External Short Circuits Research Articles

Analysis of Measures that Exclude the Non-Selective Actions of Differential Collecting Busbar Protection in External Two-Phase Short Circuits with the Saturation of Current Transformers Included in Fault-Free Phases

An analysis is made on the non-selective actuation of the differential protection of busbars with a voltage of 110 kV of an electrical distribution system substation in the transition mode of an external two-phase short circuit. The protection effect is found to be due to the saturation of the transformer cores of class P current included in fault-free phases. Methods are also analyzed to ensure the correct operation of protection in the considered mode, and methods for calculating the protection parameters at which these methods are workable are proposed.

On The Impact of the Locality on Short-Circuit Characteristics: Experimental Analysis and Multiphysics Simulation of External and Local Short-Circuits Applied to Lithium-Ion Batteries

Emulating true, field-like internal short-circuits (ISCs) by experimental methods is a complex task with mostly unsatisfactory outcome. However, understanding the evolution and impact of ISCs is crucial to mitigate safety issues related to lithium-ion batteries. Local short-circuit (LSC) conditions are applied to single-layered, small-sized (i.e. <60 mAh), and single-side coated graphite/NMC-111 pouch-type cells in a quasi-isothermal test bench using the nail/needle penetration approach. The cell’s impedance, capacity, and the contact resistance at the penetration site mainly define the short-circuit current and, hence, the terminal voltage and heat generation rate associated with polarization effects and electrochemical rate limitations, which are correlated to the cell’s behavior during external short-circuits (ESCs) at various short-circuit resistances. Measuring the electrical potential between the needle and the cell’s negative tab allows to evaluate the polarization across the electrodes and to estimate the short-circuit intensity. LSC simulation studies are used to correlate current flux and resistance to ESC conditions. Double-layered cells are penetrated to create short-circuit conditions within either a single or both electrode stacks to study the difference between multiple LSCs (e.g. during a nail penetration test) and a single LSC (e.g. due to a particle/dendrite). Post-mortem analysis reveals copper dissolution/deposition across both electrodes.

Impact of Cell Size and Format on External Short Circuit Behavior of Lithium-Ion Cells at Varying Cooling Conditions: Modeling and Simulation

A multidimensional multiphysics model is presented to describe the external short circuit behavior of lithium-ion cells of various formats and sizes at different convective cooling conditions. For this purpose, a previously published homogenized physical-chemical model of the external short circuit behavior of a small-sized lithium-ion cell was combined with an electrical and a thermal model to describe in-plane inhomogeneities in current density and heat generation rate throughout the electrodes, together with the resulting temperature distribution within the cell’s jelly roll or electrode stack. With the investigated cylindrical, prismatic, and pouch-type cell formats combined with cell capacities ranging from consumer-sized to automotive applications, a comprehensive cell design study is presented during external short circuits. The investigated surface and tab cooling strategies reveal a limited cooling capability of each cell format and size, which seems to be defined by the ratio of cooled surface area to electrode area as well as the thermal resistivity of the respective cell geometry. The simulation results show that only thin cells with a large ratio of cooling surface to electrode area can be physically maintained within an uncritical operating window of cell temperature and state of charge in case a low-resistance external short circuit is applied.

Power transformer protection using an instantaneous-current-value negative sequence differential element

This paper proposes a new algorithm for power transformer differential protection based on the instantaneous-current-value negative sequence current signals, which are reconstructed in discrete time-domain from the negative sequence phasor for the different transformer windings. Aiming to provide a more reliable operation of the proposed method, the ratio of the operating and restraint negative sequence current signals is integrated during the time. Also, as a by product, a new instantaneous-current-value harmonic restraint strategy is also proposed, to improve protection security for external faults with current transformer (CT) saturation. In order to evaluate the performance of the proposed algorithm, a wide variety of faults are simulated in the Alternative Transients Program (ATP) by varying the fault type; short-circuited turns percentage; sources strength and the power system loading. The obtained results reveal that the proposed method is able to detect turn-to-turn and turn-to-ground faults even for 1% of short-circuited turns, in such way that it may be more sensitive and faster than the traditional differential elements widespread used by manufacturers in real world protection applications. Therefore, the developed algorithm is an excellent complement to the conventional differential functions, for the most faster and sensitive operations for internal faults involving few turns, and safe for external short circuits with CT saturation.

