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Simulation study of lightning fault waveforms influenced by the arc quenching properties of wooden distribution line polesBredenoord, Carl Henk 23 May 2008 (has links)
Abstract
With an ever increasing emphasis on reliability of supply, improvement in the lightning
performance of distribution lines is required. The arc quenching properties of wooden
distribution line poles during lightning strikes are an important factor in the reduction of
switchgear operation, hence outages. Measurements were conducted on a 22 kV distribution
line and it was suspected, in some cases, that direct lightning strikes to the line did not cause
switchgear operation. Distribution lines predominantly use wooden poles with a specific
configuration which incorporates a 'wooden' spark gap. This paper provides background
to the basic configuration of a typical distribution line and the processes which govern the
electric arc. A simulation using a dynamic arc model shows that field measured lightning
overvoltages on a distribution line are reproducible through system modelling. The simplistic
dynamic arc model developed is sufficiently accurate to describe a set of arcs in a larger
system such as a distribution line.
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Investigating the effects of altitude (air density) on the HVDC breakdown voltage of small rod-plane air gapsGora, Tatenda January 2016 (has links)
A dissertation submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science in Engineering, 2016 / The validity of the atmospheric correction method presented in the IEC 60060-1 (2010)
standard is analysed and evaluated by means of theoretical and laboratory work. In
order to understand the problem, the evolution of the atmospheric correction methods,
from as early as 1914, has been presented. A procedure (Calva prediction method) for
predicting the direct current (DC) breakdown voltage for an air gap at any altitude
was discovered and was also analysed along with the IEC 60060-1 (2010). A critique of
some of the atmospheric correction methods commonly used standards was also done.
Experiments were carried out at altitudes of 1 740 m (Wits University), 130 m (UKZN
HVDC centre) and at less than 2 m above sea level (Scottburgh beach, Clansthal). More
tests were conducted using a pressure vessel where high altitude relative air density was
simulated. All tests were conducted on rod-plane air gaps using a 15 mm diameter
at tip rod. Test results from Scottburgh beach were used as the standard breakdown
voltages of the air gaps tested since the environmental conditions were the closest to the
conventional standard conditions (stp). The test results obtained were compared with
predictions using the Calva method in order to validate the method. The test results
were also corrected according to IEC 60060-1 (2010) and compared to the standard
breakdown voltages obtained at Scottburgh beach. It was shown that the IEC 60060-1
(2010) is quite suitable for atmospheric correction for data obtained at low altitudes
(about 130 m). When applied to high altitude (1 740 m) data, the correction method
is accurate and suitable for very small air gaps less than 0.1 m. As the air gap length
increased, the corrected results began to deviate from the expected standard voltage.
The same trend was shown with the corrected results from the pressure chamber tests.
The prediction method by Calva was accurate when compared to the experimental data
from the high altitude and low altitude test results. When compared to the data from
the pressure chamber, the prediction method had a linear error factor which was di erent
for each gap length. It was concluded that the IEC 60060-1 (2010) is not only unsuitable
for atmospheric correction for data at relative air densities below 0.8, but also that the
correction method is prone to an increase in error as the air gap length increases when
the relative air density is higher than 0.8. The Calva prediction method was found
to be suitable to use after additional factors are added when applied to high altitude
conditions. / GR2016
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Fuzzy logic statcom controller design with genetic algorithm application for stability enhancement of interconnected power systems /Mak, Lai-on. January 2000 (has links)
Thesis (M. Phil.)--University of Hong Kong, 2001. / Includes bibliographical references (leaves 139-145).
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A computer-aided measurement system for monopolar high-voltage direct-current coronating lines /Tong, Sai-kit. January 1986 (has links)
Thesis--M. Phil., University of Hong Kong, 1986.
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Analysis of the impact of closed-loop power flow control strategies on power system stability characteristics.Ally, As'ad. 31 March 2014 (has links)
The demand for electrical energy in industrialised countries continues to increase
steadily. As a result of this growing demand for electrical energy, there is a need for
optimisation of the power system in terms of transmission and control. One option
could possibly be an increase in transmission facilities to handle the increase in
growth; however factors such as environmental issues as well as the possible cost
incurred could hamper this particular approach. An alternative resides in loading the
existing transmission network beyond its present operating region but below its
thermal limit, which would ensure no degradation of the system. For this approach to
be realised, improved control of the flow of power in an interconnected network
would be advantageous so as to prevent unwanted loop flows and inadvertent
overloading of certain lines.
