Low Insulation Level Research Articles

Assessing and comparing the environmental impact of smart residential buildings: A life cycle approach with uncertainty analysis

While there is an increasing integration of connected devices in buildings to reduce energy consumption, little evidence exists regarding the effective environmental impact of the smart devices installed. One goal of this study is to comparatively assess the impact of integrating connected devices on the environmental performances of existing buildings. Additionally, it aims to discuss the added value regarding environmental performance between a strategy of integrating connected devices and a refurbishment strategy. A non-refurbished connected building will thus be compared with a non-connected refurbished building. The approach's novelty lies in carrying out an uncertainty analysis, which addresses uncertainties in the environmental modelling of sensors, heating gains, and other influential building parameters, such as occupancy scenarios and building lifespan. The Life Cycle Assessment model is built on the results of a dynamic building energy simulation and integrates environmental data on connected devices from ecoinvent. Environmental indicators are calculated using ImpactWorld+. The methodology is applied to a multi-storey residential tower in France, characterised by a low insulation level. The alternatives compared include the original building without sensors, two connected alternatives (monitoring and management) that lead to a reduction of heating loads by 10 and 30% respectively, and a refurbished alternative. Results confidently show that using connected devices is always better than keeping the original building state. Yet, refurbishing the building is the preferable option across almost all indicators. Finally, the results point out that energy gains allowed by connected devices should be better quantified in further work through measurement campaigns.

Research on Confidence Analysis Method of Lightning Strike Accidents on Distribution Lines

Currently, lightning is the main cause of power system faults. Due to insufficient equipment and technology, low insulation level, the distribution network being the main part of power outages, and the complex causes of distribution network faults, it is difficult to determine whether each fault in the distribution network is caused by lightning strikes. In this paper, the concept of lightning strike confidence, i.e., the possibility of a line lightning strike fault caused by falling lightning, is proposed, and a lightning strike confidence analysis is performed for a 10 kV distribution line in the mountainous region of South China to determine the possibility of a line lightning strike fault caused by falling lightning based on the lightning locating system data of the distribution line at the moment of the fault. First, the calculation method of the lightning strike confidence is derived; then the distribution law of the distribution line lightning strike confidence, the influence of the ground tilt direction, and ground tilt angle on the distribution line lightning strike confidence are analyzed; finally, the distribution line lightning strike confidence is analyzed by an example.

Assessing the influence of peak current distributions of first return strokes on the lightning performance of transmission lines: Instrumented tower distributions versus standard distributions

• The effect of peak current distributions on backflashover is shown. • Instrumented tower and standard distributions are adopted. • IEEE and CIGRE distributions overestimate backflashover for high voltage level TLs. • MCS distribution leads to largest BFOR probability for low insulation level TL. • A new formulation to reproduce high current region of MCS distribution is proposed. The influence of peak current distributions of first return strokes of instrumented towers and international standards on the calculated lightning performance of 138 kV and 500 kV transmission lines is evaluated. This performance, expressed by the backflashover probability, is determined by computational simulations using the Hybrid Electromagnetic model (HEM) and the Disruptive Effect method (DE). The performance is calculated considering the cumulative peak-current distributions obtained from direct measurements at the instrumented towers of Morro do Cachimbo (MCS) and Monte San Salvatore (MSS) stations and those provided by IEEE and CIGRE standards. According to the results, using the standard distributions yields larger backflashover probabilities of transmission lines of higher insulation level, in relation to those calculated using instrumented-tower distributions. Considering transmission lines of lower insulation level, the performances calculated using standard distributions are close to those obtained using MSS distribution, but yields lower backflashover probabilities in relation to those obtained using MCS distribution. The latter leads to backflashover probabilities about 40% and 47% larger than those obtained by using IEEE and CIGRE distributions, respectively, in the tower-footing impedance range of 20 Ω – 40 Ω.

Line Surge Arresters Applications On The Multi Circuit Overhead Lines

This paper presents application of line surge arresters (LSA) on the different voltage level multi circuit overhead lines. Double circuit shielded compact line with and without distribution circuit on the same tower is analyzed. Distribution circuit has lower insulation level, meaning that almost all flashovers will happen on that circuit. Flashovers on the distribution circuit help to improve lightning performance of the transmission circuits. Flashovers on the distribution circuit diverts fraction of the lightning current along its phase conductors, improving at the same time coupling between distribution and transmission circuits. All software simulations are performed using sigma slp software package. A short description of the modeling for multi circuit flashover rate determination is given. In order to prevent flashovers on the distribution circuit LSA are installed on this circuit only. The improvement in the transmission circuit lightning performance is similar to that obtained without LSA. LSA installed on the distribution circuit are much cheaper than transmission LSA.

