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Unformatted text preview: MuHJI?Bu6J;9>D?97B6@EKHD7B6&'$(&&/6 ). `e 7[\kX`c K_\7gifj7Xe[7Zfej7f]7Xck\ieXk`m\77 ^ifle[`e^7jpjk\dj7 8 L K ? F I 1 7 D X k j 7 { j k d X e # 7 : _ ` \ ] 7 ; \ m \ c f g d \ e k 7 < e ^ ` e \ \ i# 7 Gf n \ i 7 G c X e k 7 K\ Z _ e f c f ^ p# 7 N ¡ i k j ` c ¡ 7 Gf n \ i 7 G c X e k j K_\7^ifle[`e^7f]7\c\Zki`ZXc7jpjk\dj7 `j7jlYa\Zk7kf7X7eldY\i7f]7mXi`XYc\j%7 K_`j7Xik`Zc\7jkl[`\j7k_\7^ifle[`e^7 Xck\ieXk`m\j#7Xe[7k_\`i7`dgc`ZXk`fej% When the first commercial power systems were brought on line in the late 19th century, grounding was not a major concern. At that time there was still a struggle between competing systems for the generation and distribution of electricity; direct current (DC), and alternating current (AC), and their principal inventors Thomas Edison and Nicolai Tesla. The principle of using AC won out, mainly due to its advantage of being able to be transmitted at high voltage with relatively low losses. This was demonstrated at the 1891 international Electro-Technical exhibition in Frankfurt, Germany where energy was transmitted at 25 kV over a distance of 175 km from Lauffen am Neckar where it was generated. <Xicp7[\m\cfgd\ek Apparently the early power systems were operated ungrounded, mainly because only three wires were needed for the distribution of electric power, this in order to save on material, (the Frankfurt - Lauffen connection used 60 tons of copper wire). A simple earth fault detection could be employed by connecting Incandescent lamps between phase and ground, whereby a fault could be indicated by one lamp going dark and the other ones glowing more brightly as shown in Figure 1. One can argue that this system was the first, ”real” grounding system employed, the intention was not, however, to ground but to detect faults. In time, there was an increased awareness that electrical equipment, especially motors, on these ungrounded systems were prone to insulation failures. This led to the discovery that ungrounded systems are not ungrounded, but that a connection to ground exists by the system capacitance to ground as illustrated in Figure 5, which under certain circumstances contributed to the failures. The reaction to this was a tendency to simply connect the neutral of, for example power transformers, directly to ground, thereby creating a solidly grounded system. Solidly grounded systems offered excellent control of over voltages, but with the drawback of very high fault currents. This meant potentially extensive equipment damage and downtime, and concerns were also raised with respect to voltage gradients. The ”natural” reaction to this was the introduction of current limiting impedance in the grounding circuit. This reactance or resistance, to limit the fault currents, also limited the damage to equipment. This was particularly important in industrial systems where service continuity is a very important factor....
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This note was uploaded on 05/22/2011 for the course IBMS 123 taught by Professor Heart during the Spring '11 term at De Haagse Hogeschool.

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alternative-grounding-system-pros-cons-article -...

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