room for load swapping in emergency conditions. After these base loads are estimated, it is generally acceptable to include a factor for unknown growth if it is reasonable to do so and this is where we get the 80% practice. This number may be higher or lower based on experience with the particular load type.

You started out stating the OP should use this industrial practice of 80% loading. That practice is to allow room for growth above the current load. Well guess what?: A static load needs no allowance for growth. When called on that you came up with the silly notion that the practice was not for growth but for other things like losses. On the contrary, losses are included as part of the base load calculations.

We went down the whole road of demonstrating why this loss goofiness was a premise based on ignorance of the topic. We would not reach a 20% loss under reasonable conditions. Even if we did with a goofy scenario, this size load would be calculated as part of the base load since it is not something you would ignore and account for in the slop. A parasitic load this big would not be left up to some wild swing using some percentage grabbed out of the air.

We are now back to the beginning where you propose that the OP buy more transformer than they will ever use. What possible reason will you give now?

 

[Sahib]

The load calculations include safety margins for things like power factor estimates, parasitic loads, etc. This is the reason Laszlo said he would not load a transformer to 100% because there was not room for safety margins given the sketchy information from the OP.

Yes. I also meant that.

That went completely over your head.

No.

As part of our load estimate, we often include known near-term growth in the load calculations as well. We also include things like room for load swapping in emergency conditions. After these base loads are estimated, it is generally acceptable to include a factor for unknown growth if it is reasonable to do so and this is where we get the 80% practice. This number may be higher or lower based on experience with the particular load type.You started out stating the OP should use this industrial practice of 80% loading. That practice is to allow room for growth above the current load. Well guess what?: A static load needs no allowance for growth. When called on that you came up with the silly notion that the practice was not for growth but for other things like losses. On the contrary, losses are included as part of the base load calculations.

No, the 80% loading is not meant for load growth but to take into account any adverse conditions the transformer is likely to operate under.

We went down the whole road of demonstrating why this loss goofiness was a premise based on ignorance of the topic. We would not reach a 20% loss under reasonable conditions. Even if we did with a goofy scenario, this size load would be calculated as part of the base load since it is not something you would ignore and account for in the slop. A parasitic load this big would not be left up to some wild swing using some percentage grabbed out of the air.
We are now back to the beginning where you propose that the OP buy more transformer than they will ever use. What possible reason will you give now?

The OP has not given full details but you gave him suggestion as to the number of pole lights without stating any condition under which it would be applicable. So I brought up the 80% loading factor to make the OP realize that voltage drop in the cables can become a significant factor in some circumstances as discussed above and that he should not be misled by your earlier discussion in this thread.

 

[mivey]

No, the 80% loading is not meant for load growth but to take into account any adverse conditions the transformer is likely to operate under.

Adverse conditions will be part of selecting the proper transformer, not just picking an unrelated percentage out of the air. You can have ratings for different ambient temps, k-factors, etc. Once you have selected the proper transformer, you have the rating for your environment and work from 100% of this value, not 80%.

The OP has not given full details but you gave him suggestion as to the number of pole lights without stating any condition under which it would be applicable.

Without better info, I used typical conditions that I might see for highway lighting and erred on the worst case side.

So I brought up the 80% loading factor to make the OP realize that voltage drop in the cables can become a significant factor in some circumstances as discussed above

Your premise about a 20% loss from voltage drop is nonsense.

and that he should not be misled by your earlier discussion in this thread.

I gave my decision guidelines for several scenarios from 8 to 11 poles with an appropriate disclaimer:

I picked 8 poles and said maybe 9 poles. Better data would yield a better answer.

 

[mivey]

No, the 80% loading is not meant for load growth but to take into account any adverse conditions the transformer is likely to operate under.

