kV System Research Articles

High-Impedance Fault Identification on Distribution Networks

This paper presents a transient-based algorithm for high-impedance fault identification on distribution networks. It uses the discrete wavelet transform to monitor high- and low-frequency voltage components at several points of the power system, being able to indicate the most likely area within which the disturbance has occurred, without requiring data synchronization nor the knowledge of feeder or load parameters. The proposed algorithm is evaluated through electromagnetic transients program simulations of high-impedance faults in a 13.8 kV system modeled from actual Brazilian distribution grid data. Solid faults, capacitor bank switching, and feeder energization are also simulated, considering the system with and without distributed generation. Obtained results show that the algorithm significantly reduces the search field of the high-impedance fault, reliably distinguishing it from other disturbances.

Impact of Photo Voltaic Cells on Hybrid Microgrid

In order to reduce the green house gas emissions all over the world the investment on renewable energy infrastructure is increasing particularly in the distribution network. It is also observed that the power generated by distributed system is not only supplied through distribution system but also fed to the grid by appropriately transforming the voltage. It has the advantage that the power generated through distributed generation system is utilized in the grid for other users. The PV cell generates voltage at the distribution level. At the end of distribution line a 1 MVA three phase load is connected. In the absence of the generation from the PV cells, the voltages and currents at various lengths of the line are calculated with a single load of three phase 1 MVA. With the inclusion of PV cells, the improvement in voltage dip is also estimated. This estimate provides the power supplied by the PV cell and improvement in voltages. In order to determine the effect of additional load on voltage profile, a three phase load of 1 MVA was connected to intermediate point in the transmission system. This causes the dip in voltage at various nodes of the distribution line. Several combinations of source and loads have been examined to determine the effect on voltage and power. The above work has been carried out using Electro Magnetic Transient Program (EMTP), free version developed by university of British Columbia, Canada and made available through Indian EMTP user group. In order to simulate the system, 8.98 kV 5 km long line is divided into 5 sections of 1 km each. The sections are represented in the form of Pi-network by its series inductance, resistance and capacitance to ground. Loads are represented by R and L of appropriate magnitude and through EMTP program the calculations are done. The PV cell is represented by a source stepped up to 8.98 kV system. Both single phase and three phase lines have been examined through the above program. The results obtained for various conditions are presented in the paper.

National audit of a system for rectal contact brachytherapy

Abstract Background and purpose Contact brachytherapy is used for the treatment of early rectal cancer. An overview of the current status of quality assurance of the rectal contact brachytherapy systems in the UK, based on a national audit, was undertaken in order to assist users in optimising their own practices. Material and methods Four UK centres using the Papillon 50 contact brachytherapy system were audited. Measurements included beam quality, output and radiation field size and uniformity. Test frequencies and tolerances were reviewed and compared to both existing recommendations and published reviews on other kV and electronic brachytherapy systems. External validation of dosimetric measurements was provided by the National Physical Laboratory. Results The maximum host/audit discrepancy in beam quality determination was 6.5%; this resulted in absorbed dose variations of 0.2%. The host/audit agreement in absorbed dose determination was within 2.2%. The median of the radiation field uniformity measurements was 2.7% and the host/audit agreement in field size was within 1mm. Test tolerances and frequencies were within the national recommendations for kV units. Conclusions The dosimetric characterisation of the Papillon 50 was validated by the audit measurements for all participating centres, thus providing reassurance that the implementation had been performed within the standards stated in previously published audit work and recommendations for kV and electronic brachytherapy units. However, optimised and standardised quality assurance testing could be achieved by reducing some methodological differences observed.

A novel study for hydro-generators loss of excitation faults detection using ANFIS

This paper presents a new approach for Loss of Excitation (LOE) faults detection in hydro-generators using adaptive neuro fuzzy inference system. The proposed scheme was trained by data from simulation of a 345 kV system under various faults conditions and tested for different loading conditions. Details of the design process and the results of performance using the proposed technique are discussed in the paper. Three techniques are used in this article based on the type of inputs to the proposed ANFIS unit, the generator terminal impedance measurements (R and X), the generator RMS Line to Line voltage and Phase current (Vtrms and Ia) and the positive sequence components of the generator voltage magnitude, phase current magnitude, and angle (│V+ve│, │I+ve│, and ∟I+ve). The obtained results from these schemes are compared with each other and are compared with other techniques. The results show that the proposed technique is effective in detecting the LOE faults and the obtained results are very encouraging.

