High Voltage Engineering is an important task at the Graz University of Technology since the early 1970s. Additional importance was given by the national decission, to offer this university and research activities for Austria in Graz only. Therfore this paper reports—based on the history—the actual situation of university education and research activities in the field of high voltage engineering and gives impressions on high voltage (HV) and extra high voltage (EHV) test facilities and test examples at the accredited laboratory of this university.
This paper gives an overview of research activities in the area of high voltage engineering in UK universities. It summarises the main activities of all active high voltage research groups. Furthermore, current research drivers and funding sources for research in the area are described, and the main initiatives to safeguard the health of the discipline are presented.
This paper describes an outline of the Honshu-Shikoku Interconnecting Transmission Line which includes the first large-scale cable line. The most significant feature of this transmission line is the installation of 500kV cables along various types of bridges. This brought many previously unknown technical hurdles such as techniques to overcome movements and vibrations of a series of large bridges. These hurdles were cleared through various efforts and techniques by the concerned parties.
Analysis of the EMTP transformer model was performed with the 4kVA two windings low voltage transformer with the current injection (CIJ) measurement method to study a transient recovery voltage (TRV) at the transformer limited fault (TLF) current interrupting condition. Tested transformer's impedance was measured by the frequency response analyzer (FRA). From FRA measurement graphs leakage inductance, stray capacitance and resistance were calculated. The EMTP transformer model was constructed with those values. The EMTP simulation was done for a current injection circuit by using transformer model. The experiment and simulation results show a reasonable agreement.
Transient current distributions within the grounding systems of a wind-turbine-generator (WTG) tower struck by lightning and its neighboring WTG tower, and transient electric field inside these towers have been calculated using the finite-difference time-domain (FDTD) method. The grounding terminal for the generator inside the lightning-struck WTG tower is connected to that inside the neighboring WTG tower through a long insulated wire. About 40% of the lightning current flows in the grounding grid of the neighboring tower at 30μ s. Inside the towers, the radial component of electric field is most significant. Its peak value is about 1kV/m near the base of each tower when a lightning current having a magnitude of 30kA and a 10-to-90% risetime of 2.5μ s is injected. The electric field decreases with increasing the height of the observation point in the towers. When the grounding terminals are buried below the substructure (the grounding grids are connected via an underground insulated wire), the electric field inside the tower is significantly reduced.
Fundamental investigations were carried out to find out the admixing influence of CF3I to CO2. Firstly, thermodynamic properties at 0.1MPa were derived in a temperature range of 300-30,000K for various CF3I-concentrations XCF3I. Secondly, from the thermodynamic properties, a temperature-reduction factor was determined as a function of the temperature for different XCF3I. This determination led to the suggestion that admixture of CF3I to CO2 at XCF3I above 0.9 can produce a rapid effect on decay in the temperature of an extinguishing arc. Finally, the principal particles present after an arc extinction were obtained in consideration of the phase transformation of iodine molecules at 0.1MPa. For instance, the principal particles proved to be CO2, CF4 and CO in the gaseous phase and I2 in the solid phase for XCF3I of 0.01-0.94.
Gapless Metal (Zinc) Oxide Surge Arresters for a.c. systems contribute to the insulation co-ordination based on the suppression of lightning surges and switching surges. These gapless metal oxide surge arresters using ZnO elements are effective to HVDC systems. This paper describes basic characteristics of ZnO (zinc oxide) elements for d.c. systems and applications of gapless surge arresters to HVDC 125kV frequency converters, HVDC 250kV, upgrade HVDC 500kV converter stations, and HVDC 500kV cables of Japan through the experience of developments and applications of gapless metal oxide surge arresters.
Taking the densities of lightning strokes and electric poles into account, we calculated outage rates of each equipment on a 6.6kV distribution line due to summer (Mar.-Oct.) and winter (Nov.-Feb.) lightning for 6 years in the Chugoku region located in the western part of Japan. Furthermore, using these results, we proposed some application maps for the lightning risk assessment of power distribution lines in this region considering the effect of seasonal lightning hazard.
