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A simple and yet dependable technique for fault-type identification in HVDC transmission systems is presented in this paper. A set of indices is defined for pairs of rate of change of current measurements to identify the pole(s) involved in the fault to discriminate the ground faults from those involved with the dedicated metallic return conductor. The proposed fault discrimination method will identify the faulty pole within a 1-ms window, and therefore, it can be used to improve the sensitivity and reliability of DC fault protection. Furthermore, the knowledge—whether or not the dedicated return conductor is involved in the fault—is useful for determining the post-fault configuration of bipole grids. Considerable discrimination margins are observed during the rigorous evaluation of the technique for two-conductor and three-conductor HVDC systems under various fault scenarios, for both considerably long overhead transmission lines and cables. The indices can be computed using local current measurements made using low-bandwidth sensors. They are independent of the fault resistance, and therefore, settings can be found easily. [ABSTRACT FROM AUTHOR]

In this paper, clearing of DC faults in a hybrid multi-terminal HVDC transmission system consisting of line commutated converters (LCCs) and voltage source converters (VSCs) implemented using half-bridge modular multilevel converter (MMC) technology is investigated. While the hybrid HVDC system has several possible configurations, this paper focuses on two of them: 1) a half-bridge MMC-HVDC link piggy-backing on the transmission line of a LCC-HVDC link and 2) LCC-HVDC link tapped by half-bridge MMC inverters. The proposed dc fault recovery strategy employs a high rating series diode valve placed at each VSC inverter pole to block fault currents; AC circuit breakers to isolate the faulty VSC rectifier pole; and force retardation applied at LCC rectifier to extinguish the arc. Detailed simulations demonstrate fast fault recovery performance with the proposed fault recovery procedure. In the case where a single transmission line is shared by the LCC and VSC links, the VSC rectifier is subjected to considerably high current for a period of few hundreds of milliseconds, and the ac side voltage dips momentarily. During a single pole fault, interrupting power flow on the healthy pole of VSC rectifier may be necessary to maintain smooth operation. [ABSTRACT FROM AUTHOR]

A new impedance based fault location algorithm is proposed for a generic multi-terminal transmission network consisting of a main line and tapped branches with no direct measurements available at the intermediate tapping nodes. The core of the algorithm is a threshold free faulted branch search algorithm that systematically compares the multiple estimates of voltages for the tapping nodes, computed using synchrophasor measurements at the terminals. Once the faulted branch is identified, multi-terminal fault location problem is reduced into a two-terminal fault location problem to determine the exact location of fault within the branch. The proposed algorithm is simple and does not involve resource intensive mathematical operations such as matrix inversion. The proposed algorithm was implemented as a module in an in-house developed real-time synchrophasor application software program, and its performance was evaluated using a test setup consisting of a real-time simulator, an actual synchrophasor network, and a phasor data concentrator. The tests showed that the proposed algorithm is capable of correctly determining the faulted branch, except for few faults that are very close to tapping nodes. When the algorithm is used with practical synchrophasor measurements, the fault location error was within a typical tower span for most cases. [ABSTRACT FROM AUTHOR]

Different HVDC grid types and the respective protection options are discussed. An earthed bipole HVDC grid was modeled in PSCAD, and using simulation results, the necessity of di/dt limiting inductors to contain the rise of fault currents within the capacity of current hybrid dc breakers is demonstrated. The impact of different inductor sizes on current rise was studied. A fault detection and localization scheme using the rate of change of voltage measured at the line side of the di/dt limiting reactors is proposed. The protection system was modeled and tested under different fault types and locations. The results show that the proposed method of HVDC grid protection is feasible using the current hybrid dc breaker technology. A systematic procedure for setting the necessary protection threshold values is also demonstrated. [ABSTRACT FROM AUTHOR]

This paper presents the development and hardware implementation of a classification scheme to distinguish the transients originated by faults from other types of transients. In the proposed scheme, a set of Hidden Markov Model-based classifiers is employed to recognize the fault transients. Input features for the classifiers are the energy contained in wavelet coefficients of the measured current waveforms. A laboratory prototype of the fault recognition system was implemented on a floating-point digital–signal-processor (DSP)-based hardware platform. The classification system was tested using the transient signals generated by a real-time waveform playback unit. The test waveforms were generated by simulating an actual extra-high-voltage transmission system on an electromagnetic transient simulation program. The operation of the classification system was further verified using waveforms obtained from an actual fault recorder. The performance of the classifier was investigated under different practical scenarios, such as current transformer saturation, measurement noise, and lightning faults. [ABSTRACT FROM PUBLISHER]

This paper presents a novel algorithm to determine the location of dc line faults in an HVDC system with a mixed transmission media consisting of overhead lines and cables, using only the measurements taken at the rectifier and inverter ends of the composite transmission line. The algorithm relies on the traveling-wave principle, and requires the fault-generated surge arrival times at two ends of the dc line as inputs. With accurate surge arrival times obtained from time-synchronized measurements, the proposed algorithm can accurately predict the faulty segment as well as the exact fault location. Continuous wavelet transform coefficients of the input signal are used to determine the precise time of arrival of traveling waves at the dc line terminals. Two possible input signals–the dc voltage measured at the converter terminal and the current through the surge capacitors connected at the dc line end–are examined and both signals are found to be equally effective for detecting the traveling-wave arrival times. Performance of the proposed fault-location scheme is analyzed through detailed simulations carried out using the electromagnetic transient simulation software PSCAD. The impact of measurement noise on the fault-location accuracy is also studied in this paper. [ABSTRACT FROM PUBLISHER]

The paper first shows that the transient stability status of a power system following a large disturbance such as a fault can be early predicted based on the measured post-fault values of the generator voltages, speeds, or rotor angles. Synchronously sampled values provided by phasor measurement units (PMUs) of the generator voltages, frequencies, or rotor angles collected immediately after clearing a fault are used as inputs to a support vector machines (SVM) classifier which predicts the transient stability status. Studies with the New England 39-bus test system and the Venezuelan power network indicated that faster and more accurate predictions can be made by using the post-fault recovery voltage magnitude measurements as inputs. The accuracy and robustness of the transient stability prediction algorithm with the voltage magnitude measurements was extensively tested under both balanced and unbalanced fault conditions, as well as under different operating conditions, presence of measurement errors, voltage sensitive loads, and changes in the network topology. During the various tests carried out using the New England 39-bus test system, the proposed algorithm could always predict when the power system is approaching a transient instability with over 95% success rate. [ABSTRACT FROM PUBLISHER]