Dynamic characteristics of an orthogonal turbine and output-control systems for TPP with high-voltage frequency converter

Abstract

A mathematical description of a closed control system with allowance for pressure fluctuations in the head system, which makes it possible to analyze the regime stability of orthogonal generating sets at tidal electric power plants when operating in the complete range of heads, outputs, and rotational speeds, and to select parameters of the control system, is obtained for an orthogonal hydroturbine and a generator with a load regulator.For an orthogonal turbine, constant head variation at tidal power plants (TPP), which is defined by the in-out character of the flow, results in deviations from the optimal regime. At the Kislogubskaya TPP, a high-voltage frequency converted (HVFC) is used to maintain the turbine within the region of maximum efficiency; full-scale tests were performed after installation of this converter.The high-voltage converter varies the output of the generator with respect to the static characteristic, ensuring turbine operation at the optimum of the characteristic. A relationship relating static head to e load was derived from results of the full-scale turbine tests.The generating set at the Kislogubskaya TPP with the frequency converter, and an aeration shaft fabricated from a junction box between units, and a water conduit connecting the turbine to the basin, represent a complex dynamic system. The parameters of this system vary within a broad range as a function of the static head, which assumes values of from 0.6 to 3 m and more in the operating regimes. Figure 1 shows the "static-head/frequency" characteristic, which is encoded in the frequency converted, and which corresponds to its relationship between generator output and static head.Analysis of results of the full-scale tests indicated that the orthogonal set with the high-voltage frequency converter satisfactorily reproduces the assigned optimal relationship between rotational speed and active head on the TPP. Essentially constant positioning of the regime point on the universal turbine characteristic with reduced flow rates Q 11 ranging from 1.62 to 1.69 m 3 /sec and reduced rotational speeds n 11 ranging from 122 to 126 rpm, and a constant efficiency level of the turbine are automatically ensured as the static head varies within the range from 1.2 to 2.4 m.The water conduit connecting the turbine to the basin, and the aeration shaft consisting of a junction box between units represent a fluctuating system, which influences the frequency oscillation and output of the generating set. The full-scale tests, which were conducted in April -May 2010 with the set operating in the power system at a constant and variable rotational speed indicated that gravitational oscillations with a period of 4 sec (correspondingly, at a frequency of 0.25 Hz) develop in the water conduit and aeration shaft. The amplitude of the oscillations increases with increasing load on the set. Figure 2 compares the oscillograms of the output and pressure pulsations on the basin side with the set operating in a straight-through circuit, and via the high-voltage freq...