Load Encroachment Research Articles

Dynamic wide‐area cooperative protection: A new approach

AbstractThis paper introduces a new dynamic wide‐area cooperative protection based on cooperative control of distributed multi‐agent systems and graph theoretical methods. For power system cooperative protection, a new voting method is designed that manages each agent's cooperation according to each protection area. Cooperative protection areas work together and make a wide area of cooperative protection for the specific protection scheme. As the power system configuration varies, the voting management and the wide‐area cooperative protection dynamically change. The proposed protection method decisions are collective, while a centralized master does not exist, and local information is used. A fault detection code and a wide‐area fault detection code are presented for fault detection. The suggested dynamic wide‐area cooperative protection scheme is tested on an IEEE 39‐bus test system. The proposed protection performance is studied as backup protection for distance relays during normal, stable power swings, unstable power swings, and load encroachment conditions.

A novel superimposed voltage energy‐based approach for single phase to ground fault detection and location in distribution networks

AbstractThe structure complexity and the extended geographical area are among the factors that create challenges in accurate fault location and detection in distribution networks. The single‐phase to ground (SPG) faults are considered as most frequent reasons for distribution network interruption, which can threaten the network's reliability. Signal processing methods are usually used as common approaches to distinguish and locate faults in distribution networks. This paper proposes a novel scenario to select optimal wavelet packet transform (WPT) coefficients for SPG fault location and a method based on superimposed voltage energy to distinguish the faulty phase according to these coefficients. Furthermore, employing the energies of the superimposed voltages helps to minimize the effects of high resistance faults (HRFs) and load encroachment on the efficiency of the faulty phase detection part. Comparing the obtained results with other scenarios demonstrates the considerable efficiency of the proposed scenario. Finally, with the help of general regression neural networks (GRNN) as machine‐learning tools, a new algorithm is derived for detecting and locating the SPG fault and capacitor bank switching overvoltage (COV). Simulation results are implemented on the IEEE 34‐bus standard distribution network, demonstrating the efficiency and superiority of the suggested method.

A Wide-Area Measurement System-Based Load Encroachment Identification Method Applicable to Power Systems with High Wind Power Penetration

One of the main factors in triggering cascading outages is the unexpected tripping of backup protection caused by load encroachment (LE). Hence, LE should be identified quickly to avoid unexpected tripping. This paper proposes a fast LE identification method based on the wide-area measurement system (WAMS), applicable to transmission grids with high wind power penetration. Firstly, based on the improved shortest path algorithm, the method searches for critical lines greatly affected by the LE to determine the collected range of wide-area information. Then, by analyzing the hidden dangers of the existing calculation method for the active power estimation value (APEV) in the power system with wind farms, a fast calculation method of the APEV based on the WAMS is proposed to ensure that the existing LE identification criterion is still applicable in the high-penetration system of wind power. Finally, based on the PSASP platform, the wind farm model is integrated into the IEEE 39-bus New England system for simulation. The simulation results show that the method proposed in this paper can quickly search for the critical line set (CLS) and accurately identify the LE under high wind power penetration, effectively avoiding the unexpected tripping of backup protection and preventing cascading outages.

Online vulnerability assessment of Zone-3 distance relays against static load Encroachment: A novel approach based on fault chain theory

One of the main factors in triggering cascading outages is the undesired operation of zone-3 vulnerable distance relays under static load encroachment. In this paper, to avoid the contribution of vulnerable relays in cascading outages, a novel online vulnerability assessment method based on fault chain theory is proposed to identify the critical relays. The main idea is to use the fault chain theory to model the process of valid successive line outages that occur step by step and lead to load encroachment into zone-3 distance relay. A novel normalized prediction index based on relay margin change, margin sensitivity variation, load encroachment factor and overload tolerance of the line is proposed to predict the next possible outage. The distance relays involved in most fault chains are identified as vulnerable relays requiring to be controlled. A suitable index is presented to detect the critical relays. In this regard, an optimal control strategy is also proposed to restore the acceptable operating margins of the identified vulnerable zone-3 distance relays in the system’s emergency condition. The validity of the proposed approach is evaluated on New England 39 bus system to confirm the effectiveness and benefits of the proposed method. The obtained results are exciting.

