Atia Adrees

Optimal Compensation of Transmission Lines Based on Minimisation of the Risk of Subsynchronous Resonance

The paper proposes a framework for the selection of optimal configuration of line compensation devices, thyristor controlled series capacitors (TCSC) and conventional fixed series capacitors, for reducing the risk of subsynchronous resonance (SSR) in the network while maintaining required power transfer. The methodology developed in the paper is based on the robust risk evaluation of SSR that takes into consideration the severity of subsynchronous resonance and probability of its occurrence. The subsynchronous resonance risk index developed previously is used to assess the severity of subsynchronous resonance. The line outage model is employed to determine the probability of contingencies potentially leading to subsynchronous resonance. It is demonstrated that with relatively small participation of TCSC, even with the most basic control, in series compensation of lines, the risk of SSR can be successfully managed.

Identifying Generators at Risk of SSR in Meshed Compensated AC/DC Power Networks

The paper presents a methodology to identify generators at risk of subsynchronous resonance (SSR) in meshed AC/DC networks. Two risk indices are developed to rank generators based on the level of exposure to SSR. One of them measures the severity of subsynchronous torsional interactions, and the other indicates the gravity of transient torque problem. It is shown that proposed indices can be used to identify generators in the network that are at the risk of experiencing high mechanical torques due to SSR and to rank them based on severity of potential exposure to SSR. The methodology is demonstrated on meshed 16-machine, 68-bus IEEE test network with different series compensation levels of AC lines, asymmetrical compensation and voltage source converter (VSC) based HVDC lines. Finally, electromagnetic transient simulations are used to verify the ranking of generators obtained using developed indices.

Methodology for Evaluation of Risk of Subsynchronous Resonance in Meshed Compensated Networks

This paper proposes a methodology for evaluation of risk of subsynchronous resonance (SSR) in meshed compensated AC networks. The developed methodology takes into account the severity of SSR problem in different network configurations caused by fixed series compensation and probabilistic behavior of the power systems due to random outages of the lines. SSR risk evaluation considers severity of SSR problem, probabilities of different network configurations for different contingencies and different operating conditions of turbine generator. Probability of each contingency is determined through line outage model while the probabilities of different operating conditions are calculated from multilevel load duration curve. Using developed risk matrix, it is demonstrated that the degree of risk of SSR that the generators in the network are exposed to can be evaluated for different network configurations, different contingencies and different line compensation levels.

Risk-based framework for assessment of operational constraints for power systems focusing on small-disturbance stability and sub-synchronous resonance

This paper presents a risk-based framework to establish operational constraints for modern power systems. The methodology is established and subsequently applied to two areas of power system analysis - small-disturbance stability and sub-synchronous resonance (SSR). In the first case, probability density functions (pdfs) for critical oscillatory electromechanical modes are established based on the stochastic variation of system uncertainties such as generation and loading. These pdfs provide probabilities of unstable or poorly damped oscillations that are evaluated using risk-based approaches. For SSR analysis, frequency scans are completed to identify generators which are at risk of experiencing high mechanical torques. In both cases, evaluation using severity functions is used to ensure that acceptable levels of risk are not exceeded. The proposed methods are demonstrated using a meshed power system with capacitor series compensated AC tie lines.

Study of subsynchronous resonance in meshed compensated AC/DC network

The paper investigates the risk of subsynchronous resonance (SSR) in meshed power networks with compensated AC lines operating in parallel to voltage source converter (VSC) HVDC lines. Different compensation levels of AC line, different power transfer through VSC HVDC line and various contingencies are considered to assess the risk of mechanical torques amplification in turbine shaft due to SSR. Both, active and passive compensation of AC lines are considered.

A framework to assess the effect of reduction in inertia on system frequency response

This paper presents a framework to analyze the impact of different penetration levels of renewable generation sources (RES) and consequent reduction in inertia on grid frequency. The developed methodology is demonstrated using three operating conditions of the network. For each operating condition, the decrease in the network loading is balanced by disconnecting a part of synchronous generation. To establish the critical penetration levels of renewables and inertia limits for the grid frequency, the uncertainty of loads, intermittent and stochastic patterns of RES generation around each operating condition are simulated. The results clearly identify the critical penetration levels of RES and reduction in inertia limits of the system for frequency stability. In addition, the performed analysis quantifies the effect of primary frequency response and reduction in inertia on frequency nadir. The proposed framework is applied to the modified 16 machine and 68 bus network.

Study of frequency response in power system with renewable generation and energy storage

This paper presents the first comparative analysis of frequency support provided by a large-scale bulk energy storage system (ESS) against distributed ESS in a large meshed network. In IEEE 16 machine network, 30% of synchronous generation is replaced by renewables (RES). The analysis is further extended to investigate the effect of increased penetration of RES and reduction in inertia by decreasing synchronous generation at low network loading conditions for both types of ESS arrangements.

Probabilistic assessment of transient stability in reduced inertia systems

A probabilistic approach to assess the transient stability of power systems with increased penetration of wind and Photo-Voltaic generation is presented in this paper. The impact on transient stability due to the intermittent behavior of Distributed Energy Resources (DERs) as well as due to their dynamic response when a disturbance happens is investigated. Moreover, the effect of conventional generation disconnection and consequently inertia reduction is studied. Apart from calculating transient stability related indices, a clustering technique is also applied to provide more information considering the impact of DERs and conventional generation disconnection on transient stability.

The influence of different storage technologies on large power system frequency response

This paper investigates the contribution of energy storage systems to the system frequency response in a large meshed transmission system. The case studies compare the contribution of two types of energy storage technologies, i.e., battery energy storage system (BESS) and flywheel energy storage system (FES), to improve frequency response in the test network. Case studies examine the effect of different type of disturbance on frequency response in the presence of each type of storage technology. The effect of one bulk energy storage and distributed energy storage systems of the same capacity on frequency response of the power system is also investigated.

Impact of energy storage systems on the stability of low inertia power systems

This paper discusses the effect of energy storage systems (ESS) on power system stability. The paper first demonstrates the improvement in frequency nadir with ESS. Following this, the effect of the energy storage system (ESS) on small signal stability is investigated. The analysis is further extended to explore the contribution of ESS to improve transient stability by using the same ESS controls and parameter setting. The results demonstrate as expected that ESS can provide an enhanced primary frequency response to reduce the drop in frequency nadir. Small signal stability analysis shows that frequency control coupled with active power control does not affect the damping of interarea modes while voltage control can reduce the damping of these modes. The results also indicate that ESS installed to provide primary frequency support can also contribute to the improvement of transient stability of the system. The studies are performed in the modified version of IEEE 16 machine, 68 bus network.