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Generation, Transmission and Distribution, IEE Proceedings-

Issue 1 • Date Jan 1996

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Displaying Results 1 - 20 of 20
  • Suppression of transmission system oscillations by thyristor-controlled series compensation

    Page(s): 7 - 12
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (476 KB)  

    The role of a variable series compensator in a multimachine infinite-bus system is investigated. The proposed compensator comprises a combination of thyristor-switched capacitors (TSCs) and a thyristor-controlled reactor (TCR). The role of the TSCs is to suppress large power oscillations while that of the TCR is to damp out small power perturbations. A performance index to quantify the overall power imbalance in the system is proposed and is used to formulate the control strategies for the TSCs and TCR. The coordination between the control actions of the TSCs and TCR is established on the basis of the magnitudes of the power oscillations. Computer simulations show that the proposed scheme is effective in suppressing power flow oscillation in transmission networks View full abstract»

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  • Fault location on two-terminal transmission lines based on voltages

    Page(s): 1 - 6
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (460 KB)  

    A new method for locating faults in two-terminal transmission lines is discussed. The procedure is based on the fundamental components of fault and prefault voltage at 50/60 Hz measured at the two ends of a transmission line. The methodology allows one to establish a direct calculation procedure that is independent of fault and prefault currents, fault type, fault resistance, synchronisation condition of register devices located on line ends, and prefault condition, either balanced or not. This is achieved by defining a new concept called `distance factor'. The technique developed was validated at two levels: first, from exact data obtained using a fault simulation software program, which allows the accuracy to be evaluated, and secondly, from erroneous voltage data taken at the ends of the line or from erroneous source impedances, which allows assessment of the sensitivity against incorrect data View full abstract»

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  • Simple model for post-fault motor behaviour for reliability/power quality assessment of industrial power systems

    Page(s): 56 - 60
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (472 KB)  

    Voltage sags are more and more being considered as a severe power quality problem. However, stochastic prediction tools for voltage sags are rare. The few methods that have been proposed assume a rectangular voltage sag. This assumption is no longer true in many industrial power systems with large induction motor loads. A simple induction motor model has been developed to describe the extra current taken by the motor during the re-acceleration after a short circuit. This model has been incorporated in the method for reliability/power quality analysis of industrial power systems, as described in a previous paper. Simulations are presented to show the influence of the post-fault voltage sag due to motor re-acceleration on the reliability/power quality of the supply. The simulations result in a table with the expected number of interruptions of plant operation for different load sensitivities View full abstract»

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  • Phase-decoupled load flow method for radial and weakly-meshed distribution networks

    Page(s): 39 - 42
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (304 KB)  

    A phase-decoupled load flow method is proposed. The method is tailored for distribution networks with radial or weakly-meshed structures. The branch-current-based Newton-Raphson method is employed. The Jacobian matrix of the proposed method could be decoupled into three sub-Jacobian matrices, one for each phase, and is used to execute load flow. The proposed method is insensitive to the line parameters and is significantly faster than other methods developed so far in solving the radial or weakly looped distribution networks. Tests have shown that the proposed method has a great potential for online operations and provides a very good theoretical foundation for developing more applications and research in this area View full abstract»

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  • Application of the decomposition technique for forecasting the load of a large electric power network

    Page(s): 13 - 18
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (560 KB)  

    A reliable electric load forecasting technique for power system planning is introduced. In this technique, a suitable model to fit the data is selected before the actual forecasting algorithm is performed. The model is constructed in three steps: identification, estimation and diagnostic checking. This model is then used by two decomposition techniques (multiplicative and additive) to forecast the electric load. The techniques are illustrated by applying them to the forecast of the monthly peak loads of a large electric power network. The Egyptian electric power network peak loads data are used in this study. Analysis and comparison of the results have shown that the techniques are adequate and yield good results View full abstract»

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  • Interaction of helical arc devices with interconnected networks

    Page(s): 89 - 95
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (904 KB)  

    Rotary arcs driven electromagnetically by a fault or load current are used for interrupting duties at distribution level and as preheaters for high temperature chemical reactors. One such form of rotary arc device is the helical arc unit. The paper investigates the electrical interaction between repeated arc short circuiting and the connected network or power supply. The results are relevant to medium and high voltage AC interrupters and chemical processing preheaters View full abstract»

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  • Adequacy and reliability cost/worth implications of nonutility generation

    Page(s): 115 - 122
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (672 KB)  

