No-load losses in transformers refer to the power consumed when the transformer's secondary winding is open (i.e., not connected to a load). These losses mainly include core losses and stray magnetic losses. No-load losses are inherent to the transformer's operation and have a certain impact on the stability of both the power grid and the transformer itself. The following sections will introduce methods to reduce these no-load losses.

●Transformer material

●Reduce the Magnetic Flux Density of the Transformer Core

No-load losses are proportional to the square (or 1.2 power) of the magnetic flux density of the core. Therefore, an excessively high magnetic flux density will increase losses. In dry-type transformers, it is generally recommended to keep the magnetic flux density of the core below 1.60T. This effectively reduces losses, enhancing the efficiency and reliability of the transformer. Controlling the magnetic flux density within an appropriate range is a key consideration during transformer design to ensure the performance and lifespan of the transformer.

●Select High-Quality Silicon Steel Sheets for the Core

Dry-type transformers should generally use cold-rolled high-permeability grain-oriented silicon steel sheets, which have low unit iron loss, typically required to be below 1.3W/kg (at 1.7T). Reducing the thickness of the core sheets is also crucial, as the eddy current loss in the core is proportional to the square of the sheet thickness. Therefore, the core sheets should not be too thick. The thickness of core sheets in dry-type transformers is generally 0.3mm, 0.27mm, or 0.23mm.

●Transformer manufacturing process

●Optimize Core Manufacturing Processes

Since transformer cores typically use cold-rolled silicon steel sheets, which are anisotropic, the magnetic permeability is highest and losses are minimal when the magnetic flux flows along the rolling direction of the silicon steel sheets. When the flux flows perpendicular to the rolling direction, the magnetic properties deteriorate significantly. Therefore, the magnetization direction must be considered during the design and manufacturing of the core. Generally, a 45° mitered joint is used to minimize the angle between the magnetic flux and the rolling direction of the silicon steel sheets, helping to reduce losses. The performance of silicon steel sheets is also affected by external stresses during the core processing, so advanced tooling should be used to minimize any adverse effects on the silicon steel sheets.

●Use Fully Mitered Joint Structures in Core Design

For transformers of the same specifications, adopting a fully mitered joint structure can reduce no-load losses by 5% to 6% compared to using a straight lap joint. Therefore, fully mitered joint structures should be prioritized in core selection and design to ensure that the transformer operates more energy-efficiently.

In Summary

By effectively controlling no-load losses, we can improve the operating efficiency of transformers, achieve energy savings and emissions reductions, and promote sustainable energy development.

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LuShan, est.1975, is a Chinese professional manufacturer specializing in power transformers and reactors for 49 years. Leading products are single phase and three phase isolation transformers, electrical transformer, distribution transformer, step down and step up transformer, low voltage transformer, high voltage transformer, control transformer, toroidal transformer, R-core transformer; DC inductors, AC reactors, line and load reactor, chokes, filtering reactor, and intermediate, high-frequency products. Our power transformers and reactors are widely used in 10 application areas: rapid transit, construction machinery, renewable energy, intelligent manufacturing, medical equipment, coal mine explosion prevention , excitation system, vacuum sintering(furnace), central air conditioning.

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