Early in my career, I was asked to evaluate two tender bids for a 4 MVA, 11 kV/22 kV, distribution transformer. Two bids came in for the exact same technical specification. Bid A (Meridian Transformers) was $1,35000 cheaper upfront.
I recommended Bid A (meridian transformer) because both met the spec and efficiency looked ‘good enough.’
My manager smiled and asked: ‘What is that cheaper transformer actually going to cost us over 30 years?’ That question completely changed how I look at design engineering.”
I answered the way I remembered the formula
(η) = (Output Power) / (Output Power + Losses)My answer was straightforward:
“A transformer with lower losses has higher efficiency. If efficiency is 98.5% or 99.1%, the unit is good to go.
My manager just smiled. He asked me to go find out if that was actually true in real money terms.
Efficiency vs. Money: Why 99% Efficient Isn’t Always the Best Buy
First, I treated this as a pure efficiency problem. That felt like the whole answer, but later I understood it was wrong.
That’s the piece I was missing: we’re not just paying for efficiency. We’re paying for the losses that come along with it. Whether it’s a utility, an industrial plant, or ordinary people paying their monthly electricity bill, nobody is billed only for the power they use — they’re also billed, indirectly, for the power that gets wasted along the way.
The electricity bill is paid directly by the people, utility, an industrial plant are not only paid for consumed electricity but for waste energy.
In college, we’re trained to think of losses as relative percentages: 98.5%, 99.2%, always neat and clean. But electricity bills aren’t paid in percentages. They’re paid in money.
I was comparing percentages on paper. I should have been comparing money in the real world.
What is the Transformer Losses that we pay for?
Digging into the test reports, Real transformer losses come from two physically different places.
- No Load Loss
- Load Loss
No-load loss is constant. It’s there 24 hours a day, every day, whether the transformer is powering a whole factory or nothing at all. (Yes, We are paying for this)
Load loss is variable. It rises and falls depending on how much current is flowing at that moment — high during peak demand, low overnight. (Yes, We are paying for this)
| Parameters | No-Load Loss (Core / Iron) | Load Loss (Winding / Copper) |
| Where it happens | Steel core | Copper or aluminum windings |
| When it happens | Constant, the instant the transformer is energized | Only when current flows |
| How it scales | Fixed — independent of load | Proportional to current squared (I²) |
| Daily pattern | Runs 24/7/365, load or no load | Rises and falls with the load curve |
Note: From above we understand that one loss runs 8,760 hours a year without stopping, and the other fluctuates with demand, So you cannot price them the same way.
Evaluating Bids with Total Owning Cost (TOC)
That realization led me to know about IEEE C57.120 the Guide for Loss Evaluation of Distribution and Power Transformers and Reactors. Also later, I learned that in India, the standard reference published by the CBIP (Central Board of Irrigation and Power) follows this same financial philosophy.
TOC = Purchase Price + (A × No-Load Loss) + (B × Load Loss)
Once I saw this formula, my manager’s question finally made sense. he was really asking something closer to a business decision.
In effect: if one bid is cheaper but wastes more energy, and another costs more but saves energy every day, which one is actually cheaper after 30 years?
Breaking down the capitalization factors (A and B)
Now you might be wondering, what are Factor A and Factor B, and why do we multiply them by the losses in the first place?. So, First, I want to clarify that A and B are what’s called capitalization factors in general, the multiple used to convert an expected future stream of cost (or income) into a single value today.
In transformer terms, that basically means: what one kW of loss is worth today, if you add up its cost over the transformer’s whole 20-to-30-year life.
Factor A: (No-load loss )
From the formula you can see that A factor is multiplied by No-load loss (core loss). It doesn’t care whether the transformer is loaded or not. So Factor A is built from three things:
- The energy cost ($/kWh or ₹/kWh),
- The full 8,760 hours a year the transformer stays energized,
- Capitalization factor. (annuity factor) (Turns that yearly cost into one lump present-value number)
That factor converts a decades-long stream of energy cost into one present-value number.
A=(Energy Cost×8,760 hrs/year)×Present Value Annuity Factor
Note that because no-load loss never stops, A usually ends up two to three times bigger than B.
Factor B (load loss):
B is trickier, because load isn’t constant the way core loss is.
A transformer doesn’t run at full power all day. Sometimes it’s at full load. Sometimes it’s at half load. Sometimes almost no load. So we can’t just multiply by the full-load loss for every hour of the year. That would overestimate the cost.
To fix this, engineers use a simple formula. It’s called the Loss Factor:
Loss Factor ≈ 0.3 × (Load Factor) + 0.7 × (Load Factor)²
Don’t worry about memorizing this. Just understand what it does: All that formula is really doing is estimating what fraction of “full-load loss” actually shows up over an average day.
It’s weighted 0.3 (30%) toward the “flat load” case and 0.7 (70%) toward the “spiky load” case, because in practice, most utility load curves lean closer to the spiky/variable end than the perfectly flat end.
Why this matters: A and B aren’t one fixed numbers from a textbook. They depend on local electricity cost, how the utility values future costs, and how heavily the transformer runs during the day.
