Core Fault Research Articles

Design and Performance Analysis of Single-Phase Pre-Saturated Core Fault Current Limiters

The technology of a presaturated core fault current limiter (PCFCL) has particular importance due to its instantaneous limitation of the fault current in electric power grids and keeping its value below the ratings of the switchgear or circuit breakers with a reasonable safety margin. In this paper, a design methodology of single-phase, simple nonsuperconducting magnetic coils, PCFCL is proposed based on extensive electromagnetic time-domain finite-element simulations taking into account the relative performances of the constructive design parameters. These controlled finite-element simulations allow fine realistic details, such as the nonlinear magnetic saturation behavior of the iron core to be included, and studying the effect on general performance during dynamic reactions of the system. Moreover, the dynamic behavior of PCFCL is characterized in terms of steady-state voltage drop across its terminals, counter electromotive force induced on the dc coil terminals, and limitation factor of the fault current. Dual-core and single-core designs are investigated with a comparison of their ability of limiting the fault current. Results reveal that the dual-core design has superior performance than that of the single-core one. Finally, a design methodology flowchart has been proposed which depends on the extensive simulation results of different PCFCL topologies and published experimental results, where changing either the governing constructive parameters or the magnetic iron core design are considered.

Multi-Domain Model of Faulty Stator Core for Thermal Effects and Losses Evaluation

In this work, a multi-domain model of the stator core of an electric machine is presented. Its electromagnetic behavior and the thermal dynamics are represented using Bond Graph. This approach makes apparent the topology of the machine and the energy exchange. This feature enables the model for the easy representation of faults and analysis of their consequences in the thermal/magnetic/electric domain. The proposed model is used for reproducing the behavior of the stator core during an inter-laminar insulation test. The model is capable to reproduce the thermal distribution when a fault in the stator core occurs. This contribution helps to estimate the additional iron losses due to the stator core fault based on the thermal distribution. Additionally, this methodology could help to define the proper maintenance intervention to be performed on the machine.

Hardware implementation of fault tolerance NoC core mapping

Due to performance and reliability, network on chip (NoC) is considered to be the future generation interconnect technique for multiple cores in a chip. This paper proposes a system level core mapping technique which improves the performance of the whole system, while rectifying the temporary faults and permanent faults in the system using error correcting codes and spare core. This technique mainly focuses on the core mapping and faults on the system. This results in reliable core mapping and improved performance when a fault-related error occurs on an NoC. At last, the proposed core mapping technique is simulated and verified on FPGA board (Kintex-7 FPGA KC705 Evaluation Kit).

Performance and Optimization Study of a Novel Compact Permanent-Magnet-Biased Fault Current Limiter

The permanent-magnet-biasing saturated core fault current limiter (PMFCL) is one of the most promising devices to limit the fault current. To improve the biasing ability of permanent-magnets (PMs) and reduce the cost of PMFCL, this paper proposes a novel compact permanent-magnet-biased fault current limiter (CPMFCL). The three-limb structure can reduce the size and cost; the optimal small-section structure can improve the biasing ability of PMs and reduce the usage amount of PMs. First, the principle, equivalent magnetic circuit, and small-section optimized structure are introduced. To validate the principle and performance of CPMFCL, various finite element analysis simulation and optimization study are performed in Maxwell-3D. A 220 V/10 A CPMFCL prototype is designed and tested. The simulation and experimental results demonstrate that, compared with traditional PMFCLs, the CPMFCL has the advantages of smaller size, better biasing capacity of PMs, lower possibility of demagnetization, and excellent fault clipping performance.

Study on OPGW Cable Grounding Technology in Power System

In electric power communication, OPGW cable plays an important role. In recent years, the natural arch secondary power station to reduce the OPGW stops communication optical cable frequent lightning strike or grid CLP Pressure discharge gap, led to the suspension of OPGW cable wire broken stocks fiber core fault, transmission of power communication business caused great threat. How to improve the lightning protection level of OPGW cable, let OPGW cable for electric power communication services safely and reliably, it is a problem worth our study. This article from the mechanism of OPGW cable damage caused by lightning, and analyzes the OPGW cable broken stocks of the original, and expounds the OPGW cable lightning protection level of improvement measures, further put forward through good grounding method effective measures to improve the level of OPGW cable lightning protection.

