Medium Voltage Electrical Equipment Research Articles

New Generation of SF6-Free Medium-Voltage Switchgear for the Electrical Network: Stability and Toxicity Studies of Trans-1,1,1,4,4,4-Hexafluorobut-2-ene with N2 Gas Mixture

Binary gas mixture of N2 and trans-1,1,1,4,4,4-hexafluorobut-2-ene (HFO4E) is presented as an alternative to SF6 in medium-voltage electrical equipment. Its stability was tested under different conditions. No change was observed in the gas mixture after a permanent AC voltage of 30 kV applied for two years or during the making operations with a standard load-break switch. The same behavior was obtained under dielectric tests, electrical arcs and temperature rise tests according to the IEC 62271-1:2011 standard. For all of these conditions, the concentration of HFO4E remains practically unchanged; there is no impact on the insulation properties of the system and the degradation products formed would not affect the health and the environment if there were leaks. In these studies, gas mixtures samples were analyzed by a validated methodology based on gas chromatography coupled to mass spectrometry and thermal conductivity detectors. Finally, an OECD TG 403 acute inhalation toxicity test was also carried out with the gas mixture aged after the mentioned making operations. None of the mice used in the toxicity test were affected after 4 h of exposition to an ambient air with 30,000 ppmv of the gas mixture.

Heptafluoroisobutyronitrile (C4F7N), a gas used for insulating and arc quenching in electrical switchgear, is neurotoxic in the mouse brain

Fluoronitrile gas (C4F7N, CAS number 42532-60-5) is one of the most promising candidates as insulating and/or breaking medium in high and medium voltage electrical equipment. Besides its promising properties, C4F7N gas is however not devoid of acute toxicity when used pure or in gas mixtures. The toxicity was not extensively analyzed and reported. The aim of the present study was to analyze in mice the consequences of a single exposure to C4F7N gas, at different concentrations and different timepoints after exposure. Male and female Swiss mice were exposed to breathable air or C4F7N gas, at 800 ppmv or 1500 ppmv, for 4 h on day 0. Behavioral tests (spontaneous alternation in the Y-maze and object recognition) were performed on days 1, 7 and 14 to assess memory alterations. The animals were then sacrificed and their brains dissected for biochemical analyses or fixed with paraformaldehyde for histology and immunohistochemistry. Results showed behavioral impairments and memory deficits, with impairments of alternation at days 1 and 7 and object recognition at day 14. Histological alterations of pyramidal neuronal layer in the hippocampus, neuroinflammatory astroglial reaction, and microglial alterations were observed, more marked in female than male mice. Moreover, the biochemical analyses done in the brain of 1500 ppmv exposed female mice showed a reductive stress with decreased lipid peroxidation and release of cytochrome c, leading to apoptosis with increases in caspase-9 cleavage and γ-H2AX/H2AX ratio. Finally, electrophysiological analyses using a multi-electrode array allowed the measure of the extracellular activity of pyramidal neurons in the CA2 area and revealed that exposure to the gas not only prevented the induction of long-term potentiation but even provoked an epileptoid-like activity in some neurons suggesting major alterations of synaptic plasticity. This study therefore showed that an acute exposure of mice to C4F7N gas provoked, particularly in female animals, memory alterations and brain toxicity characterized by a reductive stress, microglial toxicity, loss of synaptic plasticity and apoptosis. Its use in industrial installations must be done with extreme caution.

Exploring the Decomposition Products of 1,3,3,3-Tetrafluoropropene and Perfluoro-(3-methylbutan-2-one) Gas Mixtures in Medium-Voltage Electrical Switchgear as Alternatives to SF6.

