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Transformer Losses

Transformers have two major components that drive losses: the core and the coils. The typical core is an assembly of laminated steel, and core losses are mostly related to magnetizing (energizing) the core.

Spreadsheet for Transformer Losses Calculation
Spreadsheet for Transformer Losses Calculation

These losses, also known as no-load losses, are present all the time the transformer is powered on – regardless of whether there is any load or not.

Core losses are roughly constant from no-load to full-load when feeding linear loads. They represent a continuous cost, 24 hours/day, for the 25-year or more life of the transformer.

Formulas in spreadsheet

  • HV Full load current = VA / (1.732 · Volt)
  • LV Full load current = VA / (1.732 · Volt)
  • HV Side I2R losses = I²R · 1.5
  • LV Side I²R losses = I²R · 0.5 · 3
  • Total I² R lossses at Amb. temp = Hv losses + Lv losses
  • Total Stray losses at Amb. temp = Measured losses – I²R losses
  • I²R lossses at 75° C temp = ((225 + 75) · losses) / (225 + Amb. temp) .
  • Stray losses at 75° C temp=((225 + Amb. temp)(Stray losses at Amb. temp)) / 300
  • Total Full load losses at 75° C = I²R losses at 75° C + Stray losses at 75° C
  • Total Impedance at amb. temp = (Imp. voltage · 1.732) / Full load current
  • Total Resistance at amb. temp = I²R losses / I²
  • Total Reactance (X) = SQRT (Impedance² – Resistance²)
  • Resistance at 75° C = (300 · resistance at amb ) / (225 + Amb. temp)
  • Impedance at 75° C = SQRT (R² at 75° C + X²)
  • Percentage Impedance = (Z at 75° C · I · 100)/V1
  • Percentage Resistance = ( R 75° C · I · 100)/V1
  • Percentage Reactance = (X · I · 100) / V
  • Regulation at Unity P.F. = (%R cosø + %Xsinø)
  • Regulation at 0.8 P.F. = (%R cosø + %Xsinø) + 1/200(%R sinø – %Xcosø)2

Efficiency at Unity P.F

  • At 125 % of Transformer Loading = (kVA · 1.25 · 100)/((kVA · 1.25)+(I²R losses · 1.25²)+(No Load Losses))

Efficiency at 0.8 P.F

  • At 125 % of Transformer Loading = (kVA · 1.25 · P.F. · 100)/((kVA · P.F. · 1.25)+(I²R losses · 1.25²)+(No Load Losses))

Contribution to transformer losses

Load level varies widely, with some installations running very heavily loaded and others more lightly loaded.

This difference substantially impacts actual losses incurred. Unfortunately, there is a small body of field data available, driven by the factors such as a lack of awareness of the cost of the losses, and the cost of gathering detailed data from a reasonable number of individual transformers.

Several variables contribute to transformer losses, the most important of which include load level, load profile, and core and coil construction.

Since there are a wide variety of transformers on the market serving different purposes, and available from different manufacturers, actual losses incurred in the field will vary substantially from installation to installation.

Software:Spreadsheet for Transformer Losses Calculation
Version:10.06.2013 New
Developer:Jignesh Parmar
Size:36 Kb
Download:Right here | Video Courses | Membership | Download Updates
Spreadsheet for Transformer Losses Calculation
Spreadsheet for Transformer Losses Calculation

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  1. Andrew Smith
    Oct 05, 2021

    Dear Sir,

    Thank you for posting this calculator. I used it to check my own which was almost correct.

    Aug 06, 2021

    Sir, please note that we have old 400 kva tranformer,year of manufactured 2007 and MAKE: CROMPTON GREAVES. OIL COOLED TRANFORMER Hence kindly suggest us for replacement of the TRANSFORMER , since it is very old.we are assuming that lot of energy getting wasted due to the above conditions.

    • Esennar Transformers
      Sep 14, 2021

      You can go with Esennar Transformers.. where you can save upto 50 thousands rupees per year..

  3. Mohd Zulhizam
    Mar 11, 2021

    Assuming the losses and impedance of the transformer is negligible, calculate the HV and LV currents if the transformer was loaded at 120%

    What formula use ?

  4. Shafique
    Jun 26, 2020

    Sir, coul you explain temperature gradient calculation of HV and LV winding , if temperature rise 40/50

  5. Rohit Saini
    Dec 12, 2019

    Please tell how to calculate no load losses of transformer.

  6. Nandini Basavarajappa Doddaveerappla
    Oct 15, 2019

    Tell me how to get transformer copper loss
    I have no load losses n total power loss

    • vivek kumar
      Jan 08, 2021

      Total Power loss = No load loss + Copper loss + Stray loss

      If assume Stray loss negligible then

      Copper loss = Total power loss – No load loss

    Aug 28, 2019

    Dear sir,
    Dry type and oil type transformer losses how to calculate.

  8. FLOYD
    Jan 19, 2019

    specs of hi pot tester from 10 to 35kv?

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