Analytical and FEM design of autotransformer with phase shifting capability by Intermediate Voltage variation

Abstract

Electrical power system grid voltages are decided by generators and connected load on it. Autotransformers are widely used to control interconnecting grid voltage under variable load operations. This autotransformer does not allow any change of phase angle between High Voltage (HV) and Intermediate Voltage (IV). Due to this limitation normally another phase shifting transformer (PST) is used in power system network. This paper addresses above issue by describing and validating design of an autotransformer having phase angle control between HV and IV with IV variation. This novel hybrid transformer can perform a function of autotransformer and PST without compromising the performance, also saves cost and space requirement. Active power flow over line can be managed by controlling phase angle between sending and receiving end voltages. A finite element method (FEM) is used to compute leakage reactance, core loss, stray loss and thermal analysis. Analytical calculation of leakage reactance is verified by finite element (FE) based magneto static, eddy current solver and circuit approach. A core loss of transformer is computed in three dimensional (3-D) FEM transient solvers for three different core materials and compared with analytical results. Placement of magnetic shunt for reduction of stray loss is carried out in 3-D FEM eddy current solver. The analytical and FEM design results shows very good agreement.