Marios N. Moschakis

Analytical calculation and stochastic assessment of voltage sags

In this paper, analytical expressions for the calculation of voltage sag magnitude due to faults at every point of a meshed or radial power network are derived. Balanced and unbalanced faults are considered and the effect of power transformers is taken into account. The following methods for stochastic assessment of voltage sag magnitude are compared using these expressions: the method of critical distances, method of fault positions, and Monte Carlo method. The minimum required number of fault positions and iterations assumed by the two methods in order to achieve results of acceptable accuracy are determined.

A detailed model for a thyristor-based static transfer switch

Industrial customers often suffer from supply voltage interruptions and sags due to the increase in the utilization of sensitive equipment in the process automation and control. An effective way to improve power quality and reliability of sensitive customers is to use a static transfer switch. This device enables a very fast change in the supply of the customer to an alternate feeder providing adequate power conditioning for several power quality problems, such as voltage sags, swells, and interruptions. In this paper, an analytical model of STS is proposed and its performance is verified using the electromagnetic transients for DC (EMTDC) simulation package. Simulations using this model are performed in order to handle voltage sags based on real measurements on an actual industrial customers supply voltage. Different phase angles and magnitudes of the two alternate source prefault voltages and different fault instances are considered.

Considerations for the application of thyristor controlled series capacitors to radial power distribution circuits

This work deals with the application of thyristor controlled series capacitors (TCSCs) suitably rated for radial distribution circuits. The various problems existing on long distribution lines that can be alleviated by the connection of variable series compensation, as a TCSC provides, are discussed. An important feature is the capability of the TCSC to operate as a short circuit current limiter. Thus, sensitive loads connected to nearby substations will not experience any voltage sags caused by faults on the distribution line where the TCSC is connected. The benefits of the connection of a TCSC on a radial distribution system are verified by means of the electromagnetic transients for DC (EMTDC) simulation package.

Adapting EV-microgrid concepts to european grid standards related to power quality

This paper deals with the adaption of Microgrid and Electric Vehicle concepts to European grid standards related to power quality. It presents a review of European norms on power quality issues including converters and EVs. Power quality issues and relevant standards dealing with the operation of EVs are discussed for interconnected and islanded (microgrid) mode of operation. Moreover, a review of connection criteria of Distributed Generation units and power quality requirements in various European countries is listed. Finally, recommendations on the adaption of microgrid-EV concepts to European power quality standards are given.

Impact of Increased RES Generation on Power Systems Dynamic Performance

In this paper, the impact of high wind power and photovoltaics penetration on the dynamic behavior of an island power system like one operates in Crete is investigated. Several simulations were performed leading to the fact that it is possible to achieve higher level of renewable energy sources penetration without significant dynamic security problems, if power units spinning reserve exists and the corresponding control systems have a sufficiently fast response.

Evaluating the Performance of Small Autonomous Power Systems Using Reliability Worth Analysis

The analysis and design of a small autonomous power system (SAPS) that contains renewable energy sources (RES) technologies can be challenging, due to the large number of design options and the uncertainty in key parameters. Renewable power sources add further complexity because their power output may be intermittent, seasonal, and nondispatchable. Due to this characteristic, reliability evaluation of a RES based SAPS cannot be implemented using the traditional deterministic and analytical methods. Moreover, in order to be complete, this evaluation has to be done within a cost-benefit framework. This chapter investigates the effect of reliability worth in the optimal economic operation of SAPS that is based on RES technologies, considering different scenarios. The optimization procedure is implemented with a combined genetic algorithm (GA) and local search procedure. In addition, this chapter examines the effect of considering SAPS components forced outage rate in the obtained optimal solutions via Monte Carlo simulation (MCS). The performance of the proposed optimization methodology is studied for a large number of alternative scenarios via sensitivity analysis, which study the effect on the results due to the uncertainty on weather data and cost data. The results show that the optimal operation of a RES based SAPS depends largely on the consideration of reliability worth as well as the inclusion of components forced outage rate.

Analytical Assessment of DC Components Generated by Renewable Energy Resources with Inverter-Based Interconnection System due to Even Harmonics

This paper deals with the assessment of DC components generated by renewable energy resources with inverter-based interconnection system to the electric grid. DC injection is a critical issue related to power quality of distribution network systems with high penetration of inverter-based interconnection systems. This type of interface systems may improve the performance of the electric generation unit and affect positively or negatively the power quality of the distribution network depending on the proper or improper designation. The investigation of the various causes of DC components and the analytical assessment of their maximum levels are crucial for the proper operation of inverter-based interface systems and the limitation of DC injection. A method based on analytical calculations using a computer software has been implemented for the assessment of DC components contained on an inverters output voltage when even harmonics are present on the network voltage. Moreover, a simulation package was used to demonstrate the existence of DC components under various conditions. It was proved by the current analysis that the amounts of DC components generated when even harmonics are present on the network voltage can be high under abnormalities on the power grid but they are not considerable under normal operating conditions.

Advanced Short-Circuit Analysis for the Assessment of Voltage Sag Characteristics

An advanced assessment of voltage sag characteristics requires analytical mathematical expressions extracted from proper short-circuit analysis. In this document, the procedure for the extraction of those expressions is analytically described. All parameters affecting the response of a power network to a fault are taken into account. The expressions extracted enable the calculation of the during-fault voltage vector for a fault not only at the network’s buses but also at every position within the network. They also enable the drawing of the voltage magnitude or the phase-angle jump in relation with the distance to the fault from the one power line end. Moreover, a simple and effective way to incorporate the phase shift introduced by devices or transformers is proposed. A test network is used for the demonstration of the effectiveness of those expressions and the understanding of voltage sag characteristics.

Effect of Power Line Conductor Resistance-to-Reactance Ratio on Voltage Magnitude during Two-Phase Faults at Electric Energy Grids

This paper deals with the effect of power line impedance characteristics on the retained voltage magnitude after a two-phase fault at electric power distribution or transmission networks. Specifically, the effect of resistance-to-reactance (R/X) ratio of power line conductors or cables on voltage magnitude during two-phase faults is studied with analytical mathematical expressions. The basic aim of this investigation is to create a tool for the automatic recognition of the type and the location of faults on electric power networks.

Adapting Smart Grid, RES Penetration, Electromagnetic Compatibility and Energy Efficiency Concepts to Electric Ship Power Systems

This paper deals with the adaption of Smart Grid, RES penetration, Electromagnetic Compatibility and Energy Efficiency concepts from land to ship power systems. It presents a review on the state-of-art on those areas as regards the land power systems and attempts to propose some of those advances and how they can be adapted to ship power systems. Ship power systems have many resemblances mainly with autonomous land power systems. Thus, autonomous power systems will be used as a model for an accurate and successive adaption of those concepts.