Single-phase magnetic cores’ faults diagnosis using FRA approach

Single phase cores made of Cold Rolled Grain Oriented (CRGO) sheets faults diagnosis method using frequency response analysis was presented in this paper. Using the Sweep Frequency Response Analysis (SFRA) approach, methodical analysis of each considered type of defect influence on FR diagrams was conducted. FR diagrams deviances noticed for analyzed faults of cores, were statistically described with interpretation, in respect to the core global condition evaluation.A developed model of inductive component tested core faults occurrence were simulated. FR diagrams deviations observed for core faults, were experimentally verified.

Development of a Saturated Core Fault Current Limiter With Open Magnetic Cores and Magnesium Diboride Saturating Coils

This paper describes the main characteristics and the performance of a saturated core type fault current limiter (FCL) rated 45 MVA (33 kV-800 A) to be provided by ASG Power Systems. The FCL, which has been submitted to preliminary laboratory testing, will be installed at a 275/33 kV substation in the U.K. and will reduce the fault current by 38%. The device is based on an open geometry of the magnetic cores which allows reduced size and the weight. Magnetic saturation of the cores is obtained by means of two magnesium diboride (MgB2) magnets. A numerical model of the FCL has been developed and validated and the interaction of the device with the power grid has been investigated. Details and results of the model are also discussed in the paper.

A Coupled Method for Evaluating Eddy Current Loss of NdFeB Permanent Magnets in a Saturated Core Fault Current Limiter

Eddy-current loss of NdFeB permanent magnets (PMs) is widely analyzed in PM motors. This paper proposes a coupled 2-D transient finite-element analysis (FEA) of the saturated core fault current limiter (SCFCL) and 3-D analytical model of PMs to evaluate eddy-current loss in SCFCL. The comparison between the result from coupled method and that from 3-D FEA verifies the applicability of the coupled method in analyzing eddy current loss of PMs in SCFCL. The 3-D analytical model of PM is applied to analyze the effect of segmentation on the reduction of PM's eddy-current loss. And the results show that segmentation along width has a better performance, which is also verified by 3-D FEA.

A Novel Hybrid Saturated Core Fault Current Limiter Topology Considering Permanent Magnet Stability and Performance

The saturated core fault current limiter (SFCL) is one of the most effective methods for limiting fault current. A permanent magnet (PM)-biased SFCL (PFCL) can reduce dc bias current and additional energy consumption. However, the thermal stability of NdFeB PMs in PFCL poses a major challenge. This paper proposes a novel hybrid-type SFCL (HSFCL) topology that can reduce this risk. In the HSFCL, a hybrid PM/dc coil is designed to saturate the core, and a fault-limiting reactor is used to guarantee fault-clipping performance. The new structure provides air-gap branches for the time-varying magnetic field produced by alternating current, which reduces the eddy current in the PMs and enhances their stability. Electromagnetic coupling is used to analyze the operating principles and characteristics of HSFCL. Finite-element analysis simulations were performed using Maxwell and compared with verification experiments, proving that HSFCL is efficient in fault clipping and PM reliability enhancement.

Textural-chemical changes and deformation conditions registered by phyllosilicates in a fault zone (Pic de Port Vieux thrust, Pyrenees)

Synkinematic phyllosilicates in fault zones can be used to deduce the deformation mechanisms and the conditions of fault activity, as their chemical composition, crystal structure and texture can record the different stages of deformation and fluid-rock interactions. The Pic de Port Vieux, a second-order thrust related to the major Gavarnie thrust in the southern central part of the Pyrenees Axial Zone, juxtaposes Triassic pelites of the hanging wall and Cretaceous limestones of the footwall. In order to investigate the mineralogical and geochemical changes and constrain the deformation conditions of thrusting, characterization of phyllosilicates was performed along a transect in the fault hanging wall pelites.The Triassic pelites are mainly composed of quartz, calcite, phyllosilicates (chlorite and K-white mica) and ±hematite. The core fault zone thickness is estimated to be about one meter of intensively foliated green pelites, whereas the damage zone is composed of several meters of red pelites. XRD data demonstrated that the difference in color is related to hematite which is only present in the damage zone. Phyllosilicates of the damage zone are mainly inherited/diagenetic K-white mica and chlorite. In the core zone, newly formed chlorite is abundant and preferentially located in veins. It is enriched in Fe compared to the chlorite of the red pelites. The well-defined foliation in the core zone is overlaid by preferentially oriented muscovite grains which have homogeneous compositions, with less Na and relatively more Fe than mica from the red pelites. Newly formed chlorite and muscovite in the core zone are synkinematic to the fault activity. They are both related to deformation processes and fluid rock interactions. Kübler index measurements and chlorite thermometry show that synkinematic phyllosilicates have registered a temperature of 270°C±23°C for the damage zone and 285°C±28°C for the core zone which are corresponding to lower-anchizone/epizone grade conditions. Numerical modelling with the geochemical modelling program PhreeqC was performed to determine the favorable conditions for the mineralogical change between red and green pelites. It suggests that the main critical parameter favoring hematite dissolution and chlorite precipitation in the core zone, is the redox conditions. According to the model, the chemical changes in the core zone occurred due to interactions with highly reductive fluids. In addition, the hematite dissolution maybe the source of iron for newly formed phyllosilicates in the core zone that are more iron rich compared to those from the red pelites.

