PROTECTION OF THE NEUTRAL WIRE FROM ITS BREAKAGE, FROM OVERLOAD CURRENTS AND SHORT-CIRCUIT CURRENTS IN NETWORKS WITH NONLINEAR LOADS

With the appearance of nonlinear loads in networks, problems have arisen with the reliability of neutral wire protections. The 3rd harmonic currents, which are arithmetically added up in the neutral wire, increase its load, so the protection of the neutral wire from overload currents becomes relevant. When constructing such protection, it is necessary to take into account the current of the 3rd harmonic. An increase in the current in the neutral wire leads to the fact that the current in the neutral wire becomes commensurate with the current of a single-phase short circuit. Therefore, The reliability of protection against single-phase short circuits decreases if the undesirable influence of the 3rd harmonic currents is not eliminated. The construction of protection against the break of the neutral conductor and the resulting overvoltages is based on the analysis of the nature of the force function, i.e., the dependence of the change in the sum of the squares of the phase currents over time. The 3rd harmonic currents for this analysis of the force function are an undesirable interference. Thus, when constructing different protections, the values of the effective current values must be measured both taking into account the currents of the 3rd harmonic and without taking them into account. Therefore, an appropriate method has been developed, while it does not use the mathematical apparatus of the discrete Fourier transform, as redundant for switch trippers. This is consistent with the purpose of creating such methods and algorithm for constructing protections that are based on the analysis of current values measured by the methods adopted in the construction of current protections. This allows the algorithm for the construction of such protections, together with the maximum current protections, to be implemented in the circuit breaker trips. In this case, the infrastructure of protection of electric networks is significantly reduced.