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 email@example.com
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Felsic HV, long lifetime and high voltage screw terminal aluminum electrolytic capacitor The Felsic HV family of aluminum electrolytic screw terminal capacitors provides great performances in energy density and ultra-long lifetime. For instance, 6 800µF @450V fit into a volume of Ø77 x 220mm and can withstand 200,000h between 0 to 70° under 37Amps, which makes them the perfect choice for use in rolling stock traction systems or the CVS. The family also has one of the lowest ESR for aluminum capacitors with less than 10m0hms in most cases. Products are available for voltages from 160 to 450 Vdc, and offer capacitance values from 1500μF up to 47 000μF offering the best compromise between reliability and compacity. Snapsic HV, high voltage snap aluminum electrolytic capacitor Because it covers voltages from 16 to 500Vdc and temperatures up to +105°C, and because it is customizable, the Snapsic HV series is very versatile and can cover all needs of energy storage in medium voltage both in rolling stock equipment or signaling systems. Thanks to its high ripple current, it is often used in SMPS and HVAC rolling stocks units with a typical variation of 470µF @450V in Ø35 x 50mm, as well as in various signaling control units, where a smaller package can be used with for example 1 000µF @250V in Ø35 x 40mm. Prorelsic, the long lifetime axial aluminum electrolytic capacitors for signaling equipment Exxelia’s range of aluminum electrolytic solutions would not be complete without the axial leaded Prorelsic series. These capacitors show high ripple current and extra-long life-time with 20 000h @105°C. The most common sizes are Ø8.5 x 19mm, Ø10 x 19mm and Ø12 x 30mm, with typical values of 47µF @40V, 100µF @25V and 47µF @100V respectively. Prorelsic capacitors are perfectly suited for smoothing, coupling/decoupling and energy storage functions in railway signaling equipment.
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.”