Experimental evaluation of the influence of a transformer with a "double zigzag with zero" winding connection scheme on the current in the 0,38 kV network neutral wire

The results of an experimental study are described where a physical model of a 380/220 V network with an asymmetric homogeneous nonlinear load demonstrates the possibility of using a transformer with a "double zigzag with zero" winding connection scheme as a shunt-balancing device for current discharge of the zero wire of a linear network. There has been given a scheme of an experimental setup, a program and the methodology of the experiment. There have been estimated the effective values of non-sinusoidal currents and voltages in various parts of the network model, power, the values of the total coefficients of the harmonic components of voltages and currents. The measurement results obtained using a certified HIOKI 3196 instrument were obtained both statically and dynamically together with the possibility of fixation and subsequent analysis. There have been obtained the equations describing currents and voltages. The oscillograms of currents and voltages recorded in the sections of the network model before and after connecting the shunt-balancing device prove that a transformer with a "double zigzag with zero" winding connection scheme, when it being switched on in front of a nonlinear asymmetric homogeneous receiver in a four-wire three-phase circuit, really significantly reduces the current in the zero wire. At the same time, when increasing in asymmetry and load power, the use of a transformer with a "double zigzag with zero" winding connection scheme to reduce the current in the neutral wire is more efficient. In addition, the currents of the zero sequence of the main and third harmonics are reduced. The results obtained can be used in practice in loaded cable lines with a zero-wire cross-section smaller than the phase one, feeding an asymmetric nonlinear load.