A shielded transformer is a two-winding transformer, usually delta"star connected and serves the following purposes:
Voltage transformation from the distribution voltage to the equipment's utilization voltage.
Converting a 3-wire input power to a 4-wire output thereby deriving a separate stable neutral for the power supply wiring going to sensitive equipment.
Keeping third and its multiple harmonics away from sensitive equipment by allowing their free circulation in the delta winding.
Softening of high-frequency noise from the input side by the natural inductance
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