5 research outputs found
Electromagnetic compatibility in various kinds of substations in Croatian transmission networks and mitigation measures
In the last two decades have been studied the conditions of electromagnetic compatibility
(EMC) in different kind of substations in transmission networks of Croatia. Investigations have been
done by measuring method using special measuring technique and also by computing simulations. In
this paper will be shown conditions of EMC which have been studied by measuring method during
normal or fault switching operations of disconnectors and circuit breakers. Conditions of EMC with
particular stress on transient voltages in secondary circuits within various kind of transmission
network objects have been carefully studied (AIS, GIS, old and new substation design type, rated
voltages from 110 kV to 400 kV).
In the paper will be given the review of some main data from those investigations made in the
long period of time. Then main findings will be given and the differences in EMC conditions will be
shown taking into account various parameters such as: design details of substations (distances, cable
types, protective measures etc.). Also, it will be given a review of measuring methods and tools
(oscilloscopes with low and deep acquisition memory, statistical tools for data processing, etc.).
Generally, it was shown that overvoltatges in secondary equipment follows normal or Gaussian
statistical distribution from which some typical data have been taken, such as 98% - probability values
etc.
Consequently, different kind of the mitigation measures have been proposed in cases of high
overvoltages in secondary circuits. Typically, changes in earthing systems, in cable sheets connections
etc. have been proposed to utilities. All proposed measures have been tested by measuring methods
too and the effects have been very satisfactory in ensuring EMC conditions within substations. Some
most interesting ways in reducing high level of TEVR in GIS substations will be shown in pictures.
Given results and effects of mitigation measures in Croatian transmission network substations
clearly show that the best method is experimental investigation which usually was followed by some
necessary mitigation measures which ensure the conditions of EMC within substations according to
international standards and recommendations
First Experience in Monitoring of Line Surge Arresters Installed on 110 kV Transmission Line Ston ā Komolac in Croatia
In paper are presented some first results and experience in real time monitoring of line surge
arresters installed on 110 kV transmission line Ston ā Komolac in southern part of Croatia. Mentioned
line is the first line in Croatian transmission network equipped with line surge arresters (LSA).
The line with its length of 43,95 km is situated in region with high soil resistance, exposed to
one of the highest level of lightning activity in Croatia. At the same time it is the most important line
in connecting HPP Dubrovnik (240 MVA) to the main part of 110 kV transmission network.
Due to all mentioned reasons and great number of annual outages, it was decided to equip the
line with LSA for improving the lightning performance and the availability of line. As result of
performed numerical simulations on simulation line model it was decided to install 110 kV gapless,
IEC Class II line arresters. Also, to improve analysis of expected results the 61 line arresters were
equipped with Excount-II type of monitoring sensors. The main goal was to determine the behaviour
of line arresters arrangement across the line during overvoltage events on towers. This installed ārealtimeā
monitoring system enables remote control and wireless exchange the collected data from local
data logger installed on LSA. Line arresters activity is monitoring through numbers, date and time and
level of surges and the condition state of LSA, through the measuring of leakage current.
First results in application of LSA are showing significant reduction of line outages with
registered relatively strong activity of monitored line arresters. Also, as it was expected some
particular part of line is espied to be exposed to higher frequency and higher level of registered
arresters surge current. During collecting the data of LSA activity, some practical problems were
encountered with time synchronization between monitoring devices and it is mentioned and discussed
in paper, too.
Although the analysed time period of eight months with LSA application is too short to allow
strong final conclusions, obtained first experience will be very helpful in assessment of further LSA
application in Croatian transmission network
First Experience in Monitoring of Line Surge Arresters Installed on 110 kV Transmission Line Ston ā Komolac in Croatia
In paper are presented some first results and experience in real time monitoring of line surge
arresters installed on 110 kV transmission line Ston ā Komolac in southern part of Croatia. Mentioned
line is the first line in Croatian transmission network equipped with line surge arresters (LSA).
The line with its length of 43,95 km is situated in region with high soil resistance, exposed to
one of the highest level of lightning activity in Croatia. At the same time it is the most important line
in connecting HPP Dubrovnik (240 MVA) to the main part of 110 kV transmission network.
Due to all mentioned reasons and great number of annual outages, it was decided to equip the
line with LSA for improving the lightning performance and the availability of line. As result of
performed numerical simulations on simulation line model it was decided to install 110 kV gapless,
IEC Class II line arresters. Also, to improve analysis of expected results the 61 line arresters were
equipped with Excount-II type of monitoring sensors. The main goal was to determine the behaviour
of line arresters arrangement across the line during overvoltage events on towers. This installed ārealtimeā
monitoring system enables remote control and wireless exchange the collected data from local
data logger installed on LSA. Line arresters activity is monitoring through numbers, date and time and
level of surges and the condition state of LSA, through the measuring of leakage current.
First results in application of LSA are showing significant reduction of line outages with
registered relatively strong activity of monitored line arresters. Also, as it was expected some
particular part of line is espied to be exposed to higher frequency and higher level of registered
arresters surge current. During collecting the data of LSA activity, some practical problems were
encountered with time synchronization between monitoring devices and it is mentioned and discussed
in paper, too.
Although the analysed time period of eight months with LSA application is too short to allow
strong final conclusions, obtained first experience will be very helpful in assessment of further LSA
application in Croatian transmission network
Effects of dispersion and particle-matrix interactions on mechanical and thermal properties of hnt/epoxy nanocomposite materials
Halloysite nanotubes (HNTs), naturally occurring as aluminosilicate nanoclay mineral, have recently emerged as a possible nanomaterial for countless applications due to their specific chemical structure, tubular shape, high aspect ratio, biocompatibility and low toxicity. In this study, HNTs were incorporated into the epoxy resin matrix to improve its mechanical properties and thermal stability. However, heterogeneous size, surface charge and surface hydrogen bond formation, result in aggregation of HNTs in epoxies to a certain extent. Three specific techniques were used to integrate HNTs into neat epoxy resin (NE). The structure and morphology of the embedded nanotubes were confirmed by Fourier-transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD). Tensile testing was carried out and the fractured surface of the tested specimen was analysed using scanning electron microscopy (SEM). The thermal stability of the prepared nanocomposite materials was investigated by thermogravimetric (TG) and derivative thermogravimetry (DTG) studies. The obtained results indicated that improved properties of HNTs/epoxy nanocomposite materials were related to the unique properties of well-dispersed HNTs, agglomerate scale, and reduced void presence, and could be controlled by the manufacturing processes