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Summary: Despite having several modern transformer protection schemes, the protection engineer prefers the universally adopted unit‐type differential protection scheme for the current transformer (CT) because of its functional flexibility. Inrush condition, external fault with current transformer saturation, over‐fluxing, or the combination of these may maloperate the unit‐protection schemes. In this article, all the above‐mentioned situations have been addressed that mislead differential protection. A multifunctional algorithm is presented that filters the disturbance for correct relay operation. The inrush condition is carefully examined with the help of the average angle of the differential current. Moreover, an adaptive algorithm takes care of the false operation of the transformer protection scheme during an external fault with CT saturation condition. Also, the momentary over‐fluxing condition is dealt with, with the help of fifth‐ and seventh‐harmonic‐based analysis of the differential current. Hence, the disturbance will be thoroughly examined and a decision signal issued accordingly to avoid unnecessary isolation of the transformer to improve system stability. The power system is simulated in PSCAD software and the algorithm is developed in MATLAB. Moreover, the proposed scheme is validated on a hardware prototype for authentication. It is found that the proposed scheme provides acceptable results and can be implemented in the real field. [ABSTRACT FROM AUTHOR]

Absrtact: Background: Nowadays, numerical relays configured through power swing blocking function are vulnerable to faults with high impedance owing to nonlinearities present in the faulty path. Identification of symmetrical high impedance faults incepting during the power swing scenario is of prime importance for protection engineers to avoid cascade tripping. It is analyzed that the classical approaches for symmetrical fault detection during power swing can mal‐operate owing to high level of uncertainty arise during validation of high impedance fault, symmetrical faults and cross country faults during power swing with varied level of compensation which has been explored in this research. Aims: This paper presents an innovative scheme for series compensated line by utilizing the capability of Relevance Vector Machine (RVM) as a disturbance classifier taking into consideration of cross country faults, CT saturation; power swings prone to symmetrical faults along with high impedance faults in comparison with prevailing methods. Materials & Methods: In order to validate the proposed RVM based disturbance classifier algorithm, different kinds of faults and power swing situations have been applied in IEEE 9 bus test system using PSCAD/EMTDC software followed by validation in MATLAB. The features of sequence components of currents are estimated using Modified Full Cycle Discrete Fourier Transform (MFCDFT). The extracted features are used as control inputs to RVM for discernment among power swing and fault under the influence of wide range of system and fault dynamics. Results: The developed RVM based disturbance classifier scheme generates a tripping signal in the event of high impedance fault during power swing and remains stable during swing conditions. It can be used in conjunction with an adaptive numerical distance relaying scheme for realizing complete protection of the power grid for all zones of protection. A comparative analysis with an existing disturbance classifier algorithm indicates relative superiority with much improved fault classification accuracy. Discussion: In order to validate the proposed algorithm, different kinds of fault and power swing scenario are realized in IEEE 9 bus test system using PSCAD and current samples are acquired at sampling frequency of 4 kHz. The phasor estimation of sampled signals has been performed using MFCDFT which is used to derive feature vector extraction from symmetrical components. The extracted features are applied to RVM based fault classifier algorithm for classification of disturbance. The obtained results are also compared with existing schemes of protections. It has been proved that developed algorithm outperforms with much improved fault classification accuracy. Conclusion: This paper discovers relevance vector machine based adaptive learning approach for dynamic disturbance classification in complex power grid network. The developed algorithm has been validated on IEEE 9 bus test system modelled in PSCAD. The fault and system dynamics are varied over a wider range which includes variation in fault type, fault impedance, fault inception angle, power flow angle, fault location and degree of line compensation level. Moreover, the validation of scripted algorithm has been performed for very complex power grid scenarios like cross‐country faults, high impedance faults with varying degree of compensation, power swing and saturation of instrument transformers etc. The feature vectors are extracted using MFCDFT and applied to supervised RVM based disturbance classifier and outperforms with classification accuracy of 99.74% which indicates it's superiority over existing classifier approaches based on SVM & ANN. [ABSTRACT FROM AUTHOR]

The differential relaying scheme is universally adopted as the main protection for power transformer. In certain situations, like temporary overfluxing, this differential protection may malfunction. This is due to unbalance in primary and secondary current, as the saturated core does not reflect equal ampere-turn on either side. This article presents detection of over-fluxing condition against the internal fault based on the fifth harmonic component of differential current. As per the estimated level of the fifth harmonic concerning the fundamental component of differential current, the pickup setting of percentage bias characteristic will be modified to avoid maloperation. Once the over-flux condition is sensed, the algorithm activates timer-based V=f protection to protect the equipment. The proposed algorithm is validated on PSCADTMsoftware and after the collection of data, MATLAB software is used for further validation. The proposed algorithm is validated under various test conditions like normal load, external fault, internal fault, and overfluxing. It is observed that the algorithm accurately detects internal fault in the transformer or blocks the relay operation under momentary over-fluxing situations. Further, to assassinate the competency of the proposed scheme, a practical test is performed on a single-phase transformer available in laboratory. The data for various test cases are captured with the help of DSO, and the collected data has been migrated to computer where the proposed algorithm is examined. After analyzing all the results, it is cleared that the proposed algorithm can prevent transformer isolation during momentary over-fluxing conditions. [ABSTRACT FROM AUTHOR]