A novel phantom and procedure providing submillimeter accuracy in daily QA tests of accelerators used for stereotactic radiosurgery*.

Stereotactic radiosurgery (SRS) places great demands on spatial accuracy. Steel BBs used as markers in quality assurance (QA) phantoms are clearly visible in MV and planar kV images, but artifacts compromise cone‐beam CT (CBCT) isocenter localization. The purpose of this work was to develop a QA phantom for measuring with sub‐mm accuracy isocenter congruence of planar kV, MV, and CBCT imaging systems and to design a practical QA procedure that includes daily Winston‐Lutz (WL) tests and does not require computer aid. The salient feature of the phantom (Universal Alignment Ball (UAB)) is a novel marker for precisely localizing isocenters of CBCT, planar kV, and MV beams. It consists of a 25.4 mm diameter sphere of polymethylmetacrylate (PMMA) containing a concentric 6.35 mm diameter tungsten carbide ball. The large density difference between PMMA and the polystyrene foam in which the PMMA sphere is embedded yields a sharp image of the sphere for accurate CBCT registration. The tungsten carbide ball serves in finding isocenter in planar kV and MV images and in doing WL tests. With the aid of the UAB, CBCT isocenter was located within 0.10±0.05 mm of its true positon, and MV isocenter was pinpointed in planar images to within 0.06±0.04 mm. In clinical morning QA tests extending over an 18 months period the UAB consistently yielded measurements with sub‐mm accuracy. The average distance between isocenter defined by orthogonal kV images and CBCT measured 0.16±0.12 mm. In WL tests the central ray of anterior beams defined by a 1.5×1.5 cm2 MLC field agreed with CBCT isocenter within 0.03±0.14 mm in the lateral direction and within 0.10±0.19 mm in the longitudinal direction. Lateral MV beams approached CBCT isocenter within 0.00±0.11 mm in the vertical direction and within ‐0.14±0.15 mm longitudinally. It took therapists about 10 min to do the tests. The novel QA phantom allows pinpointing CBCT and MV isocenter positions to better than 0.2 mm, using visual image registration. Under CBCT guidance, MLC‐defined beams are deliverable with sub‐mm spatial accuracy. The QA procedure is practical for daily tests by therapists.PACS number(s): 87.53.Ly, 87.56.Fc

Reliability Evaluation of Double 12-Pulse Ultra HVDC Transmission Systems

Double 12-pulse ultra HVDC transmission systems of $\pm $ 800 kV and $\pm $ 660 kV have larger transmission capacities, more complicated configurations, more complex operation modes, and more components, in comparison to $\pm $ 500 kV or less HVDC transmission systems. Hence, the reliability evaluation of the ultra HVDC transmission system is more complicated than that of the HVDC system. To thoroughly describe different operating modes, this paper presents two new reliability measures for ultra HVDC transmission systems, that is, partial monopole forced outage times and partial bipole-forced outage times. Reliability evaluation models for individual subsystems, including converter transformers (CT), ac filters, converter valve groups, and smoothing reactors have been built considering operation modes and configuration characteristics. In particular, the reliability model of the CT subsystem was built by considering the type and the number of standby CTs, and that of the ac filter subsystem was built by considering the capacity state table of filters. A reliability evaluation model for ultra HVDC transmission systems was proposed by combining reliability logic relationships among subsystems and using the state enumeration method. Case studies of practical ultra HVDC transmission systems illustrate the correctness of indices and the proposed models. In addition, sensitivity analysis and standby analysis of major components were also conducted.

Reduction of Power Loss from Corona Phenomena in High Voltage Transmission Line 115 and 230 kV

The Power Loss from Corona Phenomena in High Voltage Transmission Line 115 and 230 kV were studied the effects of various elements that affect the power loss from corona in high voltage transmission line between Khon Kaen and Nakhon Ratchasima and the method to reduce power loss due to corona. This paper clarifies Peek's and Peterson's formula by utilizing Matlab program with the effect from different variables including conductor spacing, conductor radius and a system voltage. The Peterson's formula was suitable for the two systems than that of Peek's formula under the condition of phase voltage to corona inception voltage ratio. In the 115 kV system uses 795 MCM ACSR conductor with 1.447 cm radius and the spacing was 320 cm could generate a less power loss, and the 230 kV system uses 1272 MCM ACSR conductor with 1.75 radius, the spacing was 500 cm could generate a less power loss. When simulated to solve the conductor radius and the spacing that would have the less power loss. In 115 kV system, the suitable was 1.36 cm radius and 266 cm spacing and in 230 kV system the suitable was 0.85 cm radius and 660 cm. It therefore could reduce power loss by selecting the conductor radius and the conductor space increasing or protecting the system from the lightning.

