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.

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%