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Machine Question No.9 - Design capacity for A generator
How do i design for a capacity of a Generator to be use in factory and bank?
i mean the kva , say maybe 150kva or 250kva, i needed to know how to calculate the total load to desigh the kva or recommend for the generator capacity. how i am going to do this?
Author : GUEST
Thu, November 6, 2008 - 18:44
The necessary power requirement is found from the sum of the connected loads. If the exact connected loads are not available, you can work with empirical values obtained from identical or similar projects.
The IEC recommendations and DIN VDE standards give no guidance on these factors and point out the individual aspects of each installation.
Estimation the diversity factor as accurately as possible avoids unnecessary investment and unrealistic application to the electricity supplier. Depending on the purpose of the building, different diversity factors for the various groups of consumers shall use in calculation.
The economic optimum choice of important system component, such as generator, power transformer and switchgear, will be greatly influenced by the ratio of the power required simultaneously to the total connected load.

Below typical values for planning power requirement is useful. (Of course this information is a little oldie and you must check them in comparison to new buildings requirements)

Type of building                                specific connected load

Offices and administration
Without air condition                                           80-120 w/m2
With air condition                                                120-150 w/m2
Per workplace                                                      2.5-3 kva

School and university                   
School general                                                    30-50 w/m2
Humanities departments                                      50-75 w/m2
Science department                                              120-200 w/m2

Hotels and dwellings
Large buildings                                                      40-80 w/m2
Per hotel room or dwelling unit                              3.5-4 kva

Depending on size and facilities                             60-120 w/m2
Up to 50 beds, per bed                                             3.5-4.5  kva
Up to 105 beds, per bed                                             3-3.5  kva
Up to 250 beds, per bed                                             2-3  kva
Up to 300 beds, per bed                                             1.5-2 kva

Department stores
Without air condition                                                100-150 w/m2
With air condition                                                      150-200 w/m2

Exhibitation halls
For exhibitor power                                                   25-50 w/m2
For hall lighting                                                          40-80 w/m2

Chemical                                                                   250-500 w/m2
Rolling mills, iron and steel                                       200-400 w/m2
metalworking                                                             100-300 w/m2
textiles                                                                       50-150 w/m2
Author : Hamid - From: IRAN
Wed, February 9th, 2011 - 18:22
Calculation is not very accurate. Connect a data logger or power analyser to the main CB and record I,V,kW,Var,pf,harmonics etc for about 8hrs(working hours) from which you will know maximum kVA and size of PFC bank required. For sizing generator you should consider starting current of largest motor(s) too. If you use CAT software it will guide you. 
Author : Sinnadurai Sripadmanaban - From: Srilankan
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