Measuring Transformer Distributed Capacitance

An informative white paper from Datatronics Romoland, Inc., provides a discussion of distributed capacitance, Cd, in transformers with emphasis on measurement. The paper explains how capacitance occurs, references to formula for calculating, how capacitance is modeled, how Cd is measured and guidelines to aid in evaluating/measuring Cd.

Capacitance in a transformer winding cannot be avoided. The voltage difference between turns, between winding layers and between windings to the core create these parasitic elements. In general, part of the designers' task is to keep capacitance to a minimum. On rare occasions winding capacitance is increased to reduce ringing in switching transformers.

There are several capacitive elements in a transformer. Capacitance occurs winding-to-winding, turn-to-turn, windings-to-core and stray capacitances between terminals and the case. This discussion will be aimed at the measured capacitance that appears across a winding in a transformer. Each winding in a transformer will add capacitance to this total. Transformer action will cause the sum of reflected capacitances to appear at the terminals of each winding.

Datatronics Romoland is a global leader in magnetic technologies with world class manufacturing, total quality management and responsive service. The company’s transformers, inductors and filters find application in aerospace/defense, medical, telecommunications, instrumentation and more.