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Home / Technical Articles / An example of calculating the technical losses of T&D lines

Introduction to Losses

There are two types of losses in transmission and distribution line.

  1. Technical Losses and
  2. Commercial Losses.
An example of calculating the technical losses of T&D lines
An example of calculating the technical losses of T&D lines

It’s necessary to calculate technical and commercial losses. Normally technical losses and commercial losses are calculated separately.

Transmission (technical) losses are directly effected on electrical tariff, but commercial losses are not implemented to all consumers.

Technical losses of the distribution line mostly depend upon electrical load, type and size of conductor, length of line etc.

Let’s try to calculate technical losses of one of following 11 KV distribution line ;)

Example – 11 kV Distribution Line

11 KV distribution line have following parameters:

  • Main length of 11 KV line is 6.18 km.
  • Total number of distribution transformer on feeder:
    25 KVA = 3 No.
    63 KVA = 3 No.
    100 KVA = 1 No.
  • 25 KVA transformer:
    – Iron losses = 100 W
    – Copper losses = 720 W
    – Average LT line loss = 63W
  • 63KVA transformer:
    – Iron losses = 200 W
    – Copper losses = 1300 W
    – Average LT line loss = 260W
  • 100 KVA transformer:
    – Iron losses = 290 W
    – Copper losses = 1850 W
    – LT line loss = 1380W
  • Maximum amp is 12 Amps.
  • Unit sent out during to feeder is 490335 Kwh
  • Unit sold out during from feeder is 353592 Kwh
  • Normative load diversity factor for urban feeder is 1.5 and for rural feeder is 2.0


Total connected load = No’s of connected transformers

Total connected load = (25×3) + (63×3) + (100×1) = 364 KVA

Peak load = 1.732 x Line voltage x Max. amp

Peak load = 264 / 1.732 x 11 x 12 = 228

Diversity factor (DF) = Connected load (in KVA) / Peak load

Diversity factor (DF) = 364 /228 = 1.15

Load factor (LF) =
Unit sent out (in Kwh) / 1.732 x Line voltage x Max. amp. x P.F. x 8760

Load factor (LF) = 490335 / 1.732 x 11 x 12 x 0.8 × 8760 = 0.3060

Loss load factor (LLF) = (0.8 x LF x LF)+ (0.2 x LF)

Loss load factor (LLF) = (0.8 x 0.3060 x 0.3060) + (0.2 x 0.306) = 0.1361

Calculation of iron losses

Total annual iron loss in KWh =
Iron losses in Watts x Nos of TC on the feeder x 8760 / 1000

Total annual iron loss (25 KVA TC) =
100 x 3 x 8760 / 1000 = 2628 KWh

Total annual iron loss (63 KVA TC) =
200 x 3 x 8760 / 1000 = 5256 KkWh

Total annual iron loss (100 KVA TC) =
290 x 3 x 8760 / 1000 = 2540 KWh

Total annual iron loss =
2628 + 5256 + 2540 = 10424 KWh

Calculation of copper losses

Total annual copper loss in KWh =
Cu Loss in Watts x Nos of TC on the feeder LFX LF X8760 / 1000

Total annual copper loss (25 KVA TC) =
720 x 3 x 0.3 × 0.3 × 8760 / 1000 = 1771 KWh

Total annual copper loss (63 KVA TC) =
1300 x 3 x 0.3 × 0.3 × 8760 / 1000 = 3199 KWh

Total annual copper loss (100 KVA TC) =
1850 x 1 x 0.3 × 0.3 × 8760 / 1000 = 1458 KWh

Total annual copper loss =
1771 + 3199 + 1458 = 6490 KWh

HT line losses (Kwh) =
0.105 x (conn. load x 2) x Length x Resistance x LLF / (LDF x DF x DF x 2)

HT line losses = 1.05 x (265 × 2) x 6.18 x 0.54 x 0.1361 /1.5 x 1.15 x 1.15 x 2 = 831 KWh

Peak power losses =
(3 x Total LT line losses) / (PPL x DF x DF x 1000)

Peak power losses = 3 x (3 × 63 + 3 × 260 + 1 × 1380) /1.15 x 1.15 x 1000 = 3.0

LT Line losses (KWh) = (PPL) x (LLF) x 8760

LT Line losses = 3 x 0.1361 x 8760 = 3315 KWh

Total technical losses =
(HT Line losses + LT Line losses + Annual Cu losses + Annual iron losses)

Total technical losses = (831+ 3315 + 10424 + 6490) = 21061 KWh

% Technical loss = (Total losses) / (Unit sent out annually) x 100

% Technical loss = (21061 / 490335) x 100 = 4.30%

% Technical Loss = 4.30%

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More Information

Jignesh Parmar

Jignesh Parmar has completed M.Tech (Power System Control), B.E (Electrical). He is member of Institution of Engineers (MIE), India. He has more than 20 years experience in transmission & distribution-energy theft detection and maintenance electrical projects.


