Differential Protection Scheme Research Articles

Global Positioning System and GLObal NAvigation Satellite System constellations for better time synchronising reliability

The demand for accurate time synchronisation available 24/7 increases with the growth of critical substation applications, such as phasor measurement, merging units, travelling-wave fault location and current differential protection schemes. In order to yield the best accuracy and granularity from such applications, the use of a common, reliable and precision-time reference is essential.

A Virtual Multi-Terminal Current Differential Protection Scheme for Distribution Networks With Inverter-Interfaced Distributed Generators

The deployments of inverter-interfaced distributed generators (IIDGs) in medium voltage distribution networks may cause undesirable trips or tripping failures of conventional two-terminal current differential protective relays. It is economically and technically unfeasible to reconfigure large numbers of time-synchronized sampling clocks and communication channels for each terminal inside the protected zone. In this paper, a more accurate IIDG mathematical equivalent model is established that considers the control strategies of IIDG, and the profile characteristics of the positive-sequence voltage at each point of common coupling are investigated. Then, a real-time estimation algorithm is introduced for the fault current contribution of grid-connected IIDGs. On this basis, this paper proposes a novel virtual multi-terminal current differential protection scheme. This scheme only necessitates exchanging the electrical quantities between the protective relays at both terminals via an existing two-terminal pilot channel, thus reducing the cost and requirements for communications. The feasibility of the proposed protection is demonstrated in both the PSCAD/EMTDC simulation platform and the RTDS hardware experimental laboratory. A comparison of the proposed protection alongside the conventional protection is also presented. Test results indicate that the proposed protection is widely applicable to various fault conditions, thereby improving the sensitivity and selectivity of conventional protection schemes.

Special protection system to cope with the unavailability of sampling values from an entire substation

A special protection system is proposed to respond to a challenge such as that a substation must be immediately taken out of service or only be protected by a remote backup protection without selectivity if the sampling system of this substation breaks down or the samplings are unavailable even though the GOOSE channel is functioning normally. After the special protection system perceives an abnormality of the sampling system of the substation, it first locates the rough fault region using a wide area measurement system based current differential protection scheme of the sound side of the lines connected to the substation with an abnormal sampling system. Then, a novel compensation voltage difference scheme is proposed to determine the faulty line within the recognized rough fault region. Combined with the zone I distance protection scheme, a comprehensive special protection scheme to address a serious sampling abnormality is proposed. Theoretical analysis and PSCAD and MATLAB based simulation studies show that the proposed scheme has the advantages of high reliability, sensitivity and capability of withstanding a fault resistance.

A Wavelet-Based Transformer Differential Protection With Differential Current Transformer Saturation and Cross-Country Fault Detection

The current transformer (CT) saturation phenomenon has been one of the main problems for the power transformer differential protection, leading to incorrect current measurements and relay misoperation. This paper proposes a fast and efficient transformer differential protection scheme with additional differential CT saturation and cross-country fault detection modules after the external fault detection, all of them based on the differential wavelet coefficient energy with border distortions in order to stabilize the relay during external faults and distinguish accurately CT saturation from cross-country internal faults. The proposed method was assessed by using representative simulations of internal faults, transformer energizations, and external faults with CT saturation followed by cross-country internal faults, and good results were achieved.

A travelling wave differential protection scheme for half-wavelength transmission line

Half-wavelength transmission technology is getting more and more attention due to its excellent characteristics such as large transmission capacity and long transmission distance. Traditional differential protection is not applicable to half-wavelength transmission line because of the impact caused by large distributed capacitance current. Travelling wave (TW) differential protection is not affected by distributed capacitance current, so it can be applied to long EHV/UHV transmission line. However, when directly applied to half-wavelength transmission line, large unbalanced differential current will appear during external faults, since the resistance of the line and the frequency-dependent feature of the line parameters which are neglected by TW differential protection have such great impact that they cannot be neglected anymore. In order to improve the performance of TW differential protection, this paper proposes a scheme which has taken the resistance into account and uses power-frequency component of the differential current to identify fault for the purpose of avoiding the influence of the frequency-dependent feature of the line parameters. Simulation results verify that the proposed scheme is effective in reducing the unbalanced differential current, and as a result, ensures the selectivity of the protection. The scheme also has high sensitivity during internal faults with large fault resistance.

