Modelling And Design Of Turn-to-Turn Fault Protection Scheme For EHV/UHV Magnetically Controlled Shunt Reactor

Shunt reactors are used in long transmission lines and distribution networks to absorb the extra reactive power generated due to the existence of capacitive charging current.The MCSR is a type of continuously controllable shunt reactors used for reactive power compensation and voltage control.From a power system reliability point of view,continuous operation of MCSR is needed.Therefore,special attention should be given to protect the equipment from all types of possible faults.Due to the design and functional differences from fixed type shunt reactors and power transformers,the protection task becomes more challenging for MCSR.The major faults which cause high magnitude fault current are phase-to-phase and phase-to-ground faults.The level of fault current is dependent upon the location of the fault.The T2TF(fault between turns within the phase winding)is not only the most common failure in shunt reactors,but it is also the most challenging fault type to detect.Once the arc between some turns has been initiated,the fault may develop to flashover the entire winding.If not detected at an incipient stage,this resulting into phase fault that can harm the healthy phases as well.Even one shorted turn will cause a high magnitude circulating current in the fault location.However,seen from the outside,the magnitudes of phase currents and the voltages do not change very much from the normal steady-state operational limits.Due to the presence of MCSR windings inside the oil tank,detection of the low-level T2TF becomes a challenging task,especially in case of a CtrW T2TF where DC is flowing and have a special configuration.The Buchholz or pressure relief protection(i.e.,mechanical way of faults protection)presents a quite dependable protection for this type of fault in case of oil-based shunt reactors.Many utilities consider mechanical protection is a main protection function due to the limitations from electrical protection schemes.However,new methods for detecting T2TFs that benefit from the possibilities offered by numerical protection have been developed in recent years.The fundamental objective of this research work is to model and design a sensitive and applicable T2TF electrical protection scheme for MCSR that can protect the equipment from all possible T2TFs.Therefore,two new protection schemes are proposed and tested in this thesis mainly.The uniqueness of the proposed protection schemes in this work are their abilities to detect the faulty phase,faulty winding,differentiation between different windings T2TFs,differentiation of T2TF from energization conditions,internal,and external faults.Moreover,these schemes can be applied on the existing MCSR without changing the basic windings configuration,body structure,or mechanical design,which is a real challenge.For this research work,the first 750kV MCSR installed in Yuqia substation having a rated voltage of 800kV and a rated capacity of 330 MVAr,is chosen as a case study.The following approaches are used to achieve the ultimate goal of modelling and designing these unique T2TFs protection schemes.First of all,basic understanding of the mathematical background of existing EHV MCSR model and its implementation in MATLAB/Simulink platform is performed.Faults analysis of the model is carried out and a comprehensive protection package for all kind of possible internal and external faults is formulated and validated through numerous simulation results.The symmetrical components behavior under PWs,CtrWs,and CpWs T2TFs is evaluated and defined a protection scheme based on angle of the negative sequence voltage(?3V2),and magnitude of the negative sequence current(|3I2|).The usefulness of the proposed symmetrical components-based protection scheme is validated through simulations.Moreover,mathematical modelling is performed for developing an algorithm for T2TF protection based on the current's magnitudes comparison at different buses,and evaluated the fundamental laws comprising of basic electric and magnetic circuit parameters.This protection scheme is also tested on the simulation model and validated its usefulness.