Calculate Size of Diesel Generator

Calculate Size of Diesel Generator having following Electrical Load. Consider Future Expansion ratio is 10%. Average use of Equipment is 0.8 (1 is Full Time Use)

  • 4 No’s of 1Ph, 230V, 80Watt CFL Bulbs, Diversity Factor is 0.8; Starting & Running P.F is 0.8.
  • 2 No’s of 1Ph, 230V, 3000Watt Air Condition, Diversity Factor is 1, Starting & Running P.F is 0.8.
  • 2 No’s of 1Ph, 230V, 500Watt Halogen Lights Diversity Factor is 0.8 Starting & Running P.F is 0.8.
  • 1 No’s of 1Ph,230V, 10KW Motor with Y-D Starter, Diversity Factor is 0.8,Starting P.F is 0.7 & Running P.F is 0.8
  • 1 No’s of 3Ph,430V, 130KW Motor with Soft Starter , Diversity Factor is 0.8,Starting P.F is 0.7 & Running P.F is 0.8

Calculation:

Type of Load Equipment Starting Current
Linear Load General Equipment
100% of Full Load Current
Non-Linear Load UPS, Inverter, Computer, Ballast 160% of Full Load Current

 

Type of Starter Starting Current
DOL 6 X Full Load Current
Star-Delta 4 X Full Load Current
Auto Transformer 3 X Full Load Current
Soft Starter 2 X Full Load Current
VFD 1.5 X Full Load Current

 

Load Calculation-1:

  • Full Load KW of CFL Bulb=(No X Watt X Diversity Factor) /1000
  • Full Load KW of CFL Bulb=(4x80x0.8)/1000=0.3KW
  • Full Load KVA of CFL Bulb=KW / P.F
  • Full Load KVA of CFL Bulb=0.3 / 0.8=0.4KVA————(H)
  • Full Load current of CFL Bulb=(No X Watt X Diversity Factor) / (Volt x P.F)
  • Full Load current of CFL Bulb=(4x80x0.8) / (230×0.8) =2 Amp—-(M)
  • Type of Load=Linear
  • Starting KVA of CFL Bulb=1 X (KW / Starting P.F)
  • Starting KVA of CFL Bulb=0.3 / 0.8=0.4KVA———————-(1)
  • Starting Current=100% of Full Load Current.
  • Starting Current=1 X 2= 2 Amp.————–(A)

Load Calculation-2:

  • Total Full Load KW of A.C=(No X Watt X Diversity Factor) /1000
  • Total Full Load KW of A.C =(2x3000x0.8)/1000=4.8KW
  • Total Full Load KVA of A.C =KW / P.F
  • Total Full Load KVA of A.C =4.8 / 0.8=6KVA————(I)
  • Total Full Load current of A.C =(No X Watt X Diversity Factor) / (Volt x P.F)
  • Total Full Load current of A.C =(2x3000x0.8) / (230×0.8) =26 Amp——-(N)
  • Type of Load=Non Linear
  • Starting KVA of A.C=1.6 X (KW / Starting P.F)
  • Starting KVA of A.C =1.6 X (4.8 / 0.8)=9.6KVA———————-(2)
  • Starting Current=160% of Full Load Current.
  • Starting Current=1.6 X 26= 42 Amp. ————–(B)

Load Calculation-3:

  • Full Load KW of Halogen Bulb=(No X Watt X Diversity Factor) /1000
  • Full Load KW of Halogen Bulb=(2x500x0.8)/1000=0.8KW
  • Full Load KVA of Halogen Bulb=KW / P.F
  • Full Load KVA of Halogen Bulb=0.8 / 0.8=1KVA————(J)
  • Full Load current of Halogen Bulb=(No X Watt X Diversity Factor) / (Volt x P.F)
  • Full Load current of Halogen Bulb=(2x500x0.8) / (230×0.8) =4 Amp—-(O)
  • Type of Load=Non Linear
  • Starting KVA of Halogen Bulb =1.6 X (KW / Starting P.F) / Starting P.F
  • Starting KVA of Halogen Bulb =1.6 X (0.8 / 0.8)=1.6KVA———————-(3)
  • Starting Current=160% of Full Load Current.
  • Starting Current=1.6 X 4= 7 Amp .————–(C)

