Investigating Effects of Distance Air-Gaps on Iron-Core Shunt Reactors

The shunt reactor plays an important role for high and super-high voltages in transmission and distribution systems. It is used to absorb excess reactive powers generated by capacitive powers on the lines for no-load or low-load cases. In addition, it is also an important component to balance reactive powers in the system, to avoid overvoltage at the end of the lines and to maintain voltage stability at the specified level as well. In order to reduce the magnetic flux density and avoid saturation of the magnetic circuit, the reluctance value has to be increased by air gaps along the iron core. This leads to decreasing the influence of fringing fluxes around the air gaps. Non-magnetic materials are often used at the air gaps to separate between iron core blocks. The fringing flux departs and re-enters the lamination perpendicularly, thus the core blocks of a large oil-immersed shunt reactor are generally made from radially laminated silicon steels. In this paper, the correction of the distance between the air gaps is proposed to reduce the fringing flux and the value of the winding inductance of shunt reactors. All parameters of the shunt reactors are calculated via an analytic method based on the theory of magnetic circuit model, then a finite element method is used to compute and simulate the winding inductance for changing the distance between the air gaps.