This approach can be made possible by the use of Flexible AC Transmission Systems
(FACTS) technology. The concept of FACTS incorporates power-electronic
compensation devices that can be typically used in an ac power system to enhance the
system's power transfer and controllability. There exists a number of FACTS devices,
where each device can be utilised differently to achieve the broad objective. One such
device is the Thyristor Controlled Series Capacitor (TCSC). The TCSC is a class of
FACTS device that makes it possible to alter the net impedance of a particular
transmission line in an effort to force the flow of power along a "contract path".
This thesis identifies, in the published literature, a set of strategies for the scheduling
of power flow by use of variable compensation; such strategies are then considered in
more detail in the analysis of the thesis. Firstly, a detailed dynamic model of a TCSC
is developed together with its various controls and associated circuitry within the
power systems simulation package PSCAD. In addition to this, a power flow
controller scheme is then implemented, which exhibits the functionality of the power
flow controller strategies reviewed in the literature. In order to test the validity and
operation of the TCSC model as well as the analysis of the power flow controller
scheme, a single-machine infinite bus (SMIB) study system model is developed and
used as part of the investigation.
This thesis, firstly, presents a theoretical analysis of two particular modes of power
flow control in an interconnected ac transmission system. Secondly it confirms the
results of an analytical study in previously published work with the implementation of
the two control modes, and further extends the scope of the previous study by
examining the impact of the power flow controller's design on the small-signal and
transient stability characteristics of the study system.
The key findings of this extended investigation are that the power flow controller's
mode of operation has an important influence on both small-signal and transient
stability characteristics of a power system: in partiCUlar, it is shown that one mode can
be detrimental while the other beneficial to both system damping and first swing
stability. Finally, the thesis applies the understanding of the power flow controller's
operation obtained from the SMIB study system to the problem of inter-area mode
oscillations on a well-known, two-area, multi-:generator study system. Real-time
simulator results are presented to exhibit the effect of the power flow controller modes
and controller design on the oscillatory characteristics of the two-area study system. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, 2005
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Analysis of the impact of a facts-based power flow controller on subsynchronous resonance.Carpanen, Rudiren Pillay. 06 November 2013 (has links)
Electric power utilities are faced with the challenge of meeting increasing demand for electric power whilst many factors prevent traditional remedies such as the expansion of transmission networks and the construction of new generating facilities. Due to issues of environment, health and rights-of-way, the construction of new generating plants and transmission lines were either excessively delayed or prevented in many parts of the world in past years. An alternative resides in loading the existing transmission network beyond its present operating region but below its thermal limit, which would ensure no degradation of the system. This alternative approach has been possible with the emergence of Flexible AC Transmission Systems (FACTS) technology. The FACTS concept involves the incorporation of power-electronic controlled devices into AC power transmission systems in order to safely extend the power-transfer capability closer of these systems to their stability limits. One member of the family of FACTS series compensators is the Static Synchronous Series Compensator (SSSC), and this thesis considers the use of the SSSC to carry out closed-loop control of AC power flow in a transmission system.
Although the SSSC has the potential to enhance the operation of power systems, the introduction of such a device can cause adverse interactions with other power system equipment or existing network resonances. This thesis examines the interaction between high-level power flow controllers
implemented around the SSSC and a particular form of system resonance, namely subsynchronous resonance (SSR) between a generator turbine shaft and the electrical transmission network. The thesis initially presents a review of the background theory on SSR and then presents a review of
the theory and operation of two categories of SSSC, namely the reactance-controlled SSSC and the quadrature voltage-controlled SSSC. The two categories of SSSC are known to have different SSR characteristics, and hence this thesis considers the impact on the damping of subsynchronous
torsional modes of additional controllers introduced around both categories of SSSC to implement AC power flow control. The thesis presents the development of the mathematical models of a representative study system,
which is an adaptation of the IEEE First Benchmark system for the study of SSR to allow it to be used to analyse the effect of closed-loop power flow control on SSR stability. The mathematical models of the study system are benchmarked against proven and accepted dynamic models of the study
system. The investigations begin by examining the effect of a reactance-controlled SSSC-based power flow controller on the damping of torsional modes with an initial approach to the design of the control gains of the power flow controller which had been proposed by others. The results show how the nature and extent of the effects on the damping of the electromechanical modes depend on both the mode in which the power flow controller is operated and its controller response times, even for
the relatively-slow responding controllers that are obtained using the initial controller design approach. The thesis then examines the impact of a reactance-controlled SSSC-based power flow controller on the damping of torsional modes when an improved approach is used to design the
gains of the power flow controller, an approach which allows much faster controller bandwidths to be realised (comparable to those considered by others). The results demonstrate that for both of the modes in which the power flow controller can be operated, there is a change in the nature and
extent of the power flow controller’s impact on the damping of some the torsional modes when very fast controller response times are used. Finally, the thesis investigates the impact of a quadrature voltage-controlled SSSC-based power flow controller on the damping of torsional modes in order to compare the influence of the design of both Vsssc-controlled and Xsssc-controlled SSSC-based power flow controllers on torsional mode
damping for different power flow controller response times. The results obtained indicate that a Vsssc-controlled SSSC-based power flow controller allows a larger range of SSR stable operating points as compared to a Xsssc-controlled SSSC-based power flow controller. / Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2012.
