S. Elangovan

Application of simultaneous active and reactive power modulation of SMES unit under unequal /spl alpha/-mode for power system stabilization

A simple and novel control strategy for damping electromechanical oscillations through control of power converter firing angles /spl alpha//sub 1/ and /spl alpha//sub 2/ of a superconducting magnetic energy storage (SMES) unit is proposed. Both active and reactive power modulations are used under unequal /spl alpha/-mode of operation. The choice of unequal mode is discussed in detail. The gains of the proposed SMES controller are determined once offline depending on the power system and the rating of the SMES unit. Simulation results show that the SMES unit can effectively suppress power system oscillations by utilizing its active and reactive power modulation capabilities. The control algorithm is simple and its realization will require very little hardware.

Design, implementation and performance evaluation of a new digital distance relaying algorithm

This paper presents the design, simulation, implementation and performance evaluation of a computationally efficient and accurate digital distance relaying algorithm. Published historical data were used in the first phase for validation purposes. Sample results illustrating highly accurate fault impedance estimates for various conditions are reported. The second phase uses voltage and current signals generated by the Alternative Transients Program (ATP) and a sample power system for various first-zone, second-zone and third-zone faults. Results of these studies, confirming the stability and computational efficiency of the algorithm, are presented and discussed. In the third phase, a prototype of the relay was developed and tested using real-time fault data generated from physical models of the transmission lines. Oscillographs for these conditions were recorded. Results of these tests indicating high speed relay operation are also discussed. The performance evaluation studies reported in this paper conclusively demonstrate that the new algorithm provides fast and accurate fault impedance estimates for the three-zone protection of transmission lines.

A fault location method for parallel transmission lines

This paper presents a fault location method for one of two individually transposed parallel transmission lines. This method only utilizes voltage and current data acquired at one common end of the two lines to estimate the equivalent source impedance at the remote end. Therefore, the current through a fault resistance in the fault-path can be computed and the effects of the fault resistance and source impedance of the remote system on the accuracy of fault location can be eliminated. However, this method requires that: (1) a fault occurs only on one of the two parallel lines; and (2) the unfaulted line remains in operation until the fault is cleared.

Symmetrical component based improved fault impedance estimation method for digital distance protection Part I. Design aspects

Abstract Recently, distance relays using digital processors have received considerable attention from researchers. The digital processor based distance relays use estimates of fault impedance (distance) in making decisions. Several methods have been suggested in the past that can be used to estimate fault distance. Researchers have proposed symmetrical component, Clarks component and modal component theories for developing distance estimation methods. The approach used in the symmetrical component based methods has resulted in a higher computational burden on the digital processor, which was addressed using special hardware or multiprocessors. In the present paper, an improved method is proposed that also uses symmetrical component transformation. The simplified approach used in the proposed method leads to a computational advantage over previously suggested symmetrical component based methods. The paper derives performance equations that are valid for ten types of shunt fault encountered on transmission lines. The basis for analyzing shunt faults on the transmission line model and developing the fault estimation method is discussed in detail. The proposed method is also validated using numerical examples, the results of which are reported in Part II of this paper ( Electr. Power Syst. Res., 26 (1993) 149–154).

Sliding mode control of a static VAR controller for synchronous generator stabilization

Abstract The paper deals with the design and evaluation of a variable-structure stabilizer for static VAR compensators using a sliding mode control technique. The static VAR system plays an important role as a stability aid for small and large signal transient disturbances in an interconnected power system. A systematic procedure for selection of switching hyperplanes in the design of variable-structure controllers is developed by using a geometric approach known as projector theory. The sliding mode control of static VAR controllers improves the transient response of the power system and provides significant damping to the electromechanical oscillations of the synchronous generator. Computer simulation results for a typical power system shows the effectiveness of a VSS static VAR stabilizer.

Microcontroller based overcurrent relay and directional overcurrent relay with ground fault protection

Abstract This paper presents the design and construction of overcurrent and directional overcurrent relays with ground fault protection for the protection of three-phase subtransmission and distribution systems, using a 16-bit microprocessor, the Intel 8096BH. The relay obtains the system currents at the rate of 12 samples per cycle and estimates the fundamental-frequency components of the current signals using discrete Fourier transform techniques. In the case of the directional overcurrent relay, the direction of the current flow is identified to determine whether the fault current is flowing into its protected zone. For this purpose, several internally stored voltage vectors, corresponding to the different directional element settings, are synchronized accurately with the system voltage and used to determine the direction of the power flow. Facilities to change relay characteristics, the time dial and plug settings are provided. The user can also set the relay as an instantaneous overcurrent relay. The desired operating characteristics are achieved by direct curve data storage in the memory.

Application of superconducting magnetic energy storage unit for damping of subsynchronous oscillations in power systems

Abstract A novel strategy for suppressing subsynchronous resonance (SSR) in power systems using a superconducting magnetic energy storage (SMES) unit is presented. The energy transfer between the power system and the SMES unit is based on simultaneous control of active and reactive power modulation of the SMES unit. The active power is controlled by an artificial neural network (ANN) based controller, while the reactive power is controlled by a conventional regulator. The gains of the controllers are determined from the power system operating conditions and the rating of the SMES unit. Unequal α -mode of firing angle control of the converters is utilized to enforce zero energy transfer in the SMES unit under steady state conditions. The proposed scheme is tested using the IEEE first benchmark model for subsynchronuos oscillations, and it is found that, with the proposed mode of control, the SMES unit can effectively restore power system stability.

Further enhancements in the symmetrical components based improved fault impedance estimation method Part I. Mathematical modelling

Abstract This paper develops an approach that can be used for further enhancement of the symmetrical components based improved fault impedance estimation method that has previously been proposed by the authors. In addition to discussing the mathematical basis of the new approach, enhanced and computationally efficient performance equations are presented. In view of the recent advancements in optical transducers and high speed optical fibre communications, the new technique uses sequence components of voltage and current samples obtained from both the ends of the protected transmission line. It is also shown in the paper that the new performance equations are independent of fault resistance. The PC based Alternative Transients Program was used to model a six bus system and to generate fault data. The results of performance assessment studies on this new method are presented and discussed in Part-II of this companion paper.

New approach to power system stabilizer design

Abstract A generalized method for the design of excitation control or a power system stabilizer (PSS) based on complex frequency is described. The method selects PSS parameters such that exact assignment of eigenvalues associated with the mechanical modes of oscillation to desired locations is achieved. Numerical examples are used to illustrate the concepts of the proposed new technique.

Enhanced power system stabilizer via integrated tabu–fuzzy knowledge based controller

Abstract An integrated tabu–fuzzy knowledge based controller applied to enhance the performance of power system stabilizer (PSS) is presented in this paper. The fuzzy knowledge based controller (FKBC) has been developed to perform the function of a PSS and to provide a supplementary signal to the excitation system of the synchronous generator. The method used for storing and representing the fuzzy rules is called the fuzzy associative memory (FAM) matrix. The well-defined FAM determines the performance of the FKBC and hence the tabu search algorithm is proposed and applied to determine the construction and optimization of the FAM. The controller has been tested in the case of single machine infinite bus and multi-machine systems for various types of disturbance. To show the effectiveness of the proposed controller, the comparison with the conventional PSS is presented.