Low-Frequency Pressure Pulsations in the Penstocks of Hydroelectric Power Plants and Swing of the Generator Rotor
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Vol. 54, No. 4, November, 2020
LOW-FREQUENCY PRESSURE PULSATIONS IN THE PENSTOCKS OF HYDROELECTRIC POWER PLANTS AND SWING OF THE GENERATOR ROTOR V. V. Berlin,1 O. A. Murav’ev,2 A. V. Golubev,3 and D. V. Rybin4
Translated from Gidrotekhnicheskoe Stroitel’stvo, No. 5, May 2020, pp. 25 – 29.
Full-scale data on the pulsations of pressure and the oscillations of the real power in units of hydraulic power plants are analyzed. The relationships among the low-frequency pressure pulsations, oscillations in the turbine torque, and oscillations in the real power of the generator are established. Keywords: pressure-frequency response; pressure pulsations; synchronous swing; generator rotor.
In nearly optimal modes, the oscillations of the power at the frequency of swing of the rotor are very weak (Figs. 1b and 2b), which suggests the hydraulic nature of the forces that induce them. To analyze the dynamics of the processes associated with the swing of the generator rotor and the pulsation of the pressure, we used the data from the full-scale tests of the hydroelectric generating units of the Kuban HPP-1, -2, and -3 performed by the Water Power Use Department of the V. V. Kuibyshev Moscow Institute of Civil Engineering (MISI) in 1967 – 1973 [1]. During the tests, the modes of operation were oscillographed with simultaneous recording of the pressure pulsations in the scroll and on the wall of the draft tube and the oscillations in the torque of the shaft and the real power of the generator. Figures 3 and 4 show the full-scale oscillograms recorded at the Kuban HPP-2 and the energy spectra of the oscillatory processes. Three typical modes of operation are considered: mode 1 with a power output of 50% of Nr and the developed cord-induced disturbances in the draft tube at frequencies of 0.8 and 1.3 Hz; mode 2, nearly optimal, with insignificant pulsations; mode 3 at maximum capacity. In modes 1 (20.4 MW) and 3 (43.5 MW), the power oscillates at the rotor swing frequency of 1.6 Hz with an amplitude of 3 – 4% of the rated power. In mode 2 (39.9 MW), the hydraulic disturbances are hardly noticeable, and the oscillations of the power are insignificant. Figure 4 shows the spectra of oscillations of the pressure and power. In mode 3, the oscillations of all the parameters at the rotor swing frequency become predominant in the fre-
Pressure pulsations of maximum amplitude in the flow path of Francis turbines are known to occur during partialload operation, are of low frequency, and are due to the rotation of the vortex core under the runner of the turbine. Numerous full-scale data show that the rotating core induces nearly periodic oscillations of flow, pressure, and real power. Moreover, at different hydroelectric power plants (HPP), not only core-induced oscillations occur, but also do pressure pulsations in the frequency range from 1.4 to 2 Hz. The source of such oscillations can be the synchronous swing of the generator rotor transferred through the shaft to the runner, which responds by changing the throughput of the turbine. Thi
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