Power Swing Research Articles

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.

Active Power Control of DFIG Wind Turbines for Transient Stability Enhancement

This paper proposes an adaptive Dynamic Power Reduction (aDPR) scheme for Type-3 Wind Turbine-Generators (WTGs) to enhance transient stability of synchronous generators (SGs), with benefits of increasing transfer limits on already fully loaded transmission paths. The scheme consists of three components to deal with a fault close to a SG. Initially, the WTG curtails its active power to a predefined level to act as a dynamic brake for the SG. Then the controller monitors the rate of change of frequency to adaptively ramp the WTG back to its original power output while minimizing the WTG pitch and rotor motion. Finally, to reduce the risk of second-swing instability, the converter uses its reactive current to damp SG power swings. The aDPR scheme can be classified as a remedial action scheme and is enabled if its action can ensure transient stability. To demonstrate the effectiveness of aDPR and to benchmark it against other WTG active current and frequency feedback control techniques, a single-machine infinite-bus system with one WTG is utilized. Next, an aDPR enabled WTG is integrated in the NPCC 68-bus system. Finally, the aDPR controller’s ability to prevent transient instability is demonstrated on the two-area system.

A new power swing detection method in power systems with large‐scale wind farms based on modified empirical‐mode decomposition method

AbstractHigh energy consumption around the world and concerns over climate change and high greenhouse gas emissions have led to a significant increase in using renewable energy resources, particularly wind power plants. In spite of using small wind farms in distribution networks as distributed generation, the interest in employing large‐scale wind farms in transmission levels has grown significantly in recent years. The presence of large‐scale wind farms with a synchronous generator to supply the energy demand can affect the power swing parameters. These effects are in a way that can mislead power swing detection methods and cause undesirable tripping of transmission line due to mal‐operation of distance relay against power swing . Therefore, in this paper, a method has been presented based on modified empirical mode decomposition (EMD) method to differentiate fault from power swing in the networks connected to the large‐scale wind farms. The results prove the efficiency of the presented method in detecting the power swing in large‐scale wind farm networks. Finally, a comparison is conducted between the proposed method and similar methods which proves the efficiency and superiority of the proposed method in terms of noise tolerance, detection fault detection speed, and multi‐mode power swing detection compared to the current methods.

An overview of power swing detection methods in distance relays and the factors involved

An overview of power swing detection methods in distance relays and the factors involved

Power Swing Detection in Parallel Transmission Lines Connected to Wind Farms Employing del2sg Method

Power Swing Detection in Parallel Transmission Lines Connected to Wind Farms Employing del2sg Method

Accurate Superimposed Component Estimation for Improved Relay Performance During Power Swing

There is continuous variation in amplitude, phase, and frequency of voltage and current signals during power swing in a power system. Such variation makes the memorized prefault data less accurate to be used as nonfault component while computing superimposed quantity for protection decisions during power swing. In this article, the voltage and current signal characteristics during power swing are analyzed and a technique is proposed to obtain correct nonfault components for superimposed quantity computation. The accuracy of the method in estimating the nonfault components is observed for different power swing conditions simulated in a 39-bus New England system and field data. The relay performance improvement as observed is also provided while applying the method to directional relaying, fault type classification, and fault location applications for faults during power swing. Comparative assessment reveals the superiority of the proposed method in improving the accuracy of the superimposed components computed during power swing.

A new simple and accurate method for fault detection in wide area protection

• The simplicity of the algorithm. • A simple and efficient trip zone. • Independency of the trip zone on the line length or its losses. • Fault classification capability. • Operation during symmetric and asymmetric power swings. Wide area protection (WAP) utilizes multiple information for faults identification. The use of several information sources leads to fault detection in a wider range and fault discrimination from other network conditions. But these methods are usually complex and require a lot of calculations. A novel WAP algorithm is proposed in this paper. The method is based on comparing active and reactive power flow directions on both sides of the related line. Active and reactive power flow directions are used for the detection of low- and high-impedance faults respectively. The polarity of active power fluctuations on both sides of the line is adopted to identify very high-impedance faults. The suggested approach benefits low computational burden and can detect and classify various faults, in addition to discriminating faulty and stress conditions. The simulation results by scientific and powerful software on the standard IEEE 39-bus system represent the capability of the proposed method.