Real‐time diagnosis of high‐speed rail traction transformer in different topologies

High-speed railway (HSR) traction transformer, as a connection between traction power supply system and the power grid, is critical in electrified railway design, which requires a drastic change of traction load and frequent external short circuits. In the actual operation process, the traction transformer can produce minor faults that are difficult to detect such as the deformation of the winding, which may result in a serious problem. This study analyses the topology structures and winding fault characteristics of six HSR traction transformers consisting of single phase, Vv, YNd11, Scott, YNvd and impedance matching wiring. Both circuit models of normal operation and fault operation of HSR traction transformer are established. Results show that real-time diagnosis of HSR traction transformer can be accomplished through measuring the voltage signal of the input and output points during operation and establishing real-time monitoring statistics of small faults standardisation（I 2 and squared prediction error）based on fast independent component analysis algorithm, as well as the signal statistics distribution, thereby improving the safety and reliability of HSR operation.

Experimental study of internal and external short circuits of commercial automotive pouch lithium-ion cells

In order to develop a deeper understanding of the behaviour of commercial automotive lithium-ion pouch cells under short-circuiting conditions, two scenarios were experimentally investigated and compared. Firstly, experiments were conducted by internally shorting 15 Ah cells by full nail penetration using three different nail materials; copper, steel and plastic. A second set of experiments involved externally shorting the cell tabs using an external circuit with a range of resistance values. In both scenarios the cell electrical and thermal response were determined by the shorting resistance. In the case of nail penetration there was a clear distinction between the outcome of the conducting and non-conducting nails, although the outcome using conducting nails suffered from poor reproducibility. The poor reproducibility was attributed to the variation in the contact resistance between the nail and the cell layers. Correlating the outcome of both tests can be used to estimate the shorting resistance and construct the current profile during nail penetration test.

Bias signal control in differential protection

The problem is to ensure the stability of the differential protection functioning at deep saturation of the cores of electromagnetic current transformers. The errors of current transformers support the greatest influence on the operation of differential protections. Features of the differential protection operation at deep saturation of current transformers in short-circuit transient modes are considered. Comparison results of various algorithms for the formation of a bias signal are given. The control capability of the bias signal generation algorithm was analyzed. The harmonic composition of the differential current on the mathematical model of two-arm differential protection in the transient mode with external and internal short circuits at saturation of the current transformers of one arm was investigated. The stability of the differential protection functioning can be enhanced by the selectivity of the bias signal generation algorithm. A bias signal control criterion using a relative level of higher harmonics to a differential signal was proposed.

Multi-Physics Modeling of Impact Safety of Lithium-Ion Batteries

As lithium-ion batteries are more and more widely used in electrical vehicles and hybrid electrical vehicles, their safety has become a primary concern due to their high energy densities and wide-range working conditions. Previously, experiments such as crush tests, have attempted to mimic the failure process of batteries under abuse conditions, but they usually only give binary pass/fail results and provide limited details of the root causes of failure. Recently, computational modeling has gained a lot of interest because it provides an efficient tool to capture fundamental mechanisms of battery failure. Nevertheless, most of existing models of battery safety either treat the battery as a homogeneous solid and only consider its mechanical response, or focus on the thermal-electrical coupling without consideration of mechanical influence. Here we present a three-dimensional multi-physics model of battery safety that is able to predict coupled mechanical, thermal, electrical and electrochemical responses of automobile lithium-ion batteries under mechanical abuse. This model resolves each component in unit cells of a large format Li-ion cell and applies one-way coupling between mechanical and other types of responses to accommodate the significant differences in time scales. In particular, the mechanical solver predicts the onset of internal or external short circuit at the initial stage of an impact, and then the coupled thermal and electrical solver captures the evolution of temperature and current distribution after short circuit initiation. The electrochemical response is captured by a spatially distributed equivalent circuit model, where empirical parameters are obtained from experimental data. This model has been applied to capture internal and external short circuits and subsequent thermal and electrical responses in different types of cells and modules. Various element formulations have been evaluated to achieve the computational efficiency that will be required for future pack simulations. Model predictions have been compared with experiment data, demonstrating the model capacity and providing insights into the failure mechanisms of batteries during an impact process.