By the way:


http://www.csemag.com/single-articl...ildings/4efa064775c5e26f27bfce4f0a61378e.html

A general approach to determining transformer capacity and selecting the proper rating for the design application is to obtain the calculated design load from the respective electrical schedule and add 20% spare capacity for future load growth to be shown in the equipment schedule, unless otherwise directed by the facility based on design parameters.

http://ecmweb.com/content/choosing-transformers-power-distribution-projects

Once you've done the individual calculations and added them up to arrive at the maximum coincident load, you should add in contingency factors for reasonable unplanned load growth (20% is common) and for planned additional load.

http://www.electrical-installation.org/enwiki/Other_field...

'Electrical Design from TRANSFORMERS to Distribution Boxes' (Conforming Indian Standards)
...Provide 20% spare capacity for future expansion

http://www3.algonquincollege.com/ph...lectricalServiceandDistribution2008-07-21.pdf

2.6 Transformers and services are to be sized to provide 25% spare capacity above maximum demand.

http://www.fs.uiuc.edu/uiucfacility...delines/Electrical Systems, Building-Rev1.doc

N.Flexible Design: As mentioned previously, the usage of spaces within University buildings, especially laboratory spaces, changes often. Remodeling is a common occurrence. Therefore, the building electrical systems shall be designed with sufficient flexibility and spare capacity to accommodate substantial future changes. Generally, a spare capacity of 25% (minimum) shall be provided throughout each electrical system, from the reserve transformer capacity to the number of spare spaces in each branch panel.

 

[Sahib]

Adverse conditions will be part of selecting the proper transformer, not just picking an unrelated percentage out of the air. You can have ratings for different ambient temps, k-factors, etc. Once you have selected the proper transformer, you have the rating for your environment and work from 100% of this value, not 80%.

Correct. But if you do not have such data readily available or the work to be carried out urgently or in the OP's case, you need to apply 80% or if you are pleased 85% factor to arrive at the transformer capacity.

Without better info, I used typical conditions that I might see for highway lighting and erred on the worst case side.

Not good. As an Engineer, you need to take into account all contingencies into account and provide an appropriate suggestion.

Your premise about a 20% loss from voltage drop is nonsense.

My point was not only about losses from voltage drop ( I did not mention anywhere that 20% loss was from voltage drop in the alone), but about all losses so that the transformer is not overloaded.

I gave my decision guidelines for several scenarios from 8 to 11 poles with an appropriate disclaimer:

That was not enough and liable to mislead the OP, IMO.

 

[Sahib]

By the way:


http://www.csemag.com/single-articl...ildings/4efa064775c5e26f27bfce4f0a61378e.html


http://ecmweb.com/content/choosing-transformers-power-distribution-projects


http://www.electrical-installation.org/enwiki/Other_field...


http://www3.algonquincollege.com/ph...lectricalServiceandDistribution2008-07-21.pdf


http://www.fs.uiuc.edu/uiucfacility...delines/Electrical Systems, Building-Rev1.doc

The 80% or 85% loading of transformer to take into account adverse conditions does not include the spare capacity as mentioned in your above references. One evidence for this is mentioned in this web page of Electrical Wing of Telco BSNL,India on page No.41,item no.2&4:

http://www.electrical.bsnl.co.in/electromechanical_book.pdf

 

[weressl]

1. Yes. I also meant that.
2. No.
3. No, the 80% loading is not meant for load growth but to take into account any adverse conditions the transformer is likely to operate under.
4. The OP has not given full details but you gave him suggestion as to the number of pole lights without stating any condition under which it would be applicable. So I brought up the 80% loading factor to make the OP realize that voltage drop in the cables can become a significant factor in some circumstances as discussed above and that he should not be misled by your earlier discussion in this thread.

1. Of course you did.
2. Of course it didn't go over your head.
3. Of course it didn't.
4. Stop misleading people Mivey and follow the example of Sahib, already.....

 

[Sahib]

You are sober today. :thumbsup:

 

[weressl]

You are sober today. :thumbsup:

I've been sober for 27 years oh all knowing Maharishi.

