Reheat Steam Turbine Research Articles

Variable Structure Fuzzy Gain Schedule Based Load Frequency Control of Non-Linear Multi Source Multi Area Hydro Thermal System

The article focuses on the issues of Load Frequency Control (LFC) under non-linear strategies in multi source multi area hydro thermal system. On practical perspective dead band, boiler dynamics, reheat steam turbine along with hydro turbine operating under two different area capacities are considered in the system. When subjected to random load variations in both the areas, the system exhibits higher oscillations. The speed governor matches the generation with the demand. The offset in the area frequencies and tie-line power is removed by using secondary Proportional Integral (PI) controller. The PI controller is tuned using Ziegler Nichols' (ZN) and Fuzzy Gain Scheduling (FGS) method. The influence of high Proportional (P) controller gain during steady state and high Integral (I) controller gain during transient affects the system performance. Variable Structure System (VSS) helps to switch from P to PI controller during transient to steady state based on control error. The concept of VSS is applied to Fuzzy Gain Scheduling (FGS) PI controller. The performance of the optimal Variable Structure Fuzzy Gain Scheduled (VSFGS) controller under non-linear environment is judged and validated using performance indices.

Design of QFT controller of superconductor flywheel energy storage system for load frequency control

In this paper, the Superconductor flywheel energy storage system (SFESS) was used for the load frequency control (LFC) of an interconnected 2 area power system. The robust SFESS controller using quantitative feedback theory (QFT) was designed to improve control performance in spite of parameter uncertainty and unexpected disturbances. An overlapping decomposition method was applied to simplify SFESS controller design for the interconnected 2 area power system. The model for simulation of the interconnected 2 area power system included the reheat steam turbine, governor, boiler dynamics and nonlinearity such as governor deadband and generation rate constraint (GRC). To verify robust performance of proposed SFESS controller, dynamic simulation was performed under various disturbances and parameters variation of power system. The results showed that the proposed SFESS controller was more robust than the conventional method.

Development of Ultra-Steam Turbine (UST) in High-pressure/High-temperature Reheat Steam Turbine Plant for LNG Carriers

Since the steam turbine plant have flexibility of fuel selection (oil only, gas only and dual), most propulsion plants for Liquid Natural Gas Carriers (LNGC) have been the steam turbine plant. However, the rising prices of fuel and shortage of the crew for the steam turbine plant, the movement to investigate higher efficiency propulsion plant has gotten active. Actually, a lot of LNGCs for European owners have adopted dual fuel diesel engine (DFE) with electric propulsion motor, and many large size LNGCs (200, 000 m3) built in Korean shipyard have adopted diesel engine with re-liquefaction plant (DRL) recently. Under such a situation, we propose new high efficiency plant; UST (Ultra Steam Turbine Plant) that has advantages of conventional steam turbines (high reliability, safety, low maintenance cost and easy operation) for the restitution of steam turbine plant, the recovery of the share and the exploitation of the new market. In this paper, we introduce the outline of the UST plant, and present the features and key technology of reheat turbine that is one of main components of UST plant.

Load frequency control for power system with reheat steam turbine and governor deadband non‐linearity by using neural network controller

AbstractIn this paper, a neural network (NN) controller is presented for load‐frequency control of power system. The NN controller uses back propagation‐through‐time algorithm. In the power system, the reheat effect of the steam turbine and the effect of governor deadband non‐linearity are considered by describing function approach in the state space model. By comparing the results of simulations, the performance of the NN controller is better than conventional controller. NN controller gives a shorter settling time and eliminates the necessity of parameter estimation time required in conventional adaptive control techniques.

Sampled data automatic generation control with superconducting magnetic energy storage in power systems

A discrete state-space model of a two-area interconnected power system with reheat steam turbine, governor deadband nonlinearity and superconducting magnetic energy storage is developed in this paper. The effect of a small-capacity superconducting magnetic energy storage (SMES) system is studied in relation to supplying sudden power requirements of real power load. The feasibility of using an IGBT power converter instead of a thyristor converter as a power conditioning system with the SMES is studied. Time domain simulation results are also presented which show the improvement of transient response with SMES.

