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Breakdown behaviour of oil-barrier insulation at lightning impulse voltage
Haller R.; Hornak J.; Trnka P.; Hamar R.; Hlaváček J.
2020 - English
The paper deals with some results of breakdown behavior of oil-barrier insulation at inhomogeneous field under lightning impulse voltage stress conditions. The investigation was performed with various types of mineral oil as well as natural and synthetic esters. To provide inhomogeneous field conditions a test arrangement tip-to-semi-sphere was used. For having some reference values also the same test set without barrier (pure oil) was investigated. Additionally, some tests were carried out at standardized conditions (homogeneous field). For generalizing of measured voltage values the electrical breakdown field strength was evaluated. At pure oil test set (reference values) the known polarity effect was measured, what means, that at positive polarity (tip) the breakdown values are significantly lower than at negative one. That was valid for all tested oil types excluding the synthetic ester (FR 3), at which an opposite result was obtained. With pressboard insulation the charging effect of the barrier leads to significant higher electrical breakdown field strength, dependent on used fluid. When the barrier insulation was tested with mineral oil NYTRO BIO, the highest breakdown field strength of ∼ 300 kV/mm was obtained (negative polarity). The measured polarity effect for the tested fluids was not so unambiguously as for reference values e.g. so for NYNAS TAURUS, LYRA and FR 3 lower breakdown values have been measured at negative polarity. Also the impact of surface charge on the barrier to the breakdown process was studied by simulation and measurement. Generally, the surface charge on barrier increase the resulting electrical field strength and leads in the insulating gap between barrier and semi- sphere to a (quasi) homogeneous field. The obtained results may contribute to a deeper understanding of the breakdown behavior of oil-barrier insulation at different oil/fluid types and inhomogeneous field condition.
Keywords:
oil-pressboard insulation; lightning impulse breakdown voltage; electrical breakdown field strength; surface charge
Available in digital repository of ČVUT.
Breakdown behaviour of oil-barrier insulation at lightning impulse voltage
The paper deals with some results of breakdown behavior of oil-barrier insulation at inhomogeneous field under lightning impulse voltage stress conditions. The investigation was performed with various ...
Methodology of electricity supplying of critical infrastructure in crisis situations
Čerňan M.; Müller Z.; Tlustý J.; Halaška J.
2020 - English
The paper focuses on the issues associated with the supply of electricity to critical infrastructure in crisis situations. In the introductory passages, the paper focuses on the methodology of selecting objects of critical infrastructure. Subsequently, attention is paid to selected aspects associated with the operation of electricity generation during a crisis situations. By using suitable types of production units (gas turbines), it is possible to gradually start island operation in the surrounding region, primarily for critical infrastructure facilities, whose main task is to protect the population. In the practical part, the paper focuses on the issues of stability of the island operation mode. The results of the case study show that for the switch-on plan it is necessary to take into account the dynamic characteristics of island operation by feeding the objects of critical infrastructure gradually after small electrical power steps.
Keywords:
Critical infrastructure supply; island operation stability; power system restoration; blackout
Available in digital repository of ČVUT.
Methodology of electricity supplying of critical infrastructure in crisis situations
The paper focuses on the issues associated with the supply of electricity to critical infrastructure in crisis situations. In the introductory passages, the paper focuses on the methodology of ...
A supervisory MPC for synchronverter
Vetoshkin L.; Müller Z.
2020 - English
The adoption of renewable energy sources leads to lower grid inertia, which brings more complications to operators of electrical grids. New control strategies for power electronics try to cope with that problem by introducing virtual inertia. Sychronverter is one of the promising algorithms. Furthermore, other control techniques combined with synchronverter might improve stability. Model predictive control (MPC) has proven to be a good tool in real applications. Therefore, the authors present a simplified mathematical model of a PV power plant with a synchronverter. The paper also proves that the presented model can be applied to MPC for synchronverter. Depending on the stated objective, MPC for synchronverter can bring different advantages to the control of grid converters.
Keywords:
Mathematical model; Inverters; Virtual Inertia; Synchronverter
Available in digital repository of ČVUT.
A supervisory MPC for synchronverter
The adoption of renewable energy sources leads to lower grid inertia, which brings more complications to operators of electrical grids. New control strategies for power electronics try to cope with ...
Lightning incidence on transmission overhead lines
Jányš P.; Procházka R.
