Fault Discrimination Research Articles

Sequence component based approach for fault discrimination and fault location estimation in UPFC compensated transmission line

This study presents an integrated approach for discrimination of internal and external fault, and to obtain pin-point location of the fault in a transmission line connected to unified power flow controller (UPFC). To detect internal fault, this method uses positive sequence component of voltage and current at the local and remote end bus. Fault location estimation technique requires both positive and negative sequence voltage and current components measured from both ends of the line. The performance of the proposed technique has been evaluated by simulating a 400 kV double circuit UPFC compensated transmission line. This technique can detect internal fault under stressed conditions, viz. high impedance fault (HIF), change in source strength, change in load angle, and power swing. Precise fault location has been achieved under wide variation of system and fault parameters. The comparative assessment has been provided to prove the efficacy of the proposed approach.

Differential voltage‐based fault detection during power swing

Any incorrect action by the distance relay is harmful to the stability of power system at a power swing condition. In this respect, discrimination of faults from power swing should be fast and accurate. This paper introduces a new fault detection method using time derivative of voltage signals at swing condition. The sample interval between two successive peaks of the derivative of a voltage signal always remains above a minimum value during power swing, while its value decreases by a significant margin after the occurrence of a fault. This discriminating feature of the differential voltage is mathematically developed and applied to detect faults under swing conditions. A 9-bus-modified WSCC system is considered for validating the method, and the simulation is carried out in an electromagnetic transient programme. The method detects both symmetrical and unsymmetrical faults accurately and quickly at power swing condition for various fault locations, power angles, fault inception times, fault resistances and swing frequencies. Its performance is satisfactory for series compensated lines and under noisy condition. The fault detection results and the comparative study with two available methods justify its potential.

Vibration Analysis of Heterogeneous Gearbox Faults using EMD Features and SVM Classifier

Gearbox is one of the important mechanical power transmission device most commonly used in automobiles and industries to get the desired change in speed and torque. The gearbox fault diagnosis has given utmost importance for its significance in preventing halts of a mechanical system and guaranteeing an advantage of sufficient maintenance. This paper presents the vibration analysis of heterogeneous gearbox faults using EMD features and SVM classifier. The vibration signal is converted into intrinsic mode functions (IMF) with decreasing order of frequencies using empirical mode decomposition (EMD) method. Feature vector consisting of information theoretic features have been computed for each IMF and concatenated to form a feature set. By using random permutations, the feature set has been divided into training and testing sets. The support vector machine (SVM) algorithm has been used as a classification technique to diagnose the gearbox faults, which consists of five-class classification. The accuracy of the developed algorithm has been validated using 100 Monte Carlo runs. A comparative study has been carried between computed features and varying IMF components. The observations made were - clear discrimination of the gearbox faults and improved classification accuracy, which contain - chipped tooth, missing tooth, root fault, surface fault and healthy working state of the gear.

Multi-scale morphological gradient algorithm based ultra-high-speed directional transmission line protection for internal and external fault discrimination

<p>This paper introduces an ultra-high-speed directional transmission line protection scheme based on multi-scale morphological gradient algorithm (MSMGA). The directional protection scheme sets down the rules for determining the fault position in relation to the relaying point. The MSMGA is used to extract the fault-induced transient characteristics contained in the voltage and current signals. The associated signals are formed from these transient characteristics and the polarity of their local modulus maxima allow the discrimination between internal and external faults.</p>

Detection and Discrimination of Islanding and Faults in distribution system with Distributed Generation by using Wavelet based Alienation approach

This paper presents a wavelet transform based alienation technique for the protection of a radial 5 bus distribution system integrated with four wind type doubly fed Induction generators (DFIG).This technique is used to detect islanding condition and faults, classification of faults and their discrimination. Islanding is simulated at point of common coupling (PCC) and faults are simulated at each DG bus of the network. Daubechies wavelet transform has been used to decompose the current signals to get approximate coefficients. The Alienation coefficients of these approximate decompositions are termed as islanding and fault indexes. These indexes have been compared with predetermined threshold to detect islanding and faults. The same threshold value is utilized to discriminate transients associated with islanding and fault. Alienation coefficients at each bus over a half cycle window clearly detect both islanding and fault. Testing of the proposed algorithm has been carried out for various angles of incidence. Hence, the proposed algorithm is more effective and successful for finding the islanding condition as well as faults in distribution system with distributed generation.

