Effect of turbine-operating regime and adjustment of automated control system on stability and critical area of surge tanks at HPP

Abstract

Materials of the works of several authors who have investigated the effect of turbine-operating regime on the stability of HPP with surge tanks are presented. A number of new results are obtained. Analytical relationships that can be used in stability calculations for a number of coefficients are compared with a large amount of actual data.A number of HPP projects with surge tanks are currently being implemented with the participation of Russian specialists. These projects include the Zelenchukskaya and Irgana HPP in Russia, the Teri in India, DongNainai and Sekaman in Vietnam, and the Nam Kong HPP in Laos. An increase in capacity is scheduled for the Khoabin and Yali HPP under construction in Vietnam. The existence of surge tanks at the above-enumerated HPP requires solutions to problems of regime stability. For lengthy intake systems with constants of inertia of 8 -10 sec, stability is achieved by increasing the area of the surge tank over and above the critical value. The critical area of the surge tank can be determined with various degrees of detailing describing the hydraulic system, turbine-control systems, and the power load. The degree of detailing defines the structural reserves introduced for compensation of difficult-to-define factors, and also for achievement of the required degree of damping of oscillatory processes.The purpose of this paper is to systematize data obtained by various authors, taking into account turbine-operating regimes in stability analyses of HPP with surge tanks, and also analysis of the influence exerted on parameter stability by adjustment of the control system.A linearized system of equations, which describes the oscillations of liquid masses in an "intake-system/tank" layout is used in analyzing stability "in the low" regimes of HPP with an upstream surge tank [1]: T dq dt z q h q W I I e I = -+ D D 2 max ;(1)where T L Q gH F I I n n I = and T St = H n F St /Q n are the constants of inertia, respectively, of the intake system and surge tank, Äz = ÄZ/H n , Äq I = ÄQ I /Q n , and Äq = ÄQ/Q n are, respectively, the deviations in level, the flow rate of the intake system, and the flow rate of the turbines from equilibrium values, q e = Q e /Q n is the relative equilibrium flow rate, and h H W W max max = are the relative head losses in the intake system and the losses of the velocity head in the surge tank at the design flow rate Q n .Equations (1) and (2) are given in relative parameters. The total maximum flow rates of the turbines, which are linked to a surge tank Q n , and the design head H n of the turbines, are adopted as basic parameters.The conditions required to maintain a constant HPP output in a certain equilibrium operating regime for small level of fluctuations in the surge tank are considered in the classical Thom and Kalamu-Hayden solutions of the problem. Constant output under a varying head is ensured by varying the flow rate of the turbines. Ideal conditions for regulation, which consist in absolutely precise tracking of the flow rate as the head varies, are ad...

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

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