Unstable Swing Research Articles

Improved Control Technique for Enhancing Power System Stability in Out-of-Step Conditions

From time to time, a series of unpredictable and conflicting contingencies can lead to angular instability of the power system and even blackouts if not adequately handled by an out-of-step (OOS) protection system. The key contribution of this research work, to the theory of out-of-step protection, is the identification and isolation after a given disruption of many unstable swings. This paper presents a proposed method to avoid false operation for distance function by out-of-step blocking to improve the system stability by using optimally placed PMUs for the fast detection of system analogue quantities. The studies were performed on a modified Eskom transmission network in the Western Cape with 765 kV and 400 kV voltage levels. The aim is to investigate the IEC 61850-90-5 standard for predictive dynamic stability maintaining systems using PMUs for out-of-step conditions of synchronous generators. The power system modelling and simulation are performed in the RSCAD-FX for the proposed multi-area power system network. An experimental lab-scale implementation is built to test the proposed out-of-step algorithm in a real-time digital simulator. Software-based PMU is incorporated to test and validate the IEC 61850-90-5 standard sampled values. Simulation and experimental results are presented.

A non-PMU-based WAN protection scheme for swing detection and stability enhancement in power systems

This paper presents a scheme for power swing detection and stability assessment for multi-machine power systems in addition to a brief survey on that topic. The scheme adopts smart grid perception. It is an asynchronous scheme that uses the rate of change of the angle of the generator bus voltage instead of synchronously estimating the absolute rotor angle value for stability assessment. Therefore, it does not require phasor measurement units (PMUs). Instead, it uses commercially available intelligent electronic devices (IEDs). It introduces a new application of the multicast Generic Object Oriented Substation Event (GOOSE) protocol or its routable version (R-GOOSE) to reflect the disturbance in the power grid on the transmission pattern of data packets over the grid data network. In this scheme, the angle change information is transmitted in the form of GOOSE packets simultaneously from the IEDs that readily measure the angles of the affected generators. On the other hand, the detecting device identifies the stability status of each affected generator. The proposed scheme is validated by simulating disturbances on the IEEE 39-bus system. The results show that the scheme can discriminate between stable and unstable swings. In addition, the loss of synchronism of the unstable generator is predicted ahead of its occurrence by enough time to take an appropriate action.

Transient Potential Power Based Supervisory Zone-1 Operation During Unstable Power Swing

Unstable power swing (UPS) may cause unwanted zone-1 tripping. This is caused due to presence of electrical center within the reach of zone-1 of distance relay. Fast detection of unstable swing can assist distance relay in taking reliable decision. This paper suggests a new coordinate system with transient potential power as the y -coordinate and angular difference of positive sequence voltage phasors across the transmission line ( ${{\boldsymbol{\delta }}_{{\boldsymbol{\text{SR}}}}}$ ) as the x -coordinate. We observed that this coordinate system can be useful to successfully differentiate an UPS from stable power swing (SPS) and three phase fault. The prediction is fast enough to prevent an unwanted zone-1 operation of distance relay. IEEE-39 bus New England test system is used to validate the proposed scheme. The suggested method showed improved and fast unstable swing detection accuracy under different pre-disturbance and fault conditions.

Dynamic State Estimation Assisted Out-of-Step Detection for Generators Using Angular Difference

Out-of-step detection methods for generators depend on impedance measurements that are mapped from the angular difference between the generator source and the Thevenin equivalent of the interconnected system. Though implemented successfully with decades of operating experience, the mapping is not the most accurate due to a simplified model. This paper proposes an improved out-of-step detection method for generators by means of the most direct indicator—angular difference. The generator's rotor angle is estimated with a particle filter-based dynamic state estimator and the angular separation is then calculated by combining the raw local phasor measurements with this estimate. The method is also enhanced with the real-time stability analysis that is able to predict marginally unstable swings. The approach is illustrated via dynamic simulations on the New England 10-generator, 39-bus system. While consistent with the traditional schemes for out-of-step detection, the proposed method is advantageous in that it does not make any simplifying assumptions in its formulation, and provides early detection for unstable swings resulting in reduced stresses on the breaker and generator. The proposed approach shows great potential to supervise the conventional relay with availability of synchrophasor measurements and computational power.

