Pastukh O. The modes and characteristics of a power unit of a power-station with an auxiliary working transformer of own necessities

This Dissertation justifies the feasibility of introducing new scheme, technical decisions for the electrical part of power stations units, in particular, new option of the power supply system implementation for the auxiliaries with an additional auxiliary working transformer. The conducteds comprehensive investigation and analysis of their modes and characteristics. The fundamental difference between such systems and the traditional ones is the application and circuitry of the inclusion of an additional auxiliary transformer, which works simultaneously with a working auxiliary transformer on the busbar of the first transformation stage of the auxiliaries power supply system. At the same time, in accordance with the chosen values of the parameters of the system elements, in particular, coefficients of transformation of the two auxiliary working transformers, the mode of operation of the additional auxiliary working transformer will be close to the current source mode, the value of which will be determined by the current load of the generator power units, both in the stable operating modes and during external short circuits in the electric network adjacent to the power units. This is the additional auxiliary working transformer mode that provides the voltage level, sufficient for their electrical power. Approach of selecting nominal and total power of the working and additional auxiliary working transformer power units of electric power stations, which gives the opportunity to take into account both characteristic operating modes of the power units and the requirement to the desired voltage is offered. Develop the methodology of evaluation of active-power losses in the new electric power supply schemes of the power units with an additional auxiliary working transformer, which allows to take into account the operating features of their elements is offered. It is shown that the magnitude of active-power loss is practically equivalent in both new and traditional schemes. The conducted analysis and the calculation example for the power units with a 200 MW turbo-generator showed that the scheme with a working and additional auxiliary working electric power transformer with without on-load tap changing (OLTC) devices by technical and economic indicators can be an alternative to the traditional schemes with the auxiliary working transformer of own with the OLTC device. A generalized equivalent circuit of replacement of two-winding transformer for calculation of the steady state modes is created in this work, which allows to take into account the features of magnetic systems without bringing the coordinates of the mode of windings to one voltage level. As also – account work transformers operates in the modes given by voltage and given by current. Developed correspondingly mathematical model. It is shown that the resonant properties of the equivalent circuit of additional auxiliary working transformer of the power units of power plants, predetermined by the way of bonding of such transformer, require high accuracy calculation of values of parameters of branches. This needs to be considered during usage of software complexes for computer simulation of the steady state modes. Computer simulation allowed revealing peculiarities of the mathematical and digital models of additional auxiliary working transformer and recommendations for their implementation. It’s shown that for the power units with an additional auxiliary working transformer in modes of generator loading with nominal active power with the voltage change of the generator and electric power system in sufficiently wide limits voltage is provided on the buses of auxiliary, sufficient for their electrical power.