97/00563 Advanced 1000 MW tandem-compound reheat steam turbine

97/00563 Advanced 1000 MW tandem-compound reheat steam turbine

Medway: A High-Efficiency Combined Cycle Power Plant Design

The Medway Project is a 660 MW combined cycle power plant, which employs two of the world’s largest advanced technology MS9001FA combustion turbine generators and an advanced design reheat steam turbine generator in a power plant system designed for high reliability and efficiency. This paper discusses the power plant system optimization and design, including thermodynamic cycle selection, equipment arrangement, and system operation. The design of the MS9001FA combustion turbine generator and the steam turbine generator, including tailoring for the specific application conditions, is discussed.

Modelling and state estimation of power plant steam turbines

The development of a robust state estimator for ill-conditioned systems based upon the Levenberg-Marquardt algorithm in connection with Givens orthogonal row processing technique is described. The estimator works in two stages: the square-root-free Givens transformation is applied to the measurement Jacobian matrix to reduces it to the product of a unit upper triangular matrix and a diagonal matrix, then the square-root-free Givens transformation is again used to transform a diagonal matrix whose diagonal element is equal to the Levenberg-Marquardt parameter. The Levenberg-Marquardt parameter is adjusted so that the reduction in quadratic cost function is downhill in successive iterations and rapid convergence of the estimator is ensured. An observability analysis algorithm is also developed which is simple and easy to implement. Both description and implementation of the square-root-free Givens transformation are presented. The estimator is applied to a 250 MW, double-flow, single reheat steam turbine which has seven feedwater heaters. Tests results show that the estimator performs well under a wide range of measurement errors and measurement redundancy ratios. A sample of estimated results for rated loading condition are presented. In the appendix, the turbine modelling procedure is discussed.

A low-order system frequency response model

The authors present the derivation of a simple, low-order system frequency response (SFR) model that can be used for estimating the frequency behavior of a large power system, or islanded portion thereof, in response to sudden load disturbances. The SFR model is a simplification of other models used for this purpose, but it is believed to include the essential system dynamics. The SFR model is based on neglecting nonlinearities and all but the largest time constants in the equations of the generating units of the power system, with the added assumption that the generation is dominated by reheat steam turbine generators. This means that the generating unit inertia and reheat time constants predominate over the system average frequency response. Moreover, since only two time constants predominate, the resulting system response can be computed in closed form, thereby providing a simple, but fairly accurate, method of estimating the essential characteristics of the system frequency response.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Load frequency self-tuning regulator for interconnected power systems with unknown deterministic load disturbances

Abstract A new method is presented for designing load frequency self-tuning regulators for interconnected power systems having unknown deterministic load disturbances. A discrete-type optimal control law is obtained by defining a cost function with a term for presenting the constraints on the control effort and then by minimizing it with respect to the control variable. An attractive feature of the proposed control scheme is that the effect of the load disturbances is decoupled from the plant output and the large value of control is discouraged indirectly by penalizing the rate of change of control. Another feature is that it considers the time delay due to the identification and control computations and the transmission time of the system data over the telemeter links to the controlling plant. The control effects of the proposed regulator are examined using digital simulations of a two-area power system provided with reheat steam turbines.

Parameter Estimation for Reheat Steam Turbines

This paper describes the problems and their solution for the identification of parameters for low-order models of reheat steam turbine generators using single input/output measurements. Because the reheater is effectively in parallel with the highpressure throttle valves but has a much greater time constant the overall system is 'stiff' and presents numerical problems to the estimator. By adopting a compound psuedo-random test signal and a two-stage estimator structure the problem is overcome, as shown by supporting field tests on a large turbine.