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Investigations into the upgrading of transmission lines from HVAC to HVDC.Naidoo, Pathmanathan. January 2007 (has links)
Emanating from the proceedings of CIGRE 2004, a new idea for higher power transmission by recycling and up rating high voltage alternating current transmission lines for high voltage direct current application was presented at the HYDC working group session. To date, there is no known application of the idea. Globally, transmission congestion, power transfer bottlenecks with restricted and limited power transfers and unobtainable servitudes challenge electric power utilities. The literature review shows that since the early sixties, several authors have studied this proposal. However, no applications were done. Admittedly, early HYDC technology was troubled by problems with multi-terminal designs, external insulation breakdown in the presence of DC stress and mercury valve rectifiers struggled with arc backs. To date, power electronic and external insulation technology has grown and matured for confident application both in point to point and multi-terminal application. The economic costs of introducing the DC technology are also more affordable given reducing prices due to higher volume of purchases. With promising developments in insulation and power electronic technology and driven by South Africa's surging growth in the consumption of electrical energy; the subject of upgrading HYAC transmission for HYDC application is revisited. For the research, the emphasis is beyond FACTS and towards a solution that could develop into a new supergrid that could overlay the existing national grid. Thus, the solution is prepared specifically for the case of recycling existing assets for higher power transfers. The working environment is defined by the difficulty in acquiring new powerline servitudes, transmission congestion in complex networks, the need for electrical islands within complex interconnections, and the need for enhanced power system stability and to promote new ancillary services energy management. The focus of this research study was to determine the technical feasibility of upgrading of existing HYAC circuits for HYDC application. It is assumed that the transmission line will remain as is in structure, layout and mechanical design. The changing of external line insulators using live line technology is an accepted modification to the original HYAC line, if required. From the study, we conclude that not all HYAC lines are recommended for upgrade to HYDe. We introduce boundary conditions as a first step towards checking on the suitability of the proposed upgrade from HVAC to HYDC mode. Emanating from this study, the first paper published introduced the initial boundary conditions as being only those lines where the "unused gap" between surge impedance loading and conductor current carrying capability is appreciable and large; generally three to four times surge impedance loading. In the case where the unused gap is the smallest or negligible, then we do nothing. In between, where the unused gap is about two to three times the surge impedance loading, then we can consider active or passive compensation using the HVAC FACTS technology options as proposed by EPRl. Having determined the candidate transmission line configuration for the proposed upgrade to HYDC application, we select the DC operating voltage as based on the voltage withstand capability of external insulation for varying environmental conditions. In addition, the DC voltage will generate allowable electrical fields and corona effects within and outside the transmission servitude. The optimum DC operating voltage would satisfy the conditions of minimum transmission power losses and volt drop for the case of maximum power transfers; within the limits of electrical fields and corona effects. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2007.
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Protection of ultra long HVDC transmission lines.Naidoo, Divoloshanan. January 2005 (has links)
HVDC transmission is today widely used in modem Power Systems as an alternative to HVAC.
Current trends indicate that many future conventional HVDC systems will be systems of
increasing power ratings, delivered over larger distances as well as multi-terminal systems. In
order to ensure the security and dependability of such systems, the current protection schemes
need to be evaluated to assess their ability to provide adequate protection for the envisaged
HVDC systems. This research work firstly reviews the present HVDC transmission line protection
systems, and highlights their advantages and disadvantages, including factors that adversely
influence their performance. The author critically evaluates the current protection schemes and
reveals the drawbacks and other factors that render them unsuitable for the protection oflong
dc transmission lines. The author then goes on to propose and develop an HVDC line protection
system that will be able to provide adequate protection for proposed long HVDC transmission
lines. The proposed protection system is able to make decisions based solely on local detection
increasing its overall reliability. The author then recommends that the proposed protection
system be used in conjunction with the existing main protection system in order to optimise the
protection response times for both close in and distant faults. The author also proposes and
develops a method of further enhancing the reliability of the protection system by the use of
the telecommunication infrastructure when available. Finally the performance and feasibility of
the proposed protection system is evaluated using the results obtained from the extensive fault
simulations performed in EMTDC and Matlab. The simulations are performed using a bipole model
of an HVDC System on which the required line and protection systems are modelled. The
simulation results obtained are very favourable and promote the use of this proposed protection
system, for the protection of long HVDC transmission lines. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2005.
