What?! There is a capacitor in my transformer?

Get a quick tutorial from James Tabbi, our Deputy Vice President of Exxelia's Magnetics Business Units, explaining what's interwinding capacitance


Exxelia recently designed an auxiliary transformer for a spacecraft application, where interwinding capacitance was of concern to the customer.  The controller chip they were using in their power supply was noted to be “rather sensitive to excess capacitance.”

Exxelia has also supplied thousands of driver transformers for use in a subsystem of the AN/TPQ-53 Radar System in which interwinding capacitance within the toroidal windings is held to a very demanding tolerance.

But what is interwinding capacitance? 

Capacitance in a transformer winding cannot be avoided. The voltage difference between turns, between winding layers and from windings to the core, creates “parasitic” capacitances in the transformer circuit.  These capacitances are shown as Cp, Cs, and Cw in this schematic diagram of an electronic transformer “equivalent circuit.”

Interwinding and distributed capacitance occur in transformers due to the physical separation of, and electrostatic coupling between, different turns of wire. In general, the capacitance presents itself between the different layers within a winding and between the outside layer of one winding and the inside layer of the next.  

In conventional magnetics, interwinding capacitance is a function of coil configuration – the geometry of adjacent conductors and separating dielectric media. Specifically, it is directly proportional to the shared surface area of the windings (shown in green and red below), the dielectric constant of the insulator between the windings (shown in gray below), and is inversely proportional to the separation distance through the dielectric media.

           

In high-frequency transformer design, leakage inductance and capacitance are often competing design requirements since the beneficial parameters that provide low leakage inductance also tend to increase the interwinding capacitance.

Excessive capacitance can cause undesirable common-mode noise transmission between transformer windings or between transformer windings and core or another ground connection.

Exxelia can assist with these design challenges when creating products that have to deal with interwinding capacitance, for all types of magnetic components.  

Important coil configuration design considerations must be made when capacitive coupling causes unacceptable signal transmission (for example, common-mode noise transmission or undesirable spurious ringing on a high voltage output).  Windings may be configured in a way that reduces the dV/dt voltages induced across dielectric media. Conductive screen(s) tied to preferred potential(s) can also be added between adjacent windings to reduce transmission.

If you’d like to learn more about interwinding capacitance or would like to discuss your specific magnetics needs, contact us sales.usa@exxelia.com 

Published on 04 Sep 2020 by Rebecca Charles

Exxelia acquires Deyoung MFG., INC.

“The DMI acquisition directly supports our Magnetics SBU expansion strategy. DMI’s strategic location in the Pacific Northwest aerospace market provides a key geographic location for driving growth and profitability,” said François Vignaud, Exxelia Magnetics’ SBU VP. “DMI is highly regarded for the quality of its products and the operational performance of its organization. DMI products can be found on most major commercial aerospace platforms, supporting in flight power, lighting and entertainment sub-systems.” “We welcome DMI into the Exxelia Group,” said Exxelia USA President Michael Thomas. “During its 40-plus years in business, DMI has built solid customer relationships with a strong brand reputation in the aerospace, medical and other high-reliability magnetics markets. Acquiring DMI creates the potential for both revenue and cost synergies related to cross selling and procurement savings as we leverage Exxelia Group’s broader global supply chain and operational excellence practices to support DMI’s operations.” According to Martin DeYoung, President & CEO of DMI, “We are excited to now be a part of Exxelia’s growth and expanded product offerings. The DeYoung’s recognized a shared business culture driven by a passion for quality and customer loyalty. By joining Exxelia Group we achieve a goal of meeting our strategic growth objectives while protecting our long standing relationships with our key aerospace customers and their contract manufacturers.” “This acquisition addresses our aerospace customers increasing requirements for global manufacturing access and timely support” stated Eric DeYoung, VP of Operations at DMI. “Together, we have global reach with the capability to serve our customers – whatever their size, location, or aerospace industry sector with one of the most comprehensive and competitive groups of design and manufacturing capabilities.”

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