Distribution Transformer Sizing
Distribution Transformer Sizing
(OP)
Can you determine the transformer size (kVA) given the estimated consumption (kWh) of that customer? If yes with what formulas?
When was the last time you drove down the highway without seeing a commercial truck hauling goods?
Download nowINTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS Come Join Us!Are you an
Engineering professional? Join Eng-Tips Forums!
*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail. Posting GuidelinesJobs |
Distribution Transformer Sizing
|
RE: Distribution Transformer Sizing
If you can estimate kwh, why can't you estimate maximum kW?
kVA=kW/pf. Assume pf of 0.8 if not known. Have some margin like 25% for growth or not stressing the system.
RE: Distribution Transformer Sizing
RE: Distribution Transformer Sizing
RE: Distribution Transformer Sizing
RE: Distribution Transformer Sizing
The engineering depts of most utilities work with the kVA (or kW) ratings. It's only the bean counters and revenue guys who hassle about the kWhrs
Bung
Life is non-linear...
RE: Distribution Transformer Sizing
Although engineering depts work with kVA or kW ratings, kWh is usually the only thing measured for individual residential customers. Many utilities have developed relationships between kWh usage and kW demand. There is no universal formula because it depends a lot on local conditions. The REA (now RUS) used to use a historic relationship for estimating feeder loads and published a series of tables. These were the basis for the "a" and "b" factors that you see in some distribution feeder analysis programs that can use kWh as input.
RE: Distribution Transformer Sizing
The load factor is defined as the ratio of the average kW (or kVA) for a service for all hours of a period, divided by the peak kW (or kVA).
LF = kWhr / (hours * kW(peak) )
Many industries or commerical services follow fairly consistant patterns. For example, a 24/7/365 automated warehouse will tend to have a laod factor of 75-85%. A 'mom'n'pop' restauraunt will have 30-45%, etc.
In my areas, feeders as a whole tend to have a monthly load factor of 70% (average/peak) and an annual load factor of 50-55%.
So long as you accept that these are averages and individiual services may vary, this can be a useful tool.
RE: Distribution Transformer Sizing
To solve sizing transformer,when three trans. are to supply a 225kva load-with connections wye to wye-can you assume supply at 480.
RE: Distribution Transformer Sizing
Appendix B of TM-5-811 on this site has some information on sizing transformers and diversity that may be applied to connecting residences to transformers.
http://www.usace.army.mil/inet/usace-docs/armytm/
RE: Distribution Transformer Sizing
RE: Distribution Transformer Sizing
Also, when you heat up a transformer you are paying for electrical generation and not getting to bill it. The practice of deliberately overloading transformers was to save on no load core losses. Since modern transformers have something like 10% of what the core loss was 100 years ago, some formulas are apt to be out of date.
Also, wound cores with very thin laminations have been able acheive losses comparable to stacked cores that use amorphous iron. The problem with stacked cores is that you have air gaps ( which increase magnetic density in adjacent laminations ) at the corners and at the corners the flux is 45 to 90 degrees against the grain orientation. Wound cores avoid that problem and Acme has found a way to economically produce wound cores.
Deliberate overloading of oil filled distribution transformers is also less acceptable if the customer has a heat pump or some other form of both air conditioning and electric heat. I have installed York's relay box for heat pumps tht are added onto a gas or oil furnace. This relay box uses an outside thermostat with form C contacts to determine when it is time to switch to fossil fuel. Add on heat pumps are apt to become more popular as gas prices go up. Here in northern Ohio most of the heating season is mild enough for heat pumps and the technology is better due in part to heftier motors.