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Safe working, tools and hazard management
Published in Tom Denton, Electric and Hybrid Vehicles, 2020
An arc flash is the light and heat produced from an electric arc supplied with sufficient electrical energy to cause substantial damage, harm, fire or injury. Note that welding arcs can turn steel into a liquid with an average of only 24V DC. When an uncontrolled arc forms at very high voltages, arc flashes can produce deafening noises, supersonic concussive-forces, super-heated shrapnel, temperatures far greater than the Sun’s surface, and intense, high-energy radiation capable of vaporizing nearby materials.
Longwall power distribution and system control
Published in Syd S. Peng, Longwall Mining, 2019
Utility companies normally deliver power to mine sites at 24 to 138 kV. At the mine site, a substation using transformers reduces the voltage to 12 to 14 kV, which is then delivered to the power centers at the longwall sections. Transformers at the power center reduce the voltage to 4160 V or less for the face equipment. Since this power transmission process involves high voltage, various safeguard and protection equipment are required to prevent electrical hazards. These hazards include fires and explosions, burns from an electric arc, shock, and electrocution. There are five main protection systems: ground fault, ground wire monitoring, undervoltage, overload, and short circuit (instantaneous).
Vacuum Dielectrics
Published in N. H. Malik, A. A. Al-Arainy, M. I. Qureshi, Electrical Insulation in Power Systems, 2018
N. H. Malik, A. A. Al-Arainy, M. I. Qureshi
An electric arc is basically a type of discharge between two electrodes. It differs from the general gaseous discharge, since in this case (1) the electrode current density is extremely high, of the order of kiloamperes per cm2; (2) a greater part of discharge current near the cathode is carried only by the electrons and not by the ions formed during the ionization of medium; and (3) the potential difference between electrodes is small, i.e., only of the order of a few tens of volts. In the vacuum, arcing is established when the current carrying electrode contacts separate, melting or explosive vaporization of the last metallic point of contact occurs initially only with a single melting point on the cathode, known as the cathode spot. The cathode spot is a small, limited region of high temperature and pressure from which ions, electrons and neutral particles are emitted. At this spot, the current density is >108 A/cm2, whereas surface temperature is close to the boiling point of the contact material. The peripheral areas of this spot represent an intense source of neutral metal vapor, which is ionized in the form of a discharge cone with its apex at the cathode. Contrary to arc discharge in a gaseous medium, more than 90% of the total current in the vacuum arc is transported by the electrons, whereas positive ions cause a neutralization of the negative space charge produced by the electrons.
Workplace exposure to particulate matter, bio-accessible, and non-soluble metal compounds during hot work processes
Published in Journal of Occupational and Environmental Hygiene, 2019
Balázs Berlinger, Ulf Skogen, Conny Meijer, Yngvar Thomassen
“Hot work” is a term used for working with ignition sources near flammable materials, and to the extent that surface grinding of metals may cause sparks, it can also be classified as hot work. Thus, welding, flame and plasma cutting, air carbon arc gouging, and surface grinding are examples of hot work. During an arc welding process, an electric arc is created and maintained between a welding electrode and the base material to melt the metals at the point-of-contact.[1] In flame cutting, the part of the material to be cut is raised to ignition temperature by an oxygen-fuel (e.g., acetylene) gas flame.[2] During plasma cutting, an arc is formed between the electrode and the workpiece, which is constricted by a fine bore, copper nozzle. The plasma gas flow is increased so that the deeply penetrating plasma jet cuts through the material, and molten material is removed in the efflux plasma.[3] During air carbon arc gouging, an electric arc is generated between the tip of a copper-coated graphite electrode and the workpiece. The molten metal is blown away by high velocity air jet streams. This is an effective process to clean metal surfaces.[4] Surface grinding is used to plane the surface of a workpiece, remove surface coatings, mistakes, or excess material. A grinding wheel of aluminum oxide or silicon carbide is usually used in this process.[5]
An investigation of molybdenum surface reinforcement on the hardness and wear properties of AISI 630
Published in Transactions of the IMF, 2018
P. Ritesh, A. Shanmugasundaram
AISI 630 stainless steel rectangular samples of size 100 × 25 × 15 mm were prepared. Initially, heat was applied onto the surface of AISI 630 samples using Lincoln Electric V205T gas tungsten arc welding (GTAW) equipment. The specimen was kept on the worktable. The workpiece speed was controlled by a PLC-based stepper motor driven manipulator and the position of the torch was held stationary in the vertically downward position. A non-consumable thoriated tungsten electrode of diameter 2.4 mm was used for its better arc stability. The required electric power was supplied from the power source and delivered to the thoriated tungsten electrode assembled into the torch. An electric arc was produced between the electrode and the workpiece by maintaining a constant electrode to workpiece distance using a constant-current welding power supply that produces energy conducted across the arc through a column of highly ionised gas.20 The fusion area was protected from the atmosphere with argon as a shielding gas which flows at a flow rate of 7 L min−1. Shielding of the fusion zone avoids the tendency of crack formation and oxidation due to the reaction of materials with atmospheric oxygen. The direct current straight polarity (DCSP) method was used in which the work is connected to the positive terminal and the electrode is connected to the negative terminal of the power supply. This type of connection is the most common and widely used DC-GTAW process.