In this work, binary and ternary gas mixtures of 1,3,3,3-tetrafluoropropene, HFO-1234ze(E), and perfluoro-(3-methylbutan-2-one), CF3C(O)CF(CF3)2, with CO2 and synthetic air, are presented as alternatives to SF6 in medium-voltage electrical equipment. They were used in four medium-voltage switchgear cubicles replacing SF6 gas, and after a period of time, under permanent 30 kV AC voltage, gas mixture samples were extracted and analyzed on the same day using a validated methodology based on gas chromatography (GC) coupled to mass spectrometry (MS) and thermal conductivity (TCD). CF4 (tetrafluoromethane), C2F6 (hexafluoroethane), C3F6 (hexafluoropropylene), C3HF7 (1,1,1,2,2,3,3-heptafluoropropane), CH2F2 (difluoromethane), and the cis and trans-C3H2F4 (1,3,3,3-tetrafluoropropene) have been identified as decomposition products in these gas mixtures. In addition, a quantity of water has been observed, as well as CO in one of the cubicles. The most abundant decomposition products identified in gas mixture samples (C3HF7 and C3F6) together with water and CO content have been quantified using commercial gas mixture reference standards. The toxicity and global warming of the analyzed compounds are evaluated to determine the most adequate gas mixture among those studied as a candidate to substitute SF6.

Новые защитно-коммутационные аппараты переменного и постоянного тока

The article considers the relation between the new technologies of components and the level of AC and DC equipment sets. It is pointed out that switching and protection apparatuses and semiconductor devices are the key components for development of low- and medium-voltage electrical equipment sets. The data and characteristics of switching and protection apparatuses made on the basis of vacuum and SF6 circuit breakers are presented. The advantages of constructing hybrid low- and medium-voltage devices by using a combination of vacuum circuit breakers, controlled surge arresters, and overvoltage suppressors that can be used in multi-substation DC cable networks (MDCN) are pointed out. The domestically produced light-activated thyristors, thyristors, and IGBT modules may serve as a basis for constructing low- and medium-voltage cable MDCNs.

Influence of trace water on decomposition mechanism of c-C4F8 as environmental friendly insulating gas at high temperature

Fluorocarbon gas has excellent environmental characteristics and insulation properties and has the potential of replacing SF6 for medium-voltage electrical equipment. While c-C4F8 will decompose under discharge or overheating faults conditions. At present, studies on the decomposition characteristics of c-C4F8 have made some achievements, but little attention has been paid to the influence of temperature and trace water. In this paper, the interaction between OH· and H· produced by H2O and c-C4F8 is analyzed based on the density functional theory (DFT) and plasma discharge decomposition experiment. The decomposition path, reaction enthalpy and activation energy, and the impact of temperature on the reaction path is discussed. It is found that the decomposition of c-C4F8 requires an endothermic heat of about 420 kJ/mol, and the decomposition of c-C4F8 to C2F4 is more likely to occur at high temperature. The H· and OH· generated by trace water will promote the decomposition of c-C4F8, which produces HF and low fluoride particles. The main decomposition products of c-C4F8 in the trace water environment are C2F4, CF4, CF3OH, CF3H, C2F6, CF2O and HF. Among them, CF2O and HF are toxic and corrosive substances, which pose a threat to the safety of operation and maintenance personnel. Relevant research results not only reveal the decomposition mechanism of c-C4F8, but also provide guidance for the application of c-C4F8 gas mixture.

Theoretical evaluation of the interaction between C5-PFK molecule and Cu (1 1 1)

C5-PFK has drawn much attention in recent years as an environmental friendly gas-insulated medium. Many studies have proved that it has the potential to replace SF6 using in medium voltage electrical equipment. However, there are few reports about the compatibility between C5-PFK and materials used in the gas-insulated switchgear. C5-PFK may react with materials such as metal inside the equipment due to the strong activity of carbonyl group (C = O) in its molecular structure. Investigations about the material compatibility between C5-PFK and the materials are required to decide about a long term behavior. In this paper, the interaction between C5-PFK and copper, a common metallic material in electrical equipment, is discussed based on the density functional theory. We found that the interaction between the O atom in the C5-PFK molecule and Cu (1 1 1) surface is strong. The interaction between F atom and Cu (1 1 1) surface is weak, which belongs to physical adsorption. Relevant results not only clarify the compatibility between C5-PFK and copper but also provide guidance for prediction of long-term behavior of C5-PFK gas mixture and the selection or modification of materials used in the equipment.