PERFORMANCE ANALYSIS AND IMPROVEMENT DESIGN OF GOLF CLUBS

Recently, golf has become a very popular sport, and most golfers focus on improving their skills and learning process. However, many researchers have studied and found that the hardness and vibration frequency of golf club, and the weight and angle of club head can result in unstable swing distance and accuracy. The golfers modify their swings attitude to adapt to the equipments, or even change the club set, and sometimes these situations cause sports injuries to golfers. Therefore, this study discusses how to design an optimal club set for individual golfers by customization and decreases the cases of sports injuries. The Taguchi method is applied to analyze and design the optimum club for shaft hardness, club head weight, spine and grip weight. The improved club is tested, and the result shows that the driving distance is increased by more than 10%, so that the maximum efficiency of hitting is increased. This study provides important reference for design of golf clubs.

Intelligent Power Swing Detection Scheme to Prevent False Relay Tripping Using S-Transform

Abstract Distance relay design is equipped with out-of-step tripping scheme to ensure correct distance relay operation during power swing. The out-of-step condition is a consequence result from unstable power swing. It requires proper detection of power swing to initiate a tripping signal followed by separation of unstable part from the entire power system. The distinguishing process of unstable swing from stable swing poses a challenging task. This paper presents an intelligent approach to detect power swing based on S-Transform signal processing tool. The proposed scheme is based on the use of S-Transform feature of active power at the distance relay measurement point. It is demonstrated that the proposed scheme is able to detect and discriminate the unstable swing from stable swing occurring in the system. To ascertain validity of the proposed scheme, simulations were carried out with the IEEE 39 bus system and its performance has been compared with the wavelet transform–based power swing detection scheme.

Prospective dynamic balance control during the swing phase of walking: Stability boundaries and time-to-contact analysis

This study examined the prospective control of the swing phase in young healthy adults while walking at preferred speed over unobstructed ground and during obstacle clearance. Three aspects of swing were examined: (1) the relation of the body Center of Mass (CoM) to the stability boundaries at the base of support; (2) a dynamic time-to-contact analysis of the CoM and swing foot to these boundaries; and (3) the role of head movements in the prospective control of gait and field of view assessment. The time-to-contact analysis of CoM and swing foot showed less stable swing dynamics in the trail foot compared to the lead foot in the approach to the unstable equilibrium, with the CoM leading the swing foot and crossing the anterior stability boundary before the swing foot. Compensations in temporal coupling occurred in the trail limb during the late swing phase. Time-to-contact analysis of head movement showed stronger prospective control of the lead foot, while fixation of the field of view occurred earlier in swing and was closer to the body in the obstacle condition compared to unobstructed walking. The dynamic time-to-contact analysis offers a new approach to assessing the unstable swing phase of walking in different populations.

Power swing and voltage collapse identification schemes for correct distance relay operation in power system

The new techniques were presented for preventing undesirable distance relay maloperation during voltage collapse and power swings in transmission grids. Initially, the work focused on the development of a fast detection of voltage collapse and a three-phase fault at transmission lines by using under impedance fault detector (UIFD) and support vector machine (SVM). Likewise, an intelligent approach was developed to discriminate a fault, stable swing and unstable swing, for correct distance relay operation by using the S-transform and the probabilistic neural network (PNN). To illustrate the effectiveness of the proposed techniques, simulations were carried out on the IEEE 39-bus test system using the PSS/E and MATLAB software.

