The paper considers the methodology of calculating the number of self-starting pump units depending on the network voltage landing and the basic calculation dependencies of the process of selfstarting of electric motors supplied from three-phase three-winding transformer; the substitution scheme for one phase of the circuit is made. Technical solutions for upgrading pump units, which allow applying the selfstart mode at ameliorative pumping stations, are proposed.

The article discusses some transformations of the equation associated with approximations in the form of a polynomial, which is quickly transferred to a convenient equation compiled with respect to the main input and output values and gives generalized dependencies for a number of nonlinear systems. As an example, a part of a magnetic circuit with longitudinal and orthogonal magnetization fields is given. Relations are presented that connect the inductions B1, B2 as input and output quantities, which in turn are directly related to the corresponding voltages U1 and U2. For all three magnetic circuits, dependencies are obtained that convert the input and output currents i1, i2 into input and output inductions B1, B2 with an approximating function in the form of a polynomial of any degree.

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