Frank Schettler

Technical Guidelines and Prestandardization Work for First HVDC Grids

This paper presents important results of the European HVDC Study Group founded on an initiative by the German Commission for Electrical, Electronic and Information Technologies in September 2010. The main task of the Study Group has been defining “Technical Guidelines for first HVDC Grids”: 1) to gain a common understanding of basic operating and design principles of HVDC grid systems, and 2) to prepare the ground for more detailed standardization work. The HVDC systems are moving from the stage of point-to-point (PTP) connectors to the stage of the transmission systems interconnecting more than two stations and utilizing multiterminal (MT), multivendor (MTMV) HVDC voltage-source converter (VSC) systems. The development will be modular, for example, in steps, starting with interconnecting PTP connectors and establishing three-pod, radial systems. Then, such simple systems may gradually be interconnected into radial and meshed HVDC-VSC systems comprising more HVDC lines and dc converter stations. This paper describes understanding, specification, and standardization of design and operation principles of the HVDC grids seen as the first needed steps toward such MTMV systems.

Power system problems solved by FACTS devices

AC power transmission started in the late 19th century from low voltage levels and restricted supply areas and changed over time towards larger distances and higher power transfers. Increased transmission voltages have been one important measure making systems capable of meeting growing demands. While in the early days power systems had high reserve capacities economical and environmental constraints gradually increased loading of existing systems closer to their power transfer limits. Long transmission distances, fast changing high power loads and growing interconnection of local area networks imposed new challenges to power transmission like untolerable voltage fluctuations due to load changes, power oscillations, stability issues or unequal load sharing of parallel transmission paths resulting in unnecessary bottlenecks. As the most obvious signs of that changes blackouts of smaller and even larger system supply areas occured. Today power systems face new requirements associated with tremendous changes of the established generation and load structure due to adding renewable energy generation partially replacing conventional power plants at distant locations. New electronically controlled system components were developed and installed to overcome such power system problems. The paper discusses devices for FACTS (Flexible AC transmission systems) like SVCs, TCSCs and VSC-based systems providing fast reactive power compensation and fast controlled active power transfer as key technologies for enforcing power systems and making them able to meet the requirements of today and tomorrow.

Application of SVCs by CenterPoint Energy to address voltage stability issues: Planning and design considerations

CenterPoint energy (CNP) is in the process of installing two SVCs on its transmission system which serves the greater Houston, Texas metropolitan area. Extensive voltage stability assessment was performed to understand the problem and determine the optimum size and location of the SVCs. This paper presents planning and design aspects of the SVC installations. As part of the planning consideration, the fundamental problem, alternative solutions evaluated, selection of the preferred option and other reactive power issues are covered. Additionally, as part of the design considerations, the SVC configuration, control strategy and other design issues are discussed.

Fault Handling at Hybrid High-Voltage AC/DC Transmission Lines With VSC Converters

The generation capacity of renewable energy sources has significantly increased during the last few years. As a consequence, high-power dc transmission systems are key technologies to reinforce the high-voltage transmission system. Regarding the long process of approving for right of way for new lines, a conversion from existing ac into dc lines might be an option. Modular multilevel converters provide the necessary features to avoid technical problems in heavily loaded ac systems; they increase the transmission capacity and system stability very efficiently and assist in preventing cascading disturbances. In this paper, high-voltage direct current transmission systems based on half-bridge topology with and without solid-state breaker and full-bridge (FB) modules are compared. The general behavior during faults on the dc side is described especially with respect to intersystem faults (i.e., faults between the ac and dc systems). Regarding the clearing capability, such disturbances lead to even higher requirements than for pure dc faults, especially the necessary transient interruption voltage (TIV) of the dc breaker design. On the other hand, this adapted design yields some disadvantages with respect to more frequently occurring dc line faults. In contrast, the controllability of the FB solution offers the possibility of an adjustable TIV and does not need to dissipate any energy since the power can be transmitted to the ac side. Therefore, the FB seems suited best for applications in hybrid high-voltage ac/dc systems.