There are two main types of CCVs, circulating current type or blocking mode type, electric power quality heydt pdf commercial high power products being of the blocking mode type. CCVs are inherently reserved for resistive load applications. The amplitude and frequency of converters’ output voltage are both variable.
The output to input frequency ratio of a three-phase CCV must be less than about one-third for circulating current mode CCVs or one-half for blocking mode CCVs. The competitive power rating span of standardized CCVs ranges from few megawatts up to many tens of megawatts. The variable-frequency output of a cycloconverter can be reduced essentially to zero. This means that very large motors can be started on full load at very slow revolutions, and brought gradually up to full speed.
A fully loaded “hard start” for such equipment would essentially be applying full power to a stalled motor. Variable speed and reversing are essential to processes such as hot-rolling steel mills. Cycloconverter-driven synchronous motors need less maintenance and give greater reliability and efficiency. 25 Hz power in the U. IGBT, GTO, IGCT and other switching devices, these older classical converters are still used at the higher end of the power rating range of these applications. Equation’s 2nd term denotes the converter’s sideband characteristic frequencies including associated interharmonics and subharmonics.
High Power Medium Voltage Drives – Innovations, Portfolio, Trends”. The power quality impact of cycloconverter control strategies”. IEEE Recommended Practices and Requirements for Harmonic Control in Electrical Power Systems”. This page was last edited on 16 August 2017, at 00:12. To secure uninterrupted distribution of electricity, effective monitoring and maintenance of power lines are needed. This literature review article aims to give a wide overview of the possibilities provided by modern remote sensing sensors in power line corridor surveys and to discuss the potential and limitations of different approaches. Monitoring of both power line components and vegetation around them is included.
The review shows that most previous studies have concentrated on the mapping and analysis of network components. In particular, automated extraction of power line conductors has achieved much attention, and promising results have been reported. ALS data or aerial images. However, in many studies datasets have been small and numerical quality analyses have been omitted. Mapping of vegetation near power lines has been a less common research topic than mapping of the components, but several studies have also been carried out in this field, especially using optical aerial and satellite images. Based on the review we conclude that in future research more attention should be given to an integrated use of various data sources to benefit from the various techniques in an optimal way.
Knowledge in related fields, such as vegetation monitoring from ALS, SAR and optical image data should be better exploited to develop useful monitoring approaches. Special attention should be given to rapidly developing remote sensing techniques such as UAVs and laser scanning from airborne and land-based platforms. To demonstrate and verify the capabilities of automated monitoring approaches, large tests in various environments and practical monitoring conditions are needed. These should include careful quality analyses and comparisons between different data sources, methods and individual algorithms. International Society for Photogrammetry and Remote Sensing, Inc. Good power quality can be defined as a steady supply voltage that stays within the prescribed range, steady a.
There are many ways in which electric power can be of poor quality and many more causes of such poor quality power. The complexity of the system to move electric energy from the point of production to the point of consumption combined with variations in weather, generation, demand and other factors provide many opportunities for the quality of supply to be compromised. Power is simply the flow of energy and the current demanded by a load is largely uncontrollable. Compatibility problems always have at least two solutions: in this case, either clean up the power, or make the equipment tougher. 5 cycle to 1 minute, the event is called a “swell”. 5 cycle to 1 minute.
Flicker is rapid visible changes of light level. Definition of the characteristics of voltage fluctuations that produce objectionable light flicker has been the subject of ongoing research. It comes from the noticeable to significant dimming of regular incandescent lights, during system faults or overloading etc. This term is in common usage has no formal definition but is commonly used to describe a reduction in system voltage by the utility or system operator to decrease demand or to increase system operating margins. Common Mode Distortion or Interharmonics at higher frequencies. The oscillation of voltage and current ideally follows the form of a sine or cosine function, however it can alter due to imperfections in the generators or loads. Typically, generators cause voltage distortions and loads cause current distortions.
These distortions occur as oscillations more rapid than the nominal frequency, and are referred to as harmonics. Low harmonic content in a waveform is ideal because harmonics can cause vibrations, buzzing, equipment distortions, and losses and overheating in transformers. Each of these power quality problems has a different cause. Some problems are a result of the shared infrastructure. A problem on one customer’s site may cause a transient that affects all other customers on the same subsystem. Problems, such as harmonics, arise within the customer’s own installation and may propagate onto the network and affect other customers. Harmonic problems can be dealt with by a combination of good design practice and well proven reduction equipment.