Cascading Failure Analysis Considering Interaction Between Power Grids and Communication Networks

This paper aims to model interdependencies between power systems and dispatching data networks, and to analyze the intricate impacts on cascading failures. The functions of communication networks are embedded into dispatching data networks in China, thus we use dispatching data networks in the paper. The structures of dispatching data networks are generally categorized into two types: 1) double-star; and 2) mesh. The correlation of nodes in double-star networks and power systems is “degree to degree,” whereas “degree to betweenness” is the correlation for mesh networks. Furthermore, the interactive model between power grids and dispatching data networks is presented by a dynamic power flow model. Taking the IEEE 39-bus system and China’s Guangdong 500-kV system as examples, in the case of random attacks on the interdependent system, simulation results show that the power grid coupled with double-star dispatching data networks has lower probability of catastrophic failures than with the mesh structure, because the double-star dispatching data network has outstanding capability of delivering information even though some communication nodes are out of order. In contrast, under intentional attacks, the decrement of the transmission performance of the double-star network is more serious than that in the mesh network. Therefore, the power system exhibits much higher vulnerability when coupled with the double-star network.

Modeling and Simulation of Electrical Resonance in EHV Transmission Line Case Study in West Java Region 500 kV System

Electrical transmission line can be approached by the second order system with the model of capacitive, inductive, and resistive elements. In the system, the capacitive element is represented by the capacitance value between phases and phase to ground. In the other side, inductance of reactor and phase conductor represent the inductance element, whereas resistance of the phase conductor represents the resistance value of the system. As a second order system, the electrical transmission line is potentially experiencing the resonance phenomena if the natural frequency reaches the 50 Hz operation frequency. This paper explains the study of resonance phenomena in Extra High Voltage (EHV) 500 kV transmission line between two 500 kV Substation in West Java Region by the modeling and simulation. The results show that the transmission line is very vulnerable to the resonance phenomenon which is indicated by the existence of voltage up to 800 kV when this transmission line is not yet energized and causing one of the line arrester broken. The results also show that under the resonance phenomena, single pole auto reclose process is potentially failed. This study is expected to increase the concern for the resonance phenomena in the transmission lines.

Comparison of Power Loss Due to Corona Phenomena Model with Peek's Formula in High Voltage 115 kV and 230 kV System

This paper studied the power loss due to corona phenomenon with Gary's model and Peek's formula using Matlab program for the power loss simulation in 115 kV and 230 kV system that the corona loss varies with transmission conductor radius and spacing. The corona phenomenon effects on leakage capacitance and inductance of transmission line. The leakage current would increase in the condition of the corona incepted. The power loss due to corona has an inverse variation with radius and spacing of conductor. The Gary‘s model is not suitable for 115 kV. Due to the operating point of power system, the model losses had the value 7.5% with difference from the formula for 115kV system and 14.5% for 230 kV system.

SVM based zonal setting of Mho relay for shunt compensated transmission line

Abstract Presence of shunt FACTS (Flexible Alternating Current Transmission System) device significantly affect the performance of protection system and may create security and reliability issues. This paper introduces a novel approach for zone identification in transmission line employing shunt FACTS devices such as Static Var Compensator (SVC) and Static Synchronous Compensator (STATCOM). The technique depends on the modified apparent impedance seen by the impedance relay for all possible operating conditions. In this technique the Support Vector Machine (SVM) is used for discriminating faulty zone (zone 1 or zone 2). In addition an optimization technique viz. Genetic Algorithm (GA) is used to optimize SVM parameters. A typical 230 kV system was simulated in PSCAD/EMTP software and the results show that the proposed scheme is secure, accurate and reliable under the wide variation in power system parameters like load angle, fault resistance, fault location, inception angle and compensation level.

An adaptive approach for three zone operation of digital distance relay with Static Var Compensator using PMU

Modern energy transmission systems suffer from great voltage dropping due to enormous loads. Therefore appropriate schemes should be devised to regulate the voltage. FACTS devices such as Static Var Compensator are often used for this purpose. However, SVC at mid-point of transmission line may leads to deteriorate of distance relay operation, resulting in inaccurate estimation of faults locations i.e. over-reach or under reach for different cases. This paper proposed a new algorithm that utilizes synchronized phasors measurement (SPM) to enhance the operation of distance protection zone in many aspects. The proposed method is tested for 230 kV system simulated in EMTDC/PSCAD with Bergeron model of transmission line. The results prevailed for adaptive approach scheme are more accurate, victor and robust in equivalence with usable transmission line distance protection with SVC.

