Dominik DUDA
Parameters of surge arresters applied to protect the outer sheaths of HV cables
Presented are methods of HV cables metal screens bonding and grounding. Explained is why outer sheaths of cables working with single point bonding of metal screens have to be protected against overvoltages. Presented are methods of determining induced voltages in the cables metal screens (screen to earth), because the induced voltage is the main criterion for selection of continuous operation voltage of surge arresters applied to protect outer sheaths of HV cables. Described is selection of continuous operation voltage and other electrical parameters of surge arresters.
Keywords: cable lines, surge arresters, induced voltage
Filip KLEPACKI
Influence of frequent changes in a unit load on durability of selected steam boiler elements
Described are damages connected with cyclic work of units and identified during technical condition assessment of boilers and pipelines of three 200 MW units in one of the Polish power plants. On the basis of interpretation of test results carried out at the time of planned overhauls, retrospections of repair and diagnostic works, calculations of durability and the analysis of construction and operational parameters, defined are the causes of the identified damages. The knowledge of direct and indirect causes made it possible to propose preventive and predictive measures for individual types of damages. During a boiler operation with frequent load changes, one of the most vulnerable to damages boiler elements are inlet holes for stubs of pipelines with a cyclic steam flow in the fresh steam system as well as welded joints of desuperheaters and tees/stubs connecting them with pipelines of a cyclic steam flow in the resuperheated steam system.
Keywords: power generation units, boilers and pipelines of 200 MW power units, influence of a unit load changes on durability of boiler elements
Andrzej BIELECKI
Intelligent monitoring of big wind turbines
Development of power industry based on renewable energy sources is a promising alternative to thermal and nuclear energy while wind power is in turn one of the more important branches of the aforementioned renewable energy. Its attractiveness results from the fact that there are big wind energy resources on earth considerably exceeding the actual global demand for electricity. But wind power is accompanied by significant operational problems. High costs of repairs and overhauls of big wind turbines create demand for efficient systems of their monitoring. Measurement of vibrations of kinematic systems and supporting structures is one of the main tasks of intelligent monitoring. Standard monitoring of wind turbines is based on setting rigid thresholds for individual parameters. Within the framework of the research on the possibility to create more elastic system of big wind turbines monitoring, investigated was the ability of the ART resonance network for clusterization of both a turbine operational condition and vibration signals. Described here the hybrid system of a wind turbine intelligent monitoring proved its efficiency as the monitoring and early warning system. The system properly classifies a turbine trouble-free condition while all defects are detected practically immediately after they occur.
Keywords: wind energy, big wind turbines, hybrid system of a wind turbine intelligent monitoring
Krystian Leonard CHRZAN, Jonathan WOODWORTH
Development of high-voltage surge arrester constructions
By the end of the nineteenth century there was a rapid development of the power industry. Longer and longer overhead power lines were built and of higher and higher voltage. At first, protective spark gaps and other protection devices were used which now we determine as “arresters”. Their objective was to reduce the peak value of a surge or to reduce its rate of rise. Arresters can be divided into three main groups: surge capacitors, choke coils and earth leakage protection devices. Characterized are here: spark gaps, Giles valves, aluminum cell lightnig arresters, oxide film arresters, spark gap arresters i.e. valve-type lightning arresters and expulsion-type arresters.
Keywords: lightning surges, high-voltage surge arresters, arrester construction development
Piotr STRUŻEWSKI
Selected remarks to ignitions of gaseous atmospheres after direct lightning strikes to buildings potentially endangered by explosions
Mechanisms of lightning influences on various types of struck objects and negative effects of these influences can be very diversified. It is a rule that if you intend to examine a certain closed set of complex problems concerning lightning protection, you must first make a selection of the mentioned objects and effects. It should be noted that such selection responds to the present clear trend to specify in detail subject areas of scientific works connected with the encountered in real life hazards caused by lightning discharges. The main focus here is put on above ground buildings with an inside atmosphere containing a mixture of gases and flammable liquids vapours with air. It is this type of buildings that is taken here into account as objects of direct lightning strikes, considering the possibility of explosion initiated inside such buildings as an aftermath of such strike. Examined are direct lightning strikes into roofing insulation, steel sheets comprising such roofing as well as structural sheets of upper parts of above ground steel tanks for flammable liquids.
Keywords: lightning influence mechanisms, above ground buildings with an atmosphere containing mixtures of gases and flammable liquids vapours with air