V.B. Powernet shielded isolation transformer usually configured as delta-wye connected. It is to convert 3 wires input to a 4 wires output with stable neutral buss for the power supply wiring going to sensitive equipment.

Providing an electrostatic shield or faraday shield between the primary and the secondary wingdings thus avoiding transformer of surge voltages passing through inter-winding capacitance and also to softening of high frequency noise from the input side by the neutral inductance of transformer.