Impact of the EHV Power System on Geomagnetically Induced Currents in the UHV Power System

Earlier calculations of geomagnetically induced currents (GICs) in Chinese power grids have mainly concentrated on the highest voltage-level system whose geomagnetic risk is considered to be the largest, thus ignoring secondary voltage-level systems. With the 1000-kV system being newly added to China's power system, it is significant to figure out the interaction between GIC in the 500 kV [extremely high voltage (EHV)] system and GIC in the 1000 kV [ultra-high voltage (UHV)] system. Based on the North China-Central China-East China Power Grids, this paper establishes a single-voltage grid by only considering the 1000-kV system and a dual-voltage grid by considering the 1000- and 500-kV systems and investigates GIC in these two grids by developing their GIC “Full-node models.” The impact of the 500-kV system on GIC in the 1000-kV system is analyzed. GIC risks in the UHV and EHV systems are assessed by comparing calculated GIC data with monitored values of GIC. The results show that the impact of the 500-kV system on GIC in the 1000-kV system is obvious, both the EHV and the UHV grid have a high GIC risk. So calculating GIC in the UHV system and in the EHV system should utilize GIC modeling methods for multivoltage power grids.

Mitigation of Geomagnetically Induced Currents by Neutral Switching

This paper presents a novel mitigation technique to reduce the effects of geomagnetically induced currents (GICs) on high-voltage power systems. The method consists of connecting switching devices at the neutral grounding connection point of transformer banks. Only one transformer bank needs to be grounded through a switch to reduce GIC in a two-terminal system. For multiterminal systems, $n-1$ switches are necessary and the operation is independent from each other. The switching frequency and the duty cycle are selected from a tradeoff between the effectiveness of the method and the detection of fault currents. Transient simulations on a two-bus 230/500 kV system show that the proposed switching at the neutral successfully mitigates the GIC. This proposed technique opens the door to a new family of GIC mitigation methods.

A Novel Ground Fault Identification Method for 2 × 5 kV Railway Power Supply Systems

The location of ground faults in railway electric lines in 2 × 5 kV railway power supply systems is a difficult task. In both 1 × 25 kV and transmission power systems it is common practice to use distance protection relays to clear ground faults and localize their positions. However, in the particular case of this 2 × 25 kV system, due to the widespread use of autotransformers, the relation between the distance and the impedance seen by the distance protection relays is not linear and therefore the location is not accurate enough. This paper presents a simple and economical method to identify the subsection between autotransformers and the conductor (catenary or feeder) where the ground fault is happening. This method is based on the comparison of the angle between the current and the voltage of the positive terminal in each autotransformer. Consequently, after the identification of the subsection and the conductor with the ground defect, only the subsection where the ground fault is present will be quickly removed from service, with the minimum effect on rail traffic. This method has been validated through computer simulations and laboratory tests with positive results.

SU-E-I-39: Combining Conventional Tomographic Imaging Strategy and Interior Tomography for Low Dose Dual-Energy CT (DECT)

Purpose: Dual-energy CT (DECT) affords quantitative information of tissue density and provides a new dimension for disease diagnosis and treatment planning. The technique, however, increases the imaging dose because of the doubled scans, and thus hinders its widespread clinical applications. The purpose of this work is to develop a novel hybrid DECT image acquisition and reconstruction strategy, in which one of the energies is dealt by interior tomography while the other one is obtained using conventional tomography approach. Methods: In the proposed hybrid imaging strategy, the projection data of one of the energies (e.g., high-energy) were acquired and processed in an interior scanning model, whereas the other energy in the conventional tomographic approach. It known that, if the ROI is piecewise constant or polynomial, the interior ROI can be reconstructed with TV or HOT minimization. Here we extend the TV based interior reconstruction method into dual-energy situation. The ROI images so obtained were overlaid in the context of conventional CT of the companion energy. A material based composition in ROI was used in the proposed reconstruction framework. Results: In the simulation experiment with a diagnostic DECT geometry and energies, we were able to derive the densities of soft-tissues and bonesmore » in the ROI with high fidelity. In the experimental CBCT study, both kV and MV data were collected using the on-board kV and MV imaging system. The MV data were truncated only across the ROI. Using the interior tomography reconstruction above, we were able to obtain the ROI images as that obtained using un-truncated MV data with known tissue densities. Conclusion: The proposed DECT imaging strategy provides an effective way to extract tissue density information in the ROI and in the context of anatomical images of CT imaging, with much reduced imaging dose.« less

