Study of non-symmetric modes of four-wire distributed networks
Keywords:
four-wire distributed network, asymmetric mode, phase load resistance, quality of electrical energyAbstract
Abstract. It is proposed method of assessment of state of asymmetry of four-wire distributed network to establish need for means of symmetry at the stage of design calculations of power supply systems. Method provides for transformation of four-wire distributed network circuit to calculated model as part of power source, power line and equivalent loads of phase of electric consumer. Mode of network is described by equations of method of symmetric components and theory of complex numbers. Given mathematical relations allow to carry out calculations of asymmetric modes of four-wire distributed network. Initial data for calculation are complex voltages of power source, complex supports of power lines and loads of phases of consumer of electric energy.
It is developed computer program "Load asymmetry", which is based on Microsoft .NET technology, and ensures accomplishment for analysis of influence of changes in asymmetry of phase loads and estimation of admissible values of phase load resistances. Program is written in C# programming language. It is specified data of four-wire distributed network model, step and range of phase load resistance change.
Results of study of influence of active, inductive and capacitive phase load on steady-state phase voltage deviation, voltage asymmetry coefficients for inverse and zero sequences are presented. It is shown that in case of change in phase load (active or reactive) within normally permissible steady-state voltage deviation (±5 %), coefficient of asymmetry in reverse sequence does not exceed limits of maximum permissible normalized values (±4 %), and coefficient of asymmetry in zero sequence significantly exceeds these values. Distributed network requires installation of voltage symmetry devices in order to reduce values of zero sequence currents in this case in this case.
Method of estimation of range of changes in values of phase loads that do not lead to output of electrical energy quality indicators for normalized values, and computer program "Load asymmetry" can be used in process of realization of designed calculations of four-wire distribution networks of cities and industrial enterprises.
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