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The development of a guideline to assist with compiling asset management plans for transmission lines.Mansingh, Sharan. January 2010 (has links)
The overhead transmission line is a fundamental component in the power supply system as it links electricity supply to the various points on the electrical network. Failure of the transmission overhead line will result in interruption of supply and depending on the network configuration may result in long term outages. It is therefore essential that the overhead transmission line asset is inspected and maintained regularly to prevent premature failure.
Newer approaches to maintenance management are required to improve the overhead transmission lines performance and reduce the cost and risk associated with the asset. Asset management is seen as the process that can be adopted to enhance overall management of the overhead transmission line. The review of maintenance practices of various Utility’s and that of a pilot site made up of selected lines within Eskom’s North East Transmission Grid revealed numerous shortcomings in the current practices largely due to the application of traditional (non-holistic) methods. This situation supports the development of asset management plans which will cater for improvement
in performance, reduction in the risk and cost and achieving service level targets. This research has used asset management principles to design a guideline in the form of a flowchart for effective maintenance management for overhead transmission lines. The key benefits/advantages of the maintenance management guideline are as follows: It is closed loop and process driven.
Decision making is more scientific because it requires the use of historical performance data, detailed asset condition information and encourages quantitative analysis. Promotes defect and condition assessment tracking via the condition database. Rather than focusing mainly on defect management, the asset manager will be directed towards the performance specifications and the condition database to establish individual action plans which can be prioritized against short, medium and long term improvement plans per specific
asset. / Thesis (M.Sc.)-University of KwaZulu-Natal, Durban, 2010.
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Dynamic characteristics of bare conductors.Eshiemogie, Ojo Evans. January 2011 (has links)
The dynamic characteristic of transmission line conductors is very important in designing and
constructing a new line or upgrading an existing one. This concept is an impediment to line
design and construction because it normally determines the tension at which the line is strung
and this in respect affects the tower height and the span length. Investigations into the
phenomenon of mechanical oscillation of power line conductors have been extensively looked
into by many researchers using concepts from mechanics and aerodynamics to try and predict the
conductor dynamic behaviour. Findings have shown that precise prediction of conductor windinduced
vibration is very difficult i.e. non-linearity.
Over the years, various analytical models have been developed by researchers to try and predict
the mechanical vibration of transmission line conductors. The first part of this dissertation
considers the analysis of the model describing the transverse vibration of a conductor as a long,
slender, simply supported beam, isotropic in nature and subjected to a concentrated force. The
solution of this beam equation was used to obtain the conductor natural frequencies and mode
shapes. Conductor self-damping was obtained by the introduction of both external and internal
damping models into the equation of motion for the beam.
Next, also using the same beam concept was the application of the finite element method (FEM)
for the dynamic analysis of transmission line conductors. A finite element formulation was done
to present a weak form of the problem; Galerkin‟s method was then applied to derive the
governing equations for the finite element. Assembly of these finite element equations, the
equation of motion for the transverse vibration of the conductor is obtained. A one dimensional
finite element simulation was done using ABAQUS software to simulate its transverse
displacement. The eigenvalues and natural frequencies for the conductors were calculated at
three different tensions for two different conductors. The damping behaviour of the conductors
was evaluated using the proportional damping (Rayleigh damping) model. The results obtained
were then compared with the results from the analytical model and the comparison showed a
very good agreement.
An electrical equivalent for the conductor was developed based on the concept of mechanicalelectrical
analogy, using the discrete simply supported beam model. The developed electrical
equivalent circuit was then used to formulate the transfer function for the conductor. Matlab
software was used to simulate the free response of the developed transfer function.
Finally, the experimental study was conducted to validate both the analytical model and the
FEM. Tests were done on a single span conductor using two testing methods i.e. free and force
vibration. The test results are valid only for Aeolian vibration. From the test results the
conductor‟s natural frequencies and damping were determined. The experimental results, as
compared with the analytical results were used to validate the finite element simulation results
obtained from the ABAQUS simulation. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2011.
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