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power methods of accounting for harmonics in billing are considered.These large differences indicate that the choice of weighting factor willbe crucial for harmonically adjusted power factor or apparent powermeasuring methods.Adherence to IEEE Standard 5 19 -1992 will reduce harmonics inthe system and system losses related to the current harmonics. It willalso promote fair and equal revenue billing of all customers connectedon the system.Discusser: A. Emanuel

96 WM 087-7PWRD, T-PWRDJanuary 1997Control Strategy and Site Selection of aShunt Active Filter for Damping of HarmonicPropagation in Power Distribution SystemsHiro fumi Akagi (Senior Mem ber, IEEE; Okay ama University,J a pa n )

This paper deals with a shunt active filter which will be installedby an electric utility, putting much emphasis on the control strategyand the best point of installation of the shunt active filter on a feederin a power distribution system. The objective of the shunt active filteris to damp harmonic propagation rather than to minimize voltagedistortion throughout the feeder. Harmonic mitigation is a welcomeby-product of the shunt active filter, which comes from dam ping ofharmonic propagation.A virtual model for a radial distribution system in a residential areais used for analysis and compu ter simulation. The rated bus voltage is6.6kV (line-to-line), and the rated frequency is SOHz. The equivalentinductive reactance upstream, including the leakage reactance of aprimary distribution transformer of ISMVA, is to be estimated fromthe short circuit capacity of 110MV A. The transformer supplies fourdistribution feeders consisting of feeders 1 - 4. For the sake of sim-plicity, only feeder 2 is considered under the assumption that feedersI , 3 and 4 are d isconnected from the transformer. Overhead distributionlines, which are classified into a primary line and branch lines in feeder2, are assumed to be LR circuits because it is reasonable to neglect theeffect of stray capacitors of the distribution lines on the 5th and 7thharmonic voltage and current. Feeder 2 supplies electric power toeleven medium-voltage consumers of 200-240kW , which install shuntcapacitors without any reactor, and to six low-voltage consumers of50-130kW, which have no shunt capacitor. The total capacity of theloads is 2.99MW, and that of the shunt capacitors for power factorimprovement is 0.99Mvar. Harmonic propagation occurs in feeder 2around the 7th harmonic frequency (XOHz), so that the 7th harmonicvoltage is amplified by four times at the rated load of 2.99MW and byeight times at no load. This results from series and/or parallel resonancebetween inductive reactances of the distribution lines, along with theequivalent inductive reactance up stream, and capacitive reactances ofthe shunt capacitors on feeder 2.First of all, this paper reveals how the stability of a shunt activefilter is affected by the control strategy and the point of installation onthe primary line in feeder 2. Three types of harmonic detection methodsin time domain, that is, load current detection, supply current detection,and voltage detection, are taken into consideration. Each harmonicdetection method plays an important role in the control strategy of theshunt active filter. The open-loop transfer function and its B ode diagramin each detection method give us the following analytical results: Ashunt active filter based on either the load current or supply currentdetection operates properly, if neither shunt capacitor nor shunt passivefilter is connected to a network down stream of the point at which theshunt active filter is installed. Thus, either of the two methods hasalready been applied to shunt active filters installed in the vicinity ofan or a few identified harmonic-producing load(s). But the computersimulation shows that the shunt active filter based on either of the twomethods becomes u nstable when it is installed on the beginning termi-nal and m idpoint of the primary line in feeder 2. Instability or sustained

oscillation appears in a frequency range from 400H z to 4SOHz. Onother hand, the voltage detection method has a phase margin overregardless of location. From the viewpoint of stability, it is the msuitable for shunt active filters which are intended to be dispersivinstalled on power distribution systems or industrial power systeThese analytical results agree well with those obtained by compusimulation.Next, this paper presents a basic concept of site selection of a sinshunt active filter based on the voltage detection, and its effectdamping of harmonic propagation. The shunt active filter, whichinstalled on the beginning terminal in the primary line, has no capabiof damping harmonic propagation in feede r 2. The shunt active fiwhich is installed in the vicinity of an identified harmonic-producload, is effective in the mitigation of harmonic voltage at the poininstallation. However, it may he im possible for an electric power copany to identify all of harmonic-producing loads on power distribusystems. Even if it is possible, it would be impractical, from an enomical point of view, to install a shunt active filter in the vicinityeach harmonic-producing load. Thus, this paper points out that inslation of the shunt active filter on the end term inal of the primary is the most effective and practical way, not only to damp harmopropagation throughout feeder 2, but also to solve harmonic interence caused by many u nidentified harmonic-producing loads on fee2. The validity of this new concept is verified by theory and com psimulation.Finally, this paper presents an optimal gain in the voltage detecmethod, leading to a practical application of the shunt active filter power distribution systems.Discussers: Z. Yao, V. Rajagopalan, S. Lahaie

96 WM 090-1PWRD, T-PWRDJanuary 1997Determination of Needed FACTS ControllersThat Increase Asset Utilization of Power SystemsL.A.S. Pilotto (Member, IEEE; CEPEL - C e n t ro de Pesquisasde , Energ ia ECtrica, Rio d e Janeiro, Brazil), WW Ping(CEPEL), A.R. Carvalho (CEPEL),A. Wey (Member, IEEE;Promon Enge nha r ia , Rio de Janeiro, Brazil), WE L o n g(Fellow, IEEE; University of Wiscon sin, M adison, W isconsin)EL. Alvarado (Fellow, IEEE; University of Wisconsin), C.L.DeMarco (Member, IEEE; University of Wisconsin), A. Edri(Senior Mem ber, IEEE; Electric Power, Research Institute, PAlto, California)

Flexible AC Transmission System (FACTS) is a concept promothe use of power electronic based and o ther static controllers to enhacontrollability and increase power transfer capability. The basic ibehind the FACTS concept is to enable the transmission systembecome active elements, playing active roles in increasing the flexibof power transfer requirements and in securing stability of the dynamof integrated power systems. Therefore, FACT S Controllers shoulddesigned with dynamic characteristics that effectively enhance dynamic performance of the associated power system.Power System engineers are currently facing challenges to increthe power transfer capability of existing transmission systems. FACoffers an economical solution to accommodate that need while mtaining sufficient steady-state and transient stability margins,The main purpose of this paper is to present a statiddynaapproach for allocation of FACTS Controllers. The proposed approis based on the combined use of a continuation power flow, an optipower flow and an eigenvalue analysis. The algorithm allocates shconnected controllers (Static Var Compensators - SVC ) to solve volcollapse problems that may occur during major faults or due to llevel increases. Series connected controllers (Thyristor Controlledries Capacitors TCSC) are allocated to guarantee the maximum trsient synchronizing torque between electrical areas during severe faThe studied transmission system is shown in Figure 1. It is c

58 IEEEPower Engineering Review, anuary