 

[mivey]

Correct. But if you do not have such data readily available or the work to be carried out urgently or in the OP's case, you need to apply 80% or if you are pleased 85% factor to arrive at the transformer capacity.

Waffling so you can refer to the percentage from your source in your next post? Please hit the ATM and buy a clue.

Not good. As an Engineer, you need to take into account all contingencies into account and provide an appropriate suggestion.

How many highway light designs have you done, sir? I suspect not many if any.

All contingencies?
Cooke's Law: In any decision situation, the amount of relevant information available is inversely proportional to the importance of the decision.

reminds me of another:
David Mahoney Jr.: You'll never have all the information you need to make a decision. If you did, it would be a foregone conclusion, not a decision.

My point was not only about losses from voltage drop ( I did not mention anywhere that 20% loss was from voltage drop in the alone), but about all losses so that the transformer is not overloaded.

Oh great fountain of experience and knowledge, what other losses are you talking about that get us to 20% loss?

That was not enough and liable to mislead the OP, IMO.

Speaking of misleading, let's move on to your next post...

 

[mivey]

The 80% or 85% loading of transformer to take into account adverse conditions does not include the spare capacity as mentioned in your above references. One evidence for this is mentioned in this web page of Electrical Wing of Telco BSNL,India on page No.41,item no.2&4:

http://www.electrical.bsnl.co.in/electromechanical_book.pdf

The link does not work but I found your reference.

Subject:- Provision of Transformer Substation & Engine Alternator in Telecom Buildings - ISSUE of Guidelines.
...
2. Transformers shall be selected for 85% loading, so that cushion is available for adverse environmental conditions.
...
7. Wherever open land is available out-door type substation may be preferred

So what does an adverse indoor environment have to do with an outdoor transformer designed for the outdoor environment?

 

[mivey]

1. Of course you did.
2. Of course it didn't go over your head.
3. Of course it didn't.
4. Stop misleading people Mivey and follow the example of Sahib, already.....

What are points about my hero?

I'll take sarcasm again for 400 points Alex.

 

[Sahib]

Waffling so you can refer to the percentage from your source in your next post? Please hit the ATM and buy a clue.
Ha Ha, you are too exacting.
How many highway light designs have you done, sir? I suspect not many if any.

All contingencies?
Cooke's Law: In any decision situation, the amount of relevant information available is inversely proportional to the importance of the decision.
reminds me of another:
David Mahoney Jr.: You'll never have all the information you need to make a decision. If you did, it would be a foregone conclusion, not a decision.

Ha Ha, you are too exacting. The OP has to take a decision not you. Better try to provide him with all relevant information at your disposal and let him choose from the data supplied.

Oh great fountain of experience and knowledge, what other losses are you talking about that get us to 20% loss?

Take allowance for primary voltage hike, losses in switch, fuse/breaker, change in air density due to height, ambient temperature etc., But don't get fixated on 20% loss: those losses won't add up to 20%. The losses due to voltage drop in the cables to be taken into account.

 

[Sahib]

So what does an adverse indoor environment have to do with an outdoor transformer designed for the outdoor environment?

The point mentioned in serial no.2 of the said reference does not specifically state that it is applicable to indoor transformer only. So please don't mislead.

 

[mivey]

The OP has to take a decision not you. Better try to provide him with all relevant information at your disposal and let him choose from the data supplied.

I used the information at my disposal. The OP provided very little. I drew upon my many years of experience to provide an educated respond with the given data. You on the other hand seem to have very limited experience with this and are just swinging wild. Perhaps you should learn what you are talking about before you talk about it.

Take allowance for primary voltage hike, losses in switch, fuse/breaker, change in air density due to height, ambient temperature etc.,

Still complete nonsense.

But don't get fixated on 20% loss: those losses won't add up to 20%. The losses due to voltage drop in the cables to be taken into account.

20% was your number, not mine. Your lack of experience made you throw that number out there and now you are trying to find a way to justify a statement made in ignorance. Just admit you stepped beyond the scope of your experience and let it go at that.