Sami Abdelrahman

Identification of Weak Areas of Network Based on Exposure to Voltage Sags—Part II: Assessment of Network Performance Using Sag Severity Index

This paper presents a new stochastic approach to the comprehensive assessment of the impact of voltage sags on large-scale power networks. The approach takes into account the stochastic nature of power system operation, including load variation, uncertainty of fault clearing time by protection relays, fault rates of network components, and the variation/uncertainty in equipment sensitivity to voltage sags. A new duration zone division method is used to derive sag duration and occurrence frequency based on the stochastic distribution of clearing time required by specific protection systems. The adopted probabilistic representation facilitates estimation of network performance based on a single-event characteristic, sag severity index (SSI), developed in the companion paper (Part I). Based on SSI, a new single-site index with respect to voltage sags (bus performance index BPIS) is developed to comprehensively represent the overall bus performance with respect to voltage sags. The index is used to identify the areas of the network, called weak areas of the network in this paper, containing buses that are most exposed to potentially disruptive voltage sags. The application, robustness, and sensitivity of BPIS are thoroughly analyzed and discussed in the paper.

Identification of Weak Areas of Power Network Based on Exposure to Voltage Sags—Part I: Development of Sag Severity Index for Single-Event Characterization

This paper presents a new single-event characteristic, sag severity index (SSI), derived with respect to equipment sensitivity to voltage sags. It is more inclusive of associated uncertainties/variation in equipment response to voltage sags than existing single-event characteristics. By changing parameter settings, the index appropriately accounts for sag duration and adequately addresses the variation in equipment sensitivity. The value of the index changes continuously at the joining regions of different sag severity levels and reflects realistically the sensitivity trend of equipment embedded in voltage tolerance curves. The properties of the SSI are analyzed and discussed through comparison with characteristics of five previously reported single-event indices including four numerical indices and one fuzzy voltage sag index.

Global assessment of power quality performance of networks using the analytic hierarchy process model

Power Quality is one of the critical issues when operating contemporary distribution networks. The increased interest in PQ is due to the increased employment of sensitive equipment loads and renewable generation technologies. Currently, the evaluation of PQ network performance is based on evaluating different phenomena separately, and a standardised way to evaluate the PQ as a whole for a bus or a network is yet to be applied or widely accepted. The paper presents a methodology for combining the performances of different PQ phenomena and expressing the PQ performance of a bus using a single index. The proposed methodology adopts an Analytic Hierarchy Process (AHP) model to combine the harmonics, unbalance and voltage sag performances in one proposed index; i.e. Compound Bus PQ Index (CBPQI). The separate and cumulative PQ performances of a 295-bus generic distribution network were evaluated, compared and demonstrated using heat maps.

Probabilistic assessment of the impact of distributed generation and non-linear load on harmonic propagation in power networks

The paper investigates the uncertainties involved in the assessment of annual harmonic performance of a distribution network with distributed generation and non-liner loads. Considering a random variable locations and injections of harmonic sources, both generation and load, a probabilistic assessment of harmonic propagation through the network is performed. The influence of variable and diverse distributed generation in particular is clearly documented.

Assessment of Power quality performance in distribution networks part I - Measurement campaign and initial analysis

Power quality (PQ) is a raising concern in distribution grids of modern industrialized countries. The PQ monitoring activities of distribution system operators (DSO) and consequently the amount of PQ measurement data increases continuously. To keep the routine assessment of PQ levels efficient, new and automated tools for validating, analysing and visualizing these data are required. The paper illustrates the challenges of processing long-term PQ monitoring campaigns by using measurement data at 8 different sites in public low voltage (LV) networks for more than one year (64 weeks). The paper is divided into two parts. The first part describes the measurement campaign, the pre-processing of the data and an easy and flexible way for routine compliance assessment. The second part is dedicated to the comparison of two different global PQ indices for assessing an average site performance as basis for e.g. benchmarking purposes.

Assessment of Power Quality performance in distribution networks part II - Performance Indices and ranking of network buses

Power Quality has become one of the main measures of distribution network operation evaluation. Utilities and customers monitor the different PQ aspects for benchmarking and compatibility check. This is a second part of a paper that investigates a long term PQ measurement campaign. In this part, global PQ indices are applied to combine a number of PQ phenomena indices into one number that represents the PQ performance of a site. Two global PQ indices are applied on 64-week PQ measurements of 8 sites. The indices are compared in terms of the final rank of sites. Different levels of flexibility are introduced to the indices to consider a variable importance or priority of the phenomena and sites.

Study of harmonic propagation in transmission networks with high penetration of power electronics devices

Power Quality (PQ) disturbances result in significant financial losses to both network operators and end users. With the increasing regulatory requirement to monitor and improve PQ, the mitigation of PQ disturbances becomes even more important. This paper focuses on assessment of the harmonic performance at transmission network level considering increasing presence of stochastic and intermittent power electronics (PE) interfaced distributed generation (DG) in the network. A number of case studies considering different levels of penetration and types of DG are performed attempting to correlate the level of DG penetration with the harmonic performance. The propagation studies are performed using probabilistic harmonic load flow. The network model adopted for the studies is 68-bus of the New England Test System and the New York Power System.