Detection and Discrimination of Islanding and Faults in distribution system with Distributed Generation by using Wavelet based Alienation approach

This paper presents a wavelet transform based alienation technique for the protection of a radial 5 bus distribution system integrated with four wind type doubly fed Induction generators (DFIG).This technique is used to detect islanding condition and faults, classification of faults and their discrimination. Islanding is simulated at point of common coupling (PCC) and faults are simulated at each DG bus of the network. Daubechies wavelet transform has been used to decompose the current signals to get approximate coefficients. The Alienation coefficients of these approximate decompositions are termed as islanding and fault indexes. These indexes have been compared with predetermined threshold to detect islanding and faults. The same threshold value is utilized to discriminate transients associated with islanding and fault. Alienation coefficients at each bus over a half cycle window clearly detect both islanding and fault. Testing of the proposed algorithm has been carried out for various angles of incidence. Hence, the proposed algorithm is more effective and successful for finding the islanding condition as well as faults in distribution system with distributed generation.

A new method for discrimination of internal fault from other transient states in power transformer using Clarke’s transform and modified hyperbolic S-transform

In this paper, a new method is proposed for discriminating internal faults from other abnormal conditions in power transformers such as inrush currents, external faults, over-excitation, and ultra-saturation. Since the differential current signals are non-stationary, a powerful tool such as S-transform is needed for their time-frequency analysis. In this study, some important characteristics are extracted using the Clark’s transform and modified hyperbolic S-transform according to which different conditions are distinguished and classified. These features include energy contour of first level, variance index, standard deviation of second harmonic component, and a special criterion. In this paper, all possible transient conditions and the effects of the saturation of current transformers are considered. Various simulations for different operating conditions of transformer are performed via PSCAD/EMTDC software. Also, the entire process of modified hyperbolic S-transform and the proposed algorithm are done in MATLAB software. Simulation results show that the proposed algorithm can be reliably used for the identification and classification of different faults in transformers.

Active protection for photovoltaic DC‐boosting integration system during FRT

Compared with traditional photovoltaic (PV) power plants, PV DC-boosting integration system faces serious DC-bus overvoltage problem due to its special structure during the fault ride-through (FRT). Based on the unique power-output features of PV array, the authors describe a design of coordinated control strategy for the converters in the PV DC-boosting integration system to maintain a stable DC voltage during FRT process. In addition, existing FRT control scheme ineluctably lowers the performance of the line protection; thus, a combination strategy of the system control and the line protection is proposed to enhance the fault discrimination ability (especially the interphase fault). A detailed model of the PV DC-boosting integration system is created in PSCAD/EMTDC; the simulation results show that the proposed method not only realises the smooth FRT process with a stable DC bus voltage but also can reliably identify the voltage sag caused by the transmission line faults.

Effect of DC Filters on Selection of Fault Discriminator for Unit Protection of Monopolar HVDC Transmission System

Various research works reported on the unit protection of monopolar high-voltage direct-current transmission system assumed either no dc filter or a certain type of dc filter in the system. From the survey of literature, it appears that no study has been made to evaluate the effect of the type of dc filter on the system performance and consequent effect on the selection of fault discriminator for development of protection schemes. The work reported in this paper aims at selection of suitable fault discriminators for unit protection of HVDC transmission system in the presence of three different types of dc filter. The study has been carried out on a 500-kV line- commutated-converter-based monopolar HVDC system equipped with any of the three filters, namely, cascaded double-tuned, parallel double-tuned or triple-tuned filter. Simulation has been carried out with PSCAD/EMTDC. Critical analysis of the simulation results shows how the type of the dc filter influences the choice of fault discriminator

Effect of DC Filters on Selection of Fault Discriminator for Unit Protection of Monopolar HVDC Transmission System

Various research works reported on the unit protection of monopolar high-voltage direct-current transmission system assumed either no dc filter or a certain type of dc filter in the system. From the survey of literature, it appears that no study has been made to evaluate the effect of the type of dc filter on the system performance and consequent effect on the selection of fault discriminator for development of protection schemes. The work reported in this paper aims at selection of suitable fault discriminators for unit protection of HVDC transmission system in the presence of three different types of dc filter. The study has been carried out on a 500-kV line- commutated-converter-based monopolar HVDC system equipped with any of the three filters, namely, cascaded double-tuned, parallel double-tuned or triple-tuned filter. Simulation has been carried out with PSCAD/EMTDC. Critical analysis of the simulation results shows how the type of the dc filter influences the choice of fault discriminator

Fault-Type Discrimination in HVDC Transmission Lines Using Rate of Change of Local Currents

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.

