Highly improved performance of a noise isolation transformer by a thin-film short-circuit ring

One of the typical phenomena observed during operations of transformers in general is the complex resonance phenomena present in high frequency ranges. Noise isolation (or cutout) transformers, which show the best performance among isolation devices, are not exempt from this difficulty, degrading their performance at high frequencies. The source of these resonance phenomena is a number of local spurious resonance circuits composed of various combinations of numerous minute stray capacitances and leakage inductances present in transformers, becoming apparent at higher frequencies. As a countermeasure against this difficulty, a short-circuit ring (made by an aluminum film) is placed near the coils inside a transformer. The effectiveness of this method is demonstrated experimentally by decreased resonance amplitudes and by 20-dB improvement of the overall attenuation level over an extended frequency range