  1. Kuldeep Ruparelia
    Mar 15, 2023

    Can you provide the reference of the formulae used here? And what is the purpose of 1.05 factor taken in calculation of HT Line Loss?

  2. Kolawole Samuel
    Oct 12, 2022

    Well done sir.
    Please explain how you arrived at 12Amps Maximum Amp. and the values for the LT Line loss.

  3. ali
    Dec 01, 2021

    how did you get average LT line losses as 63W ,260W and 290W

  4. noor jahan
    Jul 21, 2020

    how to solve it to get optimum distance ?

  5. Stephen
    Apr 16, 2020

    are the losses purely active power losses or a there is reactive power loss present as well?

  6. KHALIL Y. A.
    Jan 25, 2019

    Thanjks very much engineer Permer. Your case study of Distribution feeder loss calculation is very helpful. Thank you very much once again.
    May I please ask for some clarifications, as follows?
    1. Some calculations seems needs checking as the results does not reflect the figures calculated. Example, diversity factor calculated as 1.15 seems to be like 1.59 if correctly calculated and some more.
    2. Where is the factor of 0.105 or 1.05 obtained in calculating HT line loss? Which figure is correct? 0.105 or 1.05?
    3. Why is 8760 not used in calculating HT (and possibly LT line) losses to convert it to KWh?
    Thanks so much for the good effort, hoping that you clarify these issues, please.

    • Jawahar
      Feb 13, 2021

      1.05 is correct. Considering line sag as 5% of total length

      • Jawahar
        Feb 14, 2021

        The actual Formula for calculating annual HT Line Loss
        0.105 x(P^2 x RxLLF/(2xLDFxDF^2)

        • Kuldeep Ruparelia
          May 06, 2022

          Yes, this is the actual formula.

    Nov 03, 2018

    How to calculate the 1600KVA transformer line losses (11KV/433V), please send the step by by formulas.

    Oct 18, 2018

    what is the reason for huge transmission losses in 132kV underground cable system

    Aug 25, 2018

    please give answer in 11 kv line per meter line loss load is 7000 Amp Lt

  10. shozab
    Jun 11, 2018

    Dear Mr. Jignesh,

    It is nice meeting you, i have gone thru your blogs and find certain excel calculation sheet, actually i m looking for the excel tool for Insulation Coordination as per IEC, IEEE, IS.

    Also Line loss calculation using UG cable at HV (33kV and 11kV)

    You are requested to kindly post the blog on it electrical section or reply to me with returning email. It will be helpful. Alsot kindly let me the buying charges of these.

  11. Adefisoye Oladimeji
    May 23, 2018

    Thank you for your guide on calculating technical loss, however please I need clarification on 0.2 value used in loss load factor calculation and 0.105 used in calculating HT line losses(Kwh). Thank you

  12. Rajesh kumar
    Mar 05, 2018

    Respected sir please provide the information of 8760

    • Vatan Kuncolienkar
      Oct 20, 2019

      8760= Number of hours in a year viz.24×365

  13. batuhan alkan
    Dec 18, 2017

    Ht line losses, peak powe losses and lt line losses calculation has to much calculation mistake can you explain how are you finding 831- 3.0 – 3315

  14. Dhrumit
    Jun 13, 2017

    In Uganda my company get form Umeme 33kv. After line loss I get 28 -29 kg And my transformer set on step 5 last stape but I am not geting 415 volt. So what should I do. Please give me solution if you have.

  15. Ramprabha
    May 22, 2017

    Thank you sir for giving this information. Plz clear. In load factor it’s mentioned 8760. How, what constant.

    Jan 11, 2017

    Two Distribution transformers of 630 KVA are installed in a residential group housing society. In summer they have 60% loading and in winter they have only 30-35% loading.I want to know in winter if all load will run at one Transformer and one transformer take in idle position , how much losses we can save. LT cables will be same ,only one Transformer will be in idle position for winter period.

