Backup Protection Scheme Research Articles

Substation-area Backup Protection Scheme for the Failure of 10kV Line Protection Device

The research on wide-area backup protection for high-voltage transmission lines has made certain progress in recent years, but there are few reports published on substation-area backup protection for low-voltage 10kV transmission lines. Based on the characteristics of shared information in intelligent substation, a substation-area backup protection scheme to deal with the failure of 10kV line protection device is proposed in this paper. This scheme uses the device self-test information and heartbeat mechanism to monitor the operation status of 10kV line protection devices; to realize the substation-area backup protection for the 10kV transmission lines when any line protection device fails, the protection criterion is constructed by the action results of power directional elements of transformer protections and other 10kV line protections. The proposed scheme can greatly improve the speed of the fault isolation and has low requirements for data demand and synchronization. PSCAD simulation results show that the proposed method is with high correctness and feasibility.

A distance protection scheme for HVDC transmission lines based on the Steady-state parameter model

To improve the performance of the protection scheme for HVDC lines, a novel distance backup protection scheme is proposed in this paper. First, it is proved that the DC line model can be equivalent to lumped parameter model during the steady-state. Based on the equivalent model, the fault distance can be calculated, and the criterion of the distance relay is implemented. Secondly, a directional relay based on the transient currents is added to solve the dead zone problem of distance protection. Finally, a ± 800 kV HVDC system is built in PSCAD/EMTDC simulation environment to test the performance of the protection. Comprehensive test studies show that the proposed protection scheme can correctly distinguish internal faults from external faults. Besides, the proposed protection has a clear setting principle, low requirements of the calculation amount and sampling rate.

A Differential Voltage-Based Wide-Area Backup Protection Scheme for Transmission Network

This article proposes a differential voltage-based scheme to identify the faulted line in the transmission system. Initially, the placement of phasor measurement unit (PMU) is carried out. Based on the PMU placement, three subnetwork types are evaluated. Further, a differential voltage-based algorithm is applied to each subnetwork in a system. The tripping decisions for each dependent subnetwork are carried out in steps by providing separate timer settings for them. The load encroachment and fault conditions for a particular case is distinguished by applying modified distance relaying and sequence component-based algorithms to the proposed differential voltage-based scheme. Extensive tests are carried out for several fault and stressed conditions on a New England 39-bus system on MATLAB/Simulink platform. The proposed scheme is also validated for different test cases on a modified WSCC 9-bus system on real-time digital simulator platform for assessing its ability to perform in real time.

Integrated Wide-Area Backup Protection Algorithm During Stressed Power System Condition in Presence of Wind Farm

Stressed power system conditions such as power swing, voltage instability and load encroachment may influence the secure operation of conventional backup protection at their third zone (zone 3). In this paper, a new integrated backup protection algorithm for distance relay is proposed based on wide-area measurements to distinguish the fault-stress conditions in the presence of offshore wind farm (WF). Presence of WF creates problem for distance relay due to varying wind speed and wide fluctuations in voltage and current signal during fault condition. In this work, two criteria are proposed to analyze and to identify the events. The first criterion compares the positive-sequence bus voltages in order to identify the faulty bus. According to second criterion, the absolute positive-sequence impedance angle difference between the lines connected to that faulty bus is computed to identify the faulty line. Numerous test cases with the WSCC 3-machine, 9-bus and IEEE 39 bus power system models have been simulated using EMTDC/PSCAD software. Results for different fault cases, power swing, load encroachment and voltage instability, and various non-fault cases like capacitor switching, demonstrate the efficacy of the wide-area backup protection scheme. Comparative assessment reports with the existing methods are also presented.

A New Impedance-Based Main and Backup Protection Scheme for Active Distribution Lines in AC Microgrids

Microgrids active characteristics such as grid-connected or islanded operation mode, the distributed generators with an intermittent nature, and bidirectional power flow in active distribution lines lead to malfunction of traditional protection schemes. In this article, an impedance-based fault detection scheme is proposed as the main protection of microgrids by applying the proposed equivalent circuits for doubly-fed lines. In this scheme, relay location data and positive sequence voltage absolute value of the other end of the line are used. It can detect even high impedance faults in grid-connected and islanded modes. It is robust against load and generation uncertainties and network reconfigurations. Low sampling rate and minimum data exchange are among the advantages of the proposed scheme. Moreover, a backup protection scheme based on the conductance variations is suggested. No requirement for the communication link is a distinguished advantage of the proposed backup protection scheme. The proposed schemes have been simulated using PSCAD and MATLAB software and the results confirmed their validity.