Lightning protection of multi‐fracture arc‐quenching lightning protection gap for 35 kV distribution lines

Owing to the low insulation level of 35 kV distribution lines, lightning outage accidents and huge economic losses occur frequently. Therefore, a multi-fracture arc-quenching lightning protection gap (MFALPG) for 35 kV distribution lines is developed to ensure the safety and stability of power supply. Here, the principle of MFALPG is presented through the electromagnetic self-contraction effect and qualitative modelling theory. In order to investigate the coupling effect between high-energy compressional waves and arcs, a mathematical model of airflow coupled arc was developed to simulate and analyse the arc-quenching process. Theoretical analysis and simulation results show that the high-energy compressional wave is triggered by the impulse arc rapidly, and the arc conductivity drops abruptly in a short time. Finally, a lightning impulse discharge test and the power frequency withstand voltage test are performed to determine the 35 kV power frequency continuous current interruption test parameters. Under the action of the MFAPLG, the entire time of arc duration is less than 3 ms, and reignition phenomenon of the arc is not found after the subsequent power frequency voltage is restored.

Simulation Research on Lightning Protection Effect of Distribution Line Lightning Protection Measures

Due to the low insulation level of distribution lines, the electromagnetic transient characteristics of lightning strikes are quite different from those of high-voltage transmission lines; the lightning protection measures used in high-voltage lines cannot be well applied to distribution lines. In order to further understand the various lightning protection measures and the effect of lightning protection measures on the improvement of the lightning resistance level of distribution lines, this paper evaluates the working principles, characteristics, lightning protection effects and existing deficiencies of various lightning protection measures used in distribution lines And using ATP-EMTP software to analyze several kinds of lightning protection measures commonly used in 10kV distribution lines, it has certain reference value for the selection of lightning protection measures of 10kV distribution lines.

Assessment of MOV Deterioration under Energized Conditions

Metal oxide varistors (MOVs) are widely used to protect electrical and electronic devices that are very vulnerable to surges due to the low insulation level of the equipment. MOVs deteriorate gradually due to manufacturing defects, mechanical and thermal stress, or repeated protective operations against surges. These defects result in the thermal runaway of MOV and finally lead to the explosion and electric fire of electrical and electronic devices due to a short circuit and a line-to-ground fault. Therefore, the reliable assessment of the condition of MOV deterioration is required for electrical and electronic equipment. However, when most accelerated degradation tests for the MOV have been performed to date, an 8/20 μs standard surge current is applied under de-energized conditions, which is unlike the actual operating environment. In this study, a surge generator was designed to apply a surge current to MOVs to monitor their deterioration. Three different types of leakage currents were measured to analyze the change rates of their electrical characteristics of MOVs by comparing them with the reference voltage variation. Furthermore, the condition assessment of MOV deterioration under energized and de-energized conditions was investigated.

Effects of Built-In Varistors With Low Protection Voltages on Surge Protection Performances in Low-Voltage AC Power Systems

Voltage and current surges originated by lightning is one of the most common cause of degradation, upset, failure, and/or damage of susceptible equipment in low-voltage (LV) ac power installations. Surge protection systems realized with surge protective devices (SPDs) placed through LV power installations are used for protection of equipment against surges. However, modern electronic devices have very low withstand insulation level due to ongoing trend of miniaturization and high integration of components. Therefore, their manufacturers usually install built-in varistors inside devices' power supply units in order to provide their self-protection against overvoltages. These varistors have low protection voltages, but also low energy absorption capability. The comprehensive analysis of effects of built-in varistors with low protection voltages on surge protection system's performances is given in the paper. As analysis will show, it is very difficult to provide energy coordination of built-in varistors and installed SPDs within LV power installations. In most cases, this will lead to thermal damage and failure of the varistors due to energy overstressing, what causes overvoltages with values higher than withstand insulation level of the equipment to be protected. Possible solution to overcome these problems and to ensure adequate overall surge protection system's performances is proposed.

Electromagnetic transient analysing of neutral bus in UHVDC converter station

Transient processes at neutral bus of ultra-high value direct current (UHVDC) converter station received insufficient attention, because of the lower amplitude compare to poles. However due to the lower insulation level, electromagnetic transient processes at neutral bus may cause serious fault, and become an important issue that should be studied carefully in the design stage. A method to analyse the electromagnetic transient based on time-domain wide-band circuit simulation is proposed in this study. Models of major equipment are described. The electromagnetic transient of a ±800 kV converter station is calculated. The transient under different operation statuses is compared. Effects of suppression method such as arresters and capacitors are analysed.

A Study on Protection Requirements for DC Faults in Multi-Terminal HVDC System

Recently, the construction of large-scale offshore wind farms and dissemination of new and renewable energy has encouraged a growing interest in DC systems. In particular, HVDC (high-voltage direct current) systems have been evaluated as the best alternative because of their power system interconnection and large-scale power transmission. Because HVDC systems offer many advantages such as a low insulation level, transmission losses, and improved power system stability, many studies on DC power systems are actively underway. As compared to the point-to-point HVDC system, which connects the electricity generated from geographically scattered renewable energy sources to an existing AC power system on a 1:1 basis, the MTDC (multi-terminal HVDC) system has garnered greater attention because of its ability to control energy flow by connecting several HVDC outputs to the HVDC. Because the VSC-HVDC, which operates as an MTDC, supplies not only active power, but also reactive power, it has been deemed the optimal solution to connect a renewable energy source to a system with no existing AC power supply, such as a wind-power generation system. An MTDC system, which possesses a structure that is more complex than that of the point-to-point HVDC system, should be equipped with a high-speed DC circuit breaker that can quickly separate a conversion station from the DC transmission line to which it is connected in the event of a fault or malfunction at the station. In addition, DC protection on the MTDC grid must be reliable and operate much faster than conventional AC protection to ensure that the converter sends a trip signal before it is damaged. In this paper, we propose a protection scheme for the DC line to effectively activate the DC circuit breaker, which is essential in an MTDC system; additionally, system modeling and simulation using the PSCAD/EMTDC were performed to verify the proposed algorithm.