Fast Valving with Reheat and Straight Condensing Steam Turbines

Fast Valving with Reheat and Straight Condensing Steam Turbines

Fast Valving with Reheat and Straight Condensing Steam Turbines

Fast valving of steam turbine-generators is a method of rapidly reducing the mechanical power output to assist in preventing instability (loss of synchronism) of the steam turbine-generator with the rest of the power system. Although rarely used, fast valving can be a very effective stability aid [l]. Many operating turbines made by the authors' company have fast valving capabilities. This paper describes the current fast valving capabilities of these turbines, both reheat types and straight condensing types, and illustrates some of the benefits for system stability that can be obtained with these capabilities. Planning considerations for fast valving are also discussed, including some advanced fast valving concepts.

Decentralized suboptimal load-frequency control of a hydro-thermal power system using the state variable model

State space modelling and synthesis of decentralized suboptimal load-frequency control for hydro-thermal power systems are described in this paper. The state space models are derived by the partial fraction technique for reheat steam turbines, hydro turbines and hydro governors having numerator dynamics. Decentralized suboptimal load-frequency controls are synthesized by using the method of minimum error excitation and their performance is analysed as a function of tie-line power level. It is shown that the suboptimal control with feedback of some, but not all, of the remote area state variables is a feasible alternative to the optimal control, whereas local control without feedback of any remote state variable is inadequate for stabilizing the system.

Sampled Data Automatic Generation Control Analysis with Reheat Steam Turbines and Governor Dead-Band Effects

In this paper a systematic method of choosing the frequency bias parameter and the integrator gain of the sampled data supplementary control is presented by using the discrete version of the Lyapunov technique. The reheat effect of the steam turbines is considered in the state space model. The effect of governor dead-band nonlinearity is considered by using the describing function approach and including the linearized equations in the state space model. It is shown that the governor dead-band nonlinearity has a destabilizing effect on the transient response with deterministic and random load disturbances for purely integral ACE control. However, this destabilizing effect is reduced by proportional feedback of ACE.

Sampled Data Automatic Generation Control Analysis with Reheat Steam Turbines and Governor Dead-Band Effects

Sampled Data Automatic Generation Control Analysis with Reheat Steam Turbines and Governor Dead-Band Effects

POWER GENERATION CONTROL USING DUAL-MODE CONTROL

Abstract Dual-mode control is applied to the problem of power generation control. The proposed controller is simple in structure and easily implementable. The effect of changes in some important system parameters like self-regulation parameter, turbine time constant and generation rate constraints, on the dynamic performance of the system for reheat and non-reheat type steam turbines is also studied

Optimisation of load-frequency control parameters for power systems with reheat steam turbines and governor deadband nonlinearity

Optimisation of load-frequency control parameters for power systems with reheat steam turbines and governor deadband nonlinearity

Steam Turbine Overspeed Control and Behavior During System Disturbances

System disturbances involving partial load rejection may cause turbine overspeed control action. To provide information necessary to evaluate power plant transients during such disturbances, this tutorial paper reviews the typical normal overspeed control functions on GE reheat steam turbines with either Electro-Hydraulic Control or Mechanical-Hydraulic Control. Normal overspeed control is related to speed control and the overspeed trip. The characteristic behavior of normal overspeed control is shown for full load rejections and a representative partial load rejection. Enhancement of power plant partial load rejection capability by considering combined turbine-boiler dynamic behavior is discussed.

The Combined Reheat Gas Turbine/Steam Turbine Cycle: Part II—The LM 5000 Gas Generator Applied to the Combined Reheat Gas Turbine/Steam Turbine Cycle

Part I presented an analysis of the simple and reheat gas turbine cycles and related these cycles to the combined gas turbine Rankine cycle. Part II uses the data developed in Part I and applies the second generation LM5000 to a combined cycle using a steam cycle with 1250 psig 900 FTT (8.62MPa and 482°C) steam conditions; then the reheat gas turbine is combined with a reheat steam turbine with steam conditions of 2400 psig and 1000/1000 FTT (16.55 MPa and 538/538° C). A unique arrangement of the superheater is discussed whereby part of the steam heat load is shifted to the reheat gas turbine to obtain a minimum heat recovery boiler stack temperature and a maximum cycle efficiency. This proposed power plant is projected to have a net cycle efficiency of 50 percent LHV when burning distillate fuel.