A novel approach for resilient protection of AC microgrid based on differential phase angle of superimposed complex power

In the last decades, the penetration rates of microgrids (MG) and distributed generations (DGs) are exponentially soared. Despite the fact that MGs can improve the reliability and resilience of distribution networks, designing a reliable protection scheme for alternating current microgrids (AC-MGs) is still a challenging task. The existence of various types of DGs and frequent changes in MGs’ operational modes, islanding, sudden increment in the value of loads, and penetration rate variation of DGs are some of the main issues which should be considered to design a reliable and resilient protection scheme for MG. In this paper, a novel adaptive resilient protection scheme employing synchronous current and voltage obtained from micro phasor measurement units (μPMU) located at both ends of the protected line, is presented. A new index is also devised to detect all types of internal and external faults based on differential phase angle of superimposed complex power (DPASCP). The threshold value of the proposed index is adaptively updated according to variations created in the network. This scheme can detect various types of faults in different locations fast and accurately in both grid connected and islanded mode of operation. The performance of the proposed protection scheme is also evaluated on IEEE 33-bus and 15-bus test networks in non-fault critical conditions such as grid-islanding switching, connection and disconnection of different DGs with changing in penetration rates of them, and load encroachment. The results demonstrate the capability and superiority of the suggested protection scheme.

An Intelligent Distance Relay Sensing Methodology Immune to Power Swing and Load Encroachment

A distance relay (DR) is a complex sensor that operates based on apparent impedance computed using inputs from the current and voltage sensors. Power swing and load encroachment are two stressed conditions that a DR finds challenging to differentiate from a fault condition. Conventional DRs use additional techniques to detect such conditions and block the DR. However, a symmetrical fault goes undetected during such a block period and can lead to a blackout in the worst case scenario. Also, a highly reactive load encroachment cannot be detected by the conventional relay and, hence, may maloperate. This article critically analyzes the apparent impedance behavior during a symmetrical fault, power swing, and load encroachment. Using the insights from the analysis, an intelligent DR sensing methodology that does not use additional techniques to sense the power swing and load encroachment conditions is proposed. The results from numerous case studies of faults, power swing, faults during power swing, load encroachment, and faults during load encroachment in the WSCC nine bus system in MATLAB/Simulink prove the efficacy of the proposed methodology. The DR employing the proposed sensing methodology can refrain from issuing false trip signals during power swing and load encroachment conditions. It can detect symmetrical and unsymmetrical faults within one cycle in any given condition. The proposed methodology is superior to other methods in detecting symmetrical and unsymmetrical faults during any given condition within one cycle.

Investigation of distance relay settings under normal and stressed conditions in a wind farm environment

This paper presents an adaptive methodology for setting distance relays connected to a network integrated with a wind farm system. The proposed trip boundary setting is capable of automatic adjustment with varying system conditions making the relay more reliable, faster and more accurate. A wind farm system delivers power according to the wind speed and penetration level at that instant. Distance relays having fixed trip boundary setting may underperform in such conditions as trip boundaries need to be varied according to the wind speed, penetration level, voltage ratio, power angle, system impedance and frequency. These variations in ideal trip boundaries, due to changing conditions, have been investigated. Furthermore, a smart coordination scheme is proposed for the improvement of backup protection (Zone 3) provided by distance relays. Inaccurate sensing of fault in Zone 3 due to load encroachment results in false tripping and makes the relay unreliable. The new scheme enables discrimination between fault inception and false tripping. A typical 400 kV system has been considered for simulation and testing in Matlab®/Simulink™ environment.

Source-Agnostic Time-Domain Distance Relay

Fault response of an inverter based resource (IBR) is dictated by its control scheme, making it markedly different from the response of a synchronous source. This has led to misoperation of distance relays when fed by IBRs. Published literature is mostly focused on changing the control design of inverters, but this approach is not practical, as these controls are proprietary and beyond the reach of utilities. To resolve this issue, this paper proposes a method for a source-agnostic distance relay that works in time-domain. Using only single ended measurements, the relay detects, classifies and locates any fault on the line it monitors. The method does not require any polarization technique. It is shown to work for unbalanced lines of any length, for transmission or distribution system with any number (even 100%) of IBRs, is immune to load encroachment, decaying dc offset and prefault currents. With very limited communication, it is also shown to be immune to fault resistance.