Parameter Design and Performance Investigation of a Novel Bridge-Type Saturated Core Fault Current Limiter

A saturated core fault current limiter (SCFCL) is a promising device for limiting the fault currents effectively, and improving the safety and reliability of power systems. Due to the core structure and the coupling effect between the ac and dc windings, traditional SCFCLs suffer the drawbacks of insufficient clipping performance and large size. Moreover, theoretical analysis of fault clipping performance has received little attention. Therefore, this paper proposes a novel bridge-type SCFCL (BSFCL). Compared with the traditional type, the BSFCL effectively reduces size and cost by using a bridge-type structure. In addition, the proposed additional limiting inductor improves the fault clipping performance of SCFCL. This paper first presents the principle and characteristics of BSFCL. Then, a theoretical analysis of clipping performance and parameter design method of BSFCL are presented in detail. Finally, the principle and performance of BSFCL are validated through electromagnetic simulation and experiments. The simulation and experimental results demonstrate the effectiveness of the theoretical analysis and the structure. The influence of different BSFCL parameters on fault clipping performance is also discussed.

Electromagnetic modelling and detection of buried stator core faults

Interlamination insulation faults in the stator cores of large electrical machines can damage both winding insulation and stator core, thus confidence in electromagnetic test results is important. They may be validated by finite element (FE) methods, however the 3D models required for short faults are computationally challenged by laminated structures, requiring approximations. A homogenised 3D FE model was used to model faults buried in the teeth and yoke of the core, with a new experimental methodology developed to calibrate fault currents. Limitations were identified in modelling just a core section due to images and the constraint of axial packet air gaps on fault flux dispersion. A system of transverse 2D FE models of the principal fault flux paths in the core were constructed to estimate the differential impact on fault signals by the air gap presence and applied to the 3D FE model. Together with corrections for images this gave close predictions of experimental results, supporting the validity of the model. The verified electromagnetic test results now permit assessment of the threat that a detected buried fault presents.

Transient Modeling of Saturated Core Fault Current Limiters

A saturated core fault current limiter (FCL) essentially utilizes the dynamic and nonlinear magnetic behavior of steel cores to operate as a variable reactor. However, the nonlinear characteristic of magnetic materials has made modeling this unique device a difficult task. Hence, experimental measurements and finite-element method (FEM) analysis are the most common techniques used to characterize the transient behavior of the device. Both of these techniques, while accurate, cannot be used to analyze the transient electrical behaviour of FCLs in complex power systems, particularly when investigating power system switchgear behavior during fault events. FEM-based FCL modelling, despite its usefulness as a design verification tool, cannot be easily coupled to all electromagnetic transient programs that are in use today. This paper presents two modeling approaches to represent the saturated core FCL in transient network simulators: 1) the nonlinear reluctance model and 2) the nonlinear inductance model. Both models are implemented in pscad/emtdc and are validated by experimental results of a single-phase prototype saturated core FCL, where excellent agreement between the experimental and the modelling approaches is achieved.

Saturated Core Fault Current Limiters in a Live Grid

With two recent successful installations in a U.K. live grid, the saturated core fault current limiter (SCFCL) has become one of the leading candidates for commercial fault current limiting devices. In this work, we review the concept developed at Bar-Ilan University, which was later adapted by GridON, for a novel compact SCFCL. This SCFCL utilizes a superposition of a closed dc magnetic circuit and an open ac magnetic circuit to overcome the intrinsic problem of transformer coupling found in traditional SCFCL designs. It also allows the use of a single magnetic core for a full ac current cycle limiting. In addition, the relatively short path for the dc magnetic circuit supports copper coils as an alternative to superconducting bias coils, allowing easier market penetration. The performances of the SFCL devices installed in live grids are described.

