Research On Coordinated Protection Control Strategy Of Distribution Network Considering Grid-connected Distributed Renewable Energy Sources

With the energy revolution and the development of smart grid,the renewable energy sources based distributed generation(RES-DG)such as wind turbine generators(WTGs)and photovoltaics(PVs)are being extensively integrated into the existing power distribution system to meet the electricity demand and to the reduce the carbon footprints.This is due to massive development in green energy technologies and their economical,technical and environmental benefits.These benefits are subject to the optimal integration of RES-DGs.However,apart from the beneficial aspect,RES-DGs can also complex technical limitations,including the loss of protection coordination(PC)among the protection devices such as fuse-recloser coordination and relay-relay coordination.This can lead to the malfunctioning of the protection devices,blind protection,sympathetic tripping,delay in fault clearance,fuse blowing,and permanent outage of power supply caused by the temporary faults in distribution networks.In this dissertation,potential impacts on protection coordination due to RES-DGs integration into power system,are investigated in detail and suitable solutions are suggested for a fast,accurate and sustainable protection coordination.Firstly,a curve fitting technique is proposed to restore the much-influenced fuse-recloser coordination due to presence of RES-DGs.A midline recloser associated with directional properties for coordination with the upstream and the downstream protection devices is deployed to tackle the temporary faults.This approach is implemented in two stages.During the first stage,the fault current before and after RES-DG insertion are determined,and it is classified that either fuse-recloser coordination is lost or hold.It helps to take decision because no action is needed if coordination holds.On contrary,if the coordination is lost,then during the second stage,the ratio of fault currents in recloser and fuse is multiplied with the time dial setting(TDS)of the fast operation curve of the recloser.This shifts the recloser fast curve downward to establish fuse-recloser coordination.The detailed simulation results using electrical transient analysis program(ETAP)are provided to validate the proposed scheme.Secondly,conventional overcurrent relays(OCRs)depend upon the fault current magnitude and operate in one direction only.OCRs face serious challenges for the protection of distribution network(DN)integrated with multiple RES-DGs.Therefore,a novel user-defined dual setting directional overcurrent relay with hybrid time-current-voltage characteristics(UDDOR-TCV)is developed,which takes into account the fault voltage along with the fault current.It also operates in both directions i.e.forward and backward to tackle the reverse power flow due to the presence of RES-DGs.Further,the PC problem is formulated in a constrained non-linear optimization fashion and tackled with mixed integer non-linear programing(MINLP)solver of general algebraic modeling system(GAMS).In this way,sufficient reduction in relay operation time with zero mis-coordination is achieved.The detailed numerical analysis and simulation results are provided to validate the efficiency of proposed relay characteristics.Lastly,the characteristics of RES-DGs such as WTG are investigated which are stochastic in nature due to the intermittent behavior of the wind speed.It can cause fluctuation in the fault current level,which in turn creates the OCR coordination problem.Therefore,wind dynamics forecast based adaptive OCR coordination scheme for wind farms(WF)integration with power network is proposed.The proposed PC comprises of two steps.Initially,the seasonal autoregression integrated moving average(SARIMA)and artificial neuro fuzzy inference system(ANFIS)are deployed for forecasting periodic and non-periodic wind dynamics respectively and the fault current is calculated in advance.Secondly,hybrid Harris hawk optimizer and linear programming(HHO-LP)is proposed to optimally solve the ORC problem with pre-determined fault current.The relay settings are updated adaptively in advance,with a communication infrastructure and in this way a proper relay coordination is established.The detailed modeling of SARIMA,ANFIS and HHO-LP are provided,and the efficiency of proposed protection scheme is validated with simulation results.