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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

Calculation

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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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 13 years experience in transmission & distribution-energy theft detection and maintenance electrical projects.

39 Comments


  1. noor jahan
    Jul 21, 2020

    how to solve it to get optimum distance ?


  2. Stephen
    Apr 16, 2020

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


  3. 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)


  4. SHYAM SUNDAR ANDALURI
    Nov 03, 2018

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


  5. CHINNA RAO
    Oct 18, 2018

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


  6. BHUSHAN KUMAR SINGH
    Aug 25, 2018

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

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