Analysis of power system operation at asymmetrical load

For highly populated Asian countries like Pakistan, the smart cities may play numerous positive roles resulting in efficient utilization of available infrastructure. This can be achieved by transforming existing infrastructures into smart ones. To start with such transformation, the main emphasis would be given to energy. For this purpose, the model of a framework capable of analyzing emerging trends in upcoming power system to make it more reliable. This research work focused on the significance of implementing advanced systems like smart grids. Therefore the proposed framework addresses the provision of an integrated simulation tool for in-depth study of system to determine susceptibility of failure, critical situations and restoration scheme by adding renewable energy resources. The planned framework will be used to analyze the impact of emerging trends in power grid operation of intelligent grid which is more commonly known as the smart grid. The framework may also be used to develop contingency plans to optimize the generation, transmission and distribution schemes thus providing the more flexible solutions. The proposed framework may also be used to enhance the security features of supervisory control and data acquisition system which is essential part of such smart transformations.

This chapter presents the concept and definition of the security region, and introduces major methods used in steady-state security region analysis of power system operation: the security corridor, the traditional expansion method, the enhanced expansion method, linear programming, and the fuzzy set theory. The main idea of security regions is to obtain a set of security injections explicitly so that for security assessment one need only check whether a given injection vector lies within the security region. To enhance the calculation speed of the regions, the following measures: adoption of calculation step, constraints are divided into two groups based on the threshold value shown in the equation, are adopted in the new expanding method. The chapter presents a new approach to construct the steady-state security regions of power systems, that is, the maximal security regions are directly computed using the optimization method.

The synchronous generator excitation control system is the essential equipment for operation and control of generator and power supply. Conventionally, an excitation system was used exclusively for supplying field current to field coil and be responsible for only steady-state stability. If sufficient synchronizing torque is not provided during the operation, transient instability occurs in the synchronous generator. This can be controlled by using an exciting system with fast response and adequate forcing power. To overcome this issue, digital controllers are to be used. Many researches have been done on utilizing the transient response stabilization of generators. This chapter introduces an approach for tuning PID parameters for controlling the excitation control system. The PID parameters are adjusted using the particle swarm optimization technique.KeywordsGenerator excitationTuning of PID controllerTransient stabilityParticle swarm optimization

In this paper, we propose a novel excitation system for improvement of the transient stability. The proposed method controls the excitation voltage of synchronous generators (SGs) to promote decrease in an energy function after a disturbance. The abovementioned control action can be achieved by using wide area information obtained by a wide area measurement system (WAMS). Numerical simulations are carried out for a modified IEEE RTS-24 system with 23 generators. The numerical examples show the effectiveness of the proposed method for improvement of the first swing stability by comparing the proposed excitation system with a conventional automatic voltage regulator under three-line-to-ground faults. Impact of the communication latency in the WAMS-based method on the stabilizing effect is also investigated by setting various length of the latency in the numerical simulation.

This paper presents two methods for load angle determination for salient-pole synchronous generator. The first method uses optical encoder to detect the rotor position. In some cases the end of the rotor shaft is not free to be used and mounting of an encoder is impossible. Therefore, the second method proposes estimation of the load angle based on the measured electrical values that have been already used in excitation control system of the synchronous generator. Estimation method uses corresponding voltage-current vector diagram and parameters of the synchronous generator, transformer and transmission lines. Both methods were experimentally verified on the digital control system and synchronous generator connected to power system. The estimation and measured results were compared. The accuracy of load angle estimation method depends on voltage and current measurement accuracy as well as generator, transformer and transmission line parameter accuracy. The estimation method gives satisfactory accuracy for load angles less than 120o el. Thus, it can be applied in excitation control system to provide stable work of synchronous generator in under-excitation operating area.

A new type of flexible excitation system (FES) is proposed by using fully‐controlled power electronic devices such as IGBTs to replace the half controlled devices in the conventional static excitation system, which has the merit of independent control of rotor angle and terminal voltage of the synchronous generator. This paper proposes nonlinear adaptive control (NAC) strategies for synchronous generator with FES in a single machine infinite bus system. External disturbances and the uncertainties of all parameters as well as modelling are defined as lumped perturbation terms and estimated by perturbation observers or state and perturbation observer. The estimated perturbation terms are used to compensate the real perturbations and achieve a model‐independent and robust NAC. Merits of the FES against the conventional static excitation system and effectiveness of the proposed NAC scheme against the accurate model based multi‐variable feedback linearisation control are verified via small‐signal stability analysis and simulation studies. The simulation results have shown that the proposed NAC can achieve superior control performance with less states feedback during a three‐phase short circuit and better robustness against parameter uncertainties, compared with linear control and multi‐variable feedback linearisation control.

Aiming at the excitation control system model including dynamic, non-linear and complex problems, it is difficult to establish an accurate model. Then a fuzzy-PID control algorithm based on Mamdani fuzzy model is proposed by combining the fuzzy theory with the conventional PID control law. On the basis of establishing a simple model of excitation control system, the fuzzy Mamdani model is introduced. The rules modify the parameters of PID control, and use the fuzzy inference to convert the fuzzy set into the precise output value. The voltage control effects of two kinds of fuzzy models of PID excitation control system are compared through the simulation example of MATLAB. The research and analysis show that the new strategy has better voltage control effect than the conventional PID method, which realizes the optimal control of synchronous generator excitation system under multi-working conditions, and provides a new idea for the application of fuzzy PID control in large synchronous generator excitation control.

