Don't just compare prices when buying a transformer! No-load and load losses are the real "electricity cost traps."
By azhe
October 20th, 2026
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Key takeaway: A transformer costs you money the moment it’s energized. Losses fall into two categories: no-load losses (iron losses), which occur 24/7, and load losses (copper losses), which increase with the square of the current. To reduce no-load losses, focus on the transformer core; to reduce load losses, focus on the windings. Drawing on the national standard GB 20052-2020 and real-world case studies, this article shows you how to calculate 20 years' worth of electricity costs during the selection process—so you don't end up paying the price for a transformer that only "looks" cheap.
Last year, while visiting clients, I came across a factory owned by a Mr. Wang. He had two transformers, both with a capacity of 1250 kVA—one an older S11 model and the other a newer S20 model—yet there was a difference of nearly 100,000 yuan in their annual electricity bills. Mr. Wang showed me the statements and asked, "Neither machine is running at full load, so why is there such a huge difference in power consumption?"
When we broke it down and did the math, the answer came down to two words: loss and waste.
The moment a transformer is energized—even when there is no load connected—its iron core undergoes continuous magnetization and demagnetization. This wasted energy is known as "no-load loss," or "iron loss." It occurs regardless of whether the equipment is in active operation or idle; it consumes power 24 hours a day, non-stop. In fact, the lighter the load, the greater the proportion this loss represents in your total electricity bill.
The other component is called load loss, also known as copper loss. It increases in proportion to the square of the current based on the load being carried—if the current doubles, the loss quadruples.
A common misconception about transformers is the belief that "turning them off means no power consumption." This is incorrect. No-load losses persist regardless of whether the unit is switched on or off.
The second misconception is even costlier: the belief that "buying the cheapest option is fine." While a Tier 1 energy-efficient transformer might cost 15%–25% more upfront—a price tag that can certainly sting—I have seen many clients discover, after calculating their electricity costs over a 20-year period, that the extra initial investment is fully recouped through energy savings within just 3 to 5 years. Everything saved thereafter is pure profit.
The issue isn't whether it’s expensive or not; it’s whether you account for wear and tear as a long-term cost.
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