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Barriers against conducted disturbances
Published in Mark van Helvoort, Mathieu Melenhorst, EMC for Installers, 2018
Mark van Helvoort, Mathieu Melenhorst
A spark gap consists of two electrodes at such a distance that a flash over will occur when the voltage exceeds the specified limit. The discharge ionizes the air causing a low impedance path through which current flows. A certain minimum holding current is required to sustain the plasma. If the voltage over the spark gap has become sufficiently low the current drops below this minimum and the gap extinguishes itself. However, if a DC power source is shortened by the spark gap and this source is sufficiently strong, the gap may never extinguish. Open versions, where the plasma can escape to the sides, may be more appropriate for these applications than their closed counterparts. Some countries allow placement of a spark gap before the metering installation.
Lightning Protection
Published in T. A. Short, Electric Power Distribution Handbook, 2018
Metal-oxide surge arresters overcame many drawbacks of earlier designs. The spark gap was one of the earliest devices used to protect insulation against lightning damage. A spark gap has many of the desirable benefits of a surge arrester; the gap is an open circuit under normal conditions and when it sparks over, the gap is virtually a short circuit. The problem is that after the surge, the gap is still shorted out, so a fuse or circuit breaker must operate. In some parts of the world, notably Europe, spark gaps are still widely used to protect transformers. Spark gaps were improved by adding nonlinear resistors in series. The nonlinear material would clear the power follow current flowing through the spark gap after the surge was done. Gapped arresters with silicon carbide blocks were developed in the 1940s and used for many years. Metal oxide is so nonlinear that a gap is not required. This allows an arrester design, which is simple and highly reliable, with excellent “fast-front” response characteristics. Figure 13.11 shows the voltage–current relationships of a typical metal-oxide arrester. At distribution voltages, metal oxide was first used to provide better protection at riser poles feeding underground cables (Burke and Sakshaug, 1981).
Performance evaluation of cryogenic treated and untreated brass electrode in wire-EDM
Published in Materials and Manufacturing Processes, 2023
N.E Arun Kumar, M Subramanian, A Suresh Babu, Elakkiyadasan R
Fig. 3c displays the influence of IP on MRR for both wires in terms of both directions. When the IP is increased from 110 A to 150 A in untreated brass, the MRR rises somewhat, and when the IP is increased from 150 A to 220 A, the MRR reduces slightly. As a result of an increase in the peak current, there is a corresponding rise in the discharge frequency, which leads to an increase in the MRR. Increasing the machining speed while decreasing the value of the voltage is a common occurrence. In order to increase the spark gap set voltage, the spark gap must be increased. If the spark gap does not ionize the dielectric fluid, the MRR will drop.[19] MRR reduces linearly in proportion to the rise in the IP of cryo-treated brass. In part, this might be due to the increased conductivity of cryo-treated brass, which allows an increase in current to discharge more energy, leading to uncontrolled machining and debris collection, which ultimately results in a fall in maximum recovery rate.
Surface characteristics and recast layer thickness analysis of µed machined Inconel 718 alloy with biodiesels
Published in Materials and Manufacturing Processes, 2023
Mineral oils such as kerosene and EDM oil have proven efficient in respect of metal removal efficiency for EDM technique, but serious health issues such as skin and lung cancer are more prone in human operators.[1–4] Identification of an alternative dielectric fluid for hydrocarbon oil of EDM has become a wide research area in recent years because the dielectric fluid serves different functions in EDM Fills the gap between + and – electrodes and acts as non-conductive fluid until the breakdown voltageHelps to build a narrow plasma channel between + and – electrodesFlushes away the chip particles from the spark gap results in prevention of undesirable discharges.[5–8]
Review on tools and tool wear in EDM
Published in Machining Science and Technology, 2021
Deepak Sharma, Somashekhar S. Hiremath
The EDM process involves the removal of material by a sequence of rapid reoccurring discharges among the conductive tool and workpiece. The basic principle of EDM is, when the voltage reached to some predetermined value, the electrons break loose from the tool and accelerates toward the workpiece. During their travel within in the spark gap, the electrons collide with the neutral dielectric fluid molecules and cause ionization. Then, these electrons and ions together form the plasma channel. This plasma channel enables the spark discharge to take place through the dielectric fluid. As a result of spark, a very high temperature of the order of 10,000 °C − 12,000 °C is produced, which instantaneously melts and vaporizes the workpiece material and leaving behind a tiny crater. A small amount of the vaporized material in the form of debris is dispersed into the space surrounding the electrodes. Some portion of these dispersed debris is removed by the dielectric fluid and the remaining are solidified. The detailed mechanism of material removal in EDM is available in various textbooks (Gosh and Malik, 2010; Koc and Ozel, 2019).