A new perspective excitation systems of powerful synchronous generators, which are operating in the common energetic system, are considered, their classification and function diagram are presented. The differential equations system, transfer functions and structural diagram of excitation system, as the automatic regulation object, were obtained according to general presumptions. In the cases of deep crashes in the energetic system the mathematical description of electromechanical transient processes are very complicated and limited. In that cases the efficiency of the excitation current regulator one can be increased by using the combined algorithms of the simplex search, when the local aim function in the optimization motion approximate by separabell equation. According to obtained expressions the synthesis diagram with adaptation and optimization blocks is created. The proposed adaptive synthesis diagram enables to eliminate the error of search direction. Ill. 9, bibl. 16 (in Lithuanian; summaries in Lithuanian, English and Russian).

Excitation systems of synchronous generators contribute to effective voltage control and power system stability. Although the excitation system is tuned to enable the power system performs properly over a wide range of operating conditions, it may be necessary to retune it with the aim of improving the system stability during operating conditions not considered before. This paper shows how an unstable operating condition, of an oil refinery electric power system, after the occurrence of two simultaneous events may be avoided by simply adjusting the automatic voltage regulator gain in one of its synchronous generators.

In the paper digitally based excitation systems for the synchronous brushless generators are presented. A digital control system is realized with a digital signal processor ADSP-2001. System configuration, control functions with their structure functions are also presented. The control system has two feedback loops: the main one is based on a generator's voltage and the inner one based on excitation current of the exciter. Beside basic function of a voltage controller the digital system has some other control functions, like: limits of minimal and maximal exciter current, compensation of the voltage (based on reactive and active current characteristics), voltage/frequency characteristic, and possibility of communicating with higher system levels.

The evaluation of heat losses in excitation systems of synchronous generators is a vital part of its design process. The excitation system includes an excitation transformer and an excitation cabinet, which are sources of additional heat losses in the electrotechnical complex. The excitation cabinet contains thyristor-rectifier, AC and DC busbars, fuses and cooling system, which has strong influence on the thermal mode of semiconductor valves and their heat losses. This work covers only air-cooling system. The water-cooling systems are out of scope of this work. Since the transformer losses are well-described in literature this work is focused on heat losses of excitation cabinet equipment. To minimize design errors when calculating the heating rate of the thyristor converter we consider structure of cabinets, mutual influence of different components and environment parameters. The computer program was developed in Matlab in order to include proposed estimation method to design process.

High-voltage power line digitization is one of the key contents of intelligent inspection of transmission line. Airborne LiDAR has obvious advantages in three-dimensional digital reconstruction of high-voltage power line. In this paper, a power line extraction algorithm for transmission line corridor based on LiDAR point cloud data is proposed. According to the distribution characteristics of point clouds in transmission line corridors, rough extraction of power lines is carried out. Noise points are eliminated by improved Hough and RANSAC parabola fitting method. Then the power lines are segmented horizontally and vertically. According to the vertical parabola model of a single power line and the straight line model of water surface, the complete power lines are extracted by model growth algorithm. Line point. The experimental results show that the accuracy of the proposed algorithm is 99.6%.

The fault characteristics of converter-interfaced renewable power generators and conventional synchronous generators are radically different. Based on these characteristics and short-circuit current expression of renewable power generators, the acting performance of the distance protection on the outgoing transmission line is deduced in this paper. Typical faults including three-phase short-circuit, two-phase short-circuit, and two-phase-to-ground short-circuit faults were investigated. Simulation data validate the shortcoming that the conventional distance relays could fail to operate with domestic faults or operate in mistake for external faults.

Nowadays a strong ability of stability control is required in the increasingly complex power system. The flexible excitation system of the synchronous generator is a novel structure with full-controlled devices, which has two damping channels to provide more stable and flexible control potential compared with the conventional excitation system with silicon-controlled rectifier. It is necessary to coordinate the two damping channel controllers, i.e., power system stabilizer (PSS) and reactive power damping controller (RPDC), to effectively improve the power system stability. A novel coordinated optimization method of PSS and RPDC is proposed in this article: the phase compensation method based on the derived electromagnetic torque is employed to design the time constants of PSS and RPDC; and an optimization method considering the interactions of the oscillation modes is proposed to design the proportional gains of PSS and RPDC. The simulations and the field tests with a 55-MW hydropower generator are carried out to compare the flexible excitation system with the conventional excitation system. The comparisons of the damping ratio, steady time and peak-to-peak value of the active power demonstrate that the flexible excitation system based on the proposed method can provide more ability of stability control with satisfactory dynamic performance.

Reliable supply of consumers with electric energy largely depends on the reliability of power source function-ing. In the context of this paper it depends on synchronous generators operating in autonomous power supply sys-tems. In contrast to the power plant generators which are part of power systems and are protected from the loads by sufficiently large resistances, power supply systems withautonomous generators are characterized by rather low resistances. Abrupt changes in the supply load parameters, their own transient and emergency modes, for example, short circuits at the generator terminals, forcing excitation, etc. may lead to various failures in the synchronous gener-ator operation. This paper discusses the possibility of over-voltage in the valve excitation system of a synchronous generator with external three-phase short circuits. On the basis of analytical expressions describing the physical pro-cesses occurring in the excitation system of synchronous generators, the conditions for the occurrence of overvolt-ages are identified