Band 9, Heft 1

This paper presents the results of an investigation on evaluating room-temperature-vulcanized (RTV) silicone rubber coatings for high-voltage insulators of substations and overhead transmission lines. It is based on tests conducted for three different available RTVs that are currently used by utilities. The study compared three commercial coatings: RTV-A and RTV-B filled with ATH (aluminum tri-hydrate) as the primary filler, and RTV-C filled with silica. The relative comparison between them is based on their electrical and chemical characteristics. The evaluation employed standard and research-based evaluation methods, including the salt fog test, the inclined plane test, thermo-gravimetric analyses (TGA), thermal conductivity measurement, soaking in water, the mechanical test, and SEM photographs. Results of the inclined plane test showed that the silica-filled coating is not resistive against tracking and erosion compared with ATH-filled coatings. It was observed that filler size is one of the main reasons for better performance of RTV-A compared with RTV-B, whereas both have ATH as the primary filler. The higher thermal conductivity of RTV-A resulted in a very good performance in the salt fog test and the IPT.

This paper presents the design and implementation of a digital signal processor (DSP) based induction generator controller (IGC) to regulate the voltage and frequency of a single phase self excited induction generator (SEIG), suitable for stand alone power mode employing unregulated turbine such as micro-hydro power generation. The developed prototype model of a DSP based SEIG-IGC system is cost effective, reliable, flexible and capable of network based application for remote configuration with TCP/IP stack. The transient behavior of the developed DSP based SEIG-IGC system at different operating conditions such as the application and removal of static (resistive and reactive) and dynamic (single phase induction motor) load is investigated to demonstrate the capabilities of the proposed IGC.

The paper discusses the operating principles and control characteristics of a dynamic voltage restorer (DVR). It is assumed that the source voltages contain interharmonic components in addition to fundamental components. The main aim of the DVR is to produce a set of clean balanced sinusoidal voltages across the load terminals irrespective of unbalance, distortion and voltage sag/swell in the supply voltage. An algorithm has been discussed for extracting fundamental phasor sequence components from the samples of three-phase voltages or current waveforms having integer harmonics and interharmonics. The DVR operation based on extracted components is demonstrated. The switching signal is generated using a deadbeat controller. It has been shown that the DVR is able to compensate these interharmonic components such that the load voltages are perfectly regulated. The DVR operation under deep voltage sag is also discussed. The proposed DVR operation is verified through the computer simulation studies using the MATLAB software package.

This paper presents a novel controller for DFIG based wind parks, designed to achieve more efficient voltage regulation, reactive power compensation and to enhance the transient stability margin of the interconnected power system. The supervisory-secondary voltage control is used to generate the local voltage reference, providing an improved overall voltage profile, while combining an automatic gain controller (AGC) to improve the transient response of the primary control loop. The controller is implemented and tested with a power system comprising of a lumped, fundamental frequency model of a DFIG based wind park, and hydro and diesel generators connected to the electric grid. The performance of the controller was investigated for both steady-state improvements as well as under extreme contingencies to demonstrate its benefits.

In this work, a technical, economic and environmental analysis concerning the use of three major power generation plant types including pulverized coal, integrated gasification combined cycle (IGCC) and natural gas combined cycle, with or without carbon dioxide (CO2) capture and storage (CCS) integration, is carried out. For the analysis, the IPP optimization software is used in which the electricity unit cost and the CO2 avoidance cost from the various candidate power generation technologies is calculated. The analysis indicates that the electricity unit cost of IGCC technology with CCS integration is the least cost option with the lowest CO2 avoidance cost of all candidate technologies with CCS integration. Further investigation concerning the effect of the loan interest rate on the economic performance of the candidate plants revealed that up to a value of loan interest of approximately 5.7%, the IGCC plant with CCS retains the lowest electricity unit cost. Above this level, the natural gas combined cycle plant with post-combustion CCS becomes more economically attractive.

LCA (Life Cycle Assessment) is a well known methodology to assess the impact on the environment over the life cycle of a product, process, or activity. This methodology is based on the LCI (Life Cycle Inventory) database, a data set of all resources (material and energy) that are consumed or emitted in order to produce 1 unit of the product. Because electricity is a basic infrastructure, a Thailand electricity grid LCI database is needed to assess the environmental impact not only for the product used in Thailand, but also for any product that is exported to other countries. A complete LCI database for the electricity grid in Thailand is not yet available, and the LCI database developed in this work applies from the fuel acquisition stage to the production stage. The analysis shows the unique characteristics of the Thailand electricity grid. An LCI database for each type of fuel and for each electricity generation system was developed. The characteristics of each type of fuel and electricity generation system are indicated in terms of Life Cycle GHG (Greenhouse Gas) emissions to reflect their global warming potential. Data on the Life Cycle GHG emission per kWh of electricity produced are also provided. The first Thailand LCI database for the fuels used in the electricity generation system was developed using data obtained from the EGAT (Electricity Generating Authority of Thailand), IPPs (Independent Power Producers), and PTT (Petroleum Authority of Thailand) during the Thai fiscal year 2005 (from October 2004 to September 2005). The database was used to analyze the current situation and the characteristics of the electricity generation system in Thailand and to compare it with the systems used in other developed countries.

The intrinsic permittivity, not apparent permittivity, of semiconducting layers of high voltage cross-linked polyethylene (XLPE) cables imposes a significant influence on the design of partial discharge detecting sensors. It has extremely high permittivity, resulting in a dimensional effect, an embodiment of the difference between the intrinsic permittivity and apparent or measurable permittivity. To investigate this dimensional effect in semiconducting material, a mathematical model is set up in this paper for a capacitor with two rectangular-shaped electrodes in parallel, between which is inserted a semi-conducting sample. First, the expression of the electric field in the semiconducting material is worked out theoretically. Then, the measurable or apparent complex permittivity is expressed as a function of intrinsic permittivity, dimensions of the sample and frequency. Next, five blocks with different dimensions are introduced to study the dimensional effect. The numerical analysis demonstrates that above 10 MHz, samples with different dimensions result in different apparent permittivity or measurable permittivity if experiments are carried out for the samples with the assumed dimensions. This implies that dimensional effects should be considered when accurate intrinsic permittivity of the semiconducting materials is needed.