Transformer size mula sa demand
I-size ang transformer mula sa demand, kasama ang paglaki at losses.
Subukan ang isang job 4
Nilalagyan ng halimbawang value ang bawat job. Palitan ang mga ito ng sarili mong value.
- Size a transformer for a new siteThe rating, loading and losses for a site demand with room to grow.
- Size a transformer from a kW demandA demand in kilowatts turned into the transformer rating at its power factor.
- Check a rural single‑phase transformerThe size and voltage drop of a single‑phase transformer for a farm supply.
- Check a plant transformer regulationThe voltage a large transformer drops at a low power factor.
Mga input
Worked example gamit ang mga default na input.
- Maximum demand
- 220
- Demand sa
- kVA
- Power factor
- 0.9
- Allowance para sa paglaki
- 20 %
- Karamihan ng loading sa design load
- 100 %
- Mga phase
- Three phase
- Primary voltage
- 11,000 V
- Secondary voltage
- 400 V
- Impedance
- 4.5 %
- X/R ratio
- 4
- No-load loss, ng rating
- 0.2 %
- Load loss sa full load, ng rating
- 1.1 %
Laki ng transformer
300kVA
- Design load na may paglago
- 264kVA
- Loading sa kasalukuyan
- 73.3%
- Loading na may paglago
- 88%
- Voltage regulation na may paglago
- 2.59%
- Mga pagkawala na may paglago
- 3.16kW
- Secondary full load current
- 433.01A
- Secondary fault current
- 9,622.5A
Design aid lang ang resultang ito. I-verify ito laban sa kasalukuyang standard.
Mga hakbang ng kalkulasyon
- Design load na may 20 % na paglaki264kVA
- Pinakamaliit na karaniwang laki sa 100 % na loading300 kVA
- Loading sa kasalukuyan73.3%
- Loading na may paglago88%
- Resistance, ng rating1.09%
- Reactance, ng rating4.37%
- Voltage regulation na may paglago2.59%
- Secondary voltage sa design load389.7V
- Mga pagkawala na may paglago3.16kW
- Efficiency kasama ang paglaki98.69%
- Secondary full load current433.01A
- Secondary fault current9,622.5A
Tungkol sa calculator na ito
How this is calculated
A transformer is sized from the maximum demand it will carry, with room for the load to grow. Too small and it runs hot and drops too much voltage; too large and it costs more and wastes energy in its core every hour of the year. This tool finds the size and shows what it does at the load.
You enter the maximum demand, in kVA or in kW with a power factor, and a growth allowance. The design load is the demand plus that growth. The tool picks the smallest rating from a list of typical sizes that carries the design load within the loading limit you set. The list is common distribution and site ratings, not a standard's list.
At that size it works the loading today and with growth, then the voltage regulation: the drop through the transformer's own resistance and reactance at the design load and power factor. The impedance on the rating plate splits into the two by the X/R ratio. The losses are the core loss, which is there whenever the transformer is energised, plus the winding loss, which rises with the square of the loading. The full load and fault currents at the size come from the transformer tool.
The impedance, X/R ratio and losses are maker's data. The defaults are typical figures, and the result names them as assumptions.
| Step | Table or clause | What it decides |
|---|---|---|
| Design load | Demand plus the growth allowance | The load the size must carry |
| Size | Smallest typical rating within the loading limit | The transformer rating |
| Resistance and reactance | Impedance split by the X/R ratio | The two parts of the drop |
| Voltage regulation | Loading times the drop at the power factor | The voltage lost through the transformer |
| Losses | Core loss plus winding loss times loading squared | The heat and the running cost |
| Currents | The transformer tool | The full load and fault current at the size |
Worked examples
- A 220 kVA site with 20 % growth needs a 300 kVA transformer. It runs at 88 % with growth and loses 2.59 % of its voltage.
- A 180 kW load at 0.85 power factor with 25 % growth also needs 300 kVA, at 88.2 % with growth.
- A 420 kVA factory with 30 % growth, loaded to 80 % at most needs 750 kVA, at 72.8 % with growth.
- A 60 kVA single‑phase rural supply with no growth needs 75 kVA, at 80 %.
- A 900 kVA plant at 0.8 power factor, 6 % impedance and X/R of 7 needs 1,250 kVA. Its regulation is 3.57 % at 82.8 % with growth.
Limits
The regulation is the drop through the transformer alone. The network upstream and the cables downstream add their own drop; the total voltage drop tool adds the cable parts. A tap changer or off-load taps can raise the secondary voltage to make up for it.
The tool does not cover transformers in parallel, harmonic loads, the temperature rise of the windings or the network company's own sizing rules for a supply transformer.
See also: Transformer, Maximum demand and Fault level at a board.
Mga tanong
Design aid ang resulta. I-verify ito laban sa kasalukuyang standard.
Paano ko i-size ang transformer?
Magsimula sa maximum demand, magdagdag ng allowance para sa paglaki ng load, at piliin ang pinakamaliit na standard rating na kayang dalhin ang resulta. Pagkatapos, i-check ang voltage drop ng transformer sa load na iyon at kung gaano karami ang nawawala bilang init.
Gaano karaming growth ang dapat kong isama?
Depende ito sa site. Karaniwan ang 20 hanggang 30 % kung saan malamang dadami ang load. Tumatagal ng dekada ang transformer, at mas magastos palitan ito mamaya kaysa kumuha ng isang size na mas malaki ngayon.
Ano ang transformer voltage regulation?
Ang pagbaba ng secondary voltage mula no load hanggang load, bilang porsyento. Galing ito sa resistance at reactance ng transformer, at mas malaki ito sa mababang power factor.
Bakit hindi na lang pumili ng mas malaking transformer?
Mas mahal ang mas malaking unit at tumatakbo ang core loss nito buong araw, araw-araw, kahit magaan ang load. Kapag i-size malapit sa load, tumatakbo ang transformer sa punto kung saan pinakamababa ang losses nito para sa enerhiyang inihahatid nito.
Saan galing ang impedance at losses?
Nasa rating plate ang impedance. Nasa test report ng maker ang losses at ang X/R ratio. Karaniwang figure ang default ng tool hanggang sa makuha mo ang totoong mga figure.
Mga kaugnay na tool
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