What the numbers look like, in the real world:
- North America / Europe: A ≈ $3,000–$6,000+/kW, B ≈ $1,000–$2,500/kW
- India (CBIP guidelines): A ≈ ₹1–2 lakh/kW, B ≈ ₹0.5–1 lakh/kW
Same formula everywhere — just different local numbers.
Note: If A and B aren't published at all, the safe assumption is that the tender is being evaluated on price alone, not TOC — some tenders set a maximum loss limit instead of a cost formula, or skip loss evaluation entirely. When in doubt, raise it during the tender's official pre-bid clarification window rather than guessing.
Re-Evaluating the 4 MVA Tender
Here is how that original 4 MVA tender played out when applying loss evaluation math:
From above real world example, I took somewhat mid figures like A = $4,800/kW and B = $1,600/kW — both comfortably inside those North American/European ranges and with an Indian-context version at A = ₹2.0 lakh/kW and B = ₹0.75 lakh/kW, sitting at the higher end of the CBIP range.
Evaluation Factors: A=$4,800 / kW (or ₹2.0 Lakh/kW) | B=$1,600 / kW (or ₹0.75 Lakh/kW)
| Parameter | Manufacturer A (Low First Cost) | Manufacturer B (High Efficiency) |
|---|---|---|
| Purchase Price | $135,000 (₹35.0 Lakhs) | $148,000 (₹38.0 Lakhs) |
| No-Load Loss | 6.5 kW | 4.0 kW |
| Load Loss | 32.0 kW | 29.0 kW |
The Calculations:
Meridian Transformers: TOC=$135,000+($4,800×6.5)+($1,600×32)=$217,400(₹72.0 Lakhs)
Voltcore Industries: TOC=$148,000+($4,800×4.0)+($1,600×29)=$213,600(₹67.75 Lakhs)
Voltcore Industries’ bid costs $13,000 (₹3 Lakhs) more upfront, but saves $16,800 (₹4.25 Lakhs) in lifetime energy waste.
On pure purchase price, Manufacturer Meridian transformer wins. On Total Owning Cost, Manufacturer Voltcore Industries wins the contract.
A quick note on the rupee figures above: they aren’t a currency conversion of the dollar numbers. They’re calculated independently, using CBIP’s own ₹2.0 lakh/kW and ₹0.75 lakh/kW capitalization rates applied to the same purchase prices and loss figures. Same method, two different local markets, run separately rather than converted.
How transformer designers engineer around this
Once you understand TOC, transformer design stops being a simple materials but cost exercise and becomes a financial engineering challenge.
In short: when a manufacturer sees the A and B values published in a tender, that’s their design brief. A high factor (A) tells them to spend more on core steel. A high factor (B) tells them to spend more on conductor.
The published numbers aren’t just for evaluating bids also they’re a signal for how to build the transformer in the first place.
- High Factor A buyers: designers use higher-grade core steel — Hi-B steel, domain-refined CRGO, or amorphous metal cores — to cut no-load loss by up to 60–70%, justifying a higher upfront steel cost.
- High Factor B buyers: designers increase the cross-sectional area of copper or aluminum winding conductors to reduce resistance (I²R), trading higher conductor weight for lower operational loss.
Here is what winning transformer manufacturers actually do: they read the published A and B factors straight out of the tender specifications. Instead of pitching a generic low-loss model, they tailor the core steel and copper sizing specifically to those capitalization numbers. They don’t design for minimum losses—they design for minimum Total Owning Cost.
My Conclusion on That Tender
When I took the Total Owning Cost calculations back to my manager, the decision became obvious.
Even though Manufacturer A (Meridian Transformers) had the cheaper sticker price, Manufacturer B (Voltcore Industries) was submitted for tender evaluation. On paper, Voltcore’s bid looked $13,000 (₹3 Lakhs) more expensive on Day 1. But over its 30-year operational life, it was going to save $16,800 (₹4.25 Lakhs) in pure wasted energy.
Awarding the tender to Manufacturer B wasn’t a compromise also it was the smartest financial decision for the utility, the grid, and ultimately the ratepayer.
But unfortunately, that contract was not awarded to my company. So sad.
The Last Lines
That single project changed how I looked at electrical design forever.
As engineering students, we are taught to solve equations for 100% efficiency on a chalkboard. But in the real world, engineering isn’t just about physics but it’s also about financial engineering.
If you got a chance to evaluate an electrical equipment transformer bid, don’t stop at the purchase price. Look for the published A and B capitalization factors, run the Total Owning Cost formula, and evaluate what that machine will actually cost over its entire working life.
The bid you think is too expensive on Day 1 might just be the cheapest one you will ever buy.
Note: “Meridian Transformers” and “Voltcore Industries” are fictional names used for illustration only. Any resemblance to real manufacturers is coincidental. The bid prices, loss figures, and TOC values in this example are illustrative, meant to demonstrate the calculation method — not data from an actual tender.
Reference:
IEEE C57.120 — Guide for Loss Evaluation of Distribution and Power Transformers and Reactors
CBIP (Central Board of Irrigation and Power) Manual on Transformers
U4E — “Putting Energy Efficient Transformer Procurement into Practice” (UN Environment Programme)
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