Research On Fault Analysis And Protection Scheme For Multi-terminal HVDC Transmission Networks

The consumption of electrical energy and incorporation of renewable energy has exaggerated dramatically over the recent years.As a consequence,a dire need to interconnect these energy requirements has sprouted,which has expanded globally to effectively share the contemporary power capacity with other countries,thereby enhancing operational flexibility and security of supply.To comprehend these issues,multi-terminal high voltage direct current(MTDC)networks,utilizing voltage-source converters(VSCs),are perceived to be the preferred technology to attain such interconnections.However,technical limitations and DC faults restrain the development of MTDC networks and need to be addressed properly with subsequent disposal.Therefore,to enable widespread adoption,it is mandatory to study,analyze and contemplate potential challenges for the protection of MTDC networks.This thesis addresses the challenges related to the DC side faults,which are the foremost liabilities when the HVDC technology is under consideration.DC side faults in HVDC networks are characterized by large inrush currents due to the discharge of trapped energy in the system capacitances escalating over a very short period of time.These capacitances include lumped capacitors installed on the DC side of converters,capacitances of transmission lines and the submodule capacitors contained within modular multi-level converters.During fault incidence in MTDC networks,the DC protection system is envisaged to minimize the deleterious effects by isolating the faulty portion only,while ensuring smooth operation of the remaining healthy system.It is thereby obligatory to characterize transient DC fault current and procure a reliable,fast,sensitive and distinguished DC protection scheme for such requisitions.Hence,a major objective of this thesis is to allocate evident solutions to solve some of the potential challenges encountered in the protection of MTDC networks.Development of DC fault current and the impact of key parameters are analyzed in a four-terminal MTDC network.Moreover,in the event of DC fault,the propagation delay is meticulously scrutinized for the MTDC networks.With the facilitation of transient simulation,alternative protection schemes are proposed and analyzed.Some of the prestigious advantages of the proposed schemes include rapid fault detection,enhanced reliability,superior stability and high level of selectivity.Further validation regarding the feasibility of the proposed scheme during fault conditions is entertained by applying RTDS.It is of utmost importance,in the event of a permanent fault in HVDC transmission network,to accurately estimate the fault location,thereby restoring,minimizing the system down-time and augmenting the reliability of the system.For such purpose,this thesis also contributes towards addressing the issue regarding precise fault location in HVDC networks.It is implicated evidently that the proposed scheme can isolate the faulted segment of the transmission line in an efficient way.In conjugation to this,the sensitivity analysis deduces that the proposed schemes operate coherently against noisy inputs.