Improving Pulp and Paper Plant MV Transformer Protection

In pulp and paper plants, power transformers play a critical role in process continuity. These transformers are subject to internal short circuits, external short circuits, and abnormal operating conditions. The following protection challenges to power transformers will be explored, and methods to improve the protection are provided. First, remanence in a current transformer (CT) may cause misoperation of phase differential protection due to compromised CT performance. Heavy through-faults, sympathetic inrush, and recovery inrush all cause high current. This, combined with high remanent flux, can create a security issue. IEEE CT performance calculations will be used to support the use of dual slope differential characteristics to promote secure differential protection operation when challenged with unequal CT performance. Second, on transformer energizing, the second harmonic current has been traditionally used as a means to prevent phase differential misoperation. Certain transformers may not exhibit high enough the second harmonic, causing a dependability issue if the restraint is set too low. The use of the second and fourth harmonics for inrush detection will be shown to enhance the reliability during energizing inrush situations. Third, overexcitation can occur from abnormal operation of the utility system or the plant's excitation control. Causes of overexcitation will be outlined and the use of volts per hertz protection is explored. With overexcitation occurring from system voltage rise, the phase differential protection has been traditionally blocked using the fifth harmonic restraint. This may cause an undesired nonoperation of the phase differential protection if an internal fault occurs while the transformer is overexcited, causing a delay in tripping and severe damage to the transformer. A technique using adaptive phase differential pickup value will be illustrated to overcome this challenge. Finally, on resistance-grounded power transformers, phase differential protection sensitivity for ground faults near the neutral is decreased. The use of ground differential protection will be explored and the increased sensitivity gained will be demonstrated.

Using Traveling-Wave Processes in the Development of Relay Protection for Overhead Lines (OHL)1

The development of electric power systems has raised the requirements of relay protection — sensitivity, speed, and reliability of functioning—for all types of short circuits (SC). The raised requirements can be satisfied by using more complete damage information extracted during the traveling-wave stage of the transient process accompanying SC. The experience gained in working out directional traveling-wave relay protection is generalized and questions concerning the use of traveling-wave principles for developing smart relay protection networks with complex topology and devices making it possible to control power flows in ac lines are examined. An algorithm is proposed for tuning out external SC and determining the damaged phase by using modern methods of digital signal processing.

Preventing thermal runaway propagation in lithium ion battery packs using a phase change composite material: An experimental study

Abstract The safety issues of lithium ion batteries pose ongoing challenges as the market for Li-ion technology continues to grow in personal electronics, electric mobility, and stationary energy storage. The severe risks posed by battery thermal runaway necessitate safeguards at every design level – from materials, to cell construction, to module and pack assembly. One promising approach to pack thermal management is the use of phase change composite materials (PCC™), which offer passive protection at low weight and cost while minimizing system complexity. We present experimental nail penetration studies on a Li-ion pack for small electric vehicles, designed with and without PCC, to investigate the effectiveness of PCC thermal management for preventing propagation when a single cell enters thermal runaway. The results show that when parallel cells short-circuit through the penetrated cell, the packs without PCC propagate fully while those equipped with PCC show no propagation. In cases where no external short circuits occur, packs without PCC sometimes propagate, but not consistently. In all test conditions, the use of PCC lowers the maximum temperature experienced by neighboring cells by 60 °C or more. We also elucidate the propagation sequence and aspects of pack failure based on cell temperature, voltage, and post-mortem data.