Due to the presence of Distribution Generation (DG), power system becomes more complicated and stability of power is the main challenging task. Saturation of Current Transformer (CT) imposes great dilemma on differential relaying scheme. This manuscript presents a new differential algorithm for distribution transformer protection which adaptively set its characteristic in the event of CT saturation. The proposed scheme is capable to detect magnetizing inrush condition, high resistance internal fault and discriminate external fault with CT saturation. The validation of the proposed scheme is done by simulating a part of the power system in PSCADTM software and programming in MATLAB software. A Full Cycle Discrete Fourier Transform (FCDFT) is implemented to validate the differential protective scheme for 15 MVA, 66/11 kV distribution transformer. An adaptive concept of the differential characteristic is employed in the algorithm to maintain the stability of relay during external fault with CT saturation. Validation and authenticity of the proposed technique are carried out with various test condition generated under wide variation in system parameters. The result on 2 kVA, 230/110 V, single phase transformer shows that the proposed scheme is capable to discriminate inrush, internal and external fault also with CT saturation conditions. [ABSTRACT FROM AUTHOR]

Impedance reach of numerical distance relay is severely affected by Fault Resistance (RF), Fault Inception Angle (FIA), Fault Type (FT), Fault Location (FL), Power Flow Angle (PFA) and series compensation in transmission line. This paper presents a novel standalone adaptive distance protection algorithm for detection, classification and location of fault in presence of variable fault resistance. It is based on adaptive slope tracking method to detect and classify the fault in combination with modified Fourier filter algorithm for locating the fault. To realize the effectiveness of the proposed technique, simulations are performed in PSCAD using multiple run facility & validation is carried out in MATLAB® considering wide variation in power system disturbances. Due to adaptive setting of quadrilateral characteristics in accordance with variation in fault impedance, the proposed technique is 100 % accurate for detection & classification of faults with error in fault location estimation to be within 1 %. Moreover, the proposed technique provides significant improvement in response time and estimation of fault location as compared to existing distance relaying algorithms, which are the key attributes of multi-functional numerical relay. [ABSTRACT FROM AUTHOR]

Sudden changes in loading or configuration of an electrical network causes power swing which may result in an unwanted tripping of the distance relay. Hence, it becomes utmost necessary to rapidly and reliably discriminate between actual fault and power swing conditions in order to prevent instability in power network due to mal operation of distance relay. This paper proposes a novel method for the discrimination between fault and power swing based on rate of change of voltage and reactive power measured at relay location. The effectiveness of the proposed algorithm is evaluated by simulating series of power swing conditions in PSCAD/EMTDC® software for different disturbances such as change in mechanical power input to synchronous generator, tripping of parallel line due to fault and sudden application of heavy load. It is revealed that the distance relay gives successful tripping in case of different fault conditions and remains inoperative for power swing with the implementation of the proposed algorithm. Moreover, the proposed scheme has ability to distinguish the symmetrical and asymmetrical fault occurrence during power swing condition. [ABSTRACT FROM AUTHOR]

This article presents relevance vector machine (RVM) based relaying scheme for busbar protection which correctly differentiates between internal faults on busbar and external faults. To validate the proposed scheme, numerous computer simulations have been carried out on an existing 220 kV Indian power generating station having different types of bays such as line, transformer, reactor & generator with generator transformer (GT). Various fault conditions (test data set of 23,760) have been simulating using the power system computer aided design (PSCAD)/ electromagnetic transient direct current (EMTDC) software package (Winnipeg, MB, Canada) by varying fault & system parameters. The proposed RVM based fault discrimination scheme is executed in MATLAB software (The Math- Works, Natick, Massachusetts, USA) by loading the simulation data. Comparative evaluation of the proposed RVM based scheme with the existing support vector machine (SVM) based scheme clearly indicates the superiority of the proposed scheme in terms of decision speed (faster than SVM based scheme) and classification accuracy (more than 99%). Moreover, it does not operate under different types of external faults and system disturbances. Subsequently, the proposed scheme remains stable during severe current transformer (CT) saturation condition. [ABSTRACT FROM PUBLISHER]