Dc voltage obtained by rectifying ac power grid voltage with the help od fiode bridges, always contains higher harmonics. These harmonics are "transferred" to the supply current as well. Using multi-phase transformation circuits, consisting of two 6-phase transformers instead of one three-phase transformers should produce less harmonics in dc voltage and supply current. However, in case of distorted supply voltage this cannot be true. The paper deals with the problem, how introduction of cathode chokes into load circuit influences higher harmonics of dc voltage and ac supply current. Several supply voltage waveforms were analysed, with THD not higher than standardised 8%, but with different phase angles of 5th and 7th harmonics. 6-pulse system was used as a reference, and 24-pulse systems were investigated with rectifiers connected either in parallel or in mixed fashion (series-parallel).