Studies on Alternative Test Methods of Internal Short Circuit Test for Lithium-Ion Batteries in Vehicles

Lithium-ion batteries may experience thermal runaway when subjected to overcharging, external short-circuits, or overheating, resulting in smoke and heat generation. To prevent this, lithium-ion batteries usually have a protection circuit. However, the protection circuit cannot prevent internal short-circuits caused by contamination with foreign matter. As a result, lithium batteries have generated heat or ignition or eroded in notebook computers, airplanes, and electric vehicles. The test method to simulate this internal short-circuit is specified in IEC 62133 Ed. 2.0 as the forced internal short-circuit (FISC) test in the case of portable electronic devices.1 However, no internal short-circuit simulation test is specified for lithium-ion batteries used in vehicles, so studies for similar test methods are being conducted. In the FISC test, internal short-circuits are caused by disassembling the battery, inserting an Ni piece into the electrodes, inserting the battery into a polyethylene bag, and then applying an external force to the portion where the Ni piece is inserted. However, this test involves disassembling the battery, so sometimes it is difficult to implement due to technology and safety concerns. Therefore, the Blunt rod test and ceramic nailing test, which do not need battery disassembly, are proposed as simple and safe alternatives of this test. In the Blunt rod test, an internal short-circuit is caused by pressing the battery from the outside. In the ceramic nailing test, the short-circuit is caused by pricking the nail. In this study, we examined the validity of these tests as a substitute for the FISC test. For the tests, a total of five kinds of batteries were used, including three pouch types, one cylinder type, and one rectangular type. The main test conditions were an atmospheric temperature of 25±5 ºC, SOC of 100%, restricted or unrestricted battery, and a measurement duration of 1 hour after the voltage drop. The nailing rate was 0.05 mm/s, the voltage was measured at a sampling ratio of 1 ms, and pressurization or nailing was stopped when the battery voltage dropped by 2 mV or more and 5 mV or more. The FISC test was conducted in accordance with IEC 62133; the Blunt rod test, with nail diameters of 3 mm (r=3 mm) and 6 mm (r=6 mm); and the ceramic nailing test, with a tip angle of 45º , tip metal length of 0.3 mm and 1.0 mm, and a nail diameter of 3 mm. As an example, part of the results of tests conducted by stopping the Indenter of pouch cell A when the voltage dropped by 2 mV or more with an unrestricted battery are depicted in Table 1. Here, the short-circuited layers were counted as one each time a hole was opened in the separator between the positive and negative electrodes. In this example, the Blunt rod test had a greater voltage drop and more short-circuited layers than in the FISC test, sometimes resulting in smoking. The voltage drop in the ceramic nailing test, on the other hand, had a voltage drop in the same range resulting in the same event as in the FISC test but more short-circuited layers. This difference could have been caused by the required load and the number of short-circuited layers being larger in the Blunt rod test because the short-circuit was caused by pressing the battery with a round nail, and the load required in the ceramic nailing test was smaller because the tip of the nail was sharp. This trend was also the same in four other kinds of batteries and under other test conditions. Therefore, under these test conditions, we consider that the ceramic nailing test is more valid than the Blunt rod test as a substitute for the FISC test based on comparisons of the number of short-circuited layers, volume of voltage drop, and observed event. Acknowledgments This paper is based on results obtained from a project commissioned by the New Energy and Industrial Technology Development Organization (NEDO). References 1) IEC 62133 Ed. 2.0:2012 (b), "Secondary cells and batteries containing alkaline or other non-acid electrolytes - Safety requirements for portable sealed secondary cells, and for batteries made from them, for use in portable applications," 2012-12-06 Figure 1

An Analysis and Investigation of Methods of Braking Digital Differential Protections of Block Transformers

Modern methods of braking digital differential protections of block transformers when there are external short circuits are considered. The effect on the braked quantities of such factors as the phase difference between the side currents, and also saturation of the current transformers is described.

Organic agriculture values and practices in Portugal and Italy

Most definitions of organic farming emphasise a holistic approach that combines quality production with sustainable practices and positive impact on resource conservation, biodiversity and animal welfare. Its founding values were also connected to small-scale production, minimisation of external inputs use, diversification and short market circuits. In the last two decades, organic farming has grown very rapidly, resulting in the subordination of its values to market forces. There has been a greater specialisation, an increase of scale, the involvement of large multinational corporations and the inclusion in global trade. This conventionalisation process and the connected certification standards, primarily focussed on banning the use of pesticides and chemical fertilisers, may weaken the vision of organic farming as a more sustainable alternative to conventional farming.This paper aims to identify the factors that influence the choice of organic farmers for more sustainable practices that go beyond the strict limits imposed by certification. A probabilistic model was estimated using survey data collected from 352 Italian and Portuguese certified organic farmers. The results show that women and farmers longest engaged in organic farming are more likely to adopt sustainable practices. They also indicate that farm size, land ownership, the existence of some types of complementary activities and the sources of information used by farmers affect the adoption of such practices.