2020 - English
The paper deals with an estimation of lightning strike incidence to transmission overhead lines in the context of line outages gathered from an automatic monitoring system. The statistics of the Czech transmission system's line outages caused by lightning strikes are presented and analyzed. Lines with significantly higher outage rates are identified, and the electrogeometric model is used for lightning incidence calculation. The estimation that the lightning strikes the phase conductor, ground wire, or tower constructions of overhead line is performed. Finally, the ratio of lightning strikes that caused line outage to the total number of lightning strikes to phase conductors is evaluated and compared with the values obtained from the monitoring system.
Keywords:
Transmission overhead lines; lightning strike incidence; electrogeometric model
Available in digital repository of ČVUT.
Lightning incidence on transmission overhead lines
The paper deals with an estimation of lightning strike incidence to transmission overhead lines in the context of line outages gathered from an automatic monitoring system. The statistics of the Czech ...
Potential of technical losses reduction in low voltage feeder using small photovoltaics
Alshammari A.; Čerňan M.; Müller Z.
2020 - English
Efficiency of electricity systems is currently a high priority for the society. Our article focuses on the area of low voltage distribution system, where we focus more deeply on the possibilities of reducing technical losses. To achieve this goal, many traditional methods are known which require modification and intervention in the distribution system. Our concept is based on the possibility of reducing active losses using small photovoltaic systems installed at low voltage customers. For this purpose, a low voltage feeder model of the corresponding structure was created in this work. Using this model, a case study based on real data (solar irradiation data and typical daily diagrams of low voltage customers) was performed. The results of the simulations show considerable potential for reducing technical losses using the described concept.
Keywords:
technical losses; low voltage feeder; small photovoltaic system; losses reduction; case study
Available in digital repository of ČVUT.
Potential of technical losses reduction in low voltage feeder using small photovoltaics
Efficiency of electricity systems is currently a high priority for the society. Our article focuses on the area of low voltage distribution system, where we focus more deeply on the possibilities of ...
Calibration of burdens for instrument transformers
Draxler K.; Ulvr M.; Styblikova R.; Hlaváček J.
2020 - English
The first part of this paper deals with the influence of burden accuracy on the errors of current and voltage instrument transformers. The requirement stated in the prepared standard, corresponding to a tolerance of burden value B ± 3 % and power factor PF ± 0.02, is confronted with measurement results. The second part of the paper deals with the calibration process for instrument transformer burdens. This is followed by a description of the 3-voltmeter method for determining PF and apparent power B, including the measurement uncertainty calculation. A comparison is made between the achieved measurement uncertainties and the requirements stated in the prepared standard.
Keywords:
burden; power factor; instrument transformer; ratio error; phase displacement; uncertainty
Available in digital repository of ČVUT.
Calibration of burdens for instrument transformers
The first part of this paper deals with the influence of burden accuracy on the errors of current and voltage instrument transformers. The requirement stated in the prepared standard, corresponding to ...
RISK MANAGEMENT AT TECHNICAL FACILITIES TYPE AND SITE SELECTION
Procházková D.; Procházka J.
2020 - English
Technical facilities are created by human activities, and their goal is to provide products or services for the humans´ lives. The technical facilities architecture is the object or the network. Each type of technical facility has its own specifics. Management of technical facilities´ safety is not easy and requires the application of specific engineering tools for coping with the expected risks. Due to complex architecture of majority of present technical facilities, their behaviours are sometimes unforeseeable, and therefore, special engineering tools need to be used at their type selection and sitting.
In the past, the attention was not overly given to type selection and location of technical facility. Therefore, some technical facilities projects have not been completed, or after completing their operation have not met the expectations, or even they began to make serious problems, which meant substantial economic losses. Therefore, the book “Risk management at technical facilities type and site selection” deals with the problem of specification of the type of technical facilities and their location in the territory. It summarizes results of specific research performed in project “Řízení rizik a bezpečnost složitých technologických objektů (RIRIZIBE)“ CZ.02.2.69/0.0/0.0/ 16 _018/000”.
Since, the deciding body on the subject is the public administration, they are compiled decision support and the risk management plan.
Keywords:
risk; safety; coexistence; type selection; sitting; technical facility
Available in digital repository of ČVUT.
RISK MANAGEMENT AT TECHNICAL FACILITIES TYPE AND SITE SELECTION
Technical facilities are created by human activities, and their goal is to provide products or services for the humans´ lives. The technical facilities architecture is the object or the network. Each ...
RISK MANAGEMENT AND SETTLEMENT AT TECHNICAL FACILITIES OPERATION
Procházková D.; Procházka J.
