Medium voltage switchgear application guide

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Medium voltage switchgear application guide Appendix 5: cables (cont’d) MV cables capacitance single-pole cable individually screened three-pole cable K C C C belted three-pole cable 4 - TYPE OF CONDUCTOR A and cable mechanically is comprised united of either conductors. one conductor, or several electrically distinct The ■single-pole different types individually of cables screened insulated cables, by extruded solid dielectrics are: ■individually ■belted three-pole screened cables. three-pole cables, ■the The metal type part of metal: of the annealed conductor electrolytic is defined copper by: annealed aluminium, or 3/4 hard or sometimes ■electric ■self-induction resistance coefficient per unit (L of in length H/km) (R which in ohm/km), geometrical size and the relative disposition of depends the conductors. essentially on the ■the rated cables section capacitance. (mm2), 5 - MV CABLES CAPACITANCE The capacitance of a cable depends on the construction type: ■ single-pole cable capacitance cables:the C is that conductor measured is between surrounded the conductor by a screen and and the the which is earthed. screen ■ individually screened three-pole by a screen and the cable capacitance cables:each is that measured conductor between is surrounded conductor and its individual screen which is earthed. each ■ belted three-pole there is a capacitance cables:a K between screen conductors surrounds and a capacitance three conductors C between and a conductor and the screen which is earthed. Ic= The 3 capacitive C ωV which current causes Icof capacitance a network in C the only event to intervene of an earth whatever fault is: cable type. the In practice, C for for a star-connected individually screened capacitance, cables. the cable makers indicate: Upon ■the value request, 3 K the + C cable for belted maker cables. measured between the three inter-connected will tell you the conductors capacitance and the C2(C2= metal sleeve. 3 C) date 11/94 - B•3•2 - revised 05/2004 page 10
Medium voltage switchgear application guide Appendix 6: alternating current melting arc furnaces 1 - MELTING PROCESS Arc furnace operating principle The operations standard including processing scrap cycle metal of loading, an arc furnace melting, comprises liquid steel a refining series ofand casting. alternating current melting arc furnace scrap metal loading melting liquid bath refining casting of liquid steel in ladles and inter-casting intermediary reloading furnace ■scrap is metal stopped. loading For and a single intermediary processing loading cycle, is carried two or three out when basket the loads ■scrap are metal required. part of the energy melting is consumed. during which the solid load is liquefied and the main ■liquid bath steel refining casting which in ladles only involves requires the thermal furnace loss tipping compensation. metal is poured from the furnace into the ladles and the time so needed that the for liquid furnace to return to its original position. the The ■frequent scrap metal arcing melting and arc period suppression is characterised at the beginning by: ■strong current variations caused by arc displacement of during each the basket, period, melting ■short-circuits, generated by the metal as it collapses. 2 - OPERATING FREQUENCY The number of casts per day furnace: depends 13 on casts the type per of day. furnace. ■furnace with refining in the ladle furnace: 22 casts per day. date 11/94 - B•3•2 - revised 05/2004 page 11
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Medium voltage switchgear application guide

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