Effective algorithm for fault discrimination and estimation of fault location in transmission lines

Sensitivity, selectivity, speed of operation and reliability of the conventional current differential protection schemes are affected and limited by the distributed shunt capacitance of high-voltage long transmission lines. In this study, a new pilot protection algorithm has been proposed based on the computation of change in shunt line admittance ‘Y’ during dynamic conditions using synchronised data. Therefore, it does not require a separate compensating technique to nullify the effect of line charging current in the fault detection. This scheme can quickly discriminate the internal faults and also detects the faulty phase. Also, it has an advantage of estimation of an accurate fault location. The performance of the proposed algorithm is evaluated on 400 kV, 50 Hz two-bus system as well as IEEE-39 bus 345 kV system using EMTDC/PSCAD and MATLAB simulation tools. The simulation results confirm the proposed algorithm can effectively discriminate the faults, independent of fault location, fault resistance, type of fault, series compensation lines and source impedance. Finally, a hardware experiment using National Instruments (NI) based LabVIEW platform is carried out to check the practical feasibility of the proposed algorithm.

Renewable energy integrated multi-terminal transmission system using wavelet based protection scheme

The power plants behavior is crucial under faulted conditions and responses on protection systems. Major microgrid (MG) protection problem is the problem between the fault current in utilitygrid mode and microgrid mode. As conventional protection system doesn’t offer solution for all MG protection challenge, but it needs advanced protection strategy. Protection system must response to both the utilitygrid and MG faults. Fast response of protection is necessary as early as possible if the fault is occurs on utilitygrid and if the fault is occurs on MG, the protection scheme must seperate the small possible portion of MG to remove the fault. This work presents a typical MG protection scheme using digital relaying and satellite communication with wavelet detailed D<sub>1</sub>-coefficients of mother wavelet Bior 1.5. This research work is done for the detection, discrimination and locality of faults at distributed generators (DG’s) integration in multi-terminal transmission system. The algorithm tested under various faults with fault inception angles (FIA), fault impedances and fault distance of feeder line.

Novel protection scheme against turn-to-turn fault of magnetically controlled shunt reactor based on equivalent leakage inductance

Magnetically controlled shunt reactors (MCSRs) are key elements of extra-high voltage/ultra-high voltage (EHV/UHV) transmission systems for reactive power compensation and overvoltage suppression. Owing to the special core structure and winding connection mode, there is a complex electromagnetic relationship between faulty and non-faulty windings, which makes it challenging to accurately identify a turn-to-turn fault, which is the most common type of MCSR fault. To overcome this problem, a novel protection scheme is proposed by combining a start-up criterion with a fault discrimination criterion. The start-up criterion is based on the fundamental component of the total control current (itc) and the fault discrimination criterion is based on the identification of the equivalent leakage inductance (ELI). Firstly, based on the equivalent circuit of the power, control, and compensation windings, the corresponding ELI identification model is derived and solved using the recursive least squares (RLS) method. Subsequently, a fault discrimination scheme is derived based on the difference among three-phase ELIs. Finally, the proposed protection scheme is verified through simulations in MATLAB/Simulink and experiments on a physical model. The proposed scheme overcomes the limited sensitivity and reliability of conventional protection methods and can locate faulty windings, which is of great significance for the promotion of MCSRs and their applications in engineering.

Signal processing for fast fault detection in HVDC grids

For multiterminal or meshed Voltage Source Converter (VSC) High-voltage Direct Current (HVDC) systems, high speed protection against DC faults is essential, as power electronic components cannot withstand the rapidly increasing fault currents which would otherwise result. Recently proposed DC fault detection methods were developed based on time domain simulations in EMT-type software, which requires considerable modeling and computational efforts and results in methods specifically designed for the HVDC grid under study. To simplify the initial design of DC fault detection methods, this paper proposes general guidelines based on fundamental theory and offers a reduced modeling approach. Furthermore, the impact of non-ideal measurements is investigated and a method to choose the filters that optimally discriminate these fault signals from noise, is proposed. The approach was evaluated in a case study on fault detection in a realistically dimensioned HVDC grid. The paper shows that the initial design of fast fault detection methods can be based on the relatively simple proposed guidelines and reduced models. The paper furthermore shows that a sufficiently high sampling frequency and a filter matched to the fault signal enable fault detection within hundreds of microseconds and discrimination of DC faults from transients not related to DC faults.