An adaptive time–frequency approach based secured back-up distance protection scheme for system stress conditions

Critical operating conditions of power system may lead to distance relay security issues. Distance relay back-up protection is offered with long reach setting and due to this under sudden change in voltage and current parameters during non-fault situations also considered as a fault by the protection function in an integrated network. The conventional technique fails to discriminate system stress conditions such as power swing, voltage instability and load encroachment from an actual symmetrical fault in the back-up zone (third zone (Z3)) of the distance relay. To mitigate this, a Modified Complete Ensemble Empirical Mode Decomposition with Adaptive Noise (MCEEMDAN) technique is used to decompose the instantaneous power and to develop a reliable index. The most significant intrinsic mode function (IMFs) is extracted to estimate the energy as used as detection index. An adaptive statistical threshold selection process is developed to detect and discriminate all system stress conditions from symmetrical fault in the back-up zone of the distance relay. The proposed algorithm is a supervisory scheme for the back-up zone setting (Z3) of the distance relay. Simulation results for different stress conditions, presence of noise, sudden switching of load and symmetrical fault are presented to highlight the strength of the method.

Transmission line adaptive protection scheme: A new fault detection approach based on pilot superimposed impedance

High impedance faults, changing network structure and line series compensation can lead to overreaching or underreacting of the conventional distance relays which can imperial security, stability, and sustainability of power systems. To overcome these challenging issues, this paper presents a new adaptive primary protection scheme for transmission lines based on pilot superimposed impedance (PSI). In the proposed scheme, PSI is defined as the ratio of the superimposed component of voltage phasor obtained from the local end to the sum of superimposed component current phasors obtained from both ends of the protected transmission line. Since the proposed PSI shows the different responses for internal and external faults, it is compared with the developed threshold based on Thevenin impedance for detecting the faulted phases inside and outside the protected line. In the case of internal faults, the PSI is less than the network Thevenin impedance which is seen from the bus adjacent to the relay. Due to establishing the proposed threshold based on the Thevenin impedance seen from the bus behind the corresponding relay, it can be adaptively updated when the network structure is changed. This feature helps to yield robust protection not only in different contingencies of the network but also in the case of weak source networks. The proposed method is also tested in the case of high fault resistance, load encroachment (LE) condition and series capacitive compensation in the long-distance transmission line. The obtained results confirm the security and dependability of the proposed protection scheme.

Secured zone 3 protection during load encroachment using synchrophasor data

Three-phase fault and load encroachment are balanced phenomena. A load encroachment function is incorporated in distance relay to improve the security of protection scheme, confuses with three-phase fault during high reactive loading condition. Zone 3 malfunction during such a situation often causes cascade line tripping leading to wide-area disturbance. In this work, voltage phasors of selected buses from a wide area measurement system (WAMS) are used to prevent zone 3 maloperation of a distance relaying scheme during load encroachment. The change in magnitude and phase of bus voltages are applied to discriminate three-phase fault from load encroachment. Performance of the proposed method is tested with New England 39 bus and IEEE 118 bus system simulated in EMTDC/PSCAD. Results show high accuracy as well as the speed of operation, is very fast of the proposed method.

Phase angle-based fault detection and classification for protection of transmission lines

Fault detection in transmission network is conventionally done by distance relays. Generally, these relays mal-operate during power swings, load encroachment, and High Impedance Faults (HIFs). A novel phase angle-based approach for fault detection and classification of transmission lines is proposed in this paper. Instantaneous Phase Angles (IPAs) of local ends voltage and current measurements are estimated. These, with Discrete Fourier transform (DFT), are used to calculate Derived Phase Mean Indices (DPMIs), and Phase Mean Indices (PMIs) of each phase voltage and current of the line. A Global Fault Detector (GFD) setting is proposed for the evaluated indices to detect and classify the fault. The proposed approach is tested on a hybrid test signal and the Western System Coordinating Council (WSCC) 9 bus system in Real-Time Digital Simulator (RTDS) with different fault resistances, inception points and locations, including HIFs, power swings, topology changes, load and capacitor switching. The effects of the presence of noise, asymmetry, harmonics and phase unbalance in the test signals on the proposed method are also investigated. The results obtained from RTDS and a simulation based comparison of the proposed method with a previous method prove the efficacy of the proposed approach to detect and classify faults and also act as an inherent power swing blocker and de-blocker.

Preventing third zone maloperation during power system stressed conditions

Abstract The back-up third zone unit of distance relay may issue nuisance tripping command during different system critical events like power swing, voltage stress/instability and load encroachment. Since, such events are system symmetry phenomenon, the protection unit will not always able to discern them from three phase (symmetrical) fault in the distance relay third-zone region. The conventional relay algorithm fails to make a proper decision and results in unwanted tripping. This may further lead to system blackout. To mitigate this problem, a new approach based on the average rate of change of current (ARCC) is proposed. The method will work in integration with the conventional distance relay impedance setting algorithm to provide better results. The main advantage of the method is that it considers only local end current information. Within one power cycle, an accurate decision can be taken by the protective relay. The proposed method is validated considering IEEE 39-bus New England test system and the Indian regional power grid model modeled using EMTDC/PSCAD software. The simulation results for various critical cases and comparative analysis with existing methods shows effectiveness of the proposed method.

