By Topic

Generation, Transmission and Distribution, IEE Proceedings-

Issue 6 • Date Nov 2000

Filter Results

Displaying Results 1 - 17 of 17
  • Initial applications of complex artificial neural networks to load-flow analysis

    Page(s): 361 - 366
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (336 KB)  

    Artificial neural networks (ANNs) have been widely used in the power industry for applications such as fault classification, protection, fault diagnosis, relaying schemes, load forecasting, power generation and optimal power flow etc. At the time of writing this paper, most ANNs are built upon the environment of real numbers. However, it is well known that in computations related to electric power systems, such as load-flow analysis and fault-level estimation etc., complex numbers are extensively involved. The reactive power drawn from a substation, the impedance, busbar voltages and currents are all expressed in complex numbers. Hence, ANNs in the complex domain must be adopted for these applications, although it is possible to use ANNs in the conventional way by dividing a complex number into two real numbers, representing both the real and imaginary parts. It is shown, by illustration with a simple complex equation, that the behaviour of a real ANN simulating complex numbers is inferior to that of an ANN which is intrinsically complex by design. The structure of the complex ANN and the numerical approach in handling back propagation for online training under the complex environment are described. The application of this newly developed ANN on load flow analysis in a simple 6-busbar electric power system is used as an illustrative example to show the merits of incorporating complex ANNs in power-system analysis View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Investigation of impedance based protection technique for EHV 3-terminal double circuit lines

    Page(s): 317 - 321
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (336 KB)  

    A digital impedance based protection scheme for a 3-terminal transmission line has been implemented on a digital signal processor board and tested on a physical model of a double-circuit 3-terminal line with a source at each end. One combined relay at each terminal of the double-circuit line, instead of two relays, is proposed. Each relay is fed by three voltage and six current signals. Real-time tests conducted on the physical model for various faults show that high fault resistance at the teed point, current infeed, remote-end infeeds, fault location, source impedance and far-end faults cause no problem in proper relay operation. Also, 100% of the lines are protected View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Direct method for calculation of AC side harmonics and interharmonics in an HVDC system

    Page(s): 329 - 335
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (456 KB)  

    AC side current harmonics in an HVDC system are shown to be dependent on the commutation overlap and the DC side ripple. Interharmonics exist when the AC networks operate at different frequencies. An analytical method is proposed to represent such effects in the AC side harmonic calculation. The algorithm does not require iteration between the AC and DC sides. The result obtained using the analytical method is verified using time domain simulation View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Emission control research of spot markets for separate generation systems

    Page(s): 425 - 431
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (464 KB)  

    In a separate generation system, the ability of an optimal economic generation dispatch to satisfy emission constraints for power agencies is crucial. While attempting to minimise deadweight losses caused by emission constraints of power agencies imposed on every power agency on the emission trading market, this investigation also presents equitable criteria for the most suitable emission standard for constructing a preliminary operating model of the emission rights trading market. Owing to its ability to evaluate the quantity and price of emission trading, the operating model can serve as an index for the trading of emission rights in a separate generation system, This investigation also applies the sequential unconstrained minimisation technique (SUMT) to obtain a solution that satisfies the lowest generation cost in emission constraints. The SUMT method takes the limit of the nonlinearity equality or nonlinearity inequality, and then applies a transformation method to transfer the constraints into the unconstrained nonlinearity-programming problem. Simultaneously this method also incorporates the characteristics of the quasi-Newton method while assuming that a reliable initial value need not be assigned to determine the optimal search direction. Finally, the optimum solutions are obtained by regularly adjusting the penalty parameter. An illustrative example is presented to verify the accuracy of this technique View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • On-line dynamic security contingency screening using artificial neural networks

    Page(s): 367 - 372
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (448 KB)  

    On-line dynamic security analysis has now become realistic due to advances in computer technology and algorithms for security assessment. Details of pattern recognition based electromechanical stability screens which have been implemented within a dynamic security assessor are presented. Use of statistical functions of features is shown to overcome the dimensionality problem of applying pattern recognition techniques to large power systems. The low computational cost of this approach coupled with efficient operation has resulted in a significant step towards achieving full online dynamic security assessment View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Accurate model for contribution of generation to transmission system effect on charges and congestion management

    Page(s): 342 - 348
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (384 KB)  

    Some closed formulas that express the contribution of each generator to the power flows, loads and losses in a power system are introduced. The derivation of the formulas is based on the sensitivity and corrective action analysis of the system. The applicability of the proposed formulas is demonstrated using various test systems and they are compared with other state-of-the-art methods. Also these formulas are tested on a practical system to relieve transmission congestion problems and calculate the use-of-transmission system charges View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Analysis of voltage collapse mechanisms in state space

    Page(s): 395 - 400
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (400 KB)  

