Three-Phase Shunts for Stray Magnetic Field

In the most basic form transformer consists from a primary and secondary winding coupled with alternating magnetic field. Main part of magnetic field runs through high permeability iron core. However, every transformer also has a stray component of magnetic field which doesn't couple primary and secondary winding. The losses in metal part of a transformer induced by the stray component of magnetic field are called stray losses. Although it induces losses, the stray magnetic field in power transformer is helpful in limiting the short-circuit current in the grid. To cope with negative aspects of the stray field, power transformer manufacturers developed a number of measures to reduce the impact. The paper presents ways to control stray losses outside of winding with increasing the magnetic resistance, active and passive magnetic shields. Also it is presented a case report for three-phase shunts applied to the transformer of 245 kV, 500 MVA.