Requirements of Power Supply Technology for Electronic Transformers

 Improving efficiency is a common requirement for power supplies and electronic transformers. Although the loss of a single electronic transformer is not large, the discharge protection ball gap is a pair of spherical electrodes with the same diameter. When combined with high-voltage test transformers, control consoles, voltage regulators, water resistors, and other equipment to form a test setup, it is used for high-voltage measurement and protection of the tested objects during power frequency high-voltage tests. For example, a 100VA power transformer with an efficiency of 98% has a loss of only 2W, which is not much. However, when there are hundreds of thousands or millions of power transformers, the total loss can reach hundreds of thousands of W, or even millions of W. Moreover, many power transformers operate continuously for long periods, and the annual total loss is considerable, possibly reaching tens of millions of kW·h. Obviously, improving the efficiency of electronic transformers can save electricity. Saving electricity can reduce the need to build power plants. Building fewer power plants can reduce the consumption of coal and oil, and reduce emissions of CO2, SO2, NOx, waste gas, sewage, smoke, and ash, thereby reducing environmental pollution. This has dual social and economic benefits of both saving energy and protecting the environment. Therefore, improving efficiency is a major requirement for electronic transformers.

    The losses of electronic transformers include core loss (iron loss) and coil loss (copper loss). Iron loss exists as long as the electronic transformer is in operation and is the main part of the loss. Therefore, selecting core materials based on iron loss is a main content of electronic transformer design, and iron loss has become a key parameter for evaluating soft magnetic materials. Iron loss is related to the operating flux density and operating frequency of the transformer core. When introducing the iron loss of soft magnetic materials, it is necessary to specify the operating flux density and operating frequency. For example, P0.5/400 indicates the iron loss at an operating flux density of 0.5T and an operating frequency of 400Hz. P0.1/100k indicates the iron loss at an operating flux density of 0.1T and an operating frequency of 100kHz.

   Soft magnetic materials include hysteresis loss, eddy current loss, and residual loss. Eddy current loss is inversely proportional to the resistivity ρ of the material. The larger the ρ, the smaller the eddy current loss. The order of ρ for various soft magnetic materials from large to small is: manganese-zinc ferrite is 108～109μΩ·cm, iron-nickel-based amorphous alloy is 150～180μΩ·cm, iron-based amorphous alloy is 130～150μΩ·cm, cobalt-based amorphous alloy is 120～140μΩ·cm, high-permeability permalloy is 40～80μΩ·cm, iron-silicon-aluminum alloy is 40～60μΩ·cm, iron-aluminum alloy is 30～60μΩ·cm, silicon steel is 40～50μΩ·cm, and iron-cobalt alloy is 20～40μΩ·cm.

   Therefore, the ρ of manganese-zinc ferrite is 106～107 times higher than that of metal soft magnetic materials, so it has small eddy current loss at high frequencies and has an advantage in applications. However, when the operating frequency exceeds a certain value, the insulation between the magnetic particles of manganese-zinc ferrite is broken down and melted, ρ becomes quite small, and the loss rapidly rises to a very high level. This operating frequency is the limit operating frequency of manganese-zinc ferrite.
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