Probabilistic Risk Assessment of MV Insulator Flashover Under Combined AC and Lightning-Induced Overvoltages

The effect of lightning-induced overvoltages is more profound in overhead distribution lines due to their limited height and low insulation level. Consequently, there is a high risk of line insulation flashover when exposed to lightning-induced overvoltages. This paper presents a probabilistic method to assess the risk of insulator flashover in medium-voltage overhead lines due to lightning-induced overvoltages. In order to accomplish this, a modified Gaussian cumulative distribution function has been used to predict the probability of single-phase, two-phase, and three-phase flashover of insulators under combined ac- and lightning-induced overvoltages. The validity of the modified probabilistic model is confirmed through experiments carried out in the high-voltage laboratory. Next, Monte Carlo simulations were performed on the simplified Rusck's model to generate the distribution of peak lightning-induced overvoltages. Finally, the risk of insulator flashover is calculated based on the distributions of lightning-induced overvoltages and insulator flashover voltages. The proposed procedure could be considered beneficial to select the optimum insulation level required against lightning-induced overvoltages by distinguishing between single-phase and multiphase flashover faults.

Calculation of Lightning Flashover Rates of Overhead Distribution Lines Considering Direct and Indirect Strokes

This paper presents a procedure for evaluation of lightning performance of overhead distribution lines. Because both voltages from direct strokes and nearby strokes may cause flashovers in distribution lines, flashover rates due to them need to be analyzed. The procedure is implemented in electromagnetic transient program, and the Monte Carlo method is used to take into account the random nature of lightning parameters. The lightning-induced voltages are calculated with an equivalent circuit derived from Agrawal formula. The influence of insulation level and spacing between surge arresters on lightning flashover rates is analyzed with the procedure. For a line with low-insulation level about 150 kV above high conductivity ground or with high-insulation level about 300 kV above low conductivity ground, the spacing between arresters is best less than 400 m. But for a line with low-insulation level above low conductivity ground, it is better to reduce the spacing to 200 m.

Varieties of State in the International Political Economy of Developing Countries

This paper discusses varieties of state and their salience for prosperity by challenging the notions of decline of nation-states and demise of national diversity in international political economy. Despite the fact that increased international trade and capital movement raises the proportion of each economy exposed to world market pressures, domestic institutions have considerable resilience in the face of global constraints. State capacity and strength generally refers to an ability based on highly centralized authority to protect policy formulation and implementation apparatus from capture by particular private interests. Autonomous states do not damage public goods avoiding policy distortions which reduce total national welfare. However, this study contends that accountable engagement of state is also a crucial component of state capacity in addition to autonomous insulation. Furthermore, since the capacity level of states differs, the ability to exploit new opportunities appears much more marked in some countries than in others. Given the varieties and specificities of state, both parasitic and the Anglo-Saxon states fall into weak states. Yet, the former is because of low accountability level, whereas the latter is due to low insulation level. On the other hand, both the East Asian developmental and the Nordic states are categorized as strong states. However, the former holds higher insulation, and thus bargaining process is leaded by the interventionist state which only invites state-controlled business associations. The latter, in turn, possesses more widespread accountability, and therefore bargaining encompasses both business and labor peak organizations. The Nordic states, in fact, sustain complex but stable triangular industrial relations through institutionalized consultative mechanisms.

Effect of interior and exterior insulation on the hygrothermal behaviour of exposed walls

Massive walls exposed to the natural climate without special rain protection show a dynamic moisture equilibrium governed by the alternating events of rain and sunshine. The moisture further reduces the rather low insulation level of the walls. Therefore, thermal insulation measures have to be taken in order to improve the hygienic conditions and the thermal performance of the building. The influence of interior and exterior insulations on the hygrothermal behaviour of such walls can be determined with the aid of a recently developed computer program which has been experimentally validated by comparison with field tests. The results show that an exterior insulation leads to the drying of the wall, with the drying rate depending on the vapour permeability of the insulation system. An interior insulation, however, results in a rising water content of the wall due to the decreasing masonry temperature. This effect is almost independent of the vapour permeability of the insulating material. While an exterior insulation also improves the thermal resistance of the masonry, an interior insulation has the opposite effect and increases the frost damage risk. Therefore, the interior insulation of exposed walls should be combined with rain protection measures at the facade.