Unlike the mains utility, which for residential applications and smaller industrial applications has unlimited scope to support the starting of motors and other electrically disruptive equipment, a diesel generator must be properly sized to ensure it meets the required demands of the application.
Firstly its important to understand the rating of a generator that you might purchase. Generators are usually sold in kVA or sometimes kW. These are not same and the relationship between the two is expressed as the power factor, which is typically 0.8, so kVA x pf = kW. So if you have a 100kVA generator, at a 0.8 power factor, it will produce 80kW of electrical power.
In simple terms the kW portion of the generator is the real work done. This powers your lights, heaters and moves the air from your fans. The difference between the kVA and kW value is "wasted" power, thats called kVAr. It flows around the circuit, but does nothing useful.
Broadly these can be split into two categories - resistive and inductive. Inductive loads cause "real" and "wasted" part whereas resistive loads cause only the "real" part.
If you only have resistive loads, then the sizing is easy. You can safely add the ratings of all the items you have and work out how many kW you need. The only thing you really need to do is check the load acceptance of the generator. All generators have a load acceptance which limits the single step load to prevent the engine slowing down more than 10%. Typically this single step it might be 60% (you would fine this on the engine or generator specification sheet), so if you want to apply your full load in one attempt then you need a generator where 60% of its rating represents the load you have just calculated. If you can turn everything on gradually, you won't need it to be as big, which saves you money.
If you have inductive loads it gets more complicated. You need to be able to calculate how much "real" power ( that's kW) you need and how much "wasted" (that's the kVAr) power you will have.
When you have the kW and kVA values, you can use the kW as above. Then with the kVA you need to do a similar calculation to the alternator. With the alternator taking this kVAr (the difference between the kVA and kW), what happens is the voltage drops. This voltage drop will cause light flicker and potentially some equipment to turn off. 30% is considered the maximum, but for many controls its too much and 15% is a much more reasonable figure again you need to look at the generator or alternator specification sheet.
Two or Four Pole alternators
Its an important distinction - do you know the difference between two and 4 pole machines. Here is a short explainer video showing the difference. The faster an engine runs, the more fuel it will consume, so knowing how long you expect to run for is critical.
Speed drop on Alternator Voltage
One final consideration - as the engine speed falls, the alternator voltage also drops a little further, so you need to take this into account as well - back to the alternator specification sheet!
While for small home applications where the outcome is not critical, you can perhaps size your own, it is highly recommended to get a professional to size it for you in most situations. A local electrician is often an ideal starting point.
Tofauti na huduma ya umeme, ambayo kwa matumizi ya makazi na matumizi madogo ya viwanda ina wigo usio na kikomo wa kusaidia kuanza kwa motors na vifaa vingine vya umeme, jenereta ya dizeli lazima iwe na ukubwa sahihi ili kuhakikisha inakidhi mahitaji ya maombi. Kwanza ni muhimu kuelewa rating ya jenereta kwamba unaweza kununua. Jenereta ni kawaida kuuzwa katika kVA au wakati mwingine kW. Kwa sababu ya kuunganisha kwa nguvu, nguvu ya nguvu ya nguvu ya nguvu ya nguvu ya nguvu ya nguvu ya nguvu ya nguvu ya nguvu ya nguvu ya nguvu ya nguvu ya nguvu ya nguvu ya nguvu ya nguvu ya nguvu ya nguvu ya nguvu ya nguvu ya nguvu ya nguvu ya nguvu ya nguvu ya nguvu ya nguvu ya nguvu ya nguvu ya nguvu ya nguvu ya nguvu ya nguvu ya nguvu ya nguvu ya nguvu ya nguvu ya nguvu ya nguvu. Ikiwa una jenereta ya 100kV, kwa sababu ya nguvu ya 0.8, itazalisha nguvu ya umeme ya 80kW. Kwa maneno sahili sehemu ya kW ya jenereta ni kazi halisi kufanyika. Hii inawezesha taa zako, joto na kusonga hewa kutoka kwa mashabiki wako. Tofauti kati ya kVA na kW thamani ni "kupoteza" nguvu, thats aitwaye kVAr. Inatiririka kuzunguka mzunguko, lakini haifanyi kitu chochote chenye manufaa. Kwa ujumla hizi zinaweza kugawanywa katika makundi mawili - upinzani na inductive. Inductive mizigo kusababisha "halisi" na "kupotea" sehemu wakati resistive mizigo kusababisha tu "halisi" sehemu. Kama una tu resistive mizigo, basi ukubwa ni rahisi. Unaweza kwa usalama kuongeza ratings ya vitu vyote una na kazi nje jinsi wengi kW unahitaji. Jambo pekee unahitaji kufanya ni kuangalia mzigo kukubali ya jenereta. Jenereta zote zina upokeaji wa mzigo ambao hupunguza mzigo wa hatua moja ili kuzuia injini kupunguza zaidi ya 10%. Kwa kawaida hatua hii moja inaweza kuwa 60% (utapata faini hii kwenye karatasi ya kiolezo cha injini au jenereta), kwa hivyo ikiwa unataka kutumia mzigo wako kamili katika jaribio moja basi unahitaji jenereta ambapo 60% ya kiwango chake inawakilisha mzigo ambao umehesabu tu. Ikiwa unaweza kugeuza kila kitu hatua kwa hatua, hautahitaji kuwa kubwa sana, ambayo inakuokoa pesa. Kama una mzigo inductive inakuwa ngumu zaidi. "Kama unajua, unaweza kuamua kiasi cha nguvu ya ""kweli"" (kW) na kiasi cha ""kupoteza"" (kW) unachohitaji." Kwa mfano, ikiwa una kiwango cha kW, unaweza kutumia kiwango cha kV. Kwa mfano, kwa ajili ya kVA, unahitaji kufanya hesabu sawa na alternator. Kwa sababu ya hali ya voltage, kVAR (tofauti kati ya kVA na kW) inaweza kuonekana kama kiwango cha juu cha voltage. Kupungua kwa voltage hii kusababisha mwanga flicker na uwezekano baadhi ya vifaa kuzima. 30% ni kiwango cha juu, lakini kwa ajili ya udhibiti wengi ni sana na 15% ni takwimu ya busara zaidi, tena unahitaji kuangalia jenereta au alternator kiolezo karatasi. Kwa sababu ya tofauti ya pole mbili na nne, ni muhimu kujua tofauti kati ya pole mbili na nne. Hapa ni video fupi ya kueleza inayoonyesha tofauti. Kadiri injini inavyoendesha, ndivyo inavyotumia mafuta zaidi, kwa hiyo ni muhimu kujua ni kwa muda gani unatarajia kuendesha. Mzunguko wa voltage ya alternator: Ikiwa injini inashuka, voltage ya alternator pia inashuka kidogo, kwa hivyo unahitaji kuzingatia hii pia. Wakati kwa ajili ya matumizi madogo ya nyumbani ambapo matokeo si muhimu, unaweza labda ukubwa wako mwenyewe, ni sana ilipendekeza kupata mtaalamu ukubwa kwa ajili yenu katika hali nyingi. Mara nyingi fundi wa umeme wa mahali hapo ni mahali pazuri pa kuanza.