DC Fault Identification in Multiterminal HVDC Systems Based on Reactor Voltage Gradient

With the increasing number of renewable generations, the prospects of long-distance bulk power transmission impels the expansion of point-to-point High Voltage Direct Current (HVDC) grid to an emerging Multi-terminal high-voltage Direct Current (MTDC) grid. The DC grid protection with faster selectivity enhances the operational continuity of the MTDC grid. Based on the reactor voltage gradient (RVG), this paper proposes a fast and reliable fault identification technique with precise discrimination of internal and external DC faults. Considering the voltage developed across the modular multilevel converter (MMC) reactor and DC terminal reactor, the RVG is formulated to characterise an internal and external DC fault. With a window of four RVG samples, the fault is detected and discriminated by the proposed main protection scheme amidst a period of five sampling intervals. Depending on the reactor current increment, a backup protection scheme is also proposed to enhance the protection reliability. The performance of the proposed scheme is validated in a four-terminal MTDC grid. The results under meaningful fault events show that the proposed scheme is capable to identify the DC fault within millisecond. Moreover, the evaluation of the protection sensitivity and robustness reveals that the proposed scheme is highly selective for a wide range of fault resistances and locations, higher sampling frequencies, and irrelevant transient events. Furthermore, the comparison results exhibit that the proposed RVG method improves the discrimination performance of the protection scheme and thereby, proves to be a better choice for future DC fault identification.

System-based testing of a voltage differential protection scheme for shunt capacitor bank

Capacitor banks used in substations cause a maintenance problem, which consume time for technicians to identify the root cause of the problem which can result in voltage control issues. Therefore, aim of this project is to identify either the unit or element fails within the capacitor bank using the dedicated voltage differential protection function. The voltage differential across the capacitor bank is calculated using the Capacitor Bank Assistant (CBA) tool in AcSELerator quickset. There are two modes of operation are considered (a) Alarm and (b) Trip. The alarm mode is used to notify the system operator for small change in system voltage due to element fail within capacitor bank, whereas in trip mode operation the change in voltage reaches the maximum threshold value and send the trip signals in order to disconnect the faulty banks from rest of the power system. The paper designed the voltage differential logic in AcSELerator quickset for both alarm and trip modes respectively. The system-based voltage differential protection function testing for shunt capacitor banks is introduced in this paper. The reason for introducing the system-based testing is because two CMCs are used to make a connection for VZ and VY channels of SEL487V IED in order to test the voltage differential function. The two CMCs are synchronized in Relay SimTest software using GPS signals from SEL satellite clock (SEL-2407) and Antenna. Relay SimTest software has a provision to model the capacitor bank and simulations result are analyzed for alarm and trip mode operations respectively. In addition to the main protection (voltage differential), this manuscript provides the protection setting and simulation results for the overload backup protection for SCB’s. However, it is observed that voltage differential scheme for SCB’s is more sensitive in comparison with overcurrent backup protection. The cost of the voltage differential is more expensive than the backup overload protection because of using only with CT signals. In summary, it is a good practice to implement both Main (Voltage differential scheme) and Back-up (Overload) protection schemes in order to effectively protect the SCB’s from any kind of internal faults in the system. Finally, the IEC61850 GOOSE message application is considered for SCB’s. The engineering configuration is performed for two logical nodes A87PDIF1 (alarm mode) and T87PDIF1 (trip mode). The IEC61850 GOOSE simulation results are analyzed using IED Scout. Finally, hardwired and IEC61850 GOOSE simulation results are compared. The GOOSE operation is faster than hardwired signals for shunt capacitor banks voltage differential function.