Discrimination between in-zone and out-of-zone faults during power swing condition using synchrophasor data

A new algorithm to discriminate between in-zone fault and out-of-zone fault conditions under power swing condition for wind/synchronous generators (WG/SG) integrated power transmission network is presented in this paper. The proposed algorithm is based on the calculation of a transmission line positive sequence power loss index, derived by calculating the absolute difference between the calculated and measured values of positive sequence real power loss. The authenticity of the proposed technique is verified by performing Hardware-in-Loop (HIL) simulation in the Real-Time Digital Simulator (RTDS) framework along with physical Phasor Measurement Units (PMUs), Phasor Data Concentrator (PDC), Global Positioning System (GPS) clock, and voltage and current amplifiers. Various events such as power swing, in-zone (including close-in and high resistance) faults during power swing and out-of-zone faults during power swing are simulated by modeling WG/SG integrated IEEE-9 bus system in RSCAD (Real-Time Simulator Computer-Aided Design) framework. The single pole tripping, impact of noise and CT saturation on the proposed algorithm is also analyzed. The proposed algorithm offers accurate discernment between in-zone and out-of-zone faults during power swing conditions. The results obtained reveal increased sensitivity and improved distinguishing capability of the proposed algorithm in contrast to those of many other approaches proposed in the literature.

Decision tree approach for fault detection in a TCSC compensated line during power swing

Detection of fault in a thyristor-controlled series capacitor (TCSC)-compensated transmission line is more difficult compared to normal transmission lines. The fault detection problem becomes further complicated in such lines, especially during power swings. In this paper, a new approach is proposed for detecting fault during power swing in a TCSC-compensated transmission line, using only local end current measurements as input to a decision tree (DT)-based classifier. It is the first-ever use of the DT-based method for this application. The performance of the proposed method has been validated on numerous test cases generated on the WSCC 9-bus 3-machine system and the modified IEEE 39-bus New England system through EMTDC/PSCAD by varying the different parameters such as fault resistance, fault type, fault location, fault inception angle, firing angle of the TCSC, load switching, current transformer saturation, etc. The sensitivity of the proposed fault detection technique is found to be 100%, which is superior compared to the existing methods. Thus, justify the effectiveness of the proposed method.

Dynamic simulation and techno-economic assessment of hydrogen utilization in dual fuel (Hydrogen/biogas) micro gas turbine systems for a wastewater treatment plant

Due to the commitments of many governments, electrical power production from renewables hopefully continues to become widespread at a rapid rate to revolutionize energy infrastructures. Nevertheless, this green power seems to be wasted due to seasonal power swings, grid restrictions, and curtailment. The present research investigates the practicability of hydrogen injection into biogas from anaerobic digestion to generate electricity for a deployed wastewater treatment plant. A Polymer electrolyte membrane electrolyzer powered by Photovoltaic panels would produce hydrogen. An array of commercialized micro gas turbines has been suggested to create electrical power and thermal demand. Transient modeling was carried out using TRNSYS software to analyze the plant's performance from the thermodynamics and techno-economic perspectives. It is found that when biogas mass flow rate fluctuates, hydrogen could be effectively injected into biogas to fuel micro gas turbines. The results revealed that injecting hydrogen into biogas results in up to a 30% reduction in CO2 emissions, with two micro gas turbines producing more than 265 kW of electrical power at full load. LCOH and payback time would be 8.3 $/kg H2 and 6.5 years, respectively, for a hypothetical scenario in which electrolyzer size is anticipated to supply the maximum necessary hydrogen. Also the results indicate that electrical power and thermal energy of 70kWe-400kWe and 120kWth-500kWth could be reached annually, and the highest efficiency for the power generation, CHP, and the overall system becomes 37.5%, 83%, and 78%, respectively.

Time-Domain Techniques for Line Protection Using Three-Dimensional Cartesian Coordinates

Today high speed protection of power system elements is necessary and realizable. This paper introduces time-domain protection techniques for transmission lines using voltage and current signals in Cartesian coordinates. Three techniques are proposed using this approach for line protection. Direction of fault is obtained using change in angle between Cartesian planes of voltage and current. In the second application on unit protection scheme, internal and external faults in transmission lines are discriminated using dot product of the normals to both end current planes. Fault type identification is obtained using the angle between incremental changes in currents in Cartesian coordinates. The output of each protection function using the new concept is derived in a quarter-cycle. The performance of each of the proposed techniques is tested for load variation, high resistance fault, different fault types, power swing, fault inception angles and signal with noise. Further, the proposed techniques are evaluated using field data from a 400 kV double circuit line.

