On-line power system inertia calculation using wide area measurements

Future developments in power systems, e.g. relatively larger generator sets, the virtual power plant and synthetic inertia concept and connection of generation assets over inverters, will cause the system inertia to vary significantly. During system operation, if the inertia of the system is significantly lower than anticipated at the planning stage, then the existing, deterministic protection and control may fail to ensure system stability. Therefore, the ability to accurately determine the inertia of individual system areas, and the system as a whole, online would be very useful. In this paper, an Inertia Calculation Application (ICA), which could be implemented as part of a Wide Area Monitoring Protection and Control scheme, is presented. The necessary wide area measurements must be processed during large disturbances to the active power balance of the system. The ICA has been validated by using computer simulations, under laboratory conditions and by using real-life data recorded by a transmission system operator

Increased energy in stable dry-band arcs due to length compression

The occurrence of dry-band arcs on outdoor composite insulators can degrade the polymeric materials' surface and ultimately may lead to insulator failure. The degradation processes are generally considered as aging effects occurring over long periods of time, from years to decades. In this paper, it is shown that if a stable dryband arc is physically compressed in length by external forces, such as electrolyte deformation due to wind or gravity, the arcing activities will become more severe. This in turn, may accelerate the degradation into a short time-frame hazard. A series of experiments are carried out to investigate the electrical characteristics of the arcs as they become compressed. In this case experiments are performed on silicone rod insulators at controlled angles to the horizontal. Rapid aging is observed after such events. Measurements of arcing period, peak current, and arc resistance during the arcing compression process are analyzed. Based on the experiments, a 'Double Sinusoidal Model' is developed to simulate the current-voltage characteristics of dryband arcing during its compression. Both experiment and simulation show that arc power, arc energy and corresponding energy density will dramatically increase if arc compression occurs, which may lead to more rapid and serious damage on composite insulator surfaces than is experienced otherwise. It is suggested that aggressive erosion events may occur in short periods of time within extended test regimes or entire service histories. © 2010 IEEE

Robust Hybrid Linear State Estimator Utilizing SCADA and PMU Measurements

This paper intends to improve the accuracy of power system State Estimation (SE) by introducing a hybrid linear robust state estimator. To this end, automatic bad data rejection is accomplished through an M-estimator, i.e. a Schweppe-type estimator with Huber loss function. The method of Iteratively Reweighted Least Squares (IRLS) is used to maximize the likelihood function in the M-estimator. Leverage measurements are also treated by a simple yet effective formulation. To run the algorithm for real-world large-scale grids, cumbersome construction of the Jacobian matrix at each iteration is avoided. In addition, convergence to the local minima faced in the large-scale Gauss-Newton algorithm is not a concern as the proposed formulation is linear with no approximation. As observability and redundancy considerations mandate SE to take advantage of traditional SCADA measurements along with available PMU measurements, the linearity of the proposed SE formulation is guaranteed regardless of whether PMU-only, SCADA-only or hybrid SCADA/PMU measurements are utilized. In this regard, covariance matrix for measurements weights is derived for both types of measurements. Thanks to the linear formulation and therefore swiftness of the proposed algorithm, SE could be run for different power systems with a few up to thousands of buses

Local Frequency-Based Estimation of the Rate of Change of Frequency of the Center of Inertia

This letter proposes a novel technique for estimating the rate of change of frequency (RoCoF) of the center of inertia (CoI) in power systems. To offer a holistic picture of the system's frequency response, the proposed technique requires local frequency at the point of measurement, only. This enables the local estimation of active power deficit following a loss of generation (LoG) event, thus facilitating fast and effective remedial action. Extensive simulations conducted verify the effectiveness and applicability of the proposed technique

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 (SoSR) 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

Online Non-iterative Estimation of Transmission Line and Transformer Parameters by SCADA Data

Utilization of various measurements provided by supervisory control and data acquisition (SCADA) system has recently attracted increasing attention. Real-time estimation of transmission line parameters, utilizing voltage and power flow measurements provided by remote terminal units (RTUs) located at line terminals, has been investigated. This paper significantly improves the existing approaches by introducing a novel linear formulation of the problem, which can be solved in a closed form. The distributed-parameter model of long transmission lines is considered and its parameters are estimated in a noniterative manner using traditional SCADA measurements. The new method is further extended to estimate transformer series impedance and tap position using SCADA measurements, linearly. As such, the shortcomings associated with the previously proposed iterative approach, e.g. concern over convergence, for transmission line parameters are avoided. Moreover, the novel technique for estimating transformer parameters allows to determine the tap position as well as updated transformer series impedance. Furthermore, a thorough analysis is presented to take the measurement accuracy into account. Simulation results for different transmission lines and transformers in the IEEE 118-bus test system are reported. The results obtained indicate successful performance of the proposed algorithms

Impact of load dynamics on torsional interactions

This paper evaluates the impact of load dynamics on torsional interactions by considering a mix of static and dynamic loads aggregated at the bulk transmission level. This is essential to investigate the importance of detailed load modelling for subsynchronous resonance (SSR) studies to accurately assess damping contribution and capture system dynamics. SSR interaction with dynamic loads is investigated for both direct on line and drive connected motor loads. Damping contribution from dynamic loads is also assessed based on their location and size. The interaction of dynamic loads with classical SSR phenomenon is observed and introduced as the new concept of (Subsynchronous Resonance Load Interactions (SSR-LI)). SSRLI assumes critical importance for scenarios where the load and generation centers are in close electrical proximity and impact of loads on torsional damping is significant. Finally, the scope for using existing converter interfaced motors for torsional mode damping has been discussed

On machine learning-based techniques for future sustainable and resilient energy systems

Permanently increasing penetration of converter-interfaced generation and renewable energy sources (RESs) makes modern electrical power systems more vulnerable to low probability and high impact events, such as extreme weather, which could lead to severe contingencies, even blackouts. These contingencies can be further propagated to neighboring energy systems over coupling components/technologies and consequently negatively influence the entire multi-energy system (MES) (such as gas, heating and electricity) operation and its resilience. In recent years, machine learning-based techniques (MLBTs) have been intensively applied to solve various power system problems, including system planning, or security and reliability assessment. This paper aims to review MES resilience quantification methods and the application of MLBTs to assess the resilience level of future sustainable energy systems. The open research questions are identified and discussed, whereas the future research directions are identified