UNDERSTANDING INSULATION TEST RESULTS OF A TRANSFORMER WITH A GROUNDED ELECTROSTATIC SHIELD

摘要

A shielded transformer is a transformer that has a grounded electrostatic plate (shield) between the high-voltage and low-voltage windings (Figure 1). The grounded shield provides a low impedance path to ground by capacitive coupling which prevents unwanted high frequency signals contained in the source voltage from reaching the transformer secondary. This is valuable in protecting sensitive equipment from common-mode electrical noise and transients generated on the source side of the transformer. The shield is not always represented on a transformer nameplate. This can be very troublesome to a tester since test results for a shielded transformer will be very different compared to the expected nonshielded results.