روش هاي كاهش قدرت اتصال كوتاه در شبكه هاي توزيع و كاربرد باز يابنده ي ديناميكي ولتاژ ﴿DVR﴾

چكيده انگليسي :

AbstractIn This thesis is concerned with the application of Dynamic Voltage Restorer DVR as a fault currentlimiting device Power systems are always facing expansion and complexity due to increasing demand toelectric energy While this expansion results in both voltage profile and higher reliability it naturallyincreases the short circuit capacity of network bus bars This in turn imposes some expenses to networkoperators for upgrading network components and particularly circuit breakers Therefore network operatorsand designers always try to avoid these expenses by proper methods and without adverse effect on theadvantages of network expansion There are many methods and techniques that may be used for control andlimitation of the magnitude of short circuit current in a power system network Network reconfiguration is amethod by which the operator can reduce the number of sources contributing to short circuit currents thesereducing it s magnitude Another method is to use the so called Fault Current Limiter FCL Thetransformer type superconducting fault current limiter has many advantages such as the design flexibility ofthe current limiting device The transformer type superconducting fault current limiter is composed of aseries transformer and a superconducting current limiting device The primary winding of the transformer isconnected in series to the power system line and the secondary winding is short circuited through thesuperconducting current limiting device whose normal resistance plays an important roles in limiting the faultcurrent In this thesis the basic characteristics and the design indexes of the transformer type superconductingfault current limiter are classified and the limiting characteristics such as the dependency of the initial currentof limiting operation on the fault phase angle are shown One kinds of fault current limiters are based onresonant circuits These circuits are able to limit short current fast at preset levels This resonant circuitconsists of a switch capacitor and inductor that tuned to the supply frequency In this thesis different circuitsare presented and compared with regard to technical aspects Also it will be shown that the design ofresonant circuit offers some degree of freedom which gives the opportunity to design circuits at minimalcosts During fault current limiting the steady state and transient of fault current will be analyzed A newresonant circuit with spark gap will be introduced In this FCL the inductive reactance of the reactor iscontrolled by a spark gap The operation principle of the this limiter is based on producing a parallel resonantin series with power line In this thesis the solid state fault current limiters are also discussed A DVR is aCustom Power device which is employed to combat voltage variations in a feeders This task is accomplishedby injecting a proper voltage in series with the line This feature can also be used to reduced the magnitude ofshort circuit current which is the objecting of this thesis In this regard different control strategies of a DVRwhen used as a current limiting device is analyzed Advantages and disadvantages each strategy arediscussed Simulations in time domain are used to verify the analysis Key Words fault current reduction FCL Dynamic Voltage Restorer DVR

متوسل، مهدي

روش هاي كاهش قدرت اتصال كوتاه در شبكه هاي توزيع و كاربرد باز يابنده ي ديناميكي ولتاژ ﴿DVR﴾

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