Mechanisms governing the evolution of a long-lived northwest vortex that caused a series of disasters in Northwest China

The northwest vortex(NWV)is a type of mesoscale vortex that appears with a relatively high frequency in Northwest China.To further the understanding of the NWV’s evolution,in this study,the moisture and circulation budgets of a long-lived NWV(~132 h)that appeared in early August 2019 were calculated.This vortex induced a series of torrential rainfall events in Northwest China and Mongolia,which caused severe transmission line faults and urban waterlogging.Synoptic analyses indicate that the NWV was generated in a favorable background environment characterized by notable upper-level divergence and strong mid-level warm advection.The moisture budget shows that the East China Sea and Bohai Sea acted as the main moisture sources for the NWV-associated precipitation,and the water vapor was transported into the rainfall regions mainly by easterly and southeasterly winds.The circulation budget indicates that,during the developing stage,convergence-related vertical stretching was a dominant factor for the NWV’s development;whereas,the vortex’s displacement from regions with stronger cyclonic vorticity to those with weaker cyclonic vorticity mainly decelerated its development.In the decaying stage,divergence-related vertical shrinking and the net export of cyclonic vorticity due to the eddy flow’s transport resulted in the NWV’s dissipation.

Application of new directional logic to improve DC side fault discrimination for high resistance faults in HVDC grids

This paper proposes a simple and fast way to determine the direction of a fault in a multi-terminal high voltage direct current(HVDC) grid by comparing the rate of change of voltage(ROCOV) values at either side of the di/dt limiting inductors at the line terminals. A local measurement based secure and fast protection method is implemented by supervising a basic ROCOV relay with a directional element. This directional information is also used to develop a slower communication based DC line protection scheme for detecting high resistance faults. The proposed protection scheme is applied to a multi-level modular converter based three-terminal HVDC grid and its security and sensitivity are evaluated through electromagnetic transient simulations. A methodology to set the protection thresholds considering the constraints imposed by the breaker technology and communication delays is also presented. With properly designed di/dt limiting inductors,the ability of clearing any DC transmission system fault before fault currents exceeds a given breaker capacity is demonstrated.

Experimental studies on impedance based fault location for long transmission lines

In long transmission lines,the charging current caused by the shunt capacitance decreases the accuracy in impedance based fault location.To improve the accuracy of fault location,this paper presents a novel scheme,where two Digital Fault Recorders(DFRs)are installed in a line.They can send the transient data of the faults to the both ends of a line.To estimate the distance of a fault,impedance based fault location methods are applied with transient fault data of both ends protection relays and both DFRs installed in a line.To evaluate the proposed scheme,a laboratory setup has been developed.In the lab,several faults have been simulated and associated voltages and currents are injected to a relay IED to compare experimental results.

Robust fault analysis in transmission lines using Synchrophasor measurements

As more electric utilities and transmission system operators move toward the smart grid concept,robust fault analysis has become increasingly complex.This paper proposes a methodology for the detection,classification,and localization of transmission line faults using Synchrophasor measurements.The technique involves the extraction of phasors from the instantaneous three-phase voltages and currents at each bus in the system which are then decomposed into their symmetrical components.These components are sent to the phasor data concentrator(PDC)for real-time fault analysis,which is completed within 2–3 cycles after fault inception.The advantages of this technique are its accuracy and speed,so that fault information may be appropriately communicated to facilitate system restoration.The proposed algorithm is independent of the transmission system topology and displays high accuracy in its results,even with varying parameters such as fault distance,fault inception angle and fault impedance.The proposed algorithm is validated using a three-bus system as well as the Western System Coordinating Council(WSCC)nine bus system.The proposed algorithm is shown to accurately detect the faulted line and classify the fault in all the test cases presented.