Emanuele Ciapessoni

An Integrated Platform for Power System Security Assessment Implementing Probabilistic and Deterministic Methodologies

Power system security assessment both for planning (off-line) studies and for operational (on-line) applications is performed by various analysis methods which highlight different phenomena (steady-state violations, angle stability, voltage stability, etc.) in order to retrieve an exhaustive vision of the problems. Besides traditional deterministic tools, recently proposed probabilistic tools may highlight new interesting security aspects by introducing the concepts of probability and quantifying the risk associated with the contingencies. This paper proposes the overall architecture of a security assessment platform which integrates both probabilistic and deterministic methodologies in a simple environment.

An integrated framework for power and ICT system risk-based security assessment

The vulnerability of power systems to natural and man-related threats, as well as their increasing dependency on ICT systems and uncertainties of influent factors, urge to adopt integrated approaches for security assessment and control. Moreover, the need to analyze high impact events (causes of past blackouts) calls for the adoption of the risk concept to perform more in-depth security analyses. The present paper describes a probabilistic risk-based methodology, developed within the EU research project AFTER, aiming to perform risk assessment (including hazard, vulnerability, and impact analysis) of the integrated power and ICT systems. The paper focuses on the steps to build the assessment framework based on: threat/vulnerability identification and classification, contingency modeling, power system response modeling and computation of risk indicators for operation and operational planning purposes.

Dependability Analysis of Power System Protections using Stochastic Hybrid Simulation with Modelica

This paper addresses the dependability analysis of protection schemes of transmission grids using a computer simulator. Following modern protection schemes, a stochastic hybrid model has been developed in Modelica/Dymola environment. The model supports the evaluation of required dependability on the basis of suitable probability indices. A different simulation strategy has been implemented and its main features are discussed in detail. A logging tool has been created to supervise discrete events and assist in the results analyses. Furthermore, a custom simulation control panel helps to manage and to launch the simulation outside the Modelica environment.

Monitoring of frequency disturbances in the European continental power system

Generation from non-programmable renewable energy sources, which is endowed with dispatching priority but is not always required to participate in ancillary services, has massively increased its share of demand supply in recent years; thus, a reduced number of large conventional power plants is left to be dispatched. Therefore, active power imbalances in AC power systems can lead to more severe frequency transients (minimum/maximum instantaneous and quasi-steady-state deviations), since less operational reserves are available to contain frequency deviations and less rotating machine inertia is online to reduce the absolute value of the Rate Of Change Of Frequency (ROCOF); thus, frequency stability can be jeopardized. This paper describes some results of an experimental activity focused on the measurement of system frequency and of the ROCOF. The main features of the measurement algorithms are presented. Statistical analyses of the data collected at a low-voltage node in the European continental interconnected system over a one-year time interval are reported. A preliminary analysis of large power plant outages impacting on frequency behavior is shown.

Extended risk analysis of power and ICT systems

Power system (PS) response to natural and man-related threats is subject to a large set of uncertainties regarding both the initial conditions of the system and the vulnerabilities of the Power and ICT systems to the threats themselves. This fact, together with the need to analyze high impact events (typical causes of blackout events), calls for the adoption of novel techniques to perform more in-depth security analyses. The paper describes a probabilistic risk-based methodology, developed within the European Union (EU) research project AFTER (A Framework for electrical power sysTems vulnerability identification, dEfense and Restoration)1, which aims to perform risk assessment (including hazard, vulnerability, and impact analysis) of the integrated power and Information and Communication Technology (ICT) systems. Starting from threat/vulnerability identification and classification, and contingency scenario modeling, the paper focuses on the probabilistic simulation of the Power and ICT System response to the contingencies as well as on the computation of risk indicators for operation and operational planning purposes.