    The electrical energy component provided by conventional generating sources is expected to decline slightly in the future due to environmental concerns and the penetration of new sources of energy. Renewable forms of energy such as nonutility generation (NUG) and cogeneration will increase their market share of the total energy mix as a result of the energy policies currently being adopted by many governments and power utilities around the world, A significant portion of future power plant investments will be made by NUG and cogeneration industries, therefore, the task of evaluating the merits and demerits of such options is becoming an important function in the power utility system planning. The NUGs and cogeneration facilities are normally small generating capacity units injected at load points within the system. The reliability and economic implications of capacity additions from independent power producers (IPP) can be quite significant. The paper discusses the impacts of NUGs on the adequacy and reliability cost/worth indices in a generating capacity system and the cost of customer interruptions in a composite system adequacy assessment View full abstract»

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  • HVDC converter transformer core saturation instability: a frequency domain analysis

    Page(s): 75 - 81
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (716 KB)  

    The interaction between an HVDC converter and the saturation characteristic of a converter transformer can lead to a type of harmonic instability widely known as converter transformer core saturation instability. The paper presents a linearised direct frequency domain analysis of the mechanism behind this instability. Using linearised converter transfer functions and transformer saturation characteristics on AC and DC system equivalents, the system equations are solved to describe the phenomenon. A measure of the level of stability, saturation stability factor, is derived and utilised to predict the system dynamics. The analysis is verified by dynamic simulation of several systems View full abstract»

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  • Topology processing and static state estimation using artificial neural networks

    Page(s): 99 - 105
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (692 KB)  

    The paper presents a new approach based on artificial neural networks (ANN) for power system network topology determination and static state estimation. The state estimator model considers dynamic change in network topology and bad data processing. ANN models based on the counterpropagation network (CPN) and functional link network (FLN) have been tried out for solving topology processing and static state estimation on the IEEE 14-bus, IEEE 57-bus and a 19-bus practical Indian system. In addition the results of state estimation using the Hopfield neural network and the conventional fast decoupled state estimator (FDSE) have also been obtained and compared. It has been established that the ANN based models provide results much faster, and work well even for non-Gaussian noise and in the presence of bad data View full abstract»

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  • New method of power swing blocking for digital distance protection

    Page(s): 19 - 26
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (740 KB)  

    A new method for preventing digital distance relay operation during power swings is presented based on detection of transients in the measured reactance. The transients are detected by the difference between two reactances calculated using two parallel FIR filters based on coefficients used in the discrete Hartley transform. The transients are present under genuine fault conditions but not during power swings. Fault transient detection therefore enables the relay for faults but leaves it inherently blocked for power swings. Simulation results are presented showing that the fault transient detection method does not lead to increased relay operating time, but allows the relay to differentiate between faults and power swings. The significant advantage of this new method of blocking is that the relay can correctly operate if a genuine fault occurs during the power swing period View full abstract»

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  • Efficient load flow method for distribution systems with radial or mesh configuration

    Page(s): 33 - 38
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (576 KB)  

    The paper proposes a new and efficient method of solving the load flow problem of a distribution system. The method can be applied to both radial and mesh networks. A mesh network is converted to a radial network by breaking the loops through adding some dummy buses. The power injections at the loop break points (LBP) in the equivalent radial network are computed through a reduced order node impedance matrix. Unlike other methods, the shunt admittances are considered in the proposed load flow algorithm and the effect of load admittance is also incorporated in the calculation of power injections at the LBPs. Because of the inclusion of shunt admittances, the method can also be used to solve the load flow problem of some special transmission networks. Two different networks with various configurations were used to demonstrate the efficiency and convergence pattern of the method. The results obtained by the proposed method were also compared with some other methods View full abstract»

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  • Decoupled asymmetrical three-phase load flow study by parallel processing

    Page(s): 61 - 65
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (448 KB)  

    A decoupling-compensation technique used to break the three-phase coupled power system model into sequence-decoupled models is proposed. With such a decoupling, positive-, negative- and zero-sequence system models can be solved simultaneously. By combining these models with the well-known Newton-Raphson or fast-decoupled algorithms, two novel methods used for asymmetrical three-phase load flow study are established. Based on these the synchronous parallel algorithm can then be employed and the corresponding software used for this purpose can be implemented onto a multiprocessor system. The validity of the proposed methods is verified and the computation results are analysed View full abstract»

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  • Distribution fast decoupled state estimation by measurement pairing

    Page(s): 43 - 48
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (484 KB)  

    A three-phase fast decoupled state estimation method is presented for distribution systems. The weighted least square (WLS) approach is used. A current-based formulation is discussed first and then the decoupled version. The proposed method produces a constant symmetric gain matrix which can be decoupled into two identical sub-gain matrices. The method offers good performance in handling the distribution system and is many times faster than other formulations, especially for large systems. An observability test is discussed View full abstract»

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  • On the equivalence of uniform and two-layer soils to multilayer soils in the analysis of grounding systems

