High frequency means smaller transformers

REO UK has launched a new guide to the integration of high-frequency components, such as chokes and transformers, into applications such as drive-converters, train technologies, renewable energy and e-mobility applications. The guide is free and can be downloaded from REO’s website.

In the design of high-frequency systems, the size of the components plays an important role. HF transformers are used for battery charging circuits and switch-mode power supplies and they can be made smaller in the same way as higher frequency satellite TV transmission allows for smaller domestic receiver dishes.

Transformers operating above 50Hz mains frequencies are usually much smaller. Undesirable characteristics such as eddy current losses and leakage inductance increase proportionally to the dimensions of the device so keeping the transformer small means that these unwanted characteristics are also reduced.

REO produces high frequency components, power transformers and chokes on toroidal basis or pot core basis with a power range from 1-90kW in the frequency spectrum of up to 100kHz.

“REO’s use of amorphous, nanocrystalline and ferrite core materials ensures high-efficiency design with reduced costs and increased product life,” explained Steve Hughes, REO UK managing director.

“Size reduction prolongs the service life and enables cost savings, as well as modular design with insulation between primary and secondary windings for test voltages up to 6kV, and insulation for partial discharge less than ten per cent.”

Boasting ingress protection up to IP65, REO HF transformers use Litz wires designed to reduce skin effect, the tendency for HF current to run only at the surface of a conductor. Skin effect is also the reason why TV aerials are made from hollow tubes rather than solid rods.

The magnetic field created by the flow of current at the centre generates a current that opposes the main flow. In HF wires the copper cross-section is divided into many small individual conductors. This ensures that the diameter of each conductor is less than the skin depth so that the entire cross-section for the current flow is available.

HF wire suppresses the skin effect, minimises eddy current losses, prevents hot spots and provides high dielectric strength. With encapsulation and insulation class B, F and H, the ambient temperature range is from -40 to +85 degrees centigrade.

The benefits of REO HF transformers include the highest compatibility and low heating as well as minimal noise generation. REO components are available with various options, for example, vacuum seal. Models with an aluminium profile have improved heat dissipation and can be water-cooled by means of a cold plate.

All Components are tested under real conditions at REO’s in-house laboratory to quality standards DIN EN60310 and DIN EN60076-6, as well as DIN EN61558. Long-term tests and ‘burn in’ are performed for encapsulated transformer models. Depending on the application REO offers different winding types including stranded wire winding, wire winding and copper strip.

REO power transformers are available in plastic housings for industrial use (HF transformers for less demanding applications), mounted onto a plate with pins or in an aluminium profile case.


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