Invited Presentation: Li-Ion Battery Safety Considerations during Transportation, Storage, and Disposal

The energy of a Li-ion cell is in average about 3,250 kJ/kg. About ¼ of this energy is related to electrochemical energy (chemical energy convertible into electrical energy via normal use or short circuit) and ¾ to thermal energy (chemical energy convertible only in thermal energy released at suitable stimulation; e.g. short circuit). The main safety related events are overcharge, external heating, external and internal short circuits, and mechanical deformations of the cell/battery case. These unpredictable events may leads to a temperature increase and at T > 120 °C by internal chemical processes (SEI layer breakup, anode-electrolyte reaction) with gas development and internal pressure increase to cell container rupture at predetermined breaking points. Gas and electrolyte will escape through the rupture holes into the environment and, eventually, inflame by an external ignition source. A further temperature increase till about 200 °C triggers high rate chemical reactions (cathode decomposition with oxygen development, oxygen reaction with the electrolyte, electrolyte decomposition) leading to a very rapid temperature rise (thermal runaway) followed by flames caused by reaching the self-ignition temperature of the electrolyte (~ 450 °C) and possibly explosions. The specific occurrence of most of the above described safety related events, that may occur during the Li-ion battery life cycle phases of transportation, storage, and disposal, will be discussed in this presentation. During transportation and storage, external heating, external and internal short circuits, and mechanical deformations, are the events most likely to happen. Measures which can prevent them (e.g. reliable and low flammable packaging, thermal barriers) and transport related standards (e.g. UN 38.3) are described.The safety hazard in the disposal phase of the cell/battery are also associated with external heating, external and internal short circuits, and mechanical deformations. After collections it is to proof whether the battery is defective (not all functions properly) or damaged (loss of physical integrity). Defective batteries with capacity ≤ 80 % of the nominal value (end-of-life by definition) could be still used in lower demanding applications, e.g. stationary storage in PV houses. Damaged batteries and defective batteries with << 80 % capacity and other malfunctions have to be recycled. In order to reduce the safety risk before the recycling process (including transport), it is advisable to de-energize the battery by low current discharge and finally short it permanently.

Significance of cellulose power transformer condition assessment

Power transformers are designed to withstand system abnormalities such as over voltages and external short-circuits. Transformer monitoring and diagnostics are the effective techniques in preventing the eventual failures and contribute to ensure the plant's reliability. Transformer life mainly depends on the integrity of its solid insulation (cellulose). The solid insulation in transformers degrades with time at rates which depend on the temperature and the amount of moisture, oxygen and acids in the insulation system. Moisture and oxygen cause the paper insulation to decay much faster than normal. Moisture in a transformer accelerates the aging process and causes severe deterioration in the mechanical and electrical properties of insulation system. The aging of paper insulation is irreversible. The degree of polymerization value is a main relation between insulation deterioration and formation of aging products. To predict a failure or an unusual behavior, an accurate interpretation of monitoring, diagnostics and maintenance data is required. The monitoring of insulation system and verification of core and winding mechanical integrity allow optimization of the lifecycle management of an asset. This paper presents an investigation and condition assessment of 152 MVA, 512 kV, 1-phase, 2-winding generator step-up transformer having a history of combustible gases.

Fuzzy risk index for power transformer failures due to external short-circuits

A novel methodology to assess the risk of power transformer failures caused by external faults, such as short-circuit, taking the paper insulation condition into account, is presented. The risk index is obtained by contrasting the insulation paper condition with the probability that the transformer withstands the short-circuit current flowing along the winding during an external fault. In order to assess the risk, this probability and the value of the degree of polymerization of the insulating paper are regarded as inputs of a type-2 fuzzy logic system (T2-FLS), which computes the fuzzy risk level. A Monte Carlo simulation has been used to find the survival function of the currents flowing through the transformer winding during a single-phase or a three-phase short-circuit. The Roy Billinton Test System and a real power system have been used to test the results.