Statistical approach for detection of fault and stable and unstable power swings based on signal energy

Distance relays, as the main protection of the transmission lines, are prone to maloperation during power swings. Therefore, the detection of faults and stable and unstable power swings is vital in the proper operation of distance protection. The existence of a method that detects all of them with the same input and calculation can considerably reduce the computational burden of relays and accelerate the performance speed. Therefore, this paper proposes a new statistical approach for the detection of these disturbances based on the voltage energy signal as input. Three indices, including the proposed shape index (PSI) based on the kurtosis and skewness, the proposed dispersion index (PDI) based on the coefficient of variation, and the swing detection index (SDI), are presented to achieve this aim. The method is unaffected by current transformer saturation due to using only voltage signals. Moreover, the method has dynamic thresholds, whose equation coefficients are constant for any system with any voltage level. The method is tested on WSCC 9-bus and New England IEEE 39-bus test systems, considering challenging situations such as noise, high resistance faults, and different swing frequencies. The results of all cases of both test systems show that the method has 100% accuracy in the detection of faults with an average detection time of 0.69 ms in noise-free conditions, while, in noisy conditions, the fault detection accuracy and the average detection time are about 99.37%, and 1.75 ms, respectively. Furthermore, the detection accuracy of stable and unstable power swings is 100% with or without noise.

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.

Hydroacoustic interaction between draft tube and penstock eigenmodes under Francis turbine full load instability

At high load, Francis Turbines may experience self-sustained pressure surge leading to significant power swing and pressure fluctuations along the waterway. The physical mechanism initiating this instability phenomenon has been the subject of much research. The development of the axisymmetric cavitating vortex rope at the runner outlet modifies the hydroacoustic properties of the draft tube waterway. Very low wave speed due to high cavitation volume combined with a high swirling number initiates the unstable axial pulsations of the cavitating vortex rope which frequency corresponds to a penstock’s eigenfrequency. The 15 MW power plant of Monceaux-la-Virole in France, composed of two units fed by a single penstock, experiences such full-load surge. On-site tests have been carried out to analyze the envelope of pressure fluctuations along the penstock once instability occurs. Combined with a 1D SIMSEN model of the power plant, these measurements have allowed to enhance the understanding of this instability phenomenon. To achieve this, an advanced draft tube modelling taking into account distributed wave speed, convective terms and divergent geometry is used and frequency analysis is carried out. Unstable draft tube eigenmodes and stable penstock eigenmodes are predicted. The key draft tube model parameters such as wave speed and second viscosity are calibrated to set the draft tube eigenmode frequency to the unstable measured frequency for different operating points. This frequency analysis concludes that high load instability occurs when a matching between the draft tube and the penstock eigenfrequencies is experienced. Moreover, it is shown that the unstable draft tube eigenmode is able to interact with different order penstock eigenmodes as function of the operating point of the unit.

A Straightforward Power Swing Detection Algorithm Using Rate of Impedance Angle Change

Mal-operation of distance protection relays during power swing (PS) condition can endanger the power system stability. Therefore, it is crucial to distinguish between short-circuit faults and PS by a power swing blocking (PSB) function to prevent undesired tripping of distance relay. This paper develops a novel and straightforward PSB method based on the rate of impedance angle change (RIAC). Not only can the proposed approach fairly discriminate both symmetrical and asymmetrical faults from PS, but also it can appropriately preserve protection scheme security during PS under single-pole tripping (SPT) on a transmission line. Furthermore, there is no need to perform extensive dynamic stability studies for setting the PSB function parameters. Unlike the rate of impedance change approaches utilized two blinders, the developed approach only needs an inner blinder. Thus, it can be used for networks running near their operational limits. The proposed method is evaluated through a modified IEEE-PSRC benchmark system in PSCAD/EMTC environment. The obtained results verify superior performance of the proposed method to traditional impedance rate of change method under different scenarios.