Novel phasor sequence‐based fault detection scheme for wide‐area backup protection of series‐compensated line

For series-compensated line, the distance relay finds its limitations during voltage inversion, current inversion, load encroachment, power swing and balanced fault during the power swing. These limitations can be overcome by wide-area backup protection schemes. This study proposes a novel fault detection technique utilising the synchrophasor data of voltage and current signals at system protection centre. The algorithm compares the phase angle difference between positive-sequence voltage phasor under system intact condition and real-time positive- or negative-sequence current phasor, which is computed from the synchronised data obtained from phasor data concentrator after identifying the possible critical buses to which the faulted line is connected. Different cases of fault type, distance and resistance have been considered to validate the proposed scheme with 3-generator, 9-bus western system coordinating council using MATLAB/Simulink platform. The results justify the suitability of the proposed scheme to be deployed for achieving more reliable performance.

Wide area backup protection scheme for distance relays considering the uncertainty of network protection

Although local protection methods can perform well at speed, in a real network where network uncertainties are unavoidable, these methods may result in inaccurate performance. Therefore, the use of other methods, such as wide area protection, can lead to more accurate results because of using comprehensive information via telecommunication links. In this paper, a wide area protection algorithm is presented to cover the mal-operation of relays due to the network uncertainties. In this method, an objective function is defined based on the performance status of various zones of distance relays, the values of which will be different for each line. Depending on the position of each relay on the transmission line, weighting factors for objective function are determined based on the optimization algorithm and taking into account the possible uncertainties of the power grid. The proposed method has been implemented on IEEE 9-bus system and has proved high detection precision and performance accuracy.

Wide-Area Measurement-Based Adaptive Backup Protection for Shunt Compensation Environment

In this paper, the localization issue associated with distance relay protecting a transmission line with static synchronous compensator (STATCOM) is discussed. Generally, distance relay is mal-operated due to the dynamic behaviour of STATCOM during its inductive and capacitive modes of operation. Because, STATCOM operation creates the problem of correct measurement of fault distance and is responsible of under-reach and over-reach of distance relay. Furthermore, high fault resistance is also the reason of under-reach along with STATCOM operation. To overcome aforementioned challenges, an adaptive wide-area backup protection scheme (WABPS) is addressed which compares the calculated impedance and referenced impedance. Calculated impedance is the difference between impedance measured by relay and impedance contributed by fault resistance. Referenced impedance is the sum of fault impedance and impedance contributed by STATCOM. If calculated impedance is less than referenced impedance, then the relay will generate a trip signal. Proposed WABPS is inherent directional and provides information about fault detection, fault distance, and fault resistance during dynamic operation of STATCOM. The performance of the proposed WABPS is evaluated using technology of synchronize phasor measurement and communication channel. A 230 kV, 50 Hz system with a 24-pulse STATCOM is simulated and validated using PSCAD/EMTDC software package.

Optimal PMU allocation for high-sensitivity wide-area backup protection scheme of transmission lines

In spite of the outstanding benefits provided via phasor measurement units (PMUs) to smart grids in the field of wide area protection, they increase the cost of the infrastructure. Based on PMU location and system topology, subsets of buses and lines are formed representing backup protection zones (BPZs). This paper introduces a proposed criterion to overcome the shortage in formulating the BPZs. Also, this paper presents a proposed framework to define the optimal PMU locations regarding wide area BPZs. The framework is expressed as a multi-objective function, which aims to enhance the system observability, increase the number of transmission lines belonging to BPZs and increase the BPZ threshold sensitivity. The genetic algorithm technique (GA) is used to obtain the optimal locations of PMUs for different cases. The effectiveness of the proposed framework is evaluated by investigating the 14-bus IEEE standard system for different cases of fault location, type and resistance. Furthermore, the 39-bus system is considered for some cases as a larger system. The results show the possibility of enhancing the sensitivity of the BPZs of the system regarding optimal PMU locations.

Real‐time data‐assisted replay attack detection in wide‐area protection system

The cyber-attack surface in the power grid has widened with the deployment of the wide-area monitoring, protection, and control (WAMPAC) system. Replay attacks are one of the most challenging attacks to detect in a WAMPAC system. The authors aim to address the problem of identification and repercussions of continuous replay attacks on wide-area backup protection schemes. The continuous replay attacks introduce a permanent lag in the phasor measurement unit (PMU) data. The authors classify such attacks into small, medium, and wide-scale based on the number of compromised substations. Furthermore, the signature of a replay attack is derived using a one-step-ahead prediction of PMU data. The resulting forecast error distributions are subsequently analysed using the Kullback–Leibler divergence metric. Results using field PMU data show that this method successfully distinguishes replay attacks from normal system operation and faults in the system. Therefore, the proposed scheme can be used to detect and mitigate the effects of replay attacks on wide-area protection schemes.