  17. sathish
    Dec 03, 2016

    hi friends any buddy have IEC and other standard codes and definition

    Oct 17, 2016

    Dear Sir, do you have this article corrected? the question is because I have the same doubts with respect the ecuations and his results.

    thanks in advance

  19. Jeffery B. Ballah
    Jun 06, 2016

    Dear Sir. Thanks for your opportunity provided me to read EEP materials on line. I’m praying that one day I can get a job that will enable me subscribe as a member so that I may be able to download and read these materials daily to improve my skills as a student reading Electrical Engineering in a war ravish country Liberia where there is no research lab and internets But thanks to EEP I’m fighting hard to be myself in this my chosen career.

    Best regards.

  20. Saif ur Rehman
    Apr 08, 2016

    Dear sir
    I want to know that, how to include line losses in grid extension feasibility study please reply

  21. Hafidz
    Apr 03, 2016

    Sir, what refrence for Book of this formula ? is there from iec,ieee,or etc?

  22. vicku
    Aug 18, 2015

    1st of all tell me about max’m Ampere i.e u have taken max’m amp as 12amps , I don’t understand that that max’m ampere is of Line Conductor or Transformer..
    how max’m Ampere Will be Calculated if NOT GIVEN.

    If someone Know the Answer Than Kindly Reply me… at [email protected]

  23. Aliyu Mustapha Rufau
    Aug 14, 2015

    Thanks for the calculations

  24. Temitope
    Aug 10, 2015

    Sir, your materials seem helpful. In your calculation of HT line losses where did the constants 0.105 from and it later transformed to 1.05. please am not too clear on this. what is the name of the constant? or is the constant meant feeder. and if its for 33kv feeder, how what will be the constant

  25. ashoka r
    May 13, 2015

    sir i have very lack of knowledge about reactve power so kindly i request u to send some basic details regarding i hope u do the same.

  26. ashoka r
    May 13, 2015

    dear sir i have very lack of knowledge about reactive power (kvar) so pls teach me about it ,
    i am looking forward for ur valuable reply

  27. Aye San Dar
    Mar 08, 2015

    Dear Sir,
    I am very glad to have a chance sharing your knowledge.
    let me know one thing from your technical losses calculation that what is the meaning of No of TC on the feeder??
    I am looking forward for your valuable reply.

  28. Ashit Kumar Ray
    Mar 07, 2015

    Sir,i want to know the loss calculation in replacement of ab cable in distribution transformer sub station.Plz give an example with % of loss.
    thanking you,
    Ashit Kumar Ray,CESU,Odisha.

  29. ulaganathan
    Feb 24, 2015

    I m working as a electrical engineer in transmission line field about 33kv and 220 kv.I have a doubt about line loss per km at both 33&220kv line and how to calculate them.I need your valuable prescription.

  30. Sumit
    Feb 04, 2015

    There seems to be many calculation errors or formula errors. Also please provide clear definition of all the constants. I am very confused.

  31. Dharmin joshi
    Jan 07, 2015

    how to find out line current for 33kv overhead transmission line for 3Km? if my power plant is 2mw.
    pl mail me

  32. Rajasekar
    Oct 13, 2014

    What is 0.105 constant in line loss calculation and while calculating it shows as 1.05 and also the loss while calculating it is not 831 KWh How?
    please explain it

  33. zaffar
    Oct 11, 2014

    264÷1.732x11x12=228 how

  34. gaurav kumar goswami
    Aug 06, 2014

    hi ur providing a free and very helpfull guidline for elect engg …thanx for that sir

  35. yeanling
    Jun 11, 2014

    364 /228 = 1.15 ? not 1.6 ?


    HT line losses = 1.05 x (265 × 2) x 6.18 x 0.54 x 0.1361 /1.5 x 1.15 x 1.15 x 2 = 831 KWh

    265× 2, where it is from?

  36. ankit
    Apr 30, 2014

    if cable size is more than actual cable (depend on rated current) so what is loss?
    please give answer in technical and commercial loss.

  37. Ali BY
    Apr 28, 2014

    I’m working on a project to reduce the losses in distribution lines of the city of Casablanca (Morocco). I need the methodology used in this example to perform the calculations. Thanks to send me the required elements. ([email protected])

  38. Ayoyinka Muritala
    Apr 25, 2014

    Please, kindly assist and furnish me with the extensive list of test adopted universally performed on Power Transformers.

  39. Moh'd alqasem
    Apr 25, 2014

    Thank you

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