An auto‐reclosing scheme for DC circuit breaker in VSC‐HVDC transmission system

When a DC line fault happens, the converter will be blocked instantly. This leads to an interruption of power transmission and influences the stability of DC and AC systems. To avoid the blocking of converters, this paper presents a novel protection scheme for VSC-HVDC system, which consists fault isolation and auto-reclosing of DC circuit breaker (DCCB). First, this paper coordinates the protective actions of converters and DCCB. The DC line fault is cut immediately by DCCB while the blocking signal of converter is isolated during the fault. Second, since the faults of long overhead transmission DC lines are mostly transient, an auto-reclosing strategy is developed. The emphasise of this part, which includes fault discrimination and time sequences, between DCCB and converter is elaborated, and the value of reclosing delay is derived by analysing the charging and discharging characteristics of capacitor paralleled with converter. Finally, the protection scheme is evaluated by overcurrent, overvoltage, and recovery time of DC system, and simulation results of a point-to-point VSC-HVDC transmission system proves its validity.

Feature extraction of rotor fault based on EEMD and curve code

Feature extraction is an important part of fault diagnosis. Rotor faults are of various types with little differences between each other and rely on effective methods of feature extraction to be recognized correctly. There are many methods applied to feature extraction at present. However, fault features computed are generally based on fixed samples, which may lead to an unsatisfactory result for other samples. To solve this problem, a novel feature extraction method based on Ensemble Empirical Mode Decomposition (EEMD) and Curve Code (CC) is presented in this paper. The noisy vibration signals are first denoised using wavelet thresholding-based de-noising technology. Then EEMD is applied to decompose the de-noised signals to obtain all Intrinsic Mode Functions (IMFs), and the corresponding Standard Deviations (SDs) are calculated. Finally, the curve plotted by the SDs is coded into a digital sequence called CC as a fault feature. Results of comparative experiments, designed using a large number of samples from rotor laboratory bench, prove the validity of the proposed method and show that the proposed method has higher and more stable Fault Discrimination Rate (FDR) for rotor fault recognition.

Innovative Cos–Sin characteristics to select the faulted zone in view of CT saturation

One area of the major concern of busbar differential schemes is misoperation due to current transformer saturation through close-in out-of-zone faults. A comprehensive fault discrimination scheme is extremely needed for differential protection algorithms to overcome the CT saturation problem. This paper attempts to introduce a method based on innovative Cos–Sin characteristics that is capable of distinguishing between in-zone and out-of-zone faults of busbar protection. The results covered a wide variety of fault scenarios; these results proved the ability of the proposed algorithm to differentiate between in-zone and out-of-zone faults relating to CT saturation conditions. They further demonstrated the noticeable adaptability and performance of the algorithm since it is not affected by such fault parameters as fault type, fault resistance, and fault inception time. Experimental implementation of the devised Cos–Sin signal was conducted and manifested the capability and simplicity of its experimental constructability.

Integrated Transverse Differential Protection Scheme for Double-Circuit Lines on the Same Tower

The conventional transverse differential protection has some drawbacks, such as low sensitivity, long successive operation zone, and being significantly influenced by operation mode when applied in high-voltage and asymmetric power systems. To overcome these drawbacks, an innovative integrated transverse differential protection scheme is proposed in this paper. This scheme includes three parts: faulty phase selection, faulty line selection, and tripping and reclosing strategy. The phase-selection criterion regards the two circuits as a whole and selects only the faulty phase. The criterion of line-selection distinguishes the faulty line with the faulty phase based on the transverse impedance ratio. Tripping and reclosing strategy decreases the number of operations of breakers and achieves quasi-three-phase operation as far as possible. Results of studies with PSCAD/EMTDC and on a dynamic physical model show that the proposed protection scheme can improve the accuracy of fault discrimination, decrease the successive operation zone, and maintain more transmission power after the fault.

Fault discrimination and protection coordination for a bipolar full‐bridge MMC‐HVDC scheme

Fault discrimination and protection coordination for a bipolar full‐bridge MMC‐HVDC scheme