A novel complex current ratio-based technique for transmission line protection

With respect to sensitivity,selectivity and speed of operation,the current differential scheme is a better way to protect transmission lines than overcurrent and distance-based schemes.However,the protection scheme can be severely influenced by the Line Charging Capacitive Current(LCCC)with increased voltage level and Current Transformer(CT)saturation under external close-in faults.This paper presents a new UHV/EHV current-based protection scheme using the ratio of phasor summation of the two-end currents to the local end current,instead of summation of the two-end currents,to discriminate the internal faults.The accuracy and effectiveness of the proposed protection technique are tested on the 110 kV Western System Coordinating Council(WSCC)9-bus system using PSCAD/MATLAB.The simulation results confirm the reliable operation of the proposed scheme during internal/external faults and its independence from fault location,fault resistance,type of fault,and variations in source impedance.Finally,the effectiveness of the proposed scheme is also verified with faults during power swing and in series compensated lines.

Inherently Sinusoidal Single-phase Voltage Source Inverter Based on Modified Cuk Cell

Renewable energy has become important for electricity generation because of the high air pollution associated with conventional fossil-based energy systems.Conventional fossil-based power plants are gradually transitioning by incorporating renewable energy sources,such as photovoltaic(PV)cells.In a PV system,an inverter converts DC power from solar panels to AC power required to serve common electrical loads.A conventional H-bridge inverter topology has several disadvantages,such as the voltage being not sinusoidal,switching the DC voltage and high common-mode voltage.The common-mode voltage can cause a large leaked capacitive current,which can result in undesirable operation in solar power applications.A common solution to this problem is the addition of a large filter to the input or output of an inverter.An inherent sinusoidal voltage source inverter based on a modified Cuk converter as its basic cell,which simultaneously generates a sinusoidal output voltage and a lower common-mode voltage,is proposed.The proposed topology does not require additional input or output filters.Analytical expressions are derived to confirm the operation of the proposed topology.Simulation results confirm the mathematical analysis.A laboratory-scale experiment is performed to verify the proposed inverter.