Communication Modeling for Differential Protection in IEC-61850-Based Substations

Today's power utilities, around the world, own multiple substations that are connected together to form a complex energy network. The functions within and between these substations are being automated according to globally accepted power utility automation standard IEC 61850. This automation results in efficient operation and enhanced protection of power network with the aid of the communication system. Implementing the protection schemes modeled using communication configurations of standardized information exchange will lead to digital power grid. Designing an IEC-61850-based protection scheme to take care of the faults outside the substations is a challenge, as the typical local-area-network-based generic-object-oriented substation events and sampled-value messages need to be transmitted over a wide-area network. This paper presents communication configuration for line current differential protection schemes applied between two automated substations. It presents the simulation results of communication configuration network between two substations. Its performance is evaluated using a network simulator tool. This study intends to guide the development of a robust protection scheme with IEC-61850-based communication configuration.

浅谈配电线路差动保护方案设计

浅谈配电线路差动保护方案设计

Design and testing of a bus differential protection scheme using partial operating current (POC) algorithm

This paper presents a novel bus differential protection scheme that provides enhanced immunity against mis-operation resulted from current transformer (CT) saturation during close-in external faults and better sensitivity for internal faults. The proposed scheme incorporates a fault discrimination algorithm based on partial operating current (POC) characteristic making the scheme capable of discriminating high current internal and external faults even with CT saturation. A supervision technique based on CT saturation detection is also included in the scheme design to increase the sensitivity of the proposed relaying scheme for very high impedance internal faults. A relay model is built in Matlab platform based on the proposed scheme and the performance is validated using a transmission network simulated in Electromagnetic Transients Program (EMTP) for various fault scenarios. Documented results show the proposed scheme improves the performance in terms of reliability, sensitivity, and selectivity over traditional bus differential schemes.

Partial operating current characteristics to discriminate internal and external faults of differential protection zones during CT saturation

To protect transformers, transmission lines and busbar systems, low impedance current differential protection schemes based on percentage restraint characteristics are widely used in power systems. The main application issue of these schemes is mis-operation due to current transformer (CT) saturation during close-in external faults. A comprehensive fault discrimination algorithm is highly required for current differential protection schemes to overcome the CT saturation issue. The purpose of this study is to introduce a methodology based on partial operating current (POC) characteristics which discriminate internal and external faults of differential protection zones. The study includes the mathematical model of POC characteristics, a fault discriminating algorithm using POC features, and bus differential protection zone results. The results documented encompasses various possible short-circuit (fault) scenarios and indicate the capability of the proposed algorithm in discriminating internal and external faults under CT saturation conditions.

Numerical busbar differential protection using generalised alpha plane

This study presents a digital differential busbar protection scheme based on generalised alpha plane approach which combines the benefits of percentage differential approach and two-restrain alpha plane approach. The proposed scheme utilises one cycle current transformer (CT) secondary current signals of all the bays connected to the busbar to map the operating points on a complex alpha plane. The proposed scheme has been evaluated by modelling an existing 400 kV Indian power generating station in PSCAD/EMTDC software package. The performance of the proposed scheme has been evaluated on large numbers of cases with wide variation in system and fault parameters. In order to verify authenticity of the proposed scheme, a laboratory prototype of the proposed busbar protection scheme has been developed. From the developed prototype, CT secondary current signals are captured during internal faults and external fault with CT saturation condition. Comparison between the simulation and prototype results clearly shows the effectiveness of the proposed scheme in terms of higher sensitivity during internal faults and better stability in case of external faults. The proposed protection scheme has a high response speed (around 5 ms) and hence can be considered on par with modern busbar protection schemes.

Detection, classification, and location of faults on grid‐connected and islanded AC microgrid

Summary A new spectral energy differential protection scheme using sparse Fourier kernel fast time-frequency transform is proposed for the detection, classification, and location of faults either on the grid-connected or islanded AC microgrid. Initially, the three-phase average and differential components of the current samples measured on either side of the distribution line are processed through an alteration detection filter, which identifies the fault incipient and consequently registers an alteration index for the particular phase, which identifies the fault. The spectral energy of the differential current components are than computed to classify the type of the fault under a number of intrinsic operating conditions like the meshed and radial architectures and grid-connected or islanded mode of operation and varying fault distance ratios. Extensive numerical experimentation illustrates satisfactory results for all the cases investigated in this paper, which include detection, classification, and location of faults on the microgrid.

