Updated Electric Utility Factors 1

[saladhawks]

I am in the process of updating the service factors for the U.S. Utility that I currently work for. I was wondering what other updated resources (on-line or print) are available to check against. I am specifically interested in data related to Coincident (aka Demand) and Load Factors for residential, commerical, and industrial loads. I use these factors to determine the required utility service, transformer, and cable sizing for new projects.

Thanks in advance.

 

[cuky2000]

Below are typical parameters used by a large utility in the US for residential applications.

 

[waross]

Cuky2000;
Can you tell us what part of the US the city is in? I am under the impression that the farther south you go, the higher your diversity factor because of the increased air conditioning loading.
Thanks.
respectfully

 

[romanskat]

Hi waross,having a doubt to inter-relating air conditioning increase with higher diversity factor.Could further explain?
Thanks.

 

[waross]

In the hotter climates, more airconditioning is used than in the cooler climates. When it is hot, the air conditioning is all on and there is very little load diversity.
In the cooler climates, air conditioning tends to be a lower percentage of the load.
A utility may also decide to size the transformers for 48 or 50 weeks and accept some overloading during the hottest weeks. This would not be feasible in a climate where the "hottest" weeks may last for months.
respectfully

 

[saladhawks]

My definition of diversity factor must be different from yours.

Diversity Factor = Sum of individual Peak Demands / Peak Demand of whole System

Thus, the Diversity Factor should always be a value greater than 1.

On the other hand,

Coincident Factor = Peak Demand of whole System / Sum of the individual Peak Demands.

This is the reciprocal of Diversity Factor and is a value less than 1.

 

[tinfoil]

Further to waross:

In areas where air conditioning predominates, load peaks when the utility system has the most difficulty dispersing heat - when it is hot.

In areas where peaks are from cold weather, there's a built-in increase in the system's ability to shed heat - because it is cold out and/or the wind is blowing hard.

This is aggrevated by 'cold load' effects after a prolonged outage, or even after a peak-shed rolling blackout - The diversity factor for air conditioners approaches 100% at a time when the system is peaking, AND it is hot out. This is the worst=case you must design against when choosing a diveristy factor in the south.

In the north, there's less aircon, and the hottest day is less hot.

 

[waross]

Hi saladhawks;
I wasn't sure which was the proper terminology so I checked the graph that Cuky200 posted. The more important point that I think that we agree on is that a diversity factor that is valid in the North may not be valid in the South.
respectfully

 

[cuky2000]

Hi Waross,
The information above is from Jacksonville Electric Authority (JEA), that operate in Florida.

Those data are based in local statistic history of demand for their customer in their region. Even though this is a good generic information, those data are not universal and have to be validated based in local conditions of the load behaviour and supplemented with experience or measuments.

In colder climate, usually the higher demand happens in summer time and coincide with the lowest rating capacity of the equipment, cable and other system components. As an example, see the enclose curve for transformer rating based in 30oC for 24 hr average ambient temperature.

http://cuky2000.250free.com/Tr_Load.jpg

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Saladhawks

The definition of diversity factor could be as you say and as presented above. Please remember that those factors are statistic indicators used for load estimation purpose.

What it is important, is how you use then to calculated the estimated size of transformer, feeder and other equipment.
For instance, the following two cases are equivalent:

a) For diversity Factor, DF₁<1
Transf. Size > Est. Individual demand*No Customers* DF₁

b) For DF₂ >1
Transf. Size > Est. Individual demand*No Customers / DF_{2
Beware that utility may not require to comply with NEC. For work under the jurisdiction of NEC or other codes, the mandate requirement should be accommodated by selecting equipment and conductors that are adequate to supply the code-complying load.}

 

[rasor1514]

JEA :-D
I thought those tables looked familiar...