Generator sizing mula sa load list
I-size ang generator mula sa load list kasama ang motor starting.
Subukan ang isang job 4
Nilalagyan ng halimbawang value ang bawat job. Palitan ang mga ito ng sarili mong value.
- Size a generator for a bore pumpThe set for a 5.5 kW bore pump started direct on line after the lights.
- Size a generator with a star-delta startHow much smaller the set is when the pump starts star-delta.
- Size a standby set for a dairy shedThe set for milking plant, vacuum pump and hot water started in turn.
- Size a generator for a building chillerThe set for lighting, a chiller on a drive and lifts, derated for heat.
Mga input
Worked example gamit ang mga default na input.
- Mga phase
- Three phase
- Voltage
- 400 V
- Mga load, kasama ang step kung saan nagsisimula ang bawat isa
- 2 row
- Pinakamalaking voltage dip na pinapayagan
- 15 %
- Subtransient reactance
- 15 %
- Rated power factor
- 0.8
- Derating para sa altitude at init
- 0 %
Rating ng generator, hindi bababa sa
50kVA
- Running load
- 19.05kVA
- Laki na itinakda ng
- Starting step 2
- Pinakamalaking dip sa laking ito
- 15%
- Full load current sa laking ito
- 72.17A
- Fault current sa laking ito
- 481.13A
Design aid lang ang resultang ito. I-verify ito laban sa kasalukuyang standard.
Mga hakbang ng kalkulasyon
- Load 1: 10 kW, step 110kVA
- Load 2: 7.5 kW na motor, direct on line, step 29.8 kVA habang tumatakbo, 58.82 kVA sa pag-start
- Running real power18.33kW
- Running reactive power5.16kvar
- Running load19.05kVA
- Itakda ang kVA para sa running load, hindi bababa sa22.92kVA
- Step 1: itakda ang kVA para sa 15 % na dip8.5kVA
- Step 2: itakda ang kVA para sa 15 % na dipResulta50kVA
- Sukat na itinakda ngStarting step 2
- Pinakamalaking dip sa laking ito15%
- Full load current sa laking ito72.17A
- Fault current sa laking ito481.13A
Tungkol sa calculator na ito
How this is calculated
A generator has to do two things. It has to carry the running load, and it has to hold its voltage when a large load starts. A small set can run a pump but still dip so far as the pump starts that lights flicker and contactors drop out. This tool works both and gives the larger as the size.
You list the loads with the power each draws, its power factor and the step it starts in. Loads in the same step start together. For the running load the tool adds the real power and the reactive power of every load, then takes the kVA from both. Loads at different power factors do not add as kVA. The set must also give the real power at its own rated power factor, which is often 0.8.
A motor draws more than its running current as it starts. The tool takes the motor's running kVA from the motor tool's full load current, then multiplies it by the start: six for direct on line, a third of that for star-delta, the multiple you enter for a soft starter, and one for a variable speed drive. For each step the tool finds the smallest set whose reactance keeps the dip within the limit you set. The largest need, running or starting, divided by what is left after any reduction for altitude and heat, is the size. The generator tool then gives the full load current and fault current of a set at that rating.
AmpSize holds no generator standard. The dip limit, the reactance and the soft starter multiple are inputs, and the result says so.
| Step | Table or clause | What it decides |
|---|---|---|
| Running load | P and Q added, kVA from both | The set kVA for the running load |
| Rated power factor | Set kW = kVA × rated pf | The set kVA for the running kW |
| Motor starting kVA | The motor tool's full load current × the start multiple | The kVA each step draws as it starts |
| Voltage dip | Dip = x × step kVA ÷ (set kVA + x × step kVA) | The set kVA for each step |
| Altitude and heat | Size ÷ (1 − the reduction) | The rating to buy |
| Current and fault level | The generator tool | The full load current and fault current at that rating |
Worked examples
- Farm lights, then a 7.5 kW water pump direct on line needs 50 kVA. The pump start sets the size, as Starting step 2, against a running load of 19.05 kVA.
- The same pump on a star-delta starter needs 22.92 kVA. The running load sets the size now, at a running load of 19.05 kVA.
- A dairy shed: milking plant, vacuum pump and hot water in turn needs 50 kVA. The vacuum pump's direct-on-line start, Starting step 2, sets it, against a running load of 34.96 kVA.
- A building's lighting, chiller on a drive and lifts, derated 10 % for heat needs 97.22 kVA. The running load sets the size at a running load of 79.44 kVA.
Limits
The dip is worked from the set's subtransient reactance alone. It leaves out the voltage regulator's recovery, the engine's speed dip, and loads already running, which a maker's sizing program models. Use the size as a first pick, then check it on the maker's data.
The tool does not cover a set in parallel with the network, a non‑linear load's effect on the alternator, or the installation rules for a generating set.
See also: Generator, Motor and Maximum demand.
Mga tanong
Design aid ang resulta. I-verify ito laban sa kasalukuyang standard.
Paano ko i-size ang generator para sa motor?
Humihila ang motor ng ilang beses ng running current nito habang nagsisimula, at bumababa ang voltage ng set. Kinakalkula ng tool ang starting kVA ng bawat step at ang set size na nagpapanatili sa dip sa loob ng limit na itinakda mo.
Bakit hindi lang basta sum ng kVA ang running load?
Ang mga load na may magkakaibang power factor ay idinadagdag bilang real at reactive power. Idinadagdag ng tool ang kW at kvar, pagkatapos ay kinukuha ang kVA mula sa dalawa. Dapat ding ibigay ng set ang kW sa rated power factor nito, na kadalasan ay 0.8.
Anong voltage dip ang dapat kong payagan?
Depende ito sa mga load. Kumikislap ang ilaw sa mas maliit na dip kaysa kayang lampasan ng motor, at puwedeng mag-drop out ang contactors sa malaking dip. Walang hawak na generator standard ang AmpSize para magtakda ng limit, kaya ikaw ang mag-e-enter nito.
Gaano kaliit puwedeng maging set kapag may soft starter o VSD?
Bumababa ang starting kVA kasabay ng starting current. Ang star-delta ay nagsisimula sa isang katlo ng direct on line. Ang soft starter ay nagsisimula sa multiple na ilalagay mo, at ang variable speed drive ay malapit sa running current nito.
Isinasaalang-alang ba nito ang altitude at init?
I-enter ang derating ng maker bilang percent. Hinahati ng tool ang size sa natitira. Ibinibigay rin nito ang full load current at fault current ng set sa rating na iyon, mula sa generator tool.
Mga worked example
Background
Mga kaugnay na tool
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