Power transformer differential protection using current and voltage ratios

The main challenge in transformer protection is to find a fast and efficient differential relay algorithm that isolates the transformer from the system causing least damage. Algorithm should also avoid mal-operation while differentiating between the operating conditions. This paper presents an improved differential protection scheme for power transformer. The proposed scheme is based on the ratio of the absolute difference and absolute sum of the primary and secondary currents of each phase, supplemented by the ratio of the absolute difference and absolute sum of the primary and secondary terminal voltages of each phase. The proposed algorithm aims at avoiding mal-operation, possible with the conventional three-phase transformers differential protection scheme due to transient phenomena, including the magnetic inrush current, simultaneous inrush with internal fault, and faults with current transformer saturation. Investigation of the proposed differential protection scheme using both current and voltage ratios shows that it can provide fast, accurate, secure and dependable relay for power transformers.

A fast time-frequency response based differential spectral energy protection of AC microgrids including fault location

This paper proposes a pattern recognition based differential spectral energy protection scheme for ac microgrids using a Fourier kernel based fast sparse time-frequency representation (SST or simply the sparse S-Transform). The average and differential current components are passed through a change detection filter, which senses the instant of fault inception and registers a change detection point (CDP). Subsequently, if CDP is registered for one or more phases, then half cycle data samples of the average and differential currents on either side of the CDP are passed through the proposed SST technique, which generates their respective spectral energies and a simple comparison between them detects the occurrence and type of the fault. The SST technique is also used to provide voltage and current phasors and the frequency during faults which is further utilized to estimate the fault location. The proposed technique as compared to conventional differential current protection scheme is quicker in fault detection and classification, which is least effected from bias setting, has a faster relay trip response (less than one cycle from fault incipient) and a better accuracy in fault location. The significance and accuracy of the proposed scheme have been verified extensively for faults in a standard microgrid system, subjected to a large number of operating conditions and the outputs vindicate it to be a potential candidate for real time applications.

Research on Capacitance Current Compensation Scheme of Current Differential Protection of Complex Four-Circuit Transmission Lines on the Same Tower

Current differential protection is the main protection of transmission lines which include multi-circuit lines on the same tower, and whose sensitivity and reliability of differential protection is mainly affected by the distributed capacitive current. For the four-circuit line on the same tower, due to the influence of coupling between the loop road, the distributed capacitance current increases significantly when compared with ordinary lines, affecting the sensitivity of the current differential protection, especially for different voltage levels throughout the four-circuit lines on the same tower. The relationship of the electrostatic coupling between the circuits is more complex, and increases the difficulty of the compensating the distributed capacitance current. This paper is based on the electrostatic coupling principle of four-circuit lines on the same tower, establishes the distributed parameter model of four-circuit transmission lines on the same tower, and discusses the effect of circuit operation mode on the compensation of capacitance current differential protection when different faults occur on the complex four-circuit transmission lines on the same tower. A new compensation scheme suitable for capacitive current compensation is proposed. Simulation results show that this capacitive current compensation scheme can effectively improve the performance of current differential protection.

A novel differential protection scheme for HVDC transmission lines

Based on the compensation of the distributed capacitive current, a novel differential protection scheme for HVDC transmission lines was proposed in this study. According to the analysis, after voltage and current signals at both sides of the line are processed by the same low-pass filter the cut-off frequency of which is low enough, then the voltage distribution along the line can be regarded as linear distribution. The distributed capacitive current can be calculated by integrating the linear distributed voltage. After removing this current, the new differential criterion can be implemented. A ±800kV HVDC transmission system was built in EMTDC to test the performance of the new protection. Comprehensive test studies show that the proposed method not only can detect internal faults correctly and quickly, but also can respond to internal faults with high ground resistance.