In this study, we experimentally examined the possibility of the internal short circuit of an air switch due to the sparkover between different poles under the condition that no surge arrester exists in neighboring poles and one of three surge arresters is omitted at the pole with an air switch. Experiments at Shiobara Testing Yard and Akagi Testing Center of CRIEPI clarified the following. Fault current may flow via the grounding point of a pole with an air switch and that of the next pole on a different phase from grounded phase of the pole with an air switch. If the low-voltage wire, overhead ground wire or communication wire forms a short circuit between them, ultimately the air switch may burn out. Moreover Fault current continues even if the length of the short-circuit between different poles is increased. Although the increase of the short-circuit length results in the increase of wire impedance, the amount of increase is still small compared with source impedance.
Silicone rubber (SiR) is used as covering material for polymeric outdoor insulators, which has an advantage of surface hydrophobicity that may suppress the discharges under wet contaminated condition. Dynamic Drop Test (DDT) is suggested in CIGRE for the evaluation of stability of hydrophobicity of polymeric insulating material under combined electric and electrolytic pollution stress. In this paper, the mechanism of the hydrophobicity loss of SiR in DDT has been studied experimentally using newly devised electrode. The setup of the experiments enabled to examine the effects of charged water drops and the electric field separately. The effect of test liquid drop sliding down the surface on the hydrophobicity loss was also examined. Through these experiments, the process of the hydrophobicity loss in DDT has been explained by dividing the process into three phases. It is concluded that the effects of charged water drops and the electric field that governed the results of DDT caused the reduction of the hydrophobicity of SiR surface before the discharges, which introduce the reorientation of polar groups.
Recently, the number of outages of wind turbine generator systems has been increasing. For rational lightning protection design, the concept of lightning risk management has been proposed. In this paper, lightning risk assessment of the wind turbine generator systems is carried out and it is compared with field experiences. Furthermore, lightning risk management scheme is discussed.
Recently, numerical electromagnetic field computation methods, which solve Maxwell's equations, have become a practical choice for the lightning surge analysis of power systems. Studies of lightning surge response of a transmission tower and lightning-induced voltages on a distribution line have already been carried out using the numerical electromagnetic field computation methods. However, a direct lightning stroke to a distribution line has not yet been studied. The authors have previously carried out pulse tests using a reduced-scale distribution line model which simulate the direct lightning stroke to a distribution line. In this paper, first, the pulse test results are simulated using the FDTD (Finite Difference Time Domain) method which is one of the numerical electromagnetic field computation methods, and comparisons are shown to validate the application of the FDTD method. Secondly, we present lightning surge characteristics of an actual-scale distribution line obtained by the FDTD method. The FDTD simulation takes into account the following items: (i) detailed structure of the distribution line; (ii) resistivity of the ground soil; (iii) propagation speed of the lightning return stroke.
It is effective to design the lightning protection of transmission lines by employing simulation to be able to reproduce conditions of experienced lightning faults. As a result of the lightning faults on 275kV transmission lines in Hokuriku area, the frequency of only one-ground fault of upper or middle lines is higher. Especially, the frequency of one-ground faults of the middle lines in summer is the highest. It is thought that many one-ground faults in summer are caused by direct lightning strokes to phase conductors. Moreover, multi-ground faults caused by lightning strokes to tower tops or overhead ground wires also include many ground faults of the middle lines. In this paper, the experienced lightning faults on the 275kV transmission lines are reproduced by EMTP calculations and the characteristics of the ground-fault lines are examined.