Load Calculation-4:

  • Full Load KW of Motor=(No X Watt X Diversity Factor) /1000
  • Full Load KW of Motor =(1x10000x0.8)/1000=8KW
  • Full Load KVA of Motor =KW / P.F
  • Full Load KVA of Motor =8 / 0.8=10KVA————(K)
  • Full Load current of Motor =(No X Watt X Diversity Factor) / (Volt x P.F)
  • Full Load current of Motor =(1x10000x0.8) / (230×0.8) =43 Amp—-(P)
  • Type of Starter=Star-Delta
  • Starting KVA of Motor =4 X (KW / Starting P.F)
  • Starting KVA of Motor=4X (8 / 0.7)=45.7KVA————————(4)
  • Starting Current=4 X Full Load Current
  • Starting Current=4 X 11.4 = 174 Amp.————–(D)

Load Calculation-5:

  • Full Load KW of Motor=(No X Watt X Diversity Factor) /1000
  • Full Load KW of Motor =(1x120000x0.8)/1000=96KW
  • Full Load KVA of Motor =KW / P.F
  • Full Load KVA of Motor =96 / 0.8=120KVA————(L)
  • Full Load current of Motor =(No X Watt X Diversity Factor) / (Volt x P.F)
  • Full Load current of Motor =(1x120000x0.8) / (1.732x430x0.8) =167 Amp—-(Q)
  • Type of Starter=Auto Transformer
  • Starting KVA of Motor =3 X (KW / Starting P.F)
  • Starting KVA of Motor=3 X (96 / 0.7)=411.4KVA—————(5)
  • Starting Current=3 X Full Load Current
  • Starting Current=3 X 167 = 501 Amp.————–(E)

Total Load Calculation:

  • Total Starting KVA = (1) + (2) +(3) + (4) + (5)
  • Total Starting KVA =0.4+9.6+1.6+45.7+411.4 =468.7 KVA
  • Total Starting Current = (A) + (B) +(C) + (D) + E
  • Total Starting Current =2+42+7+174+501= 725 Amp
  • Total Running KVA =(H)+(I)+(J)+(K)+(L)
  • Total Running KVA =4+6+1+10+120= 137KVA
  • Total Running Current=(M)+(N)+(O)+(P)+(Q)
  • Total Running Current=2+26+4+43+167= 242 Amp
  • Size of Diesel Generator= Starting KVA X Future Expansion X Average Use of Equipments
  • Size of Diesel Generator=468.7 X 1.1 X 0.8
  • Size of Diesel Generator= 412 KVA

Summary:

  • Total Starting KVA =468.7 KVA
  • Total Starting Current =725 Amp
  • Total Running KVA = 137KVA
  • Total Running Current= 242 Amp
  • Size of Diesel Generator= 412 KVA
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About Jignesh.Parmar
Jignesh Parmar has completed M.Tech (Power System Control), B.E(Electrical) from Gujarat University. He has more than 14 years experience in Power Transmission-Power Distribution-Electrical energy theft detection-Electrical Maintenance-Electrical Projects(Planning-Designing-coordination-Execution). He is Presently associate with one of the leading business group as a Deputy Manager at Ahmedabad,India. He is Freelancer Programmer of Advance Excel and design useful Excel Sheets of Electrical Engineering as per IS,NEC,IEC,IEEE codes. He is technical Author for "Electrical Mirror" and "Electrical India" Magazines. He is Technical Blogger and Familiar with English, Hindi, Gujarati, French languages. He wants to Share his experience & knowledge and help technical enthusiasts to find suitable solutions and updating themselves on various Engineering Topics.