2020 - English
The monograph deals with a risk management at the technical facilities operation for the benefit of safety; the management aim is to ensure their co-existence with their vicinity throughout their life cycles. The accidents´ and failures´ studies show that important factor is correct perfor-mance of responsibilities on different management levels. Assessment of legislations and organizations of present States shows that for technical facilities safety, they are also responsible politics and public administration. The present knowledge shows that for prevention of accidents and failures, it is necessary to avoid to: large mistakes in risk prevention; and origination of small mistakes, the realization of which in short time interval is dangerous. For this purpose, it is developed tool “Decision Support System” for determination of risk level of tech-nical facility during the operation respecting the present knowledge on technical facili-ties´ risks and safety and the lessons learned from the past accidents and failures of technical facilities, the causes of which were connected with their operation. Due to dynamic world development, technical facilities parts ageing, wear and tear, and limited human knowledge, sources and capabilities, the technical facilities´ management and public administration need to be prepared for future risk realizations, which can be different from the present ones. For this purpose, it is developed tool “Risk Management Plan” respecting the present knowledge on technical facilities´ responses and the lessons learned from the past responses to accidents and fail-ures of technical facilities, the causes of which were connected with their operation.
Keywords:
technical facility; risk; safety; operation; risk management; decision support sytem; risk managenet plan
Available in digital repository of ČVUT.
RISK MANAGEMENT AND SETTLEMENT AT TECHNICAL FACILITIES OPERATION
The monograph deals with a risk management at the technical facilities operation for the benefit of safety; the management aim is to ensure their co-existence with their vicinity throughout their ...
Area of Vernacular Heritage for Zemplín Region, Slovakia
Volovár M.
2020 - English
The paper presents a project of a small hamlet of traditional timber frame buildings transferred from different places to the greenfield by a village in Lower Zemplín region in south-eastern Slovakia. The complex will serve as community center for studying an development of regional arts, crafts and architectural heritage.
Presented outline of the project contains a summary of motivational stimuli and short analysis of germinal trio of buildings – the selected local representatives of ancient frame structures with various wall fillings.
The latest examples of such buildings can be sporadically found in the countryside, decaying without use and waiting for the soon vanish. The objects lack any monumental or museum protection and chance for preservation for the future. After being dismantled and transferred to the complex, they will be installed similarly to their original urban situation and restored using traditional techniques.
Building substance of the objects will be the essential attraction of the area. Their premises will not serve to an ethnographic presentation of a traditional housing, but to the current cultural activities as are the alternative and folklore events, courses and studios of crafts, exhibitions of traditional structural artefacts as well as the contemporary local artists.
Keywords:
Building heritage; Timber framing; Community centre; Arts and crafts; Eastern Slovakia
Available in digital repository of ČVUT.
Area of Vernacular Heritage for Zemplín Region, Slovakia
The paper presents a project of a small hamlet of traditional timber frame buildings transferred from different places to the greenfield by a village in Lower Zemplín region in south-eastern ...
Influence of Voltage Distortion Shape on Partial Discharge Activity in Internal Voids
Procházka R.; Šefl O.
2020 - English
Electrical insulation materials, especially polymers, may contain miniature internal voids. Insulation systems created from such materials might hence suffer from the development of partial discharges in the voids. These discharges tend to erode the insulation material, which further increases their magnitude and quantity and leads to a significant enhancement of the degradation rate. Lately, due to the high number of power electronic components connected to the grid, repetitive high-frequency distortions occur in the parts of the network adjacent to these devices. Such distortions may cause the inception of partial discharge, which would usually not happen.This paper thus researches the effect of high-frequency voltage distortions on partial discharges in an artificially created internal void. Test samples containing the artificial voids were prepared by fused filament fabrication (FFF) method from PET-G material using a standard 3D printer. The employed FFF method of sample preparation achieved satisfactory precision in both the shape and size of the voids. The main observed parameters were oscillation waveform's frequency and its phase shift relative to the supply voltage. PRPD patterns were gathered for a variety of different setups, and the influence of both parameters was evaluated.
Keywords:
Partial discharges; insulation system; high voltage distortion
Available in digital repository of ČVUT.
Influence of Voltage Distortion Shape on Partial Discharge Activity in Internal Voids
Electrical insulation materials, especially polymers, may contain miniature internal voids. Insulation systems created from such materials might hence suffer from the development of partial discharges ...
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