Out-of-Step Detection on Transmission Lines Using Apparent Impedance Differential Method

In this paper a new method to detect power swing instability on transmission lines has been proposed that is insensitive to operating conditions and system changes. Changes in system conditions, network topology or in generator statuses effectively reflects as variations in Thevenin's (source) impedances as seen from either ends of a transmission line. Thevenin's (source) impedances can also vary during a power swing. The proposed method to detect power swing instability is based on the apparent impedance differential as measured at the sending and receiving end substations of a transmission line. In this method, a transmission line is considered a part of a two-machine equivalent with associated Thevenin (source) impedances. Using the two-machine equivalent model and the impedance differential, critical variables - the rotor angle difference between the two machines, the swing-center location and swing-center voltage – that are necessary to detect power swing instability can be determined taking into considerations the uncertainty in source impedances. Necessary and sufficient conditions based on the above critical variables have been proposed to aid in the detection of power swing instability. Necessary conditions are based on the rate-of-change of real power flow in the transmission line, the rate-of-change of the real part of the impedance differential, swing-center voltage and its rate-of-change. Sufficient condition is based on a Lyapunov function that considers the rate-of-change of the rotor angle. The proposed method has been tested on a single-machine infinite bus system, multi-machine power system using PSCAD-EMTDC software, and on a large-scale power system using the Power System Simulator Software (PSS/E) to demonstrate its effectiveness.

Power Swing and Fault Detection in the Presence of Wind Farms Using Generator Speed Zero-Crossing Moment

Nowadays, due to the entry of wind power plants into the power systems, which causes changes in the network parameters, power swing detection has become more important. Changes in the wind speed and noncontinuity of the wind power plants lead to changes in the power swing characteristic. Therefore, the impedance seen by the distance relay is changed, and so the maloperation of the relay during the stable power swing may occur. This paper proposes a new method to detect power fluctuations based on the synchronous generator speed while it is independent of the network parameters. Based on the proposed method, the generator speed at any moment does not pass through zero during the stable power swing. In contrast, it passes through zero by occurring fault types with high and low fault resistance, fault types during power swing, and an unstable power swing. Therefore, the method prevents maloperation of distance protection. It is worth noting that the proposed method is applicable for distance protection in any power system with and without wind power plants, such as in the distance protection of compensated transmission lines. The obtained results indicate that the proposed method detects power fluctuations in a short time.

Why Reduced Inspiratory Pressure Could Determine Success of Non-Invasive Ventilation in Acute Hypoxic Respiratory Failure.

The magnitude of inspiratory effort relief within the first 2 hours of non-invasive ventilation for hypoxic respiratory failure was shown in a recent exploratory clinical study to be an early and accurate predictor of outcome at 24 hours. We simulated the application of non-invasive ventilation to three patients whose physiological and clinical characteristics match the data in that study. Reductions in inspiratory effort corresponding to reductions of esophageal pressure swing greater than 10 cmH2O more than halved the values of total lung stress, driving pressure, power and transpulmonary pressure swing. In the absence of significant reductions in inspiratory pressure, multiple indicators of lung injury increased after application of non-invasive ventilation. Clinical Relevance- We show using computer simulation that reduced inspiratory pressure after application of noninvasive ventilation translates directly into large reductions in multiple well-established indicators of lung injury, providing a potential physiological explanation for recent clinical findings.

An Advanced Transmission Line Protection Algorithm to Detect Power Swing and Fault Using Speedy Wavelet

An Advanced Transmission Line Protection Algorithm to Detect Power Swing and Fault Using Speedy Wavelet

Numerical Analysis of Water Jet Injection in the Draft Tube of a Francis Turbine at Part Load Operations

Abstract The off-design operation of Francis turbines results in the onset of flow instabilities. These instabilities lead to severe pressure pulsations, power swings, fatigue damage, and torque fluctuations in the turbine unit. Axial water jet injection in the draft tube is a relatively recent method proposed to reduce the detrimental effects of flow instabilities on turbine performance. However, its efficacy at different operating points needs to be ascertained before implementing in actual prototype turbines. This work reports the findings of numerical investigations performed with water injection at three different part-load conditions. These operating points represent distinct flow regimes in the draft tube. The effect of water injection on the velocity and pressure fields in the draft tube is investigated. The results indicate that the water jet strongly influences the turbine performance at part-loads involving a precessing vortex rope. However, little influence of water jet is observed at deep part-load operation. The interaction of the jet with the draft tube bend is also investigated. The results show that the amount of water jet needs to be cautiously controlled as higher water jet injection impacting the bend may deteriorate the performance. The influence of water jet injection on the pressure recovery, power output, and efficiency of the turbine unit is also reported.