This paper presents design of phase shifting transformer to reduce source current harmonic generated by using of variable speed drive (VSD) in textile industry. Nine VSDs are used in a stenter machine of a selected textile industry. Each of these VSD generates source current total harmonic distortion (THD) in range of 43.91% to 50.34%, which contains all odd order harmonics except the triplen ones. The first method to reduce this source current harmonic is by using arrangement of three phase shifting transformers, which requires one Yy three-phase winding connection to produce 0° phase shifting, one Yz(+) three-phase winding connection to produce 20° phase shifting and one Yz(-) three-phase winding connection to produce –20° phase shifting. The second method is by using arrangement of nine phase shifting transformers, which requires one Yy three-phase winding connection with 0° phase shifting, four Yz(+) three-phase winding connections with 6.67°, 13.34°, 20° and 26.67° phase shifting respectively and four Yz(-) three-phase winding connections with –6.67°, –13.34°, –20° and –26.67° phase shifting respectively. Simulation results using MATLAB SIMULINK show that source current THD successfully reduced to 1.99% and 1.74% respectively when arrangements of three phase shifting transformers and nine phase shifting transformers are used.

Using variable speed drive for controlling speed of three-phase induction motor in industrial sector gives an advantage of reducing consumption of electrical energy; on the other hand, it also causes a disadvantage of source current harmonic.  To solve the problem of source current harmonic, a method of using phase-shifting transformer is applied. This method may be applied in a system with two VSDs or more connected to a three-phase power supply. The application of this phase-shifting transformer method could be as simple as using of two transformer with Y-y (wye-wye) and Y-d (wye-delta) three-phase winding connections to give a phase-shifting of 30 or more complex as it uses two transformer with Y-y and Y-z (wye-zigzag) three-phase winding connections to give a phase-shifting less than 30. This paper proposes design of five different phase-shifting transformer configurations to produce 30, 20, 15, 12 and 10 phase-shifting. Simulation on a computer-based software, Simulink Matlab, then confirmed that the proposed phase-shifting transformer design gives a very accurate result regarding to phase-shifting and magnitudes of input and output voltage of the phase-shifting transformers.