Vulnerability assessment approach for real‐time and regional monitoring of backup protections: minimising number of GPS‐based distance relays

Presenting an accurate and cost-effective solution to tackle static load encroachment issues in backup protection of transmission networks stand as a challenging task. Therefore, this study aims at devising a new backup protection scheme via GPS-based distance relays (GBDRs) against this issue. In this scheme, each GBDR calculates the vulnerability index locally, which helps to find out the vulnerable situation. When these indices exceeded their threshold, the protection centre is allowed for real-time monitoring in the corresponding area. In this regard, after calculating superimposed components, they are sent to the protection centre for discriminating faults from stressed conditions. Deployment of GPS-based relay in each bus brings higher costs and entails sharing large amounts of data. Therefore, a new techno-economic approach helps for the optimal deployment of these relays. To this end, zone-3 in some buses are eliminated, and the rest are equipped with GBDRs while each line at least is protected by two existing zones-3. By doing so, the network is divided into different areas that are protected with the minimum number of these relays. Whereby, coupled with the vulnerability indices, minimising the number of GBDRs alleviates the exchanged data.

A modified wide-area backup protection scheme for shunt-compensated transmission lines

In this paper, a new modified methodology has been proposed to protect shunt-compensated transmission lines as properly as uncompensated lines. The proposed scheme initially selects the nearest buses to the fault location based on data provided by the phasor measurement units (PMUs). Three buses with the minimum magnitude of the positive-sequence voltages or maximum magnitude of negative (or zero)-sequence voltages are selected as the nearest buses to the fault location. All connected lines to these buses are designated as suspected. Afterward, the suspected line with the maximum absolute difference of positive (or negative)-sequence current angle is concluded as the faulted line. The effectiveness of the proposed technique has been evaluated under various fault scenarios in WSCC 9-bus and IEEE 39-bus test systems in MATLAB/SIMULINK platform. The outputs clearly reveal that the recommended scheme finds the faulted line precisely under different fault types, fault locations, fault resistances, and shunt-compensator types within 3 ms. The modified scheme can also detect high-resistance asymmetrical faults accurately exploiting negative-sequence current angles instead of the positive ones.

DC Fault Current Clearance at the Source Side of HVDC Grid Using Hybrid MMC

This paper proposes a source-side DC fault current clearance scheme for HVDC grids under DC short-circuit faults. The scheme uses half-bridge submodules (HBSM) and full-bridge submodules (FBSMs)-based hybrid modular multilevel converter (MMC). The DC fault current behaviors of the HVDC grid is revealed as a primary criterion for the proposed approach. The additional degrees-of-freedom for control of hybrid MMC are incorporated into the HVDC grid to interrupt the fault current feeding at the source side. During the fault ride-through process, the reactive power compensation is maintained. The proposed method does not need the DC circuit breakers since the current in the fault line can be controlled to zero. The primary and backup protection schemes for hybrid MMC-HVDC grid are proposed. The effectiveness of the method is validated by electromagnetic transient simulations on PSCAD/EMTDC.

Cognitive Radio_Based Backup Protection Scheme for Smart Grid Applications

In this paper, a backup protection scheme is presented. The proposed scheme uses the concept of a cognitive radio-based wireless sensor network to implement a protection scheme without the need for conventional electric wires and/or optical fiber between current and voltage transducers, control panels, and circuit breakers. The proposed scheme uses unlicensed spectrum channels by applying spectrum sensing and frequency allocation algorithms that are used in cognitive radio based systems. The importance of the proposed scheme comes from its cost effectiveness compared to the Ethernet communication both wired and wireless if the data transfer and message exchange is done using cognitive radio_based communication for relatively long distances. The proposed scheme utilizes cognitive radio-based communication network to convey analog and digital signals within a substation. In this way, it saves the cost of the copper wires and/or optical fiber that would be used to transmit digital and analog signals. Further, it does not require the expensive spectrum licenses that would have been purchased if Ethernet long-distance wireless communications are utilized. To assess the benefits/challenges related to the application of cognitive radio_based communication, a detailed and realistic modeling of both power systems and cognitive radio_based communication systems is performed simultaneously. The proposed scheme is simulated using MATLAB/Simulink and performance of the proposed scheme was investigated under different communication scenarios.