Gait Impairments in Persons With Multiple Sclerosis Across Preferred and Fixed Walking Speeds

Remelius JG, Jones SL, House JD, Busa MA, Averill JL, Sugumaran K, Kent-Braun JA, Van Emmerik RE. Gait impairments in persons with multiple sclerosis across preferred and fixed walking speeds. ObjectivesTo investigate (1) whether previously observed changes in gait parameters in individuals with multiple sclerosis (MS) are the result of slower preferred walking speeds or reflect adaptations independent of gait speed; and (2) the changes in spatiotemporal features of the unstable swing phase of gait in people with MS. DesignCross-sectional study assessing changes in gait parameters during preferred, slow (0.6m/s), medium (1.0m/s), and fast (1.4m/s) walking speeds. SettingGait laboratory with instrumented walkway and motion capture system. ParticipantsMS group with mild to moderate impairment (n=19, 16 women) with a median Expanded Disability Status Scale score of 3.75 (range, 2.5–6), and a sex- and age-matched control group (n=19). InterventionsNot applicable. Main Outcome MeasuresGait speed, stride length, stride width, cadence, dual support time, swing time, and timing of swing foot and body/head center of mass during swing phase. ResultsIndividuals with MS walked at slower preferred speeds with longer dual support times compared with controls. In fixed-speed conditions, dual support times were longer and swing times were shorter in MS compared with controls. Stride width was wider for all speed conditions in the MS group. In fixed-speed conditions, the MS group positioned their head and body centers of mass closer to the anterior base of support boundary when entering the unstable equilibrium of the swing phase. ConclusionsLonger dual support time is part of a gait strategy in MS that is apparent even when controlling for the confounding effect of slower preferred speed. However, a gait strategy featuring longer dual support times may have limitations if potentially destabilizing swing dynamics exist, which especially occur at walking speeds other than preferred for people with MS.

Intelligent detection of unstable power swing for correct distance relay operation using S-transform and neural networks

The conventional power swing schemes used in distance relay operation are not fast enough to detect and distinguish a fault, stable swing and unstable swing and this may lead to unintended tripping of protection devices. Therefore, there is a need for fast detection of unstable swings so as to improve the reliability of distance relay operation. This paper presents an intelligent approach for detecting unstable swings during distance relay operation using the S-transform signal processing technique and artificial neural networks. To illustrate the effectiveness of the proposed approach, simulations were carried out on the IEEE 39 bus test system using the PSS/E software. Test results showed that the proposed approach using S-transform, multi layer perceptron network and probabilistic neural network can accurately detect and classify fault, stable swing, unstable swing, fault clearance and post fault events for correct distance relay operation.

Analysis of Angle Stability Problems: A Transmission Protection Systems Perspective

Postfault rotor angle oscillations lead to power swings. Both unstable and stable swings can induce distance relay tripping. For unstable swings, a new computational procedure to locate all of the electrical centers is developed. It simplifies the work associated with visual screening of all the R-X plots. For stable swings, a generic three-tier hierarchy of stability-related norms defined by branch norm, fault norm, and system norm is proposed. Ranking by branch norm leads to ranking of power swings. Ranking by fault norm leads to ranking of faults or contingencies. Magnitude and rate of change of system norm can be used to detect an out-of-step condition. Results on a ten-machine system and a utility system with detailed models are also presented.

A study of loss-of-excitation relaying and stability of a 595-MVA generator on the Detroit Edison system

This paper describes the investigation and evaluation of relationships between loss-of-excitation/field (LOF) relaying and stability of a 595-MVA generator on the Detroit Edison system. Need for the formulation of a plan of action to promote a reliable application of LOF relays is made evident. Operating guidelines are suggested which will safeguard the generator and system from damage during unstable swings while avoiding inadvertent generator tripping during stable swings. In addition, an examination of operating characteristics of a loss-of-field relay in response to changes in voltage and frequency is presented.

Conemaugh Project New Concepts for 500-kV System Protection

The Conemaugh 500-kV system stability studies indicated that stability was achieved for all faults that were cleared in 4.5 cycles. If a breaker fails to clear a 3-phase fault, it is necessary to resort to a breaker failure timing scheme of 7.5 cycles and to down grade the fault to a single phase-to-ground fault by independent pole operation of the circuit breaker in order to maintain stability. To cover abnormal conditions when instability may still occur, out-of-step relays on generators are being applied to trip the unit when the first unstable swing appears in the unit transformer.