Study on the Application of a Flux-Coupling-Type Superconducting Fault Current Limiter for Decreasing HVdc Commutation Failure

Commutation failure is a serious malfunction in high-voltage direct current (HVdc) converters and is mainly caused by ac side faults, where the change of dc current during fault conditions should be given adequate attention. Employing superconducting fault current limiters (SFCLs) for an HVdc system can suppress its dc fault current’s amplitude and maintain a small rate of the dc current change, which is helpful to inhibit the commutation voltage reduction. Accordingly, introducing SFCLs may act as one possible solution to decreasing HVdc commutation failure. In this paper, a flux-coupling-type SFCL is adopted to play this role. The SFCL’s topology structure and working principle are presented first, and then its influence mechanism to HVdc commutation failure is systematically investigated. Further, considering several different fault conditions, the transient performance of a 500-kV HVdc system equipped with the SFCLs is evaluated in MATLAB. From the results, installing the SFCLs can effectively decrease the duration of the commutation failure and facilitate the fault recovery process, and sometimes a possible successive commutation failure is avoided, as a result of improving the power transmission characteristics. Finally, in view of ac loss and equipment selection, the application feasibility of the SFCL for a high-voltage/large-scale system is preliminarily discussed, and some valuable conclusions are obtained.

Daily image-guidance in prostate cancer radiotherapy - implications for treatment margins.

Our purpose was to evaluate interfractional organ and patient movement during radiotherapy of prostate cancer and to calculate the necessary CTV to PTV margins. Fifty patients irradiated between 2009 and 2011were included into the prospective study. The 2D-2D KV system combined with the intraprostatic fiducial marker were used for daily position verification. Based on the 8629 measurements of isocentre displacement an interfractional motion of pelvis and prostate was evaluated. The CTV to PTV margins were calculated. Margins of 0.7 cm (AP), 1 cm (SI) and 0.35 cm (LR) are necessary when only bony based IGRT is performed. Margins of 1.0 cm, 1.8 cm and 0.5 cm in AP, SI and LR directions respectively are necessary in case of no IGRT.There was no clinically relevant changes in patient/target mobility throughout the whole treatment. The IGRT is essential for state of art radiotherapy of prostate cancer. Necessary CTV to PTV margins are much bigger in case of no IGRT performed. Changing of margins size throughout regular treatment is not necessary. IGRT, prostate cancer, fiducial marker.

Practical Implemention of Gaopf on Indian 220kv Transmission System

This paper presents the practical implementation of developed genetic algorithm based optimal power flow algorithms. These algorithms are tested on IEEE30 bus system and the results were presented in the paper [8]. The same algorithms now tested on 220KV Washi zone Indian power transmission system . The GAOPF with fixed penalty and Fuzzy based variable penalty tested on 220KV transmission system consists of 52 bus and 88lines. The fuel costs ,computational time and the system condition were studied and the results are presented in this paper .Also the available load transfer capability of the 220KV system for congestion management is also presented

Is it possible and expedient to create a global energy network

The world–wide distribution of primary energy resources does not correspond to the geographical allocation of zones of their consumption. Electricity production and power–plant generating capacity grow everywhere including regions where there are no resources. Electrical power systems already cover not only individual countries, but also groups of countries, and even entire regions. Therefore, the following problem arises: is it possible and expedient to interconnect regional power systems so as to form a global energy network? The technical facilities for such a network are already available: DC transmission systems with voltages up to ± 750 kV and AC transmission systems with voltage up to 1200 kV. The transfer capacities of such transmission systems can reach 5000–6000 MW. There are no technical limitations on constructing international DC electrical transmission systems through any straits. The longest existing DC submarine cable link from Finland to Sweden along the bottom of Botnic Bay has a voltage of 400 kV and a cable length of about 200 km. The efficiency of large regional and international electrical power system interconnections between East Europe–West Europe, USSR–Canada–USA, USSR–Japan, USSR–China is to be investigated. The five countries participating in these interconnections (USA, USSR, Japan, China, Canada) generate almost 60 per cent of all the electric power produced in the world.