22 Responses to Calculate Size of Diesel Generator

  1. manikandan.k says:

    Dear sir,
    Thanks for your valuable Generator calculation tips and your advice ,but now i need the calculation of lighting power density, please send to me on the below mail ID ,

  2. SALVE SANJEEV says:

    Sir,
    Thanks , this is very useful for step 5 tpm pasing stages .
    As all the associates along with officer should know how to calculate .
    All your mails are very useful to us .i want to share with you one product called Ultra .
    We took trials and our team saying there is no power saving I can share the details .
    Regards
    SANjeev
    Sr manager
    Mahindra
    91 9922900891

  3. ganesh says:

    Dear jignesh sir,
    i want to know some doubts about electrical system,
    1.why powerfactor defined by “cos phi” not tan and sin?
    2.why we are goes to higher voltage to step down 433v…11kv to 433?

  4. s.k.pal says:

    Following points may be noticed 1) PF should be considered as 0.95 as we normally use APFC but don’t consider it for calculation of capacity of DG and Substation. 2)Loading for Motors is taken as 100% which never designed for. Get some cases studies only then we may know. I have done study for three buildings where Substation capacities were 3 to 4 times than peak due to which not only huge initial investment but very high maintenance cost also.

  5. Dillip kumar garnayak says:

    dear sir pls ans me calculation in transformer load

  6. brijesh patel says:

    wery nice and easy calculation method thanks

  7. mahesh says:

    thank u very much sir
    mahesh

  8. Pabitra Kumar says:

    Sir may I want to know that single phase supply 230 v,8kw motor with star delta starter available. Or ??

  9. Kuldip Singh says:

    Dear Sir,

    Is it possible to have star /delta starter for 1 Ph motor?

    Regards

    Kuldip Singh

  10. Yasir Bashir says:

    Sir

    Sent from Yahoo Mail on Android

  11. Murali Subramanian says:

    Nice presentation.

    Could you please tell me why the starting kVAs of all the loads in the example have been added to arrive at the genset capacity? Does this approach not imply that all the loads are being simultaneously started up? If this is not intended, then will we not land up with an oversized generator?

    On the other hand if all the loads are not proposed to be started up simultaneously, then I think the right approach would be to add up the running kVAs of all the loads except that of the biggest load (130 kW motor or is it 120 kW as it appears in the calculation ?) which would be 17 kVA and then to this fig add the starting kVA of the biggest load which would be 411.4 kVA. This would give us a genset capacity of 428.4 kVA.

    Thanks

  12. Deepak patil says:

    800 kva DG is their…….? i want how much current it takes?

  13. Deepak patil says:

    800kva DG how much current it takes?

  14. hariharan gkmcet says:

    Hello Sir,
    This article is very useful for me,but how do you say CFL lamp is linear load?

  15. krishan says:

    that is very important.
    thanks

  16. krishan says:

    very useful
    thanks

  17. rashid says:

    Dear sir,
    how do i calculate DG capacity requirement to 2000 TR centrifugal chiller

  18. yogesh says:

    sir starting kva is 468 and generator size is only 412 kva ………..how can gen. bear this much load

  19. Lalit Agarwal says:

    Dear Sir,
    I have 90 KW motor with Star Delta Starter. 200 A MCCB (Schneider NSX200 is tripping. What is the correct size of MCCB to be used ??

  20. Shyam says:

    GOOD,BUT I HAVE SOME DOUBTS.YOU DIDNOT CONSIDER THE STARTING SEQUENCE OF MOTOR AND ALREADY DIVERSITY FACTOR IS CONSIDERED AND AT THE END YOU AGAIN MULTIPLIED BY THE AVERAGE USE OF EQUIPMENTS.

  21. Moses says:

    Hello sir
    The future expansion ratio is 10percent of what.

    In the final calculation, you used 1.1 as the future expansion ratio. Can you help in explaining how you got that

  22. bhavesh dabhoya says:

    Sir,
    Diversity factor is taken 0.8. But in Demand Factor-Diversity Factor-Utilization Factor-Load Factor OCTOBER 31, 2011 blog, it shows that diversity factor is always greater than 1. So in this article is it Demand factor???

    Reg.
    Bhavesh Dabhoya

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