    The effects of the generator excitation current limit, the on-load tap changer (OLTC) and load dynamics on voltage stability are analysed in state space. The variation of the number and coordinates of the equilibrium points with parameters of the system are discussed. In addition, a small-disturbance voltage stability region of a simple system is constructed. When the dynamic aspect of voltage collapse is considered, it is more convenient to analyse it in the state space rather than in the input/output parameter space. The voltage stability of a system is determined by the dynamic characteristics of both the OLTC and the load. The generator excitation current limit affects the voltage stability by changing the small-disturbance voltage stability region and the equilibrium points of the system. After a small disturbance, the mode of voltage instability, fast instability or longer-term instability, depends on the composition of the load as well as the value of the system reactance View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • New concept in AC power theory

    Page(s): 417 - 424
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (508 KB)  

    Conventional power theory is examined in the time and frequency domains, and a new definition of apparent power in single- and three-phase systems is presented. The technique is based on the instantaneous power, which satisfies the law of conservation of energy. In this technique reactive power is determined as a DC imaginary component of the instantaneous power. Apparent power is defined as the RMS or 2-Norm of instantaneous power. The technique satisfies the Plancherel's theorem both in time and frequency domain. It is shown that power factor can only be made to be unity in a three-phase balanced system if the new definition of apparent power is used View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Experimental investigation into harmonic impedance of low-voltage cables

    Page(s): 322 - 328
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (444 KB)  

    Harmonic characteristics of power cables used in low-voltage distribution systems of commercial buildings are investigated. Analytical discussion of cable resistance and reactance at harmonic frequencies is presented. An experimental procedure for obtaining full matrix impedance of cables at harmonic frequency is introduced. It is found that cable resistance increases with increasing harmonic order. Cable inductance, however, decreases due to the effect of flux cancellation. The analytical formulas presented yield reasonable accuracy for cable resistance for single-core cables, but provide an overestimation for multicore cables. The impact of various parameters on cable resistance and reactance, such as harmonic order, cable installation method, cable current distribution and the presence of magnetic material is also addressed, as well as the mechanisms for impedance variation. Finally, recommendations for using the approximate formulas for cables in low-voltage installations are provided View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Distribution system planning with evolutionary programming and a reliability cost model

    Page(s): 336 - 341
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (300 KB)  

    Cost of reliability of optimal distribution system planning is considered. The reliability cost model has been derived as a linear function of line flows for evaluating the outages. The objective is to minimise the total cost including the outage cost, feeder resistive loss, and fixed investment cost. Evolutionary programming was used to solve the very complicated mixed-integer, highly nonlinear and nondifferential problem. A real distribution network was modelled as the sample system for tests. There is also a higher opportunity to obtain the global optimum during the EP process View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Robust design of multimachine power system stabilisers using tabu search algorithm

    Page(s): 387 - 394
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (528 KB)  

    Robust design of multimachine power system stabilisers (PSSs) using the tabu search (TS) optimisation technique is presented. The proposed approach employs TS for optimal parameter settings of a widely used conventional fixed-structure lead-lag PSS (CPSS). The parameters of the proposed stabilisers are selected using TS in order to shift the system poorly damped electromechanical modes at several loading conditions and system configurations simultaneously to a prescribed zone in the left hand side of the s-plane. Incorporation of TS as a derivative-free optimisation technique in PSS design significantly reduces the computational burden. In addition, the quality of the optimal solution does not rely on the initial guess. The performance of the proposed PSSs under different disturbances and loading conditions is investigated for multimachine power systems. The eigenvalue analysis and the nonlinear simulation results show the effectiveness of the proposed PSSs in damping out the local, as well as the interarea, modes and enhance greatly the system stability over a wide range of loading conditions and system configurations View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • H-controllers for linearised time-delay power systems

    Page(s): 401 - 408
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (424 KB)  

    Three H-control schemes are developed for the stabilisation of power-system models with state delays. Two control schemes which consist of one gain term representing pure state feedback are proposed first. Then, a controller consisting of two gain terms comprising pure plus delayed state feedback is developed. The proposed controllers guarantee the asymptotic stability of the controlled system and the H-norm bound of the closed-loop transfer function of the system. The associated gains are determined in each case from the solution of a linear-matrix-inequality feasibility problem. Simulation results of the proposed schemes are presented and discussed View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Passive filter design for harmonic reactive power compensation in single-phase circuits supplying nonlinear loads

    Page(s): 373 - 380
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (472 KB)  

    The proliferation of different types of nonlinear loads into a distribution system has the potential to increase the harmonic levels in the system. The effect of attenuation on reducing the net current harmonics is reported for different nonlinear loads. Calculation of nonlinear load susceptances at different harmonic frequencies is presented. The design procedure of a reactance one-port compensator capable of reducing the voltage and current harmonics produced by nonlinear loads supplied from a source having internal inductive impedance is offered. The reactance one-port compensator application to a secondary distribution system loaded with different load types is presented. The analysis uses the Electromagnetic Transient Program (EMTP) to model different loads as well as the distribution system. Finally, physical experiments have been conducted to verify the results obtained by simulation View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Distribution feeder reconfiguration with refined genetic algorithm