Synchrophasors assisted protection scheme for the shunt‐compensated transmission line

This study presents synchrophasor assisted protection scheme for the protection of long transmission line compensated with shunt flexible AC transmission system (FACTS) device. With the advancement in synchrophasor technology, data communication medium, and wide area measurement system for transmission line protection, the differential protection scheme is a most suited scheme over the over-current, distance and directional protection schemes. The proposed scheme discriminate between internal and external fault using the time synchronised voltages and currents of both the terminal of the transmission line. The performance of proposed scheme has been evaluated on IEEE 12 bus FACTS benchmark power system model implemented in PSCAD/EMTDC. The measured voltage & current signals are pre-processed and phasors are estimated through DFT algorithm in MATLAB. The performance remains unaffected during wide variation in fault and system parameters including different line length and static var compensator rating. The test results confirm the selective, simplicity, high speed, sensitivity, and robustness of the proposed protection scheme. This scheme is also able to distinguish the faulty phase(s) from healthy phases, which enables the single-pole tripping option. Finally, comparative evaluation of the proposed technique with the existing protection schemes clearly shows its superiority.

Firefly Algorithm Optimized Robust Protection Scheme for DC Microgrid

Various topologies of the Direct Current (DC) microgrid have been proposed in the literature by considering practical requirements. One of the important criteria in topology selection is the availability of a well-functioning protection scheme. A significant part of the DC microgrid protection system literature considers differential protection schemes for various topologies. However this scheme doesn’t work satisfactorily with noisy measurements. Noisy measurements are a reality and can not be avoided for any real engineering system. This article proposes a robust protection scheme to alleviate some problems associated with topology selection. The proposed scheme considers noisy current measurements and works by estimating the time derivative of line currents. The proposed approach uses continuous finite-time convergent differentiator to estimate the derivative. The gains of the differentiator were tuned through Firefly algorithm-based optimization technique. Matlab/Simulink ®-based simulations verified the effectiveness of the proposed approach over the existing differential current scheme.

Data-Mining Model Based Intelligent Differential Microgrid Protection Scheme

This paper presents a data-mining-based intelligent differential protection scheme for the microgrid. The proposed scheme preprocesses the faulted current and voltage signals using discrete Fourier transform and estimates the most affected sensitive features at both ends of the respective feeder. Furthermore, differential features are computed from the corresponding features at both ends of the feeder and are used to build the decision tree-based data-mining model for registering the final relaying decision. The proposed scheme is extensively validated for fault situations in the standard IEC microgrid model with wide variations in operating parameters for radial and mesh topology in grid-connected and islanded modes of operation. The extensive test results indicate that the proposed intelligent differential relaying scheme can be highly reliable in providing an effective protection measure for safe and secured microgrid operation.

Intelligent busbar protection scheme based on combination of support vector machine and S‐transform

Differential protection is the main protective scheme of busbar in power systems but its operation degrades during current transformer (CT) saturation conditions. In this study, the busbar differential protection scheme is improved by the addition of a new feature extracted from differential current using S-transform analysis. S-transform as a powerful signal processing technique gives a complete visualisation of the signal in both time and frequency domains. The new extracted feature as well as the magnitude of the differential and restraint currents are utilised to increase the security of traditional busbar differential protection scheme. With the addition of this new feature, distinctive regions are created in the feature space which can be separated by an appropriate classifier. In this study, the well-known classifier, i.e. support vector machine is employed to effectively discriminate internal faults from external faults. To evaluate the performance of the proposed method, a part of Iranian 400-kV power system grid is simulated in the PSCAD/EMTDC environment. The transient behaviour of CTs during saturation conditions is simulated based on the precise Jiles–Atherton model. The obtained results justify the superiority of the proposed method in terms of speed and security even in noisy conditions.

Improved differential current protection scheme for CSC‐HVDC transmission lines

In the modern power system, current source converted high-voltage direct current (CSC-HVDC) system is playing an increasingly important role due to the advantages such as flexible control, asynchronous interconnection, and long distance transmission. However, the conventional differential current protection has exposed the shortages in operation speed and fault identification. This study proposes a novel differential current protection scheme, which is composed of the differential current unit and blocking unit. Both of them are designed based on the differences in the newly defined differential current between the internal fault and external fault. A ±800 kV UHVDC simulation system is established to verify the performance of the proposed protection. Simulation test results show that the proposed protection can accurately distinguish the internal fault from external fault in the whole fault period. The identification performance is not influenced by the fault location or fault resistance. Besides, the requirement of sampling rate is low and the calculation amount can be negligible, providing a favourable condition for the proposed protection scheme to be implemented into the real HVDC control and protection system.