A Novel Protection Scheme for MMC-HVdc Transmission Lines Based on Cross-Entropy of Charge

MMC-HVdc transmission system has become the mainstream of power construction and plays an increasingly important role in the power system. However, the dc line fault results in shutting down of the converters, which can greatly endanger the security of the power grid. So it is essential to find a fast fault identification strategy for dc line protection technology. Besides, the existing backup protection scheme has the problems of long delay and strict communication synchronization requirements. Therefore, this paper proposes a novel protection scheme for mmc-HVdc transmission lines based on the Cross-Entropy of charge. The fault current oscillation phenomenon and fault current frequency characteristics of mmc-HVdc transmission lines are analyzed first. Secondly, this paper proposes a method to filter out distributed capacitance current by charge and eliminate the current oscillation. Finally, the difference of the charge during different faults (internal fault and external fault) is analyzed, and the Cross-Entropy is introduced to express this difference. Hence, this paper proposes a new principle of identifying faults using the Cross-Entropy of the charge. Simulation results show that the protection principle is not affected by the distributed capacitive current and does not require strict communication synchronization. It has excellent performance in intolerance to fault resistance and noise interference and can be used as backup protection for the mmc-HVdc transmission system.

Wide-Area Backup Protection Against Asymmetrical Faults Using Available Phasor Measurements

This paper proposes a robust and computationally efficient wide-area backup protection (WABP) scheme against asymmetrical faults on transmission systems using available synchronized/unsynchronized phasor measurements. Based on the substitution theorem, the proposed scheme replaces the faulted line with two suitable current sources. This results in a linear system of equations for WABP, with no need of full system observability by measurement devices. The identification of the faulted line is attributed to the sum of squared residuals ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SoSR</i> ) of the developed system of equations. To preserve accuracy, the scheme limits the calculations to the assessment of the negative-sequence circuit of the gird. Relevant practical aspects that have not been properly addressed in the literature, namely the non-simultaneous opening of circuit breakers (CBs) and their single-pole tripping for single-phase to ground faults are investigated. The linearity of the formulations derived removes concerns over convergence speed and potential time-synchronization challenges. The proposed scheme is able to identify the faulted line and retain this capability for hundreds of milliseconds following the fault inception. More than 20 000 simulations conducted on the IEEE 39-bus test system verify the effectiveness of the proposed WABP scheme.

A Poverty Severity Index-Based Protection Strategy for Ring-Bus Low-Voltage DC Microgrids

The lack of an effective protection system may jeopardize resilience offered by low-voltage dc (LVDC) microgrids. This paper presents a protection strategy for ring-bus LVDC microgrids, which employs intelligent electronic devices and solid-state circuit breakers (SSCBs). This scheme is developed based on monitoring the modified squared poverty gap index difference that is calculated using the normalized fault-imposed component of current. A backup protection scheme for the case of the SSCB failure and a reclosing scheme for restoring the isolated zone in the case of temporary faults are considered in the protection scheme. The proposed strategy is capable of detecting and classifying the pole-to-pole and pole-to-ground faults within microgrid lines. Moreover, it consists of protection schemes for distributed energy resource and load laterals and is effective for high-impedance fault detection. The merits of the developed protection strategy are demonstrated through several time-domain simulation case studies.

Decentralised wide‐area back‐up protection scheme based on the concept of centre of reactive power

Here, a new decentralised approach-based wide-area back-up protection (WABP) scheme is proposed for faulted line identification (FLI). The scheme is divided into two sub-routines, i.e. possible faulted region (PFR) identification and FLI. Initially, the power system under study is divided into different coherent regions. The concept of centre of reactive power (CORP) is used to accomplish the task of PFR. Once the faulted region is identified, FLI is done by continuously monitoring the direction of reactive power flow (DORPF) of each line within the PFR. The proposed scheme is extensively tested on IEEE-39 bus test system for different types of faults. The performance of the scheme under stressed system conditions is also investigated. The obtained results show that the suggested algorithm is able to maintain the balance between dependability and security aspects of the protection logic.