A role-changeable fault-tolerant management strategy towards resilient NoC-based manycore systems

In hierarchically managed network-on-chip (NoC) based manycore systems with over one thousand processor cores, resource management is critical to efficient operation of the whole system. Meanwhile, the fault-tolerant design of the management structure is as important as the fault-tolerant design in the micro-structural level and the system level, which should require more attention towards constructing resilient manycore systems. This paper presents RCFTM, a hierarchical agent-based role-changeable fault-tolerant management strategy based on the modified role-changeable management framework for resilient NoC-based manycore systems. It is a distributed and adaptive strategy which can reconstruct the management hierarchy dynamically and it is capable of providing an intrinsic ability to tolerate various damages to the management hierarchy due to permanent core faults. The fault-tolerant capability of the RCFTM strategy is first evaluated with MATLAB for a large scale manycore system. Results show that the RCFTM strategy has better fault-tolerant capability than the conventional replacement strategy which relies only on backup cores. Then, the RCFTM strategy is implemented in C on a 5×5 NoC-based manycore system, where a full-system simulation platform is utilized. Experiments show that, with 20K bytes ROM and 35.6K bytes RAM footprint for the RCFTM strategy on each agent, the system can successfully tolerate both single and multiple core faults. Results also show that the RCFTM strategy only introduces less than 1.48% computing overhead of a working agent while the system is fault-free.

Three‐dimensional finite element analysis of large electrical machine stator core faults

Faults in the stator cores of large electrical machines can both damage local winding insulation and propagate to catastrophic failure. This study develops three-dimensional finite element models of inter-laminar insulation faults in order to obtain a deeper understanding of the electromagnetic behaviour of core faults and the sensitivity of sensing systems. The problem of developing a model that adequately reflects the laminar constraints of the structure, while remaining computable is addressed, together with eliminating images from boundaries. The model was validated by experimental measurement and results shown to be closely matched, with the fault current distribution also predicted. The sensitivity profiles for various fault positions and lengths were determined, which enables condition-monitoring sensors to be more specific about the location and true threat that a fault signal may pose to the machine.

Melanesia in Review: Issues and Events, 2013: Fiji

Melanesia in Review: Issues and Events, 2013Fiji Jon Fraenkel (bio) Papua New Guinea is not reviewed in this issue. The adoption of a new constitution figured centrally in 2013, as Fiji geared up for elections scheduled before the end of September 2014. Seven years on from the December 2006 coup, many in Fiji had become habituated to life under the military commander Voreqe Frank Bainimarama. Formerly prominent politicians hoped to make a comeback at the 2014 polls and often prepared for this by reviving old alignments. There was no sign throughout the year of the coup leader’s own much-anticipated political party. Economic recovery continued, but many investors held off, awaiting the outcome of the election. Bainimarama’s anti-Australian Pacific diplomacy figured prominently, but the stomach for continued squabbles with Fiji’s government was steadily waning in Canberra. In September, an election in Australia ended the Rudd-Gillard Labor Government and brought to office the LiberalNational Coalition under Tony Abbott with Julie Bishop as foreign minister committed to “normalizing” relations with Fiji. The year commenced with the ditching and attempted suppression of the interim government’s own Fiji Constitutional Commission (fcc) report, the shredded proofs of which were burned by police officers in the presence of a visibly distraught commission chair, Professor Yash Ghai (see Fraenkel 2013). Although the six hundred copies were impounded, the document was soon leaked and freely available on the Internet (fcc 2012). In January, President Ratu Epeli Nailatikau denounced the fcc draft as threatening “financial and economic catastrophe and ruin” (Nailatikau 2013). The commission, he said, had “succumbed to the whims of the few who have an interest in perpetuating divisions within our society.” These were bizarre claims, inspired by the regime’s discomfort with the ground-swell of popular political engagement occasioned by the fcc’s deliberations. The fcc had accommodated all of Bainimarama’s “nonnegotiable” demands, even endorsing—at least for those swearing an oath of allegiance—the far-reaching immunity provisions in its enabling decrees not only for perpetrators of the 2006 coup but also for those responsible for the 1987 and 2000 coups (fcc 2012, schedule 6, section 27; Fiji Government 2012a, 2012b; Fiji Government 1990, chapter 14). Its core fault was that it had offered a political settlement that was palatable to those still, more or less publicly, opposed to the regime. This was an affront to a government that was depicting its origins as a glorious social revolution rather than as a military coup aimed at ousting Bainima-rama’s archenemy, the former Prime Minister Laisenia Qarase. The military commander’s close ally, Land Force Commander Colonel Mosese Tikoitoga, accused Ghai of “falling in with [End Page 476] the wrong crowd,” claimed that the law professor’s attempts to distribute the fcc draft were illegal, and said that the Ghai constitution would have entailed a catastrophic return to the pre-coup order (Fiji Sun, 5 Jan 2013). For Tikoitoga, who was to become Fiji’s new military commander in early 2014, it was the army’s nation-saving experience on United Nations (UN) peacekeeping missions that was the inspiration for what he saw as its heroic role within Fiji (The Australian, 2 April 2013), and nothing could be allowed to turn back the clock. One of the locally based constitutional commissioners, women’s rights activist Peni Moore—once an enthusiast for the Bainimarama reform project (see McGeough 2009)—expressed bewilderment at the rejection of the fcc report (Fiji Times, 22 Jan 2013). Attorney General Aiyaz Sayed-Khai-yum said that “it would be highly discourteous for anyone to comment on or preempt the statement made by his excellency to the people of Fiji” (Fiji Times, 22 Jan 2013). President Nailatikau had reserved particular opprobrium for Ghai’s plans for a 144-member National People’s Assembly (including civil society appointees and representatives from the Great Council of Chiefs and tasked with initiating a national dialogue and electing the head of state), which he described as “anathema to democratic representation.” He also disliked provisions for a “transitional cabinet,” which he claimed would empower “corrupt” and often “incompetent” civil servants (Nailatikau 2013). Like his predecessor Ratu Josefa Iloilo...

