Dry-type transformers are widely used in urban power distribution, rail transit, renewable energy generation, and other fields because they are oil‑free, safe, and easy to maintain. In an electrical power system, the initial purchase cost of a dry‑type transformer often accounts for only a small part of its total cost of ownership (TCO); energy losses during its life cycle are the real long‑term operating expense. No‑load loss (also called core loss) is the energy consumed by a transformer when it is energised but has no load. It exists continuously as long as the transformer is connected to the mains, and consists mainly of hysteresis loss and eddy‑current loss in the core. This article systematically explains effective methods to reduce no‑load loss in dry‑type transformers, covering core materials, structural design, manufacturing processes, and economical operation.
No‑load loss is the active power consumed when the secondary winding of a transformer is open‑circuit and the rated voltage is applied to the primary winding. Essentially it is core loss – the energy dissipated as heat when the alternating magnetic field in the core causes the magnetic domains to continuously reorient. The magnitude of no‑load loss depends on the magnetic properties of the core material, the operating flux density, and the core construction. Because the no‑load current is very small, the resistive loss in the primary winding can be neglected; therefore no‑load loss is almost equal to core loss.
Core material is the primary factor determining no‑load loss levels. While conventional grain‑oriented silicon steel has continuously improved its specific core loss, new materials are delivering breakthroughs.
Amorphous alloy core – a landmark material for low losses. Amorphous alloy is produced by extremely rapid cooling (about 10⁶ °C/s), creating a non‑crystalline atomic structure. Its hysteresis loss is only one‑third to one‑fifth that of silicon steel. Compared with conventional silicon‑steel core transformers, amorphous alloy dry‑type transformers can reduce no‑load loss by 60‑80%. Because no‑load loss is fixed and continuous, the energy savings are particularly significant for equipment that operates with low loads for long periods or is lightly loaded at night (e.g. data centres, commercial buildings, energy storage systems).
High‑performance grain‑oriented silicon steel – an economical choice that balances performance and cost. For applications that do not require the ultimate in low no‑load loss, high‑permeability, low‑loss premium cold‑rolled grain‑oriented silicon steel (such as grades 30Q120, 27Q110, etc.) can be used. Its specific loss per unit weight is 15‑20% lower than that of ordinary silicon steel. Laser scribing can further refine magnetic domains, reducing hysteresis loss by an additional 10‑15%.
Nanocrystalline alloy core – a highly efficient choice for high‑frequency applications. Nanocrystalline alloy is produced by annealing amorphous alloy to form grains of 10‑20 nm. It has extremely high permeability and is suitable for high‑frequency applications such as photovoltaic inverters and wind power converters.
Xinhong Electrical is committed to applying the most advanced core material technologies to our products. We offer customers a multi‑level choice of core materials, from high‑performance silicon steel to amorphous alloy, matching the optimal core solution to different load factors and application scenarios – amorphous alloy cores for low‑load conditions to minimise no‑load loss, and high‑permeability grain‑oriented silicon steel for medium‑high load conditions to achieve the best balance of energy efficiency and economy.
Even with the same material, different core constructions can produce significantly different no‑load losses.
Three‑dimensional wound core technology – shortest magnetic path, lowest loss. The three limbs are arranged in a three‑dimensional equilateral triangle, making the magnetic paths completely symmetrical and greatly reducing reluctance. Dry‑type transformers using this technology show substantial improvements in magnetising current, no‑load loss, and operating noise.
Step‑lap joint technology – key to controlling joint losses. Traditional butt joints create high reluctance and eddy‑current loss at the core joints. A step‑lap or step‑overlap construction allows the magnetic flux to pass more smoothly through the joint area, significantly reducing additional losses. Precise control during core assembly is equally important – ensuring tight stacking and uniform gaps to avoid magnetic property degradation caused by mechanical stress.
Flux density optimisation – reducing loss through accurate design. Operating flux density should be kept within a reasonable range (typically 1.5‑1.7 T). Too high a value increases hysteresis loss; too low a value wastes material. Using 3‑D finite element electromagnetic analysis software makes it possible to accurately find the optimum balance between performance and economy.
Xinhong Electrical uses an advanced 3‑D electromagnetic simulation platform to customise the core construction for each transformer according to its load characteristics and application environment. We strictly control the stacking process to ensure tightness and uniformity of the core joints, so that measured losses closely match the design values.
Excellent designs and materials must be supported by good workmanship to achieve real performance improvements.
Vacuum pressure impregnation (VPI) – eliminates internal voids. VPI allows insulating resin to fully penetrate the windings, completely removing air bubbles, ensuring insulation integrity, and improving winding heat dissipation.
Upgraded insulation system – higher thermal class reduces dielectric loss. Insulation materials with high thermal class and low dielectric loss (e.g. Class H or Class C systems) not only reduce dielectric loss, but also allow the transformer to operate reliably at higher temperatures, increasing overload capability without shortening life.
