Charalambos A. Charalambous

Stray current control in DC mass transit systems

Stray current control is essential in direct current (DC) mass transit systems where the rail insulation is not of sufficient quality to prevent a corrosion risk to the rails, supporting and third-party infrastructure. This paper details the principles behind the need for stray current control and examines the relationship between the stray current collection system design and its efficiency. The use of floating return rails is shown to provide a reduction in stray current level in comparison to a grounded system, significantly reducing the corrosion level of the traction system running rails. An increase in conductivity of the stray current collection system or a reduction in the soil resistivity surrounding the traction system is shown to decrease the corrosion risk to the supporting and third party infrastructure.

A Simulation Tool to Predict the Impact of Soil Topologies on Coupling Between a Light Rail System and Buried Third-Party Infrastructure

The production of stray currents by DC light rail systems leads to the corrosion of the supporting and third-party infrastructure in close proximity to the rail system. This paper simulates two parallel tracks that are occupied by two trains: one on each track. This type of modeling constitutes a case study that is utilized to investigate the effect of soil topologies on the corrosion performance of a floating DC light rail system focusing on the supporting and third-party infrastructure. The modeling technique used involves the accurate computation of the shunt and series parameters for use in a resistive-type model using a commercially available software package. The results demonstrate the importance that soil resistivity has on the corrosion risk to traction system and third-party infrastructure. Such information could ultimately be used to vary the level of stray current protection across a light rail system to ensure a consistent lifetime across the whole system.

Solution of ac/dc power flow on a multiterminal HVDC system: Illustrative case supergrid phase I

This paper presents an algorithm for the sequential solution of the ac/dc power flow, which is proposed for the analysis of multi-terminal HVDC systems (MTDC). This sequential power flow algorithm can be implemented easily in an existing ac power flow package and is very flexible when it compared with unified methods. Gauss-Siedel algorithm is used to solve dc power balance equations, it offers two keys advantages: very fast and simple computational implementation, and errors do not accumulate during the calculation. The algorithm is tested using the WSCC 3-machine, 9-bus system with a 3-terminal MTDC network and results compared with those obtained from DIgSILENT® PowerFactoryTM demonstrating the validity of the proposed algorithm. As aggregate value, a representative test case of the projected scheme for the phase I of the Supergrid project on the North Sea is presented, the proposed approach presented in this paper is used to calculate DC power flows for some scenarios.

Dynamic Stray Current Evaluations on Cut-and-Cover Sections of DC Metro Systems

The tunneling construction in underground DC Metro Systems is mainly based on the bored tunnel method and the cut-and-cover method. Therefore, the stray current assessments and mitigation actions should be tailored according to which method of tunnel construction is used. This paper presents a topologically accurate model for assessing the dynamic stray current picture in cut-and-cover sections of DC metro systems. The dynamic stray current evaluation can provide an indication to the extent of the corrosion problem in the supporting and third-party infrastructures of the system. In this paper, the dynamic evaluations are based on a combination of various ideal and realistic train operation scenarios.

External Lightning Protection and Grounding in Large-Scale Photovoltaic Applications

The development of large-scale photovoltaic (PV) plants in rural areas is constantly increasing. However, the knowledge of performing and installing lightning and surge protection in large-scale PV plants is still premature. The main objective of this paper is to provide a method for assessing the external lightning protection and earthing designs that may be installed in large-scale solar applications. Consequently, the method and models presented in this paper may assist engineers to perform a comparison between the use of isolated and nonisolated lightning protection systems, and second to select suitable surge protection equipment.

2-D Finite-Element Electromagnetic Analysis of an Autotransformer Experiencing Ferroresonance

The key concern for transformers experiencing ferroresonance is whether the energy transferred into the transformer body during core saturation by the nonsinusoidal currents is damaging. Saturation and the consequent incompetency of the core to contain the flux manifests itself as current induced in parts of the transformer body not foreseen to conduct current. Sustained ferroresonance may last for minutes (or even hours), when no intervening operations are carried out, and may cause local overheating and thermally degrade surrounding insulation. In this paper, transient electromagnetic analysis was conducted by using 2-D finite-element models of a 240-MVA 400/132/13-kV autotransformer. As a continuing effort, the main objective of modeling is to visualize the flux flow in parts where transformer designers have not anticipated its presence. A quantitative assessment of the flux, the induced currents, and the power dissipated in these parts has been carried out to determine the degree of risk imposed on a transformer under ferroresonance.

Loss Evaluation and Total Ownership Cost of Power Transformers—Part I: A Comprehensive Method

The key techniques employed in this paper reflect on a comprehensive method for calculating the cost of the electric power and energy needed to supply the life-cycle losses of power transformers. The method is applicable to transformer users who possess their own generation and transmission facilities. The proposed loss evaluation method is based on factors derived from relevant historical and forecasted data that are combined to determine the total ownership cost of power transformers. Finally, in a companion paper, the method is evaluated on a small-scale real system.

Loss Evaluation and Total Ownership Cost of Power Transformers—Part II: Application of Method and Numerical Results

The numerical results detailed in this paper reflect on a method proposed to accurately appraise the energy and the demand component of the cost of losses for evaluating the total ownership cost of power transformers. Specifically, the proposed method is evaluated on a small-scale real system, by incorporating realistic financial data and system characteristics through appropriate technoeconomic models as well as statistical evaluations. The calculated loss components of this paper are compared to the methodology detailed in IEEE C.57.120-1991.

Modeling for Preliminary Stray Current Design Assessments: The Effect of Crosstrack Regeneration Supply

Simulators of different approaches and scales have been reported in the literature in an attempt to investigate the generation and impact of stray currents resulting from the operation of dc rail transit systems. Bearing in mind the existing methods for stray current modeling and control, this paper offers an important modeling advancement. A model is developed to quantitatively assess the more complex stray current picture arising from the effect of crosstrack regeneration supply. Crosstrack regeneration refers to the case where a train in one tunnel is collecting current from a regenerating train in an adjacent tunnel, as a power-saving endeavor.

A Holistic Stray Current Assessment of Bored Tunnel Sections of DC Transit Systems

In considering the stray current design for dc transit systems, the stakeholders should comply with the objective that the stray current design requirement is to minimize the impact of the stray current on the supporting infrastructure and on the third party infrastructure. This paper defines a holistic stray current assessment for bored tunnel sections (BTSs) of dc transit systems, by utilizing a boundary-element platform. The developed method enables the stray current performance of various design options and characteristics to be assessed on the tunnel system. Most important, the methodology proposed offers the means to evaluate the stray current performance of a BTS in terms of its geometry and topology. Finally the postprocessing steps that facilitate the benchmarking of the results against the relevant EN standards are discussed.