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Generation, Transmission and Distribution, IEE Proceedings-

Issue 6 • Date Nov 1997

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Displaying Results 1 - 8 of 8
  • Fixed/switched type shunt capacitor planning of distribution systems by considering customer load patterns and simplified feeder model

    Page(s): 533 - 540
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (684 KB)  

    A shunt capacitor planning strategy to reduce system resistive losses and improve voltage profile for distribution feeders has been proposed. The objective function consists of peak load loss, energy loss and shunt capacitor cost, while operational constraints such as bus voltage profile and real shunt capacitor size are considered throughout the overall solution procedure. A three-phase load flow program. Which accounts for the mutual coupling effect between conductors, unbalanced loading among phases, and feeders with multiple lateral branches, is applied to enhance the computer simulation. The simplified feeder model has been developed to derive the equivalent circuit of minor lateral branches so that the data processing work for the feeder configuration can be reduced efficiently. Besides, the customer load patterns as well as the feeder load curve for various seasons are derived so that the section load behaviour can be estimated more realistically. According to the reactive load duration curve of the feeders studied, the capacitor operation strategy by considering both fixed and switched shunt capacitors is developed to determine the proper size, location and switching time of capacitors to enhance the system operation efficiency. Two practical feeders in the Taipower distribution system are selected for demonstration to show the effectiveness of the proposed method. Capacitors with optimal size are installed according to the schemes derived by computer analysis. Field tests are then performed and the energy loss reduction as well as the improvement of power quality of the test feeders can be justified View full abstract»

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  • PWM-controlled series compensation with low harmonic distortion

    Page(s): 555 - 563
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (864 KB)  

    The paper describes a pulse width modulation (PWM)-controlled series compensator with continuously variable reactance, employing simple PWM duty ratio control. Each phase of the compensator comprises a switched reactor and parallel capacitor. The duty ratio control gives a wide range of capacitive and inductive compensation. The harmonics created by the switched reactor have been analysed. The switched reactor and parallel capacitor have been simulated with a range of switching frequencies and duty ratios. With appropriate choice of capacitor and reactor. A scaled-down experimental model of the compensator has been simulated and constructed. The harmonics have been found to be small even with the switching frequency of the controlled turn-off switches as low as 400 Hz. A large step change in duty ratio from maximum capacitive compensation to inductive compensation shows the rapid dynamic response of the compensator with a fast settling time. This demonstrates that the proposed compensator should be considered as another useful FACTS controller for series compensation View full abstract»

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  • Calculation of thermal fields of underground cable systems with consideration of structural steels constructed in a duct bank

    Page(s): 541 - 545
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (428 KB)  

    Structural steels are used in underground cable systems to provide a high degree of mechanical protection for electrical cables. An accurate prediction of the temperature distribution of the system needs to include not only the effect of the total cable electrical losses but the eddy current losses induced in the steel. A finite element method is proposed to evaluate the losses generated in the conductors and in the steels, these are then used as the heat sources for thermal analysis. Several steel arrangements of a cable system are solved and compared. The results are useful for the design of a cable duct bank which uses structural steels View full abstract»

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  • Voltage control by tap-changing transformers for a radial distribution network

    Page(s): 517 - 520
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (288 KB)  

    Voltage control is of interest to many researchers, and is currently being considered by many utilities for implementation in their energy control centres. Transformers with tap-changing facilities constitute an important means of controlling voltage throughout the system at all voltage levels. A new method for determining the minimal changes in transformer taps to control voltage levels is presented. The problem to be solved is cast into a nonlinear constraint optimisation. The constraints are tackled in the minimisation algorithm by forming the Lagrangian. Necessary conditions for optimality are derived and solved using the Newton-Raphson method View full abstract»

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  • Active power filter with sliding mode control

    Page(s): 564 - 568
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (444 KB)  

    The paper presents an active power filter (APF) to eliminate harmonics and to compensate reactive power and neutral current of three-phase four-wire symmetrical and unbalanced nonlinear loads. A set of three single-phase insulated-gate bipolar transistor (IGBT)-based voltage source inverter (VSI) bridges with a common DC bus capacitor is used as the APF. A sliding mode controller (SMC) over the average DC bus voltage is used for the control. A hysteresis rule bused carrierless pulse width modulation (PWM) current control is employed to generate the gating signals to the switching devices. A set of three single-phase diode bridge rectifiers with capacitive-resistive loading is used for nonlinear loading. The simulation results show that the APF is capable of compensating reactive power. Neutral current and load unbalance and reducing the harmonic level below the limit specified in IEEE-519 standard View full abstract»

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  • Fuzzy assessment of power system transient stability level based on steady-state data

    Page(s): 525 - 531
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (656 KB)  

    Following extensive analysis of the relationships between the transient instability behaviour of large-scale power systems and the corresponding prefault operating states, a novel heuristic method based on fuzzy reasoning is proposed in the paper for the fast evaluation of the power system transient stability level (TSL). A notable feature of this method is that it does not rely on the step-by-step simulation process and only system load-flow data under normal operating conditions are used for the assessment. A generalised critical clearing time (GCCT) is defined that can be predicted by the proposed method to describe the TSL. Digital simulations based on two power systems show that the proposed method provides broadly conclusive and decisive real-time information about the stability states of the studied power systems View full abstract»

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  • Surrogate worth trade-off technique for multi-objective optimal power flows

    Page(s): 547 - 553
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (548 KB)  

    Multi-objective programming techniques have been applied in a number of ways to minimise more than one objective simultaneously. Some research work has been reported on multiobjective power flow studies. In this paper, surrogate worth trade-off technique (SWT) is attempted to achieve the best compromise between cost of generation and system transmission losses and the results have been compared with the existing method. It is found that the SWT technique gives encouraging results View full abstract»

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  • Model for security of service costing in electric transmission systems

    Page(s): 521 - 524
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (376 KB)  

    The security cost of a transmission system is investigated in the paper by means of an indirect method. The theory of a basic system, which only provides transport service with an almost zero security level, is developed. Different concepts are defined for the relationships of contingency effects with branches, nodes and system. An expected load reduction in this system is obtained as a weighted average of the calculated values for different contingencies and operating conditions. Customer reliability worth is used to obtain interruption costs, which are interpreted as the costs that would be incurred if the complete power system did not not have security elements. The model is tested on the 24 bus-IEEE system. With results of system and nodal interruption cost and security indices. It is proved for the sample system that the security cost calculated with this model is a significant part of the transmission annual investment costs. Nodal security costs vary with location, though a group of them present common values View full abstract»

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