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.

Phasor Measurement Unit Incorporated Adaptive Out-of-step Protection of Synchronous Generator

The existing out-of-step protection schemes have proven deficient in the prevention of significant outages. Out-of-step protection schemes must not operate in stable power swing and rapidly isolate an asynchronous generator or group of generators from the rest of the power system in case of unstable power swing. The paper proposes a novel phasor measurement unit (PMU) incorporated a polygon-shaped graphical algorithm for out-of-step protection of the synchronous generator. The unique PMU based logic works further to classify the type of swing once the graphical scheme detects it. The novel graphical logic scheme design in this work such that it can identify the complex power swing produced in the modern power system. The proposed algorithm can take the correct relaying decision in the event of power swing due to renewable integration, load encroachment, and transient faults. In this work, It uses the original and modified Kundur two area system with a power system stabilizer (PSS) to test the proposed algorithm. In the end, It provides assessment results of the proposed relay on the Indian grid system during the July-2012 blackout. The results declared that the proposed algorithm is fast, accurate, and adaptive in the modern power system and gives better performance than the existing out-of-step protection schemes.

Prevention of Load Encroachment Using Model Predictive Control

Tripping of distance relays due to load encroachment is one of the common causes behind major disturbances occur in power systems. Several techniques have been presented in literature to differentiate an occurrence of load encroachment and a fault in a system. However, once an event of load encroachment is observed, loading condition of the power system must be rescheduled to avoid any undesired relay tripping. This paper proposes a receding-horizon Model Predictive Control (MPC) strategy to change load and generation of a power system optimally to take the apparent impedance seen by vulnerable distance relays away from their zone-3 boundaries. To apply MPC technique, a linear state-space model of power system is developed using sensitivity analysis. Rescheduled load and generation are found by minimizing the total cost required for the change, owing to the constraints of power balance, power carrying capacity of lines and relay operational margins. During step changes in inputs, adequate time gap is provided to ensure the stability of the power system. An oscillation detection technique is developed for the above purpose. Several case studies have been presented at the end to demonstrate the performance of the proposed technique under stressed operating conditions.

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.

Adaptive distance relay algorithm to detect and discriminate third zone faults from system stressed conditions

This paper presents an adaptive approach for distance relay third zone setting. The proposed method uses variational mode decomposition (VMD) approach to decompose the local end current signal into different modes. The signal extracted from the third mode is used to calculate the energy index. The apparent impedance and energy index are used to detect symmetrical and asymmetrical faults in the third zone of the distance relay. The proposed logic also helps the distance relay to operate securely during power swing, voltage instability, load encroachment, generator outage, line outage, and single-pole tripping. The effectiveness of the proposed method is tested using the simulated data generated from the IEEE 39-test bus system model and Indian Power network. EMTDC/PSCAD software is used for simulating the models. Results ensure that the presence of noise in the signal, high resistance fault path and higher sampling frequency has a negligible impact on the performance of the proposed method.

Adaptive Third-Zone Distance Protection Scheme for Power System Critical Conditions

An adaptive third-zone distance protection scheme is necessary to distinguish between faults and system stressed conditions such as power swing, voltage instability, and load encroachment. Fast and reliable detection of third-zone three-phase fault during these conditions is still a challenging issue. To address this issue and to restrict the cascaded outages, a matrix pencil method (MPM) based supervised detection index (SDI) is developed by utilizing instantaneous current. Using MPM technique the signal is reconstructed. Next, the error between the reconstructed and the original signal is estimated and the mean of the estimated error is then calculated. The absolute maximum value of mean is considered as a detection index in the proposed work. The main objective of the proposed algorithm is to provide precise detection and discrimination of third-zone three-phase fault from stressed operating conditions through an adaptive threshold. Effectiveness of the proposed algorithm is illustrated by simulation studies carried out on the IEEE 39-bus test system and 400 kV Indian Eastern Regional Grid (IERG) using PSCAD/EMTDC software. The results demonstrate that the supervised algorithm can improve power system security during critical operating conditions.