Full‑traceability quality testing – ensures loss targets are met. From core‑loss testing of incoming silicon steel to comprehensive type tests and routine tests on finished products, we guarantee that all transformer parameters – especially loss figures – meet or exceed the design requirements.
Xinhong Electrical relies on a strict manufacturing quality control system. From incoming material inspection to final factory testing, we continuously monitor the no‑load loss of each dry‑type transformer. Every unit undergoes the full set of type tests and routine tests specified in the GB/T 1094 series, ensuring that the loss data are truthful and reliable – never overstated or achieved by material downgrading.
One of the most fundamental ways to reduce no‑load loss is to optimise equipment selection and operation management.
Follow the new energy‑efficiency standard GB 20052‑2024. Effective from 1 February 2025, the mandatory national standard GB 20052‑2024 Minimum allowable values of energy efficiency and energy efficiency grades for power transformers has come into force. The standard defines three energy‑efficiency grades, with Grade 1 being the highest. For the first time, it includes dry‑type transformers used in renewable energy generation (photovoltaic, wind power, energy storage) within the scope of energy‑efficiency control. According to the Ministry of Industry and Information Technology, the adoption rate of high‑efficiency transformers will reach no less than 80% by 2027.
Comparison of no‑load loss for different energy‑efficiency grades. Taking a 1000 kVA dry‑type transformer as an example: the no‑load loss of the SCB10 model is about 1.70 kW, SCB12 reduces it to 1.46 kW, SCB13 to 1.28 kW, SCB14 to 1.09 kW, and the Grade 1‑compliant SCB18 brings no‑load loss down to 0.85 kW – a reduction of about 50% compared with SCB10. For a 630 kVA transformer, the SCB18 has a no‑load loss of only 0.60 kW, which translates into substantial annual electricity cost savings.
Load‑factor matching strategy. The share of no‑load loss in total transformer loss depends strongly on load factor – the lower the load factor, the higher the proportion of no‑load loss. For low‑load applications (e.g. commercial buildings that run at night, standby power for data centres), no‑load loss can account for more than 70% of total loss; therefore a transformer with very low no‑load loss must be chosen. For high‑load applications (load factor >60%), the trade‑off between no‑load loss and load loss can be considered, and a cost‑effective Grade 2 product may be selected.
Economic voltage control. Provided that the voltage requirements of the equipment are met, a 1% reduction in operating voltage reduces no‑load loss by about 2%. Installing an on‑load tap changer (OLTC) can automatically optimise voltage regulation.
Xinhong Electrical offers customers a complete energy‑efficiency solution – from selection advice to full life‑cycle operation management. Our SCB14 and SCB18 series dry‑type transformers strictly comply with the GB 20052‑2024 energy‑efficiency limits, helping customers achieve the most economical operating cost over the whole life cycle.
The annual electricity cost due to no‑load loss of a dry‑type transformer can be calculated as:
Annual electricity cost =
The table below compares different 1000 kVA dry‑type transformers, assuming an electricity price of 0.7 ¥/kWh (approximately US$0.10/kWh).
| Model | No‑load loss (kW) | Annual no‑load electricity cost (10 000 ¥) | Accumulated 10‑year no‑load electricity cost (10 000 ¥) |
|---|---|---|---|
| SCB10 | 1.70 | 1.04 | 10.4 |
| SCB13 | 1.28 | 0.78 | 7.8 |
| SCB14 | 1.09 | 0.67 | 6.7 |
| SCB18 | 0.85 | 0.52 | 5.2 |
As the data show, upgrading from SCB10 to SCB18 saves about 0.52 10 000 ¥ (5200 ¥) per year in no‑load electricity costs alone, accumulating to about 52 000 ¥ over ten years. For even higher‑efficiency transformers using amorphous alloy cores, no‑load loss can be reduced to less than one‑third that of conventional silicon‑steel transformers, making the energy‑saving effect even more remarkable. Typically, the payback period for a high‑efficiency transformer is only 3‑5 years, after which the savings become pure profit.
As energy prices rise and carbon‑emission policies tighten, reducing no‑load loss has changed from “nice to have” to a necessity under the carbon‑peak and carbon‑neutrality goals. Choosing a dry‑type transformer with low no‑load loss is not only an economic decision to cut electricity costs, but also a key step in fulfilling corporate social responsibility and promoting green, low‑carbon development.
Xinhong Electrical – your trusted dry‑type transformer energy‑efficiency expert. With our core product philosophy of “energy saving, environmental protection, safety”, we integrate advanced amorphous alloy technology, electromagnetic optimisation, and precision manufacturing to provide a full range of high‑voltage and low‑voltage dry‑type transformers, substations, and other power equipment. From R&D and production to sales and technical service, Xinhong Electrical is dedicated to offering one‑stop power‑system efficiency solutions to customers worldwide. Please visit our official website for more product information and technical support.