    Page(s): 49 - 55
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (628 KB)  

    An extensive study of the equivalence of uniform and two-layer soils to multilayer soils in the analysis of grounding systems has been carried out. Grounding resistances and touch voltages have been computed and compared for different equivalent soil models. The analysis presented shows how to obtain an approximate uniform or two-layer equivalent soil for some multilayer soils. It also shows that a good equivalent soil with respect to ground resistance is not necessarily good with respect to touch voltages. Examples showing the lower and upper bounds of electric responses associated with grounding systems in different equivalent soils are also presented View full abstract»

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  • Adaptive power system stabiliser based on pole-shifting technique

    Page(s): 96 - 98
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (236 KB)  

    The design of a self-tuning power system stabiliser (PSS) using the pole-shifting technique is presented. The controller uses a state-feedback law, whose gains are evaluated from the pole-shifting factor. The proposed method is simple and computationally efficient. The dynamic performance of the proposed PSS is quite satisfactory and the PSS adapts extremely quickly to varying operating conditions View full abstract»

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  • Network observability: theory and algorithms based on triangular factorisation and path graph concepts

    Page(s): 123 - 128
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (592 KB)  

    A theory is developed to test network observability, to identify possible subnetworks which might be observable, and, in case the network is not observable, to identify the minimal set of measurements (pseudo) to be added so that the network as a whole becomes observable. Algorithms to test network observability and to identify subnetworks of the entire system that might be observable are also presented. An algorithm to add a minimal set of measurements to the existing measurements, so that the network becomes observable as a whole, is developed. The theory and algorithms that result are a combination of factorisation path concepts and triangularisation of the gain matrix G. Such algorithms have the characteristics of being very simple, easy to implement, extremely fast and reliable. Algorithms resulting from this theory do not require solutions of any algebraic equation View full abstract»

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  • Models of grounded mid-tap open-wye and open-delta connected transformers for rigorous analysis of a distribution system

    Page(s): 82 - 88
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (532 KB)  

    The paper presents detailed mathematical models of grounded mid-tap open-wye and open-delta connected transformers for rigorous analysis of a distribution system. The transformers are accurately modelled in phase coordinates, The proposed transformer models consider the copper and core losses, winding connections, the phase angular displacement between primary and secondary windings, and off-nominal tapping. Open-wye and open-delta connections with mid-tap grounded on the secondary side of the transformer banks are quite often used to supply the single-phase lighting load and three-phase power load simultaneously. The detailed models of these transformers are indispensable for analysis of the inherent imbalance of a distribution system View full abstract»

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  • Fuzzy neural network and fuzzy expert system for load forecasting

    Page(s): 106 - 114
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (728 KB)  

    A hybrid neural network fuzzy expert system is developed to forecast short-term electric load accurately. The fuzzy membership values of the load and other weather variables are the inputs to the neural network, and the output comprises the membership values of the predicted load. An adaptive fuzzy correction scheme is used to forecast the final load by using a fuzzy rule base and fuzzy inference mechanism. Extensive studies have been performed for all seasons, and a few examples are presented in the paper, average, peak and hourly load forecasts View full abstract»

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  • Hybrid method of determining the transient stability margin of a power system

    Page(s): 27 - 32
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (544 KB)  

    A hybrid method of determining the transient stability margin of a power system for a given fault clearing time is presented. The method combines the desirable features of the transient energy function method and the output results of the conventional time domain simulation method to find the stability margin, which in the present case is determined for only one of the machines in the system called the critical machine. The critical machine is considered to be the one that initially runs out of synchronism and it is identified by checking the variation of machine angles generated by the time domain simulation method. The stability margin obtained by the proposed method would be very useful for guiding the selection of fault clearing time in subsequent case studies by the time domain simulation method. The proposed method was successfully demonstrated on the 7-machine CIGRE system and 17-machine reduced Iowa system View full abstract»

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  • Harmonic generation by HVDC schemes involving converters and static VAr compensators

    Page(s): 66 - 74
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (604 KB)  

    The paper makes use of interactive harmonic analysis (IHA) to examine the harmonic behaviour of an HVDC scheme. The scheme is treated as a complete system including HVDC converters, static VAr compensators, system impedance and harmonic filters. It is shown that the type and performance of the controller can have a significant effect on harmonic behaviour. The paper illustrates, by analytical and computational analysis, the effect of equally pulse spaced (EPS) controllers and voltage zero crossing (VZC) type for both the above power electronic circuits. The EPS has clear advantages for 6 and 12 pulse HVDC converters but has little influence on the behaviour of thyristor controlled reactors. The need to represent the complete systems is highlighted by example View full abstract»

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