Assessing the impact of multi-terminal HVDC grids for wind integration on future scenarios of a real-world AC power system using grid code compliant open models

The exploitation of multi-terminal (MT) HVDC (High Voltage Direct Current) grids for offshore wind farm integration into continental bulk AC system raises several technical issues, in particular the verification of the compliance of MTDC grids and offshore wind parks to the performance requirements (in terms of frequency, voltage support and fault ride through) which are being established by the grid codes, and the availability of general and customizable models to simulate their response. The goal of this work is to provide a set of “open” general models, able to fulfill the grid code requirements if suitably tuned, enabling the TSOs to perform their analyses without relying exclusively on vendor-specific models. In order to verify the realistic response of these models, an example of MTDC grid is simulated, connecting it to several plausible operating scenarios of a real world AC system (the West Denmark grid) in target year 2020: after a preliminary N-1 static security assessment study on the integrated AC/DC system, some simulations are performed to check the fulfillment of grid code requirements in case of typical contingencies.

Probabilistic assessment of Net Transfer Capacity considering forecast uncertainties

In transmission system planning, researchers propose methods to assess the effect of uncertainties of power system operating condition due to forecasting errors of intermittent generation and loads. In particular probabilistic power flow methods are used to calculate the probability distributions of the voltages and the branch currents, starting from the distributions of power injections/absorptions. These uncertainties play a key role in the operational planning of power systems, as certain configurations of load and intermittent generation can cause security problems. This paper aims to propose a probabilistic methodology to assess Net Transfer Capacity (NTC) among network areas, which quantifies forecast error uncertainties by applying the Point Estimate Method (PEM) combined with Third Order Polynomial Normal (TPN) Transformation. This approach is compared with a conventional NTC assessment technique and has been tested on an IEEE test system.

Wide area system Protection Scheme design with an Artificial Intelligence approach considering communication constraints

An approach for the design of a Special Protection Scheme (SPS) is presented, based on Artificial Intelligence and probabilistic techniques. In detail, the aim of the SPS is to maintain the synchronism of a power plant after grid outages. To improve the SPS design, the impact of communication delays is accounted for in a probabilistic way. The SPS control logic, deciding how much power to curtail in order to keep system stability, is implemented with Decision Trees and, alternatively, with Support Vector Machines. As a test case, a portion of the IEEE 39-bus grid with a Wide Area Measurement System, based on Phasor Measurement Units, is studied. The effectiveness of the designed logic is evaluated in terms of the probability of system instability, which is derived from the Probability Density Functions of the communication delay and of the Critical Delay Time, i.e. the maximum acceptable delay of the SPS action to keep the system stable. The results yield guidelines to design communication systems which, although including further delays due to packets cryptography, minimize the probability of failure of the SPS action.

Assessing security of power and ICT systems via a risk-based approach within an integrated framework

The increasing vulnerability of modern power systems to both natural and man-related threats, as well as their increasing dependency on ICT systems makes it convenient to adopt integrated approaches for security assessment and control. Moreover, the need to analyse extreme, low-probability events (from which many blackouts originated in the past) calls for the adoption of the risk concept to perform more in-depth security analyses. The present paper describes a probabilistic risk-based methodology, developed within the EU research project called AFTER, aimed to perform risk assessment (including hazard, vulnerability and impact analysis) of the integrated electrical power and ICT systems. The paper focuses on the steps to build the assessment framework (threats/vulnerabilities identification and classification, contingency modeling, power system response modeling and computation of risk indicators for operation and planning purposes).

An innovative risk control strategy in power systems involving advanced HVDC networks

In the context of power system operation, probabilistic techniques not only can provide a deeper insight into security aspects, by quantitatively considering power system uncertainties and contingency impact, but they can also be helpful to identify and suggest operators the most adequate control actions to reduce operational risk. This paper proposes an innovative risk-based strategy to control the operational risk of High-Voltage Alternating Current (HVAC) power systems connected to Multi-Terminal High-Voltage Direct Current (MT HVDC) networks like those envisaged for the integration of future, large off-shore wind farms. The proposed method minimizes the operational risk by minimizing the overall costs to re-dispatch both conventional generation and power injections from MT HVDC network, also taking into account the operating limits of the HVDC network (in particular, cable current limits). Results of the methodology applied to an IEEE test system and on a realistic power system are presented and discussed, and some conclusions are drawn.