Offline and Online Methods for Stator Core Fault Detection in Large Generators

Fault diagnosis techniques play a crucial role in large turbogenerators. Due to the fact that it can cause catastrophic damage to the machine in a very short time, the development of new and more efficient methods represents a huge challenge for the researchers. Following this, the aim of this paper is to present two real-scale experimental devices manufactured to study interlaminar short-circuit faults in the stator of large generators. The first one is based on a stack of laminations in which faulty sheets can be inserted. In the second device, a special attention is given to the development of a partial exciter of a real 125-MW turbogenerator. Experimental online and offline results are presented and show that the measurement of flux density at the level of the external key bar can provide information about a short circuit between laminations.

Dynamic core length in saturated core fault current limiters

A saturated core fault current limiter (SCFCL) is a non-linear core-reactor where the core is saturated by an external superconducting DC bias source to achieve a low core permeability at nominal AC currents. Fault current levels in the AC coils de-saturate the core and transform it to a higher permeability state, hence limiting the fault current. In this work we describe the transition between saturated and de-saturated states in three SCFCL configurations. The ‘effective core length’, Leff, of the SCFCL, defined as the length of the de-saturated AC core limb, is introduced for exploring this transition as a function of the current, I, in the AC coil. Practically, Leff allows one to see the SCFCL as an inductor with a variable core length, allowing calculations of the impedance of the SCFCL over the whole range of operating currents. The Leff(I) curve is further used to calculate the dynamics of the demagnetization factor in a SCFCL. We show that the strong change in the magnetic induction of a SCFCL at high current is the result of both increasing the effective core length and decreasing the demagnetization factor. The method and results presented here serve as an important tool for comparing between various SCFCL concepts not only by comparing their impedance values at the extreme fault and nominal current conditions but also by providing an insight into the full de-saturation process.

Effect of Magnetostriction on the Core Loss, Noise, and Vibration of Fluxgate Sensor Composed of Amorphous Materials

This paper presents a new multistructure fluxgate magnetic sensor composed of Metglas® Fe-based amorphous HB1 material. The core thickness of the fabricated structure is 0.0254 mm × 30 pieces, and its width is 5 mm. The magnetic loss of the fluxgate core is simulated through finite element analysis. The fluxgate sensor is experimentally analyzed over a frequency range 0.5-3 kHz. The sensor performance exploits the advantages of the multistructure core-shaped magnetic material as well as the second-harmonic operation mechanism. Excellent flux responses are detected for the triangular core sensor, which has different operating frequencies for magnetostriction variation, harmonic response, total harmonic distortion, noise level, sensor vibration, and sensitivity. The influence of magnetostriction, magnetic loss, and permeability in multiangled cores for different frequencies is analyzed. Our multistructure fluxgate sensor is suitable for various applications including power transformer and inverter for interior magnetic core fault detection, owing to its thin-film configuration, high sensitivity, high resolution, and low magnetic loss.