Portal Vein Segmentation of a 3D-Planning System for Liver Surgery—In vivo Evaluation in a Porcine Model

Computer systems allow the planning of complex liver operations. The segmentation of intrahepatic vessels builds the basis for the calculation of liver segments and resection proposals. For surgical use, it is essential to know the capabilities and limitations of the segmentation. The aim of this study was to determine the sensitivity and precision of the portal vein segmentation of a computer planning system for liver surgery in vivo. Segmentations were performed with the software system HepaVision on computed tomography (CT) scan data of domestic pigs. An in situ corrosion cast of the portal vein served as the gold standard. The segmentation results of the portal vein and the corrosion cast were compared with regard to sensitivity, precision, and amount of short-circuit segmentations. The methodology demonstrated high resolution ex situ. The in vivo sensitivity of the portal vein segmentation was 100% for vessels of more than 5 mm in diameter and 82% for vessels of 3-4 mm. All segment branches were detected as well as 84% of the first subsegment branches with a diameter of more than 3 mm. The precision of the system was 100% for segment branches and 89% for the first subsegment vessels. The amount of internal short-circuit segmentations was less than 3.0%. No external short-circuits were found. The system has a high precision and sensitivity under clinical conditions. The segmentation is suitable for portal vein branches of the first and second order and for vessels of >/=3 mm in diameter.

Comparison of Safety of Two Primary Lithium Batteries for the Orbiter Wing Leading Edge Impact Sensors

The Extended Wide Band Micro-Tri-axial Assembly Wing Leading Edge (EWBMTAU-WLE) consists of impact sensor, receiver and relay units that are installed in the Orbiter for its two flights. There are 22 sensor and 2 relay units on each wing. There are two receiver units inside the cabin. All sensor, relay and receiver units are powered by batteries. The batteries used for the first two flights after the Orbiter returns to flight are made up of battery assemblies that contain two LiFeS2 cells in series. Extensive testing was performed on the LiFeS2 and LiBCX cells to determine the safety of these cells under nominal and abuse conditions. The LiFeS2 cells were found to be extremely safe under all the conditions tested. The battery pack has diodes on each cell to prevent cell reversal and a fuse to prevent external short circuits from affecting the cells. The cells are internally fitted with PTCs (positive temperature coefficient) to reduce the load on the cell in the event of an external short. The batteries have undergone extreme environmental tests as single cells, battery packs and as part of the sensor units. This paper will discuss the results of the tests performed on the LiBCX and LiFeS2 cells.

Mechanical stresses in transformer windings

The forces and stresses set up in transformer windings and their clamping structures, as the result of external or internal short-circuits or of switching operations, are considered in detail.Various arrangements of windings and tappings in large power transformers are described. Points at which particularly high mechanical stresses occur in concentric windings are discussed in detail. Axial forces between the top and bottom halves of each winding or between different windings are responsible for bending stresses in turns near the ends or adjacent to gaps in the windings, for compressive stresses in the body of the winding, and for tensile and compressive stresses in the clamping gear. Radial forces produce tensile stresses in the outer and buckling stresses in the inner winding. Such stresses are more pronounced in coils adjacent to the main leakage duct. The excessive mechanical stresses which can be caused by internal electrical breakdowns are discussed. The mechanism of cumulative shrinkage, the loss in clamping pressure due to switching stresses and thermal cycles, and the danger of subsequent movement of the windings causing abrasion of the insulation and final electrical breakdown, are considered in detail. A rule is given for the minimum clamping pressure that should be maintained within the windings. Readers interested in the mathematical treatment of the subject-matter are referred to E.R.A. Reports, Refs. Q/T101, 103, 105 and 106, in which quantitative expressions are derived for the maximum values of currents, forces and stresses which can occur in the windings. Certain statements made in this paper on the merits of various forms of design represent the personal opinion of the author. They do not necessarily express the official opinion of the E.R.A.