    Page(s): 349 - 354
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (332 KB)  

    A refined genetic algorithm for a distribution feeder reconfiguration to reduce losses is presented. The problem is optimised in a stochastic searching manner similar to that of the conventional GA. The initial population is determined by opening the switches with the lowest current in every mesh derived in the optimal power flow (OPF), with all switches closed. Solutions provided by OPF are generally the optimum or near-optimal solutions for most cases, so prematurity could occur. To avoid prematurity, the conventional crossover and mutation scheme was refined by a competition mechanism. So the dilemma of choosing a proper probability for crossover and mutation can be avoided. The two processes were also combined into one to save computation time. Tabu lists with heuristic rules were also employed in the searching process to enhance performance. The new approach provides an overall switching decision instead of a successive pattern, which tends to converge to a local optimum. Many tests were conducted and the results have shown that RGA has advantages over many other previously developed algorithms View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Three-dimensional thermal imaging for power equipment monitoring

    Page(s): 355 - 360
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (832 KB)  

    It is well known that most faults in a power system appear as localised hot spots in their early stage of development and gradually grow into accidents that are not remediable, such as total insulation breakdown or even explosion. Through the detection of hot spots and abnormal rise in working temperature of conductors or insulators, infrared thermography has been one of the most useful tools in identifying potential failures, so that preventive measures can be taken to avoid the occurrence of any hazard. However, this method has not attracted worldwide attention and popularity because it is extremely difficult to visually analyse thermal images of power equipment and, very often, only skillful maintenance engineers are able to make correct judgements based on these images due to a lack of three-dimensional sense. The employment of techniques in virtual reality to produce three-dimensional thermal images is described, so that users are able to manipulate the three-dimensional object on the screen under both geometrical mode and thermal mode. Hot spots can easily be identified as a means of condition-based maintenance. This system can provide vital indications of the equipment's condition, providing warnings of potential problems. This technique is totally noninvasive and it can keep the plant in service throughout the whole period of assessment. Furthermore, this system should also be useful for training maintenance engineers. The whole system (including the hardware set-up and the associated mathematics) is described View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Extending health considerations in subtransmission systems to include reliability worth

    Page(s): 381 - 386
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (420 KB)  

    The basic concepts associated with quantitative reliability assessment of electric power systems are reasonably well established, and well accepted within the power industry. The evaluation of the costs and benefits of competing investments is now becoming a standard practice in power-system planning. To justify the use of new facilities and system modification specific reference to reliability has normally been included, and one approach that has received considerable attention is the evaluation of the societal worth (benefit) of system reliability, or conversely the costs incurred by consumers due to power supply interruptions. To make a consistent appraisal of economics and reliability, it is necessary to compare investment cost needed to attain a specified level of reliability with the reliability worth or benefits derived by the society at that level of system reliability. The wellbeing framework is extended to include the societal worth of electric service reliability in subtransmission systems. System well-being is defined in terms of three system states: (i) healthy, (ii) marginal and (iii) at risk, thus combining the deterministic and probabilistic approaches into a single framework. The determination of reliability worth indices of expected energy not supplied (EENS), expected cost of interruptions (ECOST) and interrupted energy assessment rate (IEAR) are discussed, for both the healthy and at risk states in the well-being framework. The concepts associated with extending the well-being framework to include reliability worth parameters are illustrated by application to a small reliability test system View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Instantaneous phase-angle estimation algorithm under unbalanced voltage-sag conditions

    Page(s): 409 - 415
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (424 KB)  

    If a negative sequence is generated by voltage sag and/or unbalance, it appears as an oscillating error in a synchronous reference frame (SRF). In power conditioning equipment, the exact value of a positive sequence is needed to achieve the unity power factor and constant output voltage, whereas the exact value of a negative sequence is needed for unbalance compensation. To measure the positive sequence separately from the negative sequence, a low pass or notch filter having a narrow bandwidth is normally used. However, such a filter causes a lot of phase delay, thus the response time of the system tends to be lengthened. A method of estimating the positive- and the negative-sequence voltages separately is presented, without a significant delay, by utilising the weighted least-squares estimation (WLSE) method with the covariance resetting technique. A frequency update law is also proposed to accommodate the frequency varying environments. The authors demonstrate through simulation and experiment the superior performance of the proposed scheme in measuring the positive- and the negative-sequence voltages at the time of abrupt transition. This method can be applied to uninterruptable power supplies (UPS), pulsewidth modulation (PWM) AC/DC converters, active filters, AC voltage compensators etc View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.