Silicone rubber for polymer insulator has an excellent hydrophobicity with recovery properties, resulting in higher pollution performance. However it is inevitable that even silicone rubber polymer insulators start generating corona discharge with time under humid and polluted conditions. And such a corona discharge causes rubber damage because of acid generation. Since it is assumed that the corona discharge characteristics depend on humidity and polluted conditions, corona discharge tests were conducted on silicone rubber polymer insulators by changing humidity and polluted conditions. As a result, it was verified that the corona discharge phenomena were affected by humidity and pollution even on silicone rubber polymer insulators, and that contribution of corona rings to suppressing the discharge was not large.
The operating voltages of low-voltage control circuits in power plants and substations have become lower owing to the installation of digital-control equipment. This significantly increases the risk of faults and malfunctions of such circuits due to abnormal voltages in the control circuits induced by lightning and switching surges. Therefore, the prediction of the induced voltages is strongly required for protecting such circuits from abnormal voltages. Recently, the FDTD (Finite Difference Time Domain) method, which solves Maxwell's equations numerically, is applied to the simulation of surge phenomena on conductors placed in three-dimensional arrangements such as transmission towers and buildings. The FDTD method can easily take into account the finite conductivity and relative permittivity of the ground soil and ground structure in detail. These parameters affect the induced voltages on control circuits. In this paper, first, we perform the FDTD calculations for a grounding grid whose size corresponds to a distributing-substation area. Second, we calculate the potential rises of the grounding grid, currents flowing through the grounding grid, and induced voltages on a control wire above the grid. Comparing the calculated results with the measured ones, we confirm the applicability of the FDTD method to the calculation of the induced voltages on the control wire generated by current flowing into the grounding grid.
Output power in photovoltaic systems changes steeply with the change of the solar radiation intensity. The change of the output power has influence on the electric power quality of the system. This paper proposes a residential distributed-generating system with solar cells and fuel cells. In order to smooth the output power which changes steeply the fuel cells are connected to the PV system in parallel. Thus the generated power of all the system can be smoothed. However, the steep changes of the electric power generated in the PV system can not be smoothed. The electric energy storage system with the EDLC is connected in parallel with the PV and FC systems. It is confirmed by the simulation that the proposed distributed-generating system is available for a residential supply. Provided that the proposed system is introduced in 2020, the cost of the proposed system is compared to that of the present system.
NaBH4-Fuel Cell system, which can respond to increasing demands for power in a mobile device, has attracted much attention as an alternative power source for lithium batteries due to the advantages. However, before the system can be of practical use, hydrogen must be efficiently generated from the NaBH4. We have conducted optimization of the hydrogen generation reactor as function of several factors, which we present in this paper. An optimized aspect ratio between diameter and length of catalyst layer in a reactor exists, and the value can be conducted as a function of hydrogen generation rates and the catalyst mass. The reactor which supplies hydrogen to a 1.2kW class fuel cell system has only 53.1ml of the internal volume, and it can generate 21L/min of hydrogen with 100% efficiency. For the purpose of adding a pressure buffer to the reactor, it has been recognized that pressurized conditions bring no influence in H2 generation up to 0.4MPa. Moreover, we have developed and validated a NaBH4-Fuel Cell system that uses a pressure-buffer to supply hydrogen stably under variable loads.
Electricity price forecasting is becoming increasingly relevant to power producers and consumers in the new competitive electric power markets, when planning bidding strategies in order to maximize their benefits and utilities, respectively. This paper proposed a method to predict hourly electricity prices for next-day electricity markets by combination methodology of ARIMA and ANN models. The proposed method is examined on the Australian National Electricity Market (NEM), New South Wales regional in year 2006. Comparison of forecasting performance with the proposed ARIMA, ANN and combination (ARIMA-ANN) models are presented. Empirical results indicate that an ARIMA-ANN model can improve the price forecasting accuracy.
The purpose of this research is to minimize a transmission loss and the number of times of VAR devices motions in power system. We formulate Voltage Reactive Power Control (VQC) with Particle Swarm Optimization (PSO) on this problem, and propose Multi Objective PSO (MOPSO) whose objective functions are a transmission loss and the number of times of VAR devices motions.