Integrating switchgear breakers and contactors into a safety instrumented function

In the process industries, electrical circuit breakers are tripped for a variety of reasons including hazard prevention and mitigation. This paper will discuss the application of tripping electrical breakers for process safety reasons. It often occurs that a risk assessment study has determined the need to include the shutdown of a large electric motor as part of a safety instrumented function (SIF). In the process industries, it is common practice to control and protect large horsepower motors (typically 2000 HP and above), with medium-voltage switchgear breakers. Safety instrumented functions that include electric motors utilizing medium-voltage switchgear for tripping have unique final element subsystems, which require specialized knowledge in order to implement correctly. This paper will discuss the design considerations for integrating medium-voltage switchgear used for shutdown of an electric motor into a safety instrumented function. First, an overview of typical low and medium-voltage electrical equipment used for controlling and protecting electric motors will be discussed. Next, a review of generic sourced failure data for medium-voltage switchgear breakers will be presented. Focus will be on the taxonomy used to classify different breaker types and the relevant failure modes and effects used for quantifying performance. Next, specific SIF design details for tripping medium-voltage switchgear breakers will be analyzed in the context of achieving a certain integrity level. Parameters to be considered include hardware fault tolerance requirements, voting, available diagnostics, energize vs. de-energize to trip shutdown circuits, certified equipment vs. proven-in-use, and alternate means of shutdown (including manual intervention and protective relaying). This paper will also analyze the common electrical equipment that is shared among potential protection layers used to trip the same breaker, and determine how much credit can be taken considering common cause failure. Finally, inspection, test, and preventive maintenance (ITPM) of medium-voltage switchgear will be discussed as a means for maintaining the electrical equipment in the “as good as new” condition.

Reductions of SF6 emissions from high and medium voltage electrical equipment in Europe

Electrical equipment using SF6 forms an integral part of the electricity networks, providing a safe and reliable power supply throughout the world including most European countries. SF6-emissions potentially occur in all lifecycle-phases of electrical equipment—manufacture, use and decommissioning. A study summarized in this paper finds that SF6 emissions throughout the life-cycle have substantially been reduced since the mid-nineties. Almost all available and economically feasible reduction options have been accessed at least partly. The study demonstrates that, until 2020, further reductions can be achieved if these reduction options are fully implemented throughout Europe. This paper gives an overview of reduction potentials and costs, as well as the real and projected emission development between 1995–2020.

Brand equity in the business-to-business market

Brands have been developed by consumer companies but have been slow to develop in business-to-business marketing. This article explains the concept of brand equity in a specific industrial marketing setting. In addition, the sources of brand equity are investigated as well as the appropriate communications strategy and the relative importance of brand relative to other purchase criteria. The research method used was a conjoint analysis experiment. The subjects were decision-making unit (DMU) members of industrial companies in South Africa that purchase medium-voltage electrical equipment. Research results suggest that while brand equity has a role to play, price and delivery were more important. However, a price premium can be obtained when a company has high brand equity. Implications for managers are discussed.

Partial discharge theory and technologies related to medium-voltage electrical equipment

Partial discharge (PD) monitoring is an effective online predictive maintenance test for medium-voltage (MV) motors, MV generators, and MV switchgear at 4160 V and above, as well as other electrical distribution equipment. The benefits of online testing allow for equipment analysis and diagnostics during normal production. Corrective actions can be planned and implemented, resulting in reduced unscheduled downtime. An understanding of the theory related to PD, and the relationship to early detection of insulation deterioration is required to properly evaluate this predictive maintenance tool. This paper presents a theory to promote the understanding of PD technology, as well as various implementation and measurement techniques that have evolved in the industry. Data interpretation, corrective actions, and application to electrical distribution equipment is also reviewed.

Practical experiences of on-line partial discharge measurements on a variety of medium-voltage electrical equipment

In recent years, there has been a considerable amount of discussion concerning partial discharge (PD) measurements on medium-voltage motors and generators. If one considers the total plant electrical distribution system and production equipment, motors comprise only a small part of the plant electrical equipment. If a motor should fail, part of production will likely be shut down and there will be lost revenue. However, there is a wide variety of other equipment in a facility, besides a motor, that can fail and can have a much more devastating effect on the plant's production. Additional items to consider for PD monitoring are the plant incoming transformers (they may be owned by the plant if the plant is purchasing primary power), the incoming switchgear, cables, bus duct, other remote substation switchgear, and power center transformers. Methods have been developed to monitor PD in all types of medium-voltage equipment. This paper discusses application of sensors, methods of measurement and data interpretation and present several case studies.