Zero-flux(Hall Effect)current transformer
In this case the sensing element is a semi-conducting wafer that is placed in the gap of a magnetic concentrating ring.This type of transformer is also sensitive to d.c. currents.The transformer requires a power supply that is fed from the line or form a separate power supply.The sensing current is typically 0.1% of the current to be measured. in its simplest shape, the hall effect voltage is directly proportional to the magnetising current to be measured.for more accurate and more sensitive application,the sensing current is fed through a secondary, multiple-turn winding, placed around the magnetic ring in order to balance out the gap magnetic field. this zero-flux or null-flux version allows very accurate current measurements in both